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Matt Ansell (21200472) • Johan Backstrom (21444569) • Malika Boukhoubza (21388523) • Todd Curedale (21256705) • Nadine Hussfeldt (21414248) 2014 Cottesloe Ecosystem Research Project_____ _____________________________ Distribution and abundance of algae and seagrass across an ecological gradient at Cottesloe reef Matt ANSELL • Johan BACKSTROM • Malika BOUKHOUBZA • Todd CUREDALE • Nadine HUSSFELDT 1 Abstract The Cottesloe reef contains a unique and diverse range of marine life and habitat. The ecological and social significance of the reef has been recognized by the Department of Fisheries in 2001 when a Fish Habitat Protection Area (FHPA) was created. The University of Australia has contributed to the research of the Cottesloe FHPA since 2008, focusing on collecting and analyzing data for primary producers, invertebrates and fish population. In this study, we focused on the benthic macro flora and hypothesized that primary producers will vary in abundance depending on the ecological gradient of the reef environment. Data on primary producers were collected in three separate zones, the lagoon area, flat reef and broken reef. For each habitat zones an estimated percentage of ground cover for seagrass, brown algae, red algae and green algae species were recorded using 0.25 m2 quadrats haphazardly placed. Our results showed seagrass dominated the lagoon area (56%) while Brown algae had the highest coverage in broken reef (44%) and in the flat reef (29%). Red algae’s highest percentage cover was in the broken reef (16%). Green algae’s coverage was least significant, with an average cover of 0.42% across all zones. Seagrasses uses their root system for anchorage and nutrient extraction from the ocean floor. The lagoon area, with its nutrient rich, sandy substrate provides an ideal environment for seagrass species to flourish. All algae species lack roots, leaves or stems, they gather nutrients through diffusion from the surrounding water and anchor themselves to the hard surfaces using holdfasts. The flat reef and broken reef areas of Cottesloe offers a natural environment for algae to use as an anchorage platform. Keywords – Primary Producers, Algae, Seagrass, reef, Cottesloe 2 Introduction Coastal environments are the most productive subtidal benthic environments (Levinton 1995). Reef communities are particularly important because of their abundant and diverse life (Fagerstrom 1987). In the reef, benthic autotrophs play an important role in fixing carbon through photosynthesis. The greater portion of photosynthesis is achieved by algae, while vascular plants and eubacteria contribute to a smaller extent (Mann 1973). Primary producers directly supply energy to herbivores, making them the pillar of food webs (Cyr and Pace 1993). They also play an essential nursery role, providing spawning habitats for many fish and invertebrates (Vermeij et al 2013). For this reason there is growing concern about negative changes affecting benthic producers due to anthropogenic factors such as pollution, fishing, and coastal development or natural stresses such as global warming (Vermeij et al 2013). The intra-­‐reef habitat can typically be classified in distinctive zones. The lagoon was characterized by a predominantly sandy substrate that may contain patches of rock (Fagerstrom 1987). It is usually less affected by wave energy due to reef structures further out forming a protective barrier. In the Cottesloe Fish Habitat Protection Area, the depth of the lagoon was approximately two metres. Flat reef zone was a levelled rocky area with medium wave energy and a depth range between three to four metres. It lies between the outer (broken) reef and the lagoon. Broken reef was the outermost section with high wave energy. It lies between the flat reef and the outermost reef drop-­‐off and has a water depth of between three to five metres with sporadic coral bommies. This study investigated the benthic composition of the Cottesloe FHPA across the ecological gradient of the reef system. We hypothesised that seagrass will be more abundant in sandy areas of the lagoon and algae abundance will be skewed towards the outer, rocky reef areas. This is due to the fact that seagrass have evolved back into the ocean from land plants millions of years ago (Hemminga & Duarte 2000) and have certain phenotypic structures that limit their habitats in the ocean. Seagrass possess root structures that are required for anchorage and nutrient extraction from ocean sediment (Hemminga & Duarte 2000). This makes hard sediments such as reef an unviable substrate for seagrass growth. We anticipate that the predominantly sand substrate of the lagoon will provide a good substrate from which seagrass can anchor itself and extract nutrients from. As brown, green and red algae do not have a root system, they attach to hard substrates with a holdfast and take up nutrients from the water that surrounds them (Mann 1973). Therefore, we anticipate that results will show seaweeds to grow in the flat and broken reef where they can attach to the hard substrate. 