Download Adaption to climate-related changes in seagrass ecosystems in

Adaption to climate-related
changes in seagrass
ecosystems in Chwaka Bay
(Zanzibar)
Duncan Geere
Uppsats för avläggande av masterexamen i naturvetenskap
30 hp
Institutionen för biologi och miljövetenskap
Göteborgs universitet
June 2014
Abstract
This report presents a case study of the causes and effects of seagrass loss and artisanal fshery decline
on the rural coastal communities around Chwaka Bay in Zanzibar, and their capacity to adapt to
these changes. The results of semi-structured interviews with 51 fshermen living in the area are
presented, and assessed in the context of economic and social development and resilience to future
change.
The vast majority of interviewees reported a decline in fsh catches and the size of fsh caught, as well
as a reduction in seagrass coverage and more fshermen. These changes were blamed on the use of
destructive fshing methods and an increasing number of fshermen due to unemployment, while
attempts to regulate the fshing industry have proved unsuccessful due to corruption. Most
interviewees named farming and forestry as alternatives to fshing, however neither are likely to be
sustainable over a longer timeframe. Meanwhile, stresses on seagrass (and the artisanal fsheries as a
result) are projected to increase as a result of rising maximum temperatures, greater rainfall variability
and increasing sea level.
Without diversifcation of economic activity, clear fsheries regulation and effective enforcement of
those regulations, Chwaka Bay and many similar rural coastal communities around the Indian Ocean
will fnd it increasingly diffcult to adapt to future global change.
Keywords
Adaptation, Climate change, East Africa, Zanzibar, Seagrass, Chwaka Bay, Interviews, Fisheries,
2
Introduction
Global extent of seagrasses has dramatically reduced over the past century, due to human and natural
pressures [Björk et al, 2008]. Signifcant anthropogenic threats to seagrass ecosystems include
eutrophication and sedimentation caused by poor farming and forestry practices, and destructive
fshing methods such as bottom trawling [Waycott et al, 2009]. These pressures are expected to
become greater due to the effects of climate change, with an increase in both rainfall and the
frequency of extreme events increasing the rate at which sediment and nutrients are transported into
the ocean [Bjork et al, 2008]. Meanwhile, coastal communities depend on the ecosystem services
provided by seagrasses - they provide nutrition to more than half the world's fsheries, flter water,
reduce the effects of coastal pollution, eutrophication and sedimentation, protect coastlines from
erosion and act as a buffer against extreme weather events [Nelleman et al, 2009].
It is poorly-understood at a global level how aware many rural coastal communities are of the threats
facing the ecosystems they depend on, and whether they are taking adaptive action on a local level.
Seagrass ecosystems are affected by both human and climate drivers, and their interaction is complex
and differs around the globe. Some changes seen in these systems can be attributed to climate effects,
while others are not as discernable [IPCC, 2014]. A coastal adaptation knowledge network between
scientists, policymakers, stakeholders and the general public is well-developed in the USA, European
Union, Mediterranean, Australia, Caribbean and Pacifc islands but is much less so outside of these
areas and particularly in developing countries [IPCC, 2014]. Tropical east Africa does not have, at
the time of writing, an effective network of this nature despite its large and increasing population and
limited social and economic resilience [Silva, 2006].
The aim of this study is to address this gap in knowledge for the settlements surrounding Chwaka Bay
on the island of Zanzibar in Tanzania. This report will frst discuss the biology of seagrasses and the
factors that limit their growth rates, then the reliance of coastal communities around the globe on the
ecosystem services that seagrasses provide. The global decline of seagrass meadows is then examined,
followed by the reasons for this decline and how climate change may increase the rate of loss. The
study area is next discussed in terms of its geography and climatology, along with the methodology of
this research. Interviews are reported with fshermen, farmers, tourism operators, government offcials
and other relevant stakeholders in the area to ascertain the impact of projected local climate change,
followed by an assessment of the local effects of climate change on seagrasses in this region using the
output of mathematical general circulation models. Comparisons are fnally made with other areas of
study.
Gullström et al (2006) wrote of the need for "regular assessments of the social-ecological sustainability
of different human activities taking place in [Chwaka] bay", and IPCC (2014) noted that there are
signifcant gaps in vulnerability assessment of specifc coastal impacts. By examining the local effects of
climate change in this region, and presenting an assessment of what the societal impacts of these
effects may be, it is hoped that this study can contribute toward these requirements.
Seagrasses
Seagrasses are fowering plants that grow in shallow water environments around the world - both
oceanic and estuarine [Green & Short, 2004]. They're the descendants of terrestrial plants that
recolonised the ocean between 100 and 65 million years ago, which have evolved to tolerate
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submergence and high salinities [Björk et al, 2008]. They have leaves, stems, rhizomes and roots, and
complete their entire lifecycle (including fowering, pollination, seed dispersal and germination)
underwater. They can also propagate vegetatively by extending their rhizomes [Björk et al, 2008].
There are about 60 species of seagrass worldwide that are functionally similar, though not
taxonomically unifed [Green & Short, 2003]. Most grow in single-species meadows, though in
tropical areas mixed stands can be found containing up to 14 species. The distribution of seagrasses
can be seen in fgure 1, divided into six major bioregions. About half of seagrass species are tropical,
and half are temperate [Short et al, 2007].
Fig 1 - Global seagrass distribution shown as blue points and polygons and geographic bioregions: 1 Temperate North
Atlantic, 2. Tropical Atlantic, 3. Mediterranean, 4. Temperate North Pacifc, 5. Tropical Indo-Pacifc, 6. Temperate
Southern Oceans [Reprinted with permission - Short et al, 2007].
Seagrass growth is limited predominantly by light availability. The amount of solar irradiance
reaching a meadow controls daily growth and seasonal productivity. This is affected by geographical
location, weather, water depth, turbidity, and the state of surface waves and ripples [Björk et al, 2008].
Seagrasses need more than ten percent of the surface irradiance during cloudless middays (>200 µmol
photons m-2s-1) to survive, meaning that seagrasses are limited to a depth of 70 metres under optimum
conditions [Short et al, 2007] and signifcantly less in regions with cloudy weather or turbid water
[Björk et al, 2008]. Some seagrasses in temperate regions survive very low irradiances during the
winter by building up carbohydrate reserves stored in rhizomes during summer [Björk et al, 2008].
Temperature and salinity also affect growth. Temperature tolerance varies widely between species,
and while data is lacking for many it appears that temperatures above 25C will reduce growth rates of
temperate seagrasses and temperatures above 43C impact tropical seagrasses [Ehlers et al. 2008].
