Download A Look into the Relationship between the Bluestreak

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“A Look into the Relationship
between the Bluestreak Cleaner
Wrasse’s (Labroides Dimidiatus)
Abundance and Reef Fish Body
Size & Diversity in Nosy Be,
Madagascar”
BTEC Advanced
Diploma Report
Margaux Steyaert
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Introduction
Coral reef ecosystems are some of the most diverse in the marine world (5), harvesting an
array of intriguing organisms and behaviors known to science. Although they encompass a
complex matrix of ecological interactions, these ecosystems are fragile and especially
vulnerable to change (1). Positive interspecific interactions such as mutualistic relationships
(e.g. cleaning symbiosis) are important to maintain species richness and abundance. The
lack of these may have a serious detrimental knock-on effect to other species.
Cleaning behavior can be observed in many species of shrimps and fish, but one of the
most commonly observed and studied is that of the bluestreak cleaner wrasse (Labroides
dimidiatus). L.dimidiatus which performs the function of removing ectoparasites, unwanted
food particles, as well as diseased or dead tissue from other coral reef fishes (1). They
perform this service over certain patches of coral reef know as cleaning ‘stations’ where,
through a series of complex swimming patterns, body orientation, and erratic tail
movements, they attract other fish species known as ‘clients’ that are looking to be cleaned.
A congregation of various coral reef fish species can be observed at a cleaning station at the
same time, often leading to a decrease in interspecific predatory behaviors and competition
via the tactile stimulating behavior of the cleaner wrasse (4).
Sharing species with most of the Indo-Pacific Ocean, but although frequently overfished,
Malagasy coastlines still contain some of the most diverse coral reefs in the world. No known
previous surveys or research has been conducted on cleaner wrasse abundance in southern
Nosy Be. This is why I have chosen to focus this BTEC project on assessing the
relationship, if there is one, between coral reef fish body size & diversity and the abundance
of bluestreak cleaner wrasse stations. Southern Nosy Be reefs are relatively shallow and
regularly fished, and so it was important to choose 5 survey sites that could be compared.
Further information regarding the designated survey sites can be found in the methodology
and discussion sections of this report.
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Methodology
A total of 3 survey dives/snorkels were carried out at 5 varying sites around southern Nosy
Be. The aim of the surveys was to actively search for and observe cleaning stations during
30 minute surveys. The chosen sites were as follows:
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NOSY LEFT = 13°25’30’’
48°21’46’’
Average depth = 6m
Range of depth = 2-10m
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HOME REEF = 13°24’25’’
48°20’42’’
Average depth = 3m
Range of depth = 1-5m
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3 BROTHERS = 13°25’46’’
48°21’14’’
Average depth = 4.5m
range of depth = 2-7m
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TURTLE TOWERS = 13°27’12’’
48°19’27’’
Average depth = 4m
Range of depth = 3-11m
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LOKOBE = 13°25’46’’
48°18’53’’
Average depth = 5.5m
Range of depth = 2-9m
Each survey would start once a first cleaning station would be found. Once found, the
following were recorded within a 5 minute window:
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depth of station
substrate upon/around which the station was located
position of station (e.g. under ledge, inside long-branching etc.…)
size of cleaners/no of cleaners
client species at station (contact between cleaner and client has to be observed
for the fish species to be classed as a client)
estimated length of clients (0-10cm, 11-20cm, 21-30cm, 30+cm)
time spent by client at station
survey site/date of survey
notes/comments on behavior observed
The surveys were carried out either by scuba diving or snorkeling, depending on
tides, sea state as well as boat or equipment availability. They were carried out in a
buddy pair, where the other diver would time the observation as well as be present for
safe dive-practice. The following equipment was used for each survey: dive gear
(BCD, regs etc…), dive computer, dive compass, camera and the BTEC survey slate I
designed for this project (Fig 1.0). As this project was carried out whilst being a
volunteer on the Frontier Marine Conservation and Diving Program, the permits
required for the dive sites belong to Frontier. The mode of transport used was by boat,
driven by the local staff, Victor. The following members of Frontier staff were involved
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in the surveys: Justin Lennon, Rob MacFarlane, Catie Gutmann Roberts, Aramintha
Critchley, Tom Quigley as well as Research Assistant Volunteers. The surveys are
recorded both in the logbook as well as on the data sheets I have compiled. Surveys
were carried out either as a specific BTEC survey dive or I would conduct the search
for cleaning stations alongside an Active Search or Baseline Survey Protocol dive.
Following the data collection, the index of diversity of coral reef fish species for each
site may be worked out using Simpson’s index of diversity for comparison.
Fig 1.0 Replica of the dive slate used
during cleaner wrasse surveys.
Map of Nosy Be, Madagascar
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Results
Observing the change of abundance of Labroides dimidiatus across the survey sites
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Total number of cleaners
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Total number of stations observed
5
0
Home Reef
Nosy Left
3 Brothers
Turtle
Towers
Lokobe
Average number of cleaners per
station
Survey sites
(Fig 2.0) Chart showing the data collected regarding L.dimidiatus.