3 The reef system at Cottesloe beach is of great importance to the surrounding marine life. This was acknowledged in 2001 when the department of Fisheries declared it a Fish Habitat Protection Area (Department of Fisheries 2010). The legislation restricts the use of potentially destructive activities such as spearfishing, commercial fishing and specimen collection. Being in close proximity to densely populated urban area, the Cottesloe reef is a central recreational area and has great social significance as well as being ecologically important. 4 Materials and Methods Study Area The study site was located within the Cottesloe Fish Habitat Protection Area (CFHPA) in the western suburb of Perth, Western Australia. Four distinct habitat zones were identified within the area, the lagoon, flat reef, broken reef and front reef (Fig. 1). This study examined the first three zones. (Fraser, 2014) Fig1: Site area located at 32.007709°S, 115.750784°E, within the Cottesloe Fish Habitat Protection Area. The geomorphology of the CFHPA follows the standard reef pattern (Fig. 2) with a sandy lagoon, flat reef, broken reef (or reef crest) and front reef (or fore-­‐reef). (Source: Downtown Campus, Image by U nknown) Fig2: Reefs are separated from the coast by a lagoon. In the Cottesloe FHPA, the lagoon has a sandy floor and is protected from waves and currents. The flat reef is shallow and nearly levelled with sand and coral patches. The broken reef (or reef crest may be an algal ridge when wave action is strong. (Fringing and barrier reefs, n.d.) 5 Data Collection The study was conducted over two days on 30 March 2014 and 6 April 2014 by second year students from the University of Western Australia. For each habitat zones 0.25 m2 quadrats were placed haphazardly and an estimated percentage of ground cover of individual primary producers were recorded on waterproof datasheets. Four replicates of the treatment yielded a total of 87 quadrats for the three habitat zones. An ID guide was available to assist in identification and underwater photographs were taken when possible. Visibility and water depth were recorded for each quadrat sample. Data Analysis The data collected for each species was grouped into four categories green algae, brown algae, red algae and seagrass. The mean percentage composition of primary producers for 2014 was analysed for each habitat zone. The standard error was represented in each figure. 6 Results Table 1: Minimum and maximum depth recorded in each reef area at Cottesloe FHPA Min of Depth (m)
Max of Depth (m)
Lagoon
2
3
Flat Reef
1
4
Broken Reef
3
5
Table 2: Average percentage cover of primary producers in each reef area (2014) Seagrass
Green algae
Brown algae
Red algae
Total
Lagoon
56.79
0.00
3.79
0.24
15.21
Flat Reef
21.15
0.38
28.65
11.23
15.36
Broken Reef
0.00
0.87
44.00
16.30
15.29
Grand Total
25.98
0.42
25.48
9.26
Depth of the Cottesloe reef For each of the 87 quadrats, the depth and visibility was recorded. The distance in the lagoon varied between two to three metres, while in flat reef the distance to the substrate varied between one and four metres. The broken reef reached the greatest depth to five metres (Table 1). Percentage Cover
80
Average of Seagrass
Average of Green algae
70
Average of Brown algae
60
Average of Red algae
50
40
30
20
10
0
Broken Reef
Flat Reef
Lagoon
Fig3: The average percentage cover for each reef area shows a dominance of seagrass in the lagoon. In the broken reef and flat reef brown algae are the dominent species. 7 Percentage Cover
Seagrass
Percentage Cover
Green Algae
1.2
80
70
1.0
60
0.8
50
40
0.6
30
0.4
20
0.2
10
0.0
0
Lagoon
Flat Reef
Lagoon
Broken Reef
Flat Reef
Broken Reef
Fig4.1: Mean seagrass cover (with standard error) for each reef area shows no seagrass in the broken reef while the lagoon was composed of 57% of Seagrass. Fig4.2 Mean green algae cover (with standard error). Green algae species are the least abundant in the Cottesloe FHPA, with 0.42% on average for all areas. The sampling in the broken reef yielded the most green algae (0.87%). Percentage Cover
Brown Algae
60
Percentage Cover
Red Algae
25
50
20
40
15
30
10
20
5
10
0
Lagoon
Flat Reef
0
Broken Reef
Lagoon
Flat Reef
Broken Reef
Fig4.3: Mean brown algae cover (with standard error). Brown algae was present throughout the Cottesloe reef with 44% coverage in the broken reef, 29% coverage in the flat reef and 4% in the lagoon. Fig4.4 Mean red algae cover (with standard error). The mean red algae cover was greater in the broken reef (16%) while it covered 11% of the flat reef. 8 Primary Producers -­‐ average coverage for each reef system The composition of the benthic marine life (Fig. 3) varied throughout the three reef zones of the Cottesloe FHPA. Seagrasses were dominant in the lagoon (57%) and brown algae in the broken reef (44%). The flat reef showed a bigger species diversity, with all four main types of primary producers represented. Overall, the seagrasses were the most recorded benthic producers for all areas combined with an average of 28% (Table 2) followed by the brown algae covering 24% of the study area. Primary Producers – algae and seagrasses Our analysis revealed a preference for all algae (green algae, red algae and brown algae) for the broken reef (Fig. 4.2, Fig. 4.3, Fig. 4.4) where a highest concentration was present. All four primary producers groups were present in the flat reef with brown algae dominating the composition with 29%. Seagrasses had a significantly lower distribution in the flat reef and broken reef while in the lagoon, they covered 57% of the subfloor (Fig. 4.1). 