Salinity tolerance also varies dramatically, with species surviving in water as low as 0 ppt and as high
as 140 ppt [Walker, 1989]. Seagrasses are eaten directly by sea urchins, fsh and molluscs [Heck &
Valentine, 1995], but they also provide a habitat to many more creatures. Animals at all trophic levels
appear in seagrass meadows, from dugongs and manatees and sea turtles in tropical water to swans
and geese in temperate water [Björk et al, 2008].
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Seagrass areas supply an estimated 50 percent of the world's fsheries, providing nutrition to almost
three billion people [Nelleman et al, 2009]. Animals that rely on seagrass meadows represent a large
proportion of the protein consumed by coastal communities in tropical areas, making them crucial to
their survival, and they're also fshed commercially. As well as acting as a fsh habitat, seagrasses offer
multiple ecosystem services, including sediment trapping and binding which prevents coastal erosion
[Laffoley and Grimsditch, 2009]. They're also used as traditional medicine, for flling mattresses, for
roof covering, house insulation and to fertilise gardens [de la Torre-Caste & Rönnbäck, 2004]. In total,
the global value of all ecosystem services provided by seagrass beds has been estimated by Costanza et
al (1997) at US$ 3.8 trillion per year. Waycott et al (2009) found their their nutrient cycling functions
alone have a value of US$ 1.9 trillion per year. However it's worth noting that ecosystem valuation is
far from uncontroversial and there are many competing systems for evaluating an ecosystem (For
details, see the 1998 special issue of Ecological Economics on ‘The value of ecosystem services’).
Since seagrasses were frst recorded in 1879, 29 percent of the known areal extent has disappeared
[Björk et al, 2008]. These rates of decline are accelerating – before 1940 the median rate of loss was
0.9 percent per year, which has risen to seven percent per year since 1990. These rates are
comparable to those reported for mangroves, coral reefs and tropical rainforests [Waycott et al.,
2009]. While there is some natural variability in seagrass extent due to extreme weather, predation
and the spread of disease [Short & Wyllie-Echeverria, 1996], there are many anthropogenic threats to
seagrass populations. Unfortunately, few records of seagrass meadows survive from before 1900 and
the study of many meadows has only begun in recent decades [Green and Short, 2003]. This makes it
impossible to ascertain whether the currently-seen rates of loss are precedented in modern, human, or
even geological history. Past natural climate change will undoubtedly have had an effect on seagrass
meadows, but there is no data available to compare to the current anthropogenic changes.
The largest human impacts on seagrass populations worldwide are eutrophication and sedimentation
caused by poor farming and forestry practices, and destructive fshing methods such as bottom
trawling [Björk et al (2008), Nelleman et al (2009), Marbà (2009), Crooks et al (2011), Handisyde
(2006), Jackson (2009), Fortes (2010), Waycott et al (2009)]. These have contributed to a
disappearance of 29 percent of the known areal extent since 1879, at a rate that has accelerated from
a median of 0.9 percent per year before 1940 to seven percent per year since 1990 [Waycott et al,
2009]. These rates are comparable to those of mangroves, coral reefs and tropical rainforests.
Climate change may exacerbate these factors, and seagrass meadows are already under stress due to
climate change - particularly where maximum temperatures already approach their physiological limit
[IPCC, 2014]. Increases in water temperature can attract invasive species [IPCC, 2014] and may
decrease production at thermal tolerance levels - heatwaves lead to widespread seagrass mortality
[Reusch et al, 2005, Marbà and Duarte, 2010, Rasheed and Unsworth, 2011]. Before those tolerance
levels are reached, water temperature increases may increase productivity, but it may also increase the
productivity of algae that shades seagrasses from sunlight [Watkiss, 2012]. Warming has been shown
to increase seagrass fowering but the larger recruitment rate is insuffcient to compensate for the losses
resulting from elevated temperature [Diaz-Almela et al, 2009]. Any increase in the duration or
intensity of rainfall combined with poor farming and forestry practices may increase the amount of
nutrients and sediment in the water, again reducing productivity [Björk et al, 2008]. Finally, an
increase in the frequency or severity of tropical storms may cause signifcant additional mechanical
damage to the seagrass beds [Watkiss, 2012].
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Species of seagrasses that have been studied so far represent a large carbon sink, due to their slow rate
of decomposition [Björk et al, 2008]. It's thought that while seagrasses represent up to one percent of
the total carbon fxed on the oceans, they represent 12 percent of the stored ocean carbon [Duarte
and Cebrian 1996]. Full analysis of the carbon sink capabilities of seagrass is not yet complete for
every species, and it's possible that this may be an overestimate [Personal communication, Martin
Dahl, 2014]. Nonetheless, Fourqurean et al. (2012) estimate that the present rates of seagrass loss may
account for ten percent of all emissions attributed to changes in land use, and could result in the
release of up to 299Tg of carbon per year (about three percent of 2012's anthropogenic global carbon
emissions [Le Quéré et al, 2012]). The loss of coastal wetlands and seagrass meadows combined
results in the release of 0.04 to 0.28 Pg of carbon annually from organic deposits [Pendleton et al,
2012]. Recent studies have shown that restoration of lost seagrass meadows may be an effective tool to
mitigate global emissions. Restored meadows are expected to accumulate carbon at a rate comparable
to those of undisturbed seagrass beds within 12 years of seeding [Greiner et al, 2013].
Site description
Chwaka is located on the western shore of Chwaka Bay (6°13–25'S and 39°37–58'E), which is in turn
located on the eastern coast of the island of Zanzibar. It lies due north of the Tanzanian capital of Dar
Es Salaam on the eastern coast of Africa. Figure 2 shows its position.
Fig 2: Geographical location of Chwaka off the east coast of Tanzania
Chwaka Bay
Chwaka Bay is a shallow body of saltwater about 50 square kilometres in size. It has a strong,
asymmetric, semidiurnal tidal regime with a tidal range of 0.9 metres during neap tides and 3.2 metres
during spring tides [Cederlöf et al. 1995] Salinity ranges from 21 psu to 25.5 psu [Eklöf et al., 2005].
Analysis conducted by Gullström et al. (2006) indicates that the seagrass covers 24.4 percent of the
base sediment of the bay with little seasonal variation. The seagrasses are concentrated within
meadows, inside which between 52 and 70 percent of the base sediment is covered with seagrass.
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Spatial variability is large, and distribution of the species is complex, however both plant and
productivity variables reported for the bay fall within the reported ranges for the western Indian ocean
region, and it has been described as “relatively pristine” [Gullström et al. 2006]. Eleven different
species of seagrass have been recorded in the bay by Mohammed & Jiddawi (1999). The dominant
species are Enhalus acoroides, Thalassia hemprichii, Cymodocea rotundata, Cymodocea serrulata and
Thalassodendron ciliatum. Syringodium isoetifolium, Halodule uninervis, Halodule wrighthii and Halophila ovalis are
also relatively common in the area, while Halophila stipulacea and Nanozostera capensis are sparsely
distributed. This represents almost all of the 14 known species found in the western Indian ocean
region [Gullström et al. 2006].