The bar chart above shows that the blue-streak cleaner is indeed present at each
survey site, proving it is an abundant species. Although the highest number of cleaners
(21) and the most cleaning stations (12) were found in Lokobe, the average number of
cleaners per station remains constant through the 5 sites (averaging two cleaners per
station). The least number of stations (4) were observed at Home Reef, as well as only
8 cleaner wrasse in total.
Total number of client individuals
Looking at the difference in numbers of territorial and schooling species
present in cleaning stations for each survey sites
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20
15
Number of territorial fish
species
10
Number of schooling species
5
0
Home Reef Nosy Left 3 Brothers
Turtle
Towers
Lokobe
Survey Sites
(Fig 3.0) Graph showing the data collected on client fish species.
Fig 3.0 indicates that more territorial species are present throughout cleaning stations
across the survey sites than schooling species. Again the most considerable data was
collected at Lokobe, where the highest number of territorial species (20 in total) and
schooling species (12 in total) were observed. 3 Brothers had the lowest recorded
number of territorial species (11) whilst both Home Reef and Nosy Left had the lowest
number of schooling fish observed with only 3 species recorded. Overall, Home Reef
has the least total amount of client species present (16).
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Territorial species
Sulphur damsel
White belly damsel
Black damsel
Blue damsel
Three-line damsel
Jewelled damsel
Yellow-tail demoiselle
Regal demoiselle
Triple-tail demoiselle
Arabian spinecheek
Dusky gregory
Humbug dascyllus
Cardinal fish
Skunk anemonefish
Scissor-tail sergeant
Indo-Pacific sergeant
Chocolate hind
Copper sweeper
Racoon butterfly fish
Red-fin butterfly fish
Thread-fin butterfly fish
Vagabond butterfly fish
Bennett's butterfly fish
Chevroned butterfly fish
Map puffer
Black puffer
Slatey sweetlips
Black -spotted sweetlips
Black sweetlips
Giant moray eel
Masked bannerfish
Fangblenny
Schooling species
Moorish idol
Ruddy fusiliers
Scissor-tail fusiliers
Red/Twin-spot snapper
One-spot snapper
Black snapper
Yellow-tail barracuda
Mimic filefish
Dash-dot goatfish
White-saddled goatfish
Crescent wrasse
Barred thicklip wrasse
Black-edge thicklip wrasse
Sling-jaw wrasse
Checkerboard wrasse
Tube-lip wrasse
Six-bar wrasse
Indian-Ocean bird wrasse
Blue-barred parrotfish
Weedy surge wrasse
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(Table 1.0)
Table 1.0 above outlines all the client species recorded during surveys, as well as
showing which client species were territorial or schooling.
SITE
Home Reef
Nosy Left
3 Brothers
Turtle Towers
Lokobe
TERRITORIAL
81.25%
88.24%
64.71%
68.00%
62.50%
SCHOOLING
18.75%
11.76%
35.29%
32.00%
37.50%
(Fig 4.0) Table showing the percentage of territorial and schooling client species for
each survey site.
This table shows that Lokobe had the highest percentage of schooling species
observed in comparison to the percentage of territorial species. Nosy Left had the
lowest percentage of schooling species with only 11.76%.
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Comparing the body size of client individuals at the 5
sites
Total number of client individuals
250
200
150
0-10cm
11-20cm
100
21-30cm
30+cm
50
0
Home Reef
Nosy Left
3 Brothers Turtle Towers
Survey Sites
Lokobe
(Fig 5.0) Chart showing the range in body size of client fish species across the 5 sites
The highest total number of individuals recorded at cleaning stations was at Turtle Towers
with 273 individuals, followed by Nosy Left with a total of 271 individuals. However only one
individual with a body size exceeding 30cm was recorded at Turtle Towers, the lowest of all
sites. Lokobe had the lowest range in client body size out of all the sites as the most
individuals with a 30cm+ body size were recorded there (18 in total). 3 Brothers had the
highest number of individuals recorded with a body size of 11-20cm (234 individuals).
HOME REEF
NOSY LEFT
3 BROTHERS
TURTLE TOWERS
LOKOBE
0.7635
0.7018
0.6407
0.6782
0.9215
(Fig 6.0) Table showing the index of diversity of client species for each site (using Simpson’s
Index of Diversity)
Lokobe was found to be the most diverse site of all with an index of diversity of 0.9215.
Adversely, 3 Brothers had the lowest diversity of all sites with an index of only 0.6407.
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Discussion
Previous research carried out in Australia suggests that the bluestreak cleaner wrasse has
a major influence on the local species assemblage and habitat choice of coral reef fishes
and may in part explain the distribution of many fishes (2). Surveys showed that areas with
more cleaner wrasse present also have higher numbers of fish species observed in stations
(see Fig 2.0 and Fig 3.0). I believe however that the presence of the bluestreak cleaner
wrasse is more highly affected by the diversity of client species than vice versa. Since the
cleaner wrasse isn’t fished for food consumption in Nosy Be (regular visits to the local fish
market were carried out to ensure of this), a reason for the change in the cleaner abundance
at the various sites could be down to numbers and average size of client fish species
present (see Fig 2.0, Fig 3.0 and Fig 5.0).