9 Discussion Seagrasses and algae have evolved with very different phenotypic traits that restrict their ability to colonise certain habitats. The results of this study demonstrates these limitations, showing a correlation between the ecological gradient of the reef and species distribution and habitats. The evolution of primary producer species and their survival traits play a role in their ability to colonise certain areas. Our results show seagrasses prefer sandy habitats and this was evident by their distribution towards the sandy lagoon area. Algae use holdfasts to attach to rock and other hard substratum and this restricted it to the reef areas as indicated in Fig. 4. Seagrasses have evolved back into the ocean from land plants millions of years ago (Hemminga & Duarte 2000). As a result of this evolutionary pathway, they have limitations to growing in marine habitats. Seagrass have root structures similar to land plants that require an anchorage and nutrient extraction from ocean sediment (Hemminga & Duarte 2000). Such limitations make hard substratum such as reef an unviable habitat for seagrass growth. This root structure makes the lagoon an ideal habitat for seagrass as demonstrated by Fig. 4.1, showing the highest percentage cover in the lagoon section (57%). The flat reef zone contained limited areas of soft sediment allowing for some patchy seagrass growth (21%). There was very limited soft substrate in the broken reef zone and this is reflected in Fig. 4.1 showing virtually no seagrass growth in this zone. The different depth between the zones creates different strengths of wave energy on the seabed. The majority of the wave energy was lost in the broken reef and flat reef due to these zones acting as a “barrier”. This means that by the time waves reach the lagoon much of the wave energy has dissipated. Seagrass prefers areas with lower currents and turbidity making the lagoon the most suitable area for seagrass to grow in the study area (Greve & Binzer 2004). This is reinforced by our results in Fig. 4.1, showing a skewed distribution of seagrass towards the lagoon. The varying depth in the reef also leads to different levels of sunlight reaching the ocean floor. Due to the high biomass of seagrass and small leaf surface area limiting photosynthetic ability, seagrass must grow in areas of higher light intensity (Greve & Binzer 2004). Across the three zones we found seagrass growing most prolifically in the shallowest sections. This may have been related to the difference in substrates, however the difference in light intensity between the zones may also be a contributing factor. The three algae (seaweed) groups studied (brown, red, green) evolved within the ocean from simply constructed eukaryotic cells into photosynthetic plants with neither roots nor leafy shoots and also lack vascular tissues (Hoek, Mann & Jahns 1995). Seaweeds have successfully colonized areas below tide level (sublittoral zone) of temperate latitudes (Mann 1973) replicated in the area that was studied in Cottesloe. There are many gradients of environmental factors that determine the distribution of seaweed. Factors of 10 light, depth, temperature, wave action and competitive interactions (Mann 1973) would play their part in the determining the distribution of species in Cottesloe. The abundance of the brown (Phaeophyta), red (Rhodophyta) and green (Chlorophyta) algae studied, was mostly found, as expected in the reef areas (Fig. 3). The 4% of algae species found in the sandy area of the lagoon could have either been attached to the seagrass as epiphytes (Fuhrer 1981) or attached to lone rocks or shell substrates. Our results show that of the three algae species, the brown algae was predominant on the flat reef and broken reef, higher in the broken reef (Fig 4.3). Brown algae species are found to produce the largest biogenic structures within benthic marine environments and can conventionally dominate the reef sections of the world’s marine habitats (Steneck et al. 2002). This is confirmed by the results of this study and it is plausible that brown algae has out competed both red and green algae for dominance of both reef sections. The second highest was red algae with a higher percentage cover in the broken reef than the flat reef (Fig. 4.4). Red algae only require a small living space and can be found at greater depths, requiring only about 0.001% of the sea surface light incident remaining available for photosynthesis (Hoek, Mann & Jahns 1995). Our results found a higher percentage cover of red algae in the deeper broken reef, this is in line with other research findings as it only requires a small living space and is able to cohabit with brown algae as its understory, requiring less light for photosynthesis. The small percentage cover of green algae recorded (Fig. 4.2) could possibly be due to the fact that this species prefers rocky coastline in the upper part of the intertidal zone (Hoek, Mann & Jahns 1995). Both