Chwaka is the largest village on the bay, with a population of about 4,000. Smaller settlements include
Michamvi, Uroa and Marumbi. Its people are a homogenous group, sharing a language (Kiswahili), a
religion (Islam), and a long cultural tradition with the dominant economic activities being fshing and
seaweed cultivation [de la Torre-Caste & Rönnbäck, 2004]. The seagrass areas in the bay have been
reported by local fshermen to be the best fshing grounds, compared to other nearby marine habitats
– such as mangroves, coral reefs and sand fats. [de la Torre-Caste & Rönnbäck, 2004] The bay is
divided into 22 fshing grounds which were identifed by Bergstén (2004). These are seen in fgure 3.
These vary in popularity among fshermen, primarily due to the abundance and structure of the
seagrass contained within. Fishing grounds composed of long, dense and patchy seagrass beds are
preferred by fshermen, with some variation based on the fshing gear used. Thalassodendron ciliatum and
Enhalus acariodes were the most popular seagrass species among fshermen [Bergstén, 2004].
Fig 3: Map of fshing zones in Chwaka Bay [Reprinted with permission - Bergstén, 2004]
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Due to the village's rising population and demand for fsh and lack of livelihood alternatives, the socioecological system of the Chwaka Bay area may become vulnerable to shock and stress [Badrango,
2007]. Today the region is functional, despite confict between different villages and a lack of
collaboration among stakeholders over diminishing resources, but the ever-increasing number of
fshermen and use of harmful fshing practices may lead to the erosion of the resilience of this system
in the future [Badrango, 2007] unless decision-making processes are substantially reformed.
Historical climate of Zanzibar
Meteorological data was provided by the Institute of Marine Science from a station situated at
Zanzibar International Airport on the west side of the island. No meteorological data was available
closer to Chwaka Bay.
Fig 4: Climate of Zanzibar - temperature and precipitation, 1992-2013 (Tanzania Meteorological Agency)
Zanzibar has a tropical climate (see fgure 4) with a fairly constant average temperature year-round. It
experiences heavy rains between March and May, and less intense rains between November and
December. June to October is dry. Precipitation is somewhat high compared to other coastal zones
along the East African coast [Watkiss et al, 2012]. The region is affected by East African climate
extremes associated with El Nino and La Nina years – these events bring heavy precipitation and dry
spells respectively, and have a major economic impact on the island at a macroeconomic level
[Watkiss et al, 2012].
Variations in temperature are small due to Zanzibar's tropical location. Average temperatures tend to
be highest between January and March, rising to 28C, and lowest in July when they fall to 24C.
Average daily maximum temperatures follow the same pattern - hitting a high of 32C between
January and March and falling to a low of 27C in July. The highest daily average temperature
recorded at the Zanzibar Airport meteorological observation point was 34.6C on 16 June 2010, and
the highest maximum temperature (50.0C)was also recorded on the same day. Maximum
temperatures of 40C or above were also recorded on 25 January 2013, 3 March 2010, 18 October
2007 and 2 May 2003.
8
Wind speeds vary seasonally and also due to time of day. At 9am, winds are usually strongest between
December and February with notable peaks in 1995, 2003 and 2005. At 3pm, winds are usually
strongest between June and August, with notable peaks in 1997, 1998 and 2003. Mean 9am wind
speed has decreased from 8.24 knots between 1990-1999 to 7.86 knots between 2000 and 2009, while
mean 3pm wind speed decreased from 12.46 knots between 1990-1999 to 12.26 knots between 2000
and 2009. Wind gust data is rarely recorded at the Zanzibar Airport meteorological station, but of the
times when it has been, it has only been recorded at 39 knots or greater on fve occasions - on 8 June
2011 (highest recorded gust at 52.1 knots), and on 26 February, 10 October, 19 October and 15
November 2012.
Figure 5 shows rainfall totals from 1971-2011. Precipitation tends to be highest between March and
May and lowest between June and August. Exceptionally wet years since 1970 include 1978, 1979,
1986, 1997, 1998, and 2007. The wettest year was 1979 with a total of 2,802mm of rain compared to
a 1971-2011 average of 1,680mm. 2003 was an exceptionally dry year, with rainfall just 704mm. No
major precipitation trends can be seen, though rainfall appears to have become more variable in the
last decade - standard deviation of 2002-2011 is 468mm compared to 377mm for 1971-2001, and
average deviations from the mean rise from 305.6mm to 371.3mm over the same periods. More than
150mm of rain in 24 hours fell on just seven occasions at Zanzibar Airport, all but one of which
occurred during 1986 (3 January, 23 February, 8 March, 31 July, and 20 and 24 September). The
remaining occurrence was on 16 December 1985.
Fig 5: Seasonal rainfall totals by year, 1971-2011
There is strong observational data showing recent changes in the climate of Zanzibar. Average and
maximum temperatures have been rising for the last 30 years, with the increase highest
(approximately 0.2-0.5C) in the months of December to May [Watkiss et al. 2012]. There is not a
simple precipitation trend for the whole island, but higher intensity events have been recorded in
recent years - including the highest ever recorded precipitation event in 2005. Low and erratic rainfall
9
led in 2006/07 to a major crop failure on the island [Watkiss et al., 2012]. Evening wind speeds have
increased by approximately two m/s over the last 20 years (though a similar trend is not seen in
morning winds), with an increase in extreme wind events. Major wind storm events in 2009 and 2011
led to widespread building damage, as well as injuries and a fatality [Watkiss & Bonjean, 2012].
Finally, monthly mean high water level increased about 0.7m between 1984 and 2004 [Watkiss et al.
2012].
Extreme temperature, precipitation, wind and storm events cause signifcant economic and social
disruption to rural coastal communities [IPCC, 2014], and any increase in their frequency is likely to
have negative impacts on tourism, agriculture, health, energy supply and demand, infrastructure,
water resources and demand, and ecosystem services. The combined effects of these communities'
current climate vulnerability and future climate change may disrupt Zanzibar's ability to achieve
development, economic growth and poverty reduction targets [Watkiss et al. 2012].
Methodology
To collect primary data on the impact of the local effects of climate change on seagrasses in this
region, semi-structured scientifc interviews of fshermen were judged to be the most useful tool.
Interviews were conducted with the assistance of an interpreter over a period of six days in the villages
of Chwaka, Marumbi, Uroa and Michamvi on the shore of Chwaka Bay.