3 Brothers, Nosy Left and Home Reef were more heavily fished than Lokobe and Turtle
Towers. A smaller amount of schooling fish were observed at the 3 sites, as well as a lower
abundance of cleaner wrasse, leading to the assumption from this data that the abundance
of cleaner wrasse is affected by the presence or therefore lack-of schooling species. This
assumption can be backed up by the fact that there has been previous research conducted
that proves that schooling fish and cleaner wrasse numbers are highly dependent on one
another (3). The data collected in this study seems correlative but not necessarily causal.
Since this study was conducted at relatively shallow sites (maximum depth was 11m), it is
hard to assume that the cleaning stations observed were representative of all stations
around Nosy Be. This is because it is known that greater numbers of schooling species (as
well as L.dimidiatus) are found at deeper depths (this was observed in sites such as the
MPA Tanikely and Gorgonia II where depths would reach +20m).
It was important to choose 5 different sites with varying physical and ecological aspects in
order to successfully compare the local habitats and their effect on fish numbers.
Home reef is a shallow reef situated just outside a mangrove forest, therefore the visibility
at this site was not always very good. The mangroves were highly fished, which leads to a
decrease in juvenile fish entering the reef, possibly explaining why this was the site with the
least client species observed.
There is also extensive fishing occurring in both Nosy Left and Three Brothers, sites that
both regularly have strong currents. Schooling fish species such as snappers, emperors and
surgeonfish are know to have been fished in these sites (these were found on the fish
market and the fishing sites were recognized when locals were asked). This could be the
explanation as to why Three Brothers has the highest number of clients with a body size of
11-20 cm but little numbers of clients with a body size exceeding 20cm (Fig 5.0).
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Turtle Towers is the deepest site containing the greatest hard coral cover (including longbranching, short-branching, tabular), ideal substrates for cleaning stations.
Finally, Lokobe is located alongside the Lokobe National Protected Reserve (forest), and
has the highest diversity of wrasse and other schooling fish out of all sites (this is known by
looking at Frontier’s past BSP and AS data).
To improve and further this study, 6 replicates per site would have been carried out in
order to increase the reliability of these results, as well as to produce more conclusive
data. Surveys would also principally be carried out as snorkels, as this is less intrusive
and may enable me to observe timid species that are easily disturbed in cleaning
stations (such as schooling fish species like parrotfish). Scuba diving is more intrusive
and may also interfere with interspecific interactions. I would also include the MPA
Tanikely as one of the designated sites, so as to compare cleaner wrasse populations
between protected reefs and overfished ones.
A study on the abundance of the Labroides bicolor cleaner wrasse would have also
been undertaken, as I would have liked to study the difference in cleaning behavior
between the two cleaner species. Unfortunately, due to the lack of abundance of the
bicolor species around the designated survey sites that was observed during preliminary
snorkels, I decided to only survey bluestreak cleaner wrasse stations. However sightings
and behaviors were observed of L.bicolor. There were two different sightings, one at 25m
around Gorgonia II and another at Turtle Towers. Originally the lack of abundance of the
bicolor was thought to have been due to the lack of depth or specific client species of
schooling fish at the 5 designated sites around southern Nosy Be. However the unusual
second sighting has proved this wrong, as the bicolor was seen to be sharing a cleaning
station with two bluestreak individuals with no apparent signs of competition between the
two species.
Summary
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The L.dimidiatus specie is abundant in Southern Nosy Be reefs, however the
L.bicolor is not.
The abundance of cleaning stations varies between the five different survey sites,
as well as the diversity of coral reef fish species.
Lokobe is the most diverse site whilst also having the highest total number of
cleaning stations and cleaners of all sites.
Sites like 3 Brothers and Nosy Left have lower numbers of schooling fish species
as they are highly over fished.
In conclusion, this survey shows promise of producing conclusive data, however more time
and replicates would have been needed to accomplish this. In fact, after this project was
completed, the data and parts of the methodology produced from this BTEC were used to
continue on research work on the bluestreak cleaner wrasse in Southern Nosy Be, as part of
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a research proposal by Frontier (led by Justin Lennon). Hopefully this will enable us to better
understand cleaner wrasse behavior and the importance of their role in coral reef ecology in
Nosy Be.
References:
(1) Dr Dan Exton, Operation Wallacea, IH279: The behaviour and functional role of
reef fish cleaners in Indonesia.
(2) Alexandra S. Grutter, Jan Maree Murphy and J. Howard Choat Cleaner Fish
Drives Local Fish Diversity on Coral Reefs (2008).
(3) Peter A. Waldie, Simon P. Blomberg, Karen L. Cheney, Anne W. Goldizen,
Alexandra S. Grutter Long-Term Effects of the Cleaner Fish Labroides dimidiatus
on Coral Reef Fish Communities.
(4) Karen L. Cheney,a Redouan Bshary,b and Alexandra S. Gruttera Cleaner fish
cause predators to reduce aggression toward bystanders at cleaning stations.
(5) G. Paulay, Life and Death of Coral Reefs (1997), pp. 298-353.
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