reef sections were on average four to five meters deep, which may be the outside the preferred environment for the green algae species. Overall it is evident that the evolutionary structure of seagrass and algae species plays a significant role in its ability to colonise coastal habitats. The substrate appears to be the most limiting factor with areas of predominantly rock having almost no seagrass present but dominated by algal species. As hypothesized, seagrass was the dominant species in the sandy nutrient rich lagoon while algae were found in greater abundance in the reef areas. We could not conclude that depth in the Cottesloe reef contributed to the distribution of primary producers. However depth may play a significant role as a correlation with light penetration and wave energy has been documented in other studies. Acknowledgements We acknowledge and thank the Department of Fisheries for allowing UWA student to access the Cottesloe Fish Habitat Protection Area to gather data and monitor the marine ecosystem of the Cottesloe reef. 11 References Cyr H, Pace ML (1993) Magnitude and patterns of herbivory in aquatic and terrestrial ecosystems. Nature 361:148–150 Fraser, M 2014, 2014 Cottesloe Ecosystem Research Project, lecture notes distributed in Marine Systems (SCIE2204) at The University of Western Australia, Crawley on 1 April 2014. Fringing and barrier reefs, n.d. photograph, viewed <http://dtc.pima.edu/blc/183/13_183/images/barrier_reef_answers.jpg>. 1 May 2014, Fuhrer, BA 1981, Seaweeds of Australia, Sydney : Reed, Sydney p 9. Greve, Tina M., and Thomas Binzer. Which factors regulate seagrass growth and distribution, European seagrasses–an introduction to monitoring and management (2004): 19-­‐23.Seagrass ecology book Hemminga & Duarte, M & Duarte CM 2000, Seagrass ecology, Cambridge University Press, Cambridge, UK, pp 4, 17. Hoek, Cvd, Mann, DG & Jahns, HM 1995, Algae : an introduction to phycology, Cambridge University Press, Cambridge, UK, pp 2, 9, 45, 49, 301. Mann, KH 1973, Seaweeds: Their Productivity and Strategy for Growth: The role of large marine algae in coastal productivity is far more important than has been suspected, Science (New York, N.Y.), vol. 182, no. 4116, p. 975. Plan Of Management For The Cottesloe reef Fish Habitat Protection Area, Fisheries Management Paper No. 155, 2001 Steneck, RS, Graham, MH, Bourque, BJ, Corbett, D, Erlandson, JM, Estes, JA & Tegner, MJ 2002, Kelp forest ecosystems: biodiversity, stability, resilience and future, Envir. Conserv., vol. 29, no. 4, pp. 436-­‐459. Vermeij, M.J.A., Heijden, R.A., Olthuis, J.G., Marhaver, K.L., Smith, J.E. & Visser, P.M. 2013, Survival and dispersal of turf algae and macroalgae consumed by herbivorous coral reef fishes, Oecologia, vol. 171, no. 2, pp. 417-­‐425. 12 Press Release Off the Cottesloe shores lies a unique reef system which provide habitat for feather stars, sea corals, both weedy and leafy seadragons and a myriad of fish. Cottesloe is also a nursing area for many species such as the Port Jackson sharks, stingrays and squids. Such diversity is found in close proximity to the relatively large urban population of Perth, making it is vulnerable to disturbance by human activity. The Department of Fisheries and the Cottesloe community have recognized the importance of this ecosystem declaring it a Fish Habitat Protection Area (FHPA) in 2001 and since 2008, the University of Western Australia (UWA) has undertaken annual research to estimate the population and distribution of fish, invertebrates and marine plants. Algae and seagrass play a vital role in the Cottesloe reef ecosystem, they not only supply food and oxygen to the marine fauna, but also provide a good hiding place from predators and a safe nursing ground. As part of the UWA research program, this study looks at the distribution of algae and seaweed in three distinct area of the Cottesloe reef, namely the lagoon (close to the beach), the flat reef (levelled area further from the lagoon), and the broken reef (further from the shore). We collected field data by separating the Fish Habitat Protection Area into three different zones; the lagoon, flat reef and broken reef. Samples were collected from each zone using randomly placed, .25 m2 quadrats and estimating species coverage within. The study concluded that seagrass was found predominantly in the lagoon area as it needs a soft, nutrient rich floor bed for its roots to extract nutrients. Algae species have no root system, instead they absorb nutrients directly from water through diffusion. Algae need a hard surface to anchor themselves to in order to prevent them from being moved by currents and waves. The three types of algae observed, brown algae, red algae and green algae were found predominantly in the rocky reef areas of the flat reef and broken reef. A healthy reef system at Cottesloe provides great enjoyment to fishermen, snorkelers, divers and the community at large. It also offers a vital and safe environment to a great variety of marine life. It is therefore important to continue the scientific research and monitoring programs in order to understand the different species’ biology, productivity, abundance and vulnerability. (393 words) 13 14