Chwaka Bay was selected as it is environmentally representative of the western Indian ocean region it contains almost all seagrass species found in the area (however the high diversity of species is in itself
somewhat unusual), plant and productivity variables fall within the reported ranges for the region, and
many of the threats to seagrasses common to the region can be identifed here. The area is also
10
culturally representative of many rural coastal communities in developing countries in the western
Indian ocean. Within this area, Chwaka was initially selected as the sole study location as it has a long
history of both seagrass and cultural research meaning that there is ample previous work to draw from
and interview responses are less likely to be as affected by the presence of researchers.
Pilot interviews were conducted in Chwaka on the frst day of the study to refne the questions in an
attempt to both reduce the amount of time the interviews took and gather the most relevant
information – such as the number of years of fshing experience in place of the number of years living
in the town. Following this refnement process, it was also decided to broaden the area of study from
just Chwaka to include Marumbi, Uroa and Michamvi villages for two reasons. Firstly, one subject
warned us of possible political bias in the answers we might were collecting. The subject claimed that
Chwaka supports the local opposition party to the government, and interviewees may be giving
answers that would embarrass the ruling party. It was diffcult to establish the veracity of this claim,
but the study area was expanded nonetheless to reduce any potential resulting bias. Secondly, some of
those approached for the survey exhibited a degree of hostility due to a perceived failure for the
research conducted in the village over many decades to have delivered results. It was reported that
some respondents were being harassed for being willing to participate in the research, and as a result it
was decided that to minimise disruption to the village it would be prudent to spread the interviews
among multiple locations.
The interpreter was an employee of the Institute of Marine Sciences and has long experience of both
the subject of the study and the area where the study was conducted, however the interpreter did not
come from the study area. The interviewer stayed in the study area throughout the survey to establish
communication and trust with the local people. Subjects were selected by representatives who knew
each village, nominated by a council of fshermen. Interviews were recorded and brief written notes
were also taken at the same time. Each interview consisted of 14 questions, with a few additional
questions to clarify certain answers during some interviews. The full list of questions common to all
interviews can be found in appendix one. Additional unstructured interviews were conducted with
members of the local fsheries committee in Chwaka and Uroa to learn more about local conservation
techniques, with the owner of Marumbi village farm to investigate opportunities for local agriculture,
and with Dr Narriman Jiddawi from the Tanzanian Institute of Marine Science to clarify some
uncertainties related to the study area. Some information was also gathered during informal
discussions with local residents.
Results
A total of 51 interviews were conducted in Chwaka (n=14), Marumbi (n=14), Uroa (n=16) and
Michamvi (n=7). Subjects ranged in age from 17 to 70, with a median of 34 and standard deviation of
13.28. Years of fshing experience ranged from 1 to 54, with a median of 15 and a standard deviation
of 12.23. The youngest interviewees were found in Chwaka and the oldest were found in Michamvi .
These villages also had the least and most experience of fshing respectively. Marumbi's fshermen
were older but with fewer years of experience than those in Uroa. Table A shows these statistics in full.
11
Table A: Median age and fshing years of the interview sample
Area
Median age
Median fshing years
Chwaka
26.5
9
Marumbi
39
13
Uroa
34
18.5
Michamvi
46
26
All
34
15
In the region of study, it's common for men to work more than one job to increase household income.
Fishing is extremely common, with some interviewees noting that unemployed men will join a fshing
crew to provide for their family while searching for work. Every one of the interview subjects had
worked as a fsherman and all but two did so at the time of the interviews. The exceptions were both
teachers, who were unable to fsh due to school working hours. Fishing was the most common
occupation, as fshermen were deliberately sought out to interview. The second most-common
occupation was farming, followed by a small number of other diverse occupations - seaweed farming,
shopkeeping, teaching, small businessmen, driving, police, tour guiding and building.
The vast majority of interviewees fshed in Chwaka Bay with only four reporting that they fshed in
the deep sea region outside. Inside the bay, the Michamvi region was most popular, followed by Bimbi
Kobwa, Bimbi, Kichongwe, Mapangani, Bimbi Ndogu, Ngoro and the Mamea Mwari protected area
at Marumbi village - where dragnet fshing is banned.
When asked how the bay has changed since they started fshing and allowed to answer freely, the vast
majority (96%) of respondents cited a decline in fsh catch, with 41% also identifying a decrease in the
size of caught fsh. 90% noted that there were more fshermen, 70% noted a decline in seagrasses and
22% reported that coral had been destroyed. Almost half the respondents (49%) reported "big
changes" or words to that effect, though the proportion was much greater in Marumbi (86%) than in
other villages. Finally, 18% reported the appearance of sand dunes in the bay, and 12% said that
there had been no change in the seagrasses. All changes reported by more than one respondent can be
seen in table B.
Table B: responses to the question "How has the bay changed?"
How has the bay changed?
Chwaka
Marumbi
Uroa
Michamvi
Total
Percentage
Decline in fsh catch
13
13
16
7
49
96.08%
Increase in number of fshermen
13
13
16
4
46
90.20%
Less seagrass
11
9
10
6
36
70.59%
"Big changes"
3
12
4
6
25
49.02%
Smaller fsh
4
9
6
2
21
41.18%
5
1
5
11
21.57%
2
3
3
9
17.65%
6
11.76%
Coral destroyed
Appearance of sand dunes
1
Seagrasses no change
1
5
New protected area
5
5
9.80%
Illegal fshing
3
3
5.88%
3
5.88%
3
5.88%
Fewer fshermen
No change in size of fsh
3
1
2
12
Shallower water
2
1
3
5.88%
Increase in fsh catch
1
1
2
3.92%
Price of fsh is higher
1
1
2
3.92%
2
3.92%
More erosion
1
1
When asked for the reasons for the changes seen in fsh catches (number and size), more than 70% of
respondents identifed the use of dragnets by fshermen from Chwaka, rising to 92% of residents of
Marumbi. Almost 22% identifed an increasing number of fshermen as the cause, and eight percent
pointed to poor enforcement of existing protected areas. Six percent blamed the removal of seagrass,
and four percent attributed changes in fsh catches to permanent changes in weather patterns affecting
the island. The full breakdown of responses can be seen in table C.
Table C: Reported reasons for changes observed in fsh catch and size
Reasons for fsh changes
Chwaka
Marumbi
Uroa
Michamvi
Total
Percentage
Use of nets
6
13
10
7
36
70.59%
More fshermen
4
6
1
11
21.57%
4
7.84%
Poor enforcement of protected areas
4
Removal of seagrasses
2
1
3
5.88%
Weather is changing
1
1
2
3.92%
The reasons given for changes in seagrasses follow a similar pattern - the most common answer (from
35% of interviewees) was that the observed changes were caused by dragnet fshermen from Chwaka,
though no respondents from Chwaka gave this as the cause. Instead, Chwaka residents blamed
increased numbers of sea urchins for the disappearing seagrass. Other reasons given include seaweed
farming, the appearance of sand dunes, natural variability and the effects of the 2004 tsunami.The full
breakdown of responses can be seen in table D.
Table D: Reported reasons for changes observed in seagrass extent
Reasons for seagrass changes Chwaka
Nets
Marumbi
Uroa
Michamvi
Total
Percentage
8
3
7
18
35.29%
7
13.73%
Sea urchins
6
1
Seaweed farming
2
4
6
11.76%
Sand dunes
1
2
3
5.88%
Natural
1
1
2
3.92%
1
1
1.96%
Tsunami
Unemployment is the primary cause of increasing numbers of fshermen within Chwaka Bay,
according to 57% of interview respondents. An increase in population in the bay was also named as a
contributing factor by 10% of interviewees. In Michamvi, where a small number of people said that
the quantity of fshermen was decreasing, catch decline and tourism were named as the reasons for this
decrease. The full breakdown can be seen in table E.
13
Table E: Reasons for changes in fshermen numbers in Chwaka Bay (+ = increase, - = decrease)
Reasons for fshermen changes
Chwaka
Marumbi
Uroa
Michamvi
Total
Percentage
3
10
12
4
29
56.86%
2
3
5
9.80%
Unemployment (+)
Population size (+)
Catch decline (-)
2
2
3.92%
Tourism (-)
1
1
1.96%
Interviewees were asked if they remembered any years with particularly bad storms affecting the bay.
The majority (59%) said that they didn't remember any, and of those that did, 13 erroneously
reported the 2004 tsunami as a storm - with effects ranging from none at all to lost fshing gear,
emptied fsh breeding sites, removal of seagrass and a permanent 20-30% decline in catches. Of the
remaining interviewees, three named a supposedly week-long storm around the late 1960s which had
no effect on fsh catches. Two pointed to a storm in the mid-1970s which removed a lot of seagrass
and scared fsh away. Finally, three more named a storm or storms in the mid to late 2000s which
caused between a 98% and 50% decline in catches and made fshing diffcult.
A similar question was asked for years with memorable rainfall. In response, 1978, 1994, 1995-6,
2002, 2007, 2008-9, and 2012 were all identifed as high rainfall years. In almost all cases (with the
exception of 1995-6), it was reported that the rainfall caused large amounts of freshwater to collect in
the bay, killing the saltwater fsh. No effects were reported on seagrasses. A selection of years with
extreme hot temperatures were also identifed in the same way. 1994, 2000, 2004, 2007, 2008, 2010
and 2011 were all reported as exceptionally hot. In most cases, the result was that some fsh (a species
of triggerfsh locally referred-to as "Kikande" was mentioned by two interviewees) were found foating
dead in the sea, causing in one case a decline in catch of about 30% for two months. Effects on
seagrasses varied from none at all to 50% mortality which took four months to regrow.
Table F: Responses to the question: "What will happen to the village?"
What will happen to the village?
Chwaka
Marumbi
Uroa
Michamvi
Total
Percentage
Farming
9
5
14
4
32
62.75%
Life will be hard
9
1
6
4
20
39.22%
Forestry
2
3
8
5
18
35.29%
Won't be enough to support the village
3
4
7
3
17
33.33%
Nothing to do except fshing
5
2
3
2
12
23.53%
1
3
5
9
17.65%
2
1
5
9.80%
5
9.80%
5
9.80%
4
7.84%
3
5.88%
2
3.92%
2
3.92%
2
3.92%
2
3.92%
Tourism
Charcoal
1
1
Not enough land
4
1
Things will be ok
1
3
1
1
2
Small businesses
People will leave
2
Fishing in deep sea
1
Crime
2
1
1
1
Building
1
People sitting around
2
14
1
Finally, interviewees were asked what will happen to their village if fsh catches continue to decrease
and allowed to answer freely (Table F). The most common answer (63%) was that people will farm
fruit and vegetables to sell, though 10% said that increasing farming would be diffcult as all the land is
already owned. 35% of respondents said people would turn to forms of forestry, including cutting
frewood, whilst 18% (mostly from Uroa and Michamvi) said tourism would offer a solution to
preserving livelihoods. Other potential industries identifed included making charcoal, fshing in the
deep sea, helping to build tourism infrastructure, and the formation of small businesses such as shops
or handicrafts. 39% of respondents answered that "life will be hard" or words to that effect, and an
additional 33% said that other industries won't be enough to support the village. 24% of interviewees
said that there is nothing to do in their village except fshing. Finally, 6% said that people would leave
for other areas, 4% said that people would turn to crime and 4% said that people would just sit
around.
Discussion
Effects of future climate change
To understand how future climate change may affect the seagrass meadows of Chwaka Bay and in
turn how that may affect local society, it's important to how Zanzibar's climate may change. To do
this, downscaled projections of climate change from the Coupled Model Intercomparison Project
Phase 5 at the World Climate Research Programme (WCRP) were used. These projections are based
on the RCP8.5 representative concentration pathway, which represents +8.5W/m2 of radiative
forcing in the climate system in the year 2100 relative to pre-industrial values and follows a zero
mitigation 'business as usual' scenario. Choosing representative concentration pathways with more
mitigation reduces the magnitude of the change, but not its direction.
15
Temperature
Warmer water temperatures increase seagrass productivity, but only up to their maximum thermal
tolerance limit (which differs between species) [Reusch et al, 2005, Marbà and Duarte, 2010, Rasheed
and Unsworth, 2011]. Beyond this point, the seagrass leaves die back leaving behind the rhizomes
buried in the seabed. The leaves regrow when temperatures become more hospitable, but the plant
must expend energy to do so [Jordà et al, 2012]. Following temperature disturbances, Vizzini et al
[2010] reported that seagrass remains stressed for three years after the disturbing event. Meanwhile,
invasive species attracted by rising water temperatures may spread pathogens and compete for
resources, causing further harm to stressed populations [Jordà et al, 2012]. Downscaled model
projections using the SRES A1B scenario in the Western Mediterranean combined with studies of the
links between mortality rates and maximum seawater temperature led Jorda et al. (2012) to state that
seagrass meadows in this location may become functionally extinct by 2050 to 2060. However, there is
also limited evidence that elevated CO2 will increase seagrass survival or resistance to warming
[Alexandre et al., 2012, Jorda et al., 2012], Ehlers et al (2008) showed that genetic diversity allowed
the temperate species Zostera marina to cope better with high summer temperatures, and Rice and
Emery (2003) showed that evolutionary change can occur within a few generations. These factors
combined may give genetically-diverse, mixed-species meadows such as those in Chwaka Bay greater
resilience to projected temperature increases.
Figure 6 shows a projection of maximum temperature anomalies from monthly mean maximum
temperatures under an RCP8.5 scenario, It indicates that maximum temperatures are projected to
rise to between 1.5C and 2C above pre-industrial values by 2050 and greater than 4C by 2100.
Global climate models, statistically downscaled using local meteorological data for Zanzibar and
published by the Climate Systems Analysis Group (CSAG) based at the University of Cape Town
[Jack, 2010] support this projection, showing signifcant increases in temperature in Zanzibar. Jack's
results report that maximum monthly temperature is projected to increase uniformly throughout the
year between 1.5 and 2C by the 2050s and 2 to 4C by the 2090s [Watkiss & Bonjean, 2012].
Fig 6: Ensemble mean of projected maximum temperature anomalies from monthly mean maximum temperatures (18611930) under an RCP8.5 scenario. Created using Royal Netherlands Meteorological Institute's Climate Explorer:
http://climexp.knmi.nl/
16
Precipitation
More variable precipitation, including an increase in the number of high-intensity events, was
reported in interviews to have several major effects on seagrass and fsh stocks in Chwaka Bay. When
the bay is diluted by freshwater during rainstorms, many interviewees reported that fsh that are
adapted to saltwater die off in large numbers. High-intensity rain events also wash sediment and
nutrients into the bay from the land around Zanzibar's coast, which Watkiss et al (2012) reported as
increasingly being farmed more intensively. Signs of deposition and changes in fow patterns in the
Bay are evident from a reported increase in the number of sand dunes, and this sediment transport,
combined with eutrophication caused by increasing fertiliser use, will increase the turbidity of the
water and reduce the productivity of the seagrass meadows [Björk et al, 2008]. Increasing intensity of
dry spells is unlikely to directly affect the underwater environment, however a reduction in farming
output may further increase pressure on fshing stocks as local people turn to other sources of food [de
la Torre-Castro and Rönnbäck, 2004], and lead to greater erosion when the rains return.
Figure 7 shows a precipitation projection, which indicates that precipitation means are unlikely to
change but that rainfall will become substantially more variable over the next century. These
projections are consistent with those reported by others for the region, eg Watkiss & Bonjean [2012],
Jack [2010], and IPCC [2013], which also report that precipitation changes are more complex than a
simple increase in variability, and are likely to differ between seasons. Increasing rainfall is projected
between January and May, including the March-May wet season, and decreasing rainfall between
June and October (the existing dry season) [Watkiss & Bonjean, 2012]. Similarly, an intensifcation of
heavy rainfall is projected, particularly during the rainy season, along with increasing intensity of dry
spells during the dry season [Watkiss & Bonjean, 2012].
Fig 7: Ensemble mean of projected precipitation anomalies from monthly mean precipitation (1861-1930) under an
RCP8.5 scenario. Created using Royal Netherlands Meteorological Institute's Climate Explorer:
http://climexp.knmi.nl/
17
Storms
While Chwaka Bay is not located within an area prone to tropical storms, wind storm events
associated with the regional monsoon were reported in interviews to have caused signifcant damage
in recent years - including a fatality. These events are often accompanied by storm surges that affect
the underwater environment - mechanically removing seagrasses due to wave action, as well as stirring
up sediment and in turn increasing the turbidity of the water. While, most models project a fall in
average wind speeds over the year, any seasonal increase may still result in stronger waves that cause
further damage to seagrass meadows and fsh populations. Koch (2001) showed that high current
velocities (possibly above 100 cm s-1) and wave action (particularly in areas with weak currents) can
adversely affect the growth and distribution of healthy seagrass beds, though maximum velocities and
wave tolerance vary widely between species.
Two aspects of "storminess" can be considered using the WCRP CMIP3 multi-model dataset (see
appendix B). During storms, air pressure tends to drop and wind speeds tend to increase [Ahrens,
1994]. Daily model projections of both variables were averaged over the three "epochs" defned in the
IPCC's Special Report on Emissions Scenarios (2000) as 1960-2000, 2046-2065 and 2080-2100.
Tables G and H show the output of each individual model for mean sea-level pressure and two-metre
wind speeds, along with the trends calculated between the frst and second, and second and third
epochs respectively. In table G, the models are almost evenly split between projections of a rise and
fall in mean sea-level pressure. In table H, the ensemble shows more agreement - more models show a
fall in wind speed than a rise, and this is particularly true in the latter half of the coming century. In
both cases, the magnitude of changes is about half of one standard deviation, so there is little evidence
to support projections of increased "storminess" defned in this manner.
Table G: Downscaled mean sea-level pressure projections from CMIP3 ensemble (Pa)
Model
1960-2000
2046-2065
CGCM3.1(T47)
100544
100581
↑
100544.8
↓
CGCM3.1(T63)
100575
100545
↓
100552
↑
CNRM-CM3
100833
100859
↑
100865.7
↑
CSIRO-Mk3.0
100715
100673
↓
100696.9
↑
CSIRO-Mk3.5
100623
100580
↓
100638.8
↑
GFDL-CM2.0
100728
100735
↑
100769.7
↑
GISS-AOM
100849
100853
↑
100803.4
↓
GISS-ER
100493
100473
↓
100460.1
↓
FGOALS-g1.0
100807
100825
↑
100830.3
↑
INGV-ECHAM4
100464
100427
↓
100548.5
↑
INM-CM3.0
100524
100460
↓
100417.9
↓
IPSL-CM4
100693
100684
↓
100676
↓
ECHO-G
100742
100724
↓
100696.5
↓
ECHAM5/MPI-OM
100669
100676
↑
100591.7
↓
MRI-CGCM2.3.2
100700
NaN
N/A
100719.5
↑
AVERAGE
100664
100650
↓
100654.1
↑
Rise
6
8
Fall
8
7
18
Trend 2080-2100 Trend
Table H: Downscaled two-metre wind speed projections from CMIP3 ensemble (m/s)
Model
1960-2000
2046-2065
Trend
cccma_cgcm3_1
7.1
6.9
↓
6.8
↓
cccma_cgcm3_1_t63
7.8
7.1
↓
7.1
↓
cnrm_cm3
9.1
9
↓
8.8
↓
csiro_mk3_0
10.4
10.4
↓
10.4
↓
csiro_mk3_5
8.8
8.9
↑
8.8
↓
gfdl_cm2_0
4.9
5
↑
4.8
↓
giss_aom
5.4
5.4
↓
5.4
↓
giss_model_e_r
3.6
3.5
↓
3.5
↓
iap_fgoals1_0_g
9.7
9.5
↓
9.5
↓
ingv_echam4
9.7
9.8
↑
9.5
↓
6
6
↓
5.9
↓
ipsl_cm4
3.1
3.1
↓
3.2
↑
miub_echo_g
4.7
4.9
↑
5
↑
mpi_echam5
8.9
8.7
↓
8.7
↓
mri_cgcm2_3_2a
4.3
4.4
↑
4.3
↓
AVERAGE
6.9
6.8
↓
6.8
↓
inmcm3_0
2080-2100 Trend
Rise
5
2
Fall
10
13
Sea level rise
Finally, the relative shallowness of Chwaka Bay means that sea level rise is unlikely to signifcantly
affect the geographical extent of seagrass meadows in the bay except in the very long term.
Nonetheless, Jackson (2009) noted that increased water depth causes a decline in the sunlight reaching
the seabed, so any rise in water level will reduce the ability of seagrass to photosynthesise and
therefore damage its productivity. As well as this, much of the land around Chwaka Bay is low-lying
and vulnerable to coastal erosion, saltwater intrusion and fooding. More than 220,000 people (29
percent of the population of Unguja) live below the fve-metre contour line that represents the land
area most at risk from storm surges and high tides [Watkiss et al, 2012]. Sea level rise has a slower
response time than temperature and precipitation, and this is therefore likely to be a longer-term
change [Watkiss & Bonjean, 2012]. The Intergovernmental Panel on Climate Change [2013] reports
that sea levels are projected to rise globally by 0.52 to 0.98 metres under a RCP8.5 representative
concentration pathway.
19
Overfshing and destructive fshing gear
Speaking to the people of Chwaka Bay, it's clear that many realise that their situation is untenable in
the medium to long term, yet feel powerless to effect meaningful change.
An increasing population combined with increasing unemployment means more fshermen, which in
turn means greater pressure on the marine resources of the bay. The resulting declines in individual
catches motivates unscrupulous individuals to use more-effective but highly destructive fshing gear,
such as dragnets, to increase their share of the catch. Short et al (1996) and many others have
described how these fshing methods mechanically damage the seagrasses that play a major role in fsh
lifecycles, limiting fsh stock recovery. This reduction in fsh numbers allows for an increase in the
population of sea urchins, a species whose numbers are normally kept under control by fsh predation.
Sea urchins, in turn, are enthusiastic consumers of seagrass so the resulting population boom has been
shown by Heck and Valentine (1995) to coincides with a reduction in seagrass extent, again limiting
fsh stock recovery.
This decrease in fsh stocks has a feedback effect, both directly as it further reduces fsh predation, but
also because it may cause local fshermen to redouble their efforts to increase their share of the catch
by increasing the intensity of their fshing efforts. In many countries this is countered by legislation
that protects geographical areas or bans certain fshing equipment [Björk at al, 2008], but the
effectiveness of similar legislation in Chwaka Bay has been thwarted by political corruption.
Interviewees from Marumbi reported that even when police are called over illegal fshing activity in
the Mamea Mwari protected area, the same boats often reappear in the same area the next day. It was
also reported that a former Marumbi village leader was questioned by police after complaining about
illegal fshing activity.
20
That leaves a situation where a number of powerful human effects are taking place on a background
of projected climatic changes that may reduce the ability of seagrass species to survive population
shocks. All these drivers of changes in seagrasses in Chwaka Bay and their effects, outcomes and
feedbacks can be summarised in a simple diagram. Figure 8 shows how destructive fshing methods,
overfshing, increased rainfall variability, increased maximum temperatures and sea level rise combine
to create an ever-worsening situation in the bay.
Fig 8: Summary of drivers of changes in seagrasses in Chwaka Bay and their effects, outcomes and feedbacks.
Other vulnerabilities
These projected effects of overfshing, destructive fshing gear and climate change on seagrass and fsh
stocks are not the only vulnerabilities shown by interviews with the people of Chwaka Bay. When
asked what their communities will do if fsh stocks continue to decline, many named farming and
forestry as possible alternatives. Others pointed to tourism, fshing in the deep sea, seaweed cultivation
or starting small businesses.
While many fsherman cultivate small plots of land close to their homes for vegetables to use within
the household [de la Torre Castro and Rönnbäck, 2004], the soils surrounding Chwaka Bay are poor,
somewhat shallow and often raided by monkeys [Salum, 2009], making them unsuited in most cases
to larger scale agriculture. There are some exceptions however - a few cash crops, such as lemons, are
cultivated, while a plot of land near Marumbi has proved to be unusually fertile and the village leaders
have started a community farm there. At the time of the feldwork (April 2014) a well had been dug,
but more investment was being collected to develop an irrigation system. Even if the soil in the wider
Chwaka Bay area was more suitable for intensive agricultural activity, some interviewees noted that
21
every parcel of land is already owned and cultivated by individuals, and that there is "no more room"
for an expansion in farming activity.
Forestry is another common occupation in the area. Mangroves are cut for both frewood and for use
as construction poles [de la Torre-Castro and Rönnbäck, 2004]. Few surveys have been made of the
extent of this practice outside of the nearby Jozani-Chwaka Bay national park, but the formation of
the park (where forestry is limited) has already displaced some wood-collectors to territory closer to the
villages surveyed in this feldwork [Salum, 2009]. As a result, it's likely that any increases in this
industry would be unsustainable in the medium-term.
While tourism infrastructure (hotels, restaurants, diving centres and so on) is widespread in many
areas of Zanzibar, it is almost entirely absent in Chwaka Bay. A small string of hotels along the coast
between Chwaka and Uroa, and some development east of Michamvi on the ocean-facing shore are
the only exception. Many tourism operators consider the bay to be "unattractive" due to its large tidal
range and the seagrass meadows exposed at low tide [Personal communication, manager of Chwaka Bay
Resort]. Even if there were not the case, interviewees in Michamvi noted that the hotels tend to employ
staff from mainland Tanzania or foreigners before locals due to a perception that the locals are
untrustworthy or don't possess the necessary skills. Nonetheless, some locals have successfully started
small businesses supplying food and other goods to hotels, and if the seagrass extent continues to
decline in the bay then there may be some resultant growth of the tourism industry as the seascape
during low tide becomes more "attractive". Sea level rise is also likely to damage shoreline tourist
infrastructure, and much of the land surrounding Chwaka Bay lies below fve metres, making the
communities more vulnerable to fooding in the longer-term [Watkiss et al. 2012].
22
While only three of the ffty-one interviewees reported fshing in the deep sea beyond Chwaka Bay,
the practice is likely to become more common if catches drop further. For this to happen, however,
signifcant investment in equipment - larger boats, engines, and gear - will be needed to safely
transition to this more hazardous working environment.
Seaweed cultivation is the other major economic activity performed in the bay. The introduction of
this industry in the early 1990s has had a positive economic and social effect, partly as it is dominated
by women, but it is extremely labour-intensive [Fröcklin et al, 2012]. It also has a negative effect on
seagrass meadows, so any expansion may further hasten their decline [Eklöf, 2005].
Finally, there is some fnancial support available for entrepreneurs wishing to start small businesses in
the region. Interviewees reported that some communities operate lending clubs where funds are
available to start up businesses whose profts are then returned to lenders. In most cases the funds
available are very small, limiting the scale of what can be achieved.
In summary, it's unlikely that any of the alternatives proposed by interview respondents alone can
offer Chwaka Bay's communities the economic opportunities that they seek. As nearly as quarter of
survey respondents noted, there is "nothing to do except fshing". Combined, they may offer the bare
bones of an adaptation strategy, albeit with the stresses and hardships that will bring. But further work
will be required to fesh out that strategy and ensure that the villages surrounding Chwaka Bay endure
a minimum of suffering during that adaptation process.
Limitations of the study
Subjects in each location were chosen by a representative of the council of fshermen, rather than at
random, so it's plausible that some bias may have entered here in terms of the individuals selected for
interviews. Every one of the interviewees was also male, due to the male-dominated nature of the
fshing industry in Zanzibar. Female respondents may have given different answers. Some work has
been done on female perspectives of village life in Chwaka (See de la Torre Castro & Lyimo, 2012,
Fröcklin et al, 2012).
The village of Chwaka has been extensively surveyed for a period of more than 30 years [Personal
communication, Mats Björk]. Some individuals are frustrated by this constant attention from researchers
with no perceived beneft, and actively avoid participating in research – so in this location the
selection of subjects cannot be said to be wholly representative of the village. While the interpreter was
well-trained in the subject of the study and has many years of experience of translation, some
modifcation and simplifcation of the responses is almost certain to have occurred during the
translation process.
Chwaka Bay has been described as “relatively pristine” [Gullström et al, 2006], and while there has
been a small amount of tourism development on the coastline north of Chwaka, the area is not
signifcantly developed. This study can therefore not be taken as representative of the heavily
developed areas of coastline in the western Indian ocean.
23
Conclusion
The communities surrounding Chwaka Bay have subsisted successfully for centuries on the rich
resources of the its waters. Low-impact fshing methods and a relatively stable climate allowed a small
population to survive without disrupting the delicate seagrass ecosystems of the bay. But that is no
longer the case.
A rapidly-rising population has increased the number of fshermen drawing from the waters of
Chwaka Bay, creating a classic "Tragedy of the Commons" -- where individuals fght to increase their
share of a dwindling resource while accelerating its decline in the process. Increasing use of destructive
fshing techniques means that catches are decreasing in both size and number. Speaking to the people
of Chwaka Bay it is clear that many realise that their status quo is unsustainable, but attempts to
regulate the artisanal fshing industry in the bay are having little effect due to poor enforcement -supposedly as a result of local corruption.
Meanwhile, in the background, global climate change is eroding the ability of the bay's ecosystems to
cope with these stresses. Increasing maximum temperatures, more variable rainfall and rising sea
levels are all -- on differing timescales -- aversely affecting the fsh and seagrass beds that play a crucial
role in the region's marine ecosystems, and damaging the capacity of the local communities to achieve
key economic growth, development, and poverty reduction goals, as well as adapt to future changes.
While this is a case study of just one location, the communities surrounding Chwaka Bay are
representative in many ways of the rural fshing communities that surround the Indian ocean. These
populations are among the most vulnerable to economic stresses due to their overreliance on revenue
from artisanal fshing industries and the widespread corruption that dramatically reduces the
effectiveness of management strategies. Suggestions of management strategies are beyond the scope of
this document, but it's clear that diversifcation of economic activity, clear regulation of fshing gear
and effective enforcement of those regulations should be considered vital in any attempt to lay out a
plan for the sustainable development of rural fshing communities anywhere in world.
Acknowledgements
Sincere thanks are due to Hans Linderholm for supervising this report and providing crucial feedback
and comments. David Rayner, Martin Gullström and Mats Björk offered valuable guidance. Said
Juma Shaaban was a fantastic translator. David Rayner and Narriman Jiddawi provided important
meteorological data and climate projections. Fred Short and Maria Bergstén kindly allowed their
fgures to be reproduced. Brian Eno created music that is excellent to work to, and Silvia Hüttner was
an endless source of support and encouragement.
This work contributes to the project 'Assessment of carbon sequestering capacity in East African seagrass
ecosystems affected by multiple stressors in a changing climate', funded by the Swedish International
Development Cooperation Agency SIDA.
Finally, a debt of gratitude is owed to the people of Chwaka Bay, without whom this study would not
have been possible.
24
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Appendix A: Questions answered by fshermen in Chwaka Bay
1) Name / Age / Occupation
2) Where do you fsh?
3) How long have you been fshing in Chwaka Bay?
4) How and why has the bay changed in this time?
5) (a) Do you remember any bad storm years
(b) Do you remember any bad rain years?
(c) Do you remember any bad heat years?
6) Was there any effect on fsh catches or seagrass?
7) Has the number of fshermen changed and why?
8) If fsh catches continue to decrease, what will happen to the village?
9) Does anyone protect the seagrass?
Appendix B: Climate models in CMIP3 ensemble
CMIP3 I.D.
Originating Group(s)
Country
CGCM3.1(T47)
Canadian Centre for Climate Modelling & Analysis
Canada
CGCM3.1(T63)
Canadian Centre for Climate Modelling & Analysis
Canada
CNRM-CM3
Météo-France / Centre National de Recherches Météorologiques
France
CSIRO-Mk3.0
CSIRO Atmospheric Research
Australia
CSIRO-Mk3.5
CSIRO Atmospheric Research
Australia
ECHAM5/MPI-OM
Max Planck Institute for Meteorology
Germany
ECHO-G
Meteorological Institute of the University of Bonn, Meteorological Research Institute of
KMA, and Model and Data group.
Germany
/Korea
FGOALS-g1.0
LASG / Institute of Atmospheric Physics
China
GFDL-CM2.0
US Dept. of Commerce / NOAA / Geophysical Fluid Dynamics Laboratory
USA
GISS-AOM
NASA / Goddard Institute for Space Studies
USA
GISS-ER
NASA / Goddard Institute for Space Studies
USA
INGV-ECHAM4
Instituto Nazionale di Geofsica e Vulcanologia
Italy
INM-CM3.0
Institute for Numerical Mathematics
Russia
IPSL-CM4
Institut Pierre Simon Laplace
France
MRI-CGCM2.3.2
Meteorological Research Institute
Japan
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