the marine habitat gradient of cottesloe reef: increasing fish … · 2013. 8. 7. · this study...

SCIE2204 May 2013 Marine Systems

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The marine habitat gradient of Cottesloe Reef: increasing fish abundance and diversity towards outer reef ________________________________________________________________________ Tim Angeloni (20950811), Leah Campbell (21112688), Harrison Davis 20916292), Oliver Fredriksson (21148011), Charlotte Patrick (21139276), Natalie Prinz (21015903), Jessica Schaefer (21235688), Katherine Werndly (20940935) University of Western Australia, Crawley Abstract This study investigates fish species presence and abundance in three different habitat zones within the Fish Habitat Protection Area (FHPA) of Cottesloe Reef. It was hypothesized that the diversity and abundance of fish species would increase with increasing distance from shore through lagoon, flat reef and broken reef habitat zones. The results of this study supported our hypothesis; total fish counts as well as species diversity increased moving from near shore to offshore zones. We analysed previous research conducted on the study site and compared it with our own fieldwork results, allowing us to draw longer-scale conclusions and detect patterns of change over time. Unexpected results in the population structure of three individual species also arose, and provided insight into the value of varying habitat types at an individual species level, as well as at an overall fish abundance and diversity level. The results of this study are applicable in identifying areas of reef ecosystems for protection in order to conserve maximum biodiversity in a reef system existing in close proximity to anthropogenic activities. This study provides an insight into the spatial relationship between abundance and diversity of fishes and varying habitat type. We also offer explanations for trends seen in our data, based on similar published studies and on Cottesloe Reef data from previous student groups. The patterns seen in this FHPA provide insight into the value of different habitat types for fish abundance and diversity at both a broad level and an individual species level.

Introduction

Habitat selection by fish is affected by numerous factors. Marine species inhabit areas based primarily on availability of shelter, predator risk, abundance of potential food sources such as invertebrates, community structure and overall productivity of the given habitat (Levin et al., 1997). Thus, the distribution of fishes throughout different habitats gives insight into the structure of complex reef ecosystems, and is an important consideration in the creation of marine reserves for conservation purposes. Furthermore, measuring abundance and diversity of fish across a variety of habitat types can allow for conclusions to be drawn on the value of particular habitat types for conservation efforts. Previous studies on reef-dwelling fish have shown that species numbers are greater in areas of high topographical complexity, with a diverse substrata providing shelter for fish living on the reef (Friedlander and Parrish 1998). In a study of fish communities at Ningaloo Reef, Western Australia, Wilson et al. (2012) found that the total abundance of fish was significantly greater in reefs of greater structural complexity, and the correlation between fish abundance and habitat complexity was stronger in areas experiencing high fishing pressure. Hence it was hypothesised in our study that species abundance and diversity will increase with increasing distance from the shore as the habitat becomes more complex toward the outer reef.


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We examined spatial patterns of fish abundance and biodiversity at the Fish Habitat Protection Area (FHPA) of Cottesloe Reef, located in Perth, Western Australia. The Cottesloe Reef, located south of popular tourist destination Cottesloe Beach, was declared a FHPA in 2001 due to its value as a unique habitat for a variety of fish and invertebrate species. For the purpose of this study, we divided the Cottesloe Reef Protection Area into three habitat zones with distinct seabed topographical and biotic features: lagoon, flat reef and broken reef. Topographical complexity and seabed vegetation increased moving offshore through the three habitat zones, from lagoon to broken reef. To test the habitat gradient hypothesis, we examined total fish counts (from a list of 31 species) across these three zones. We also selected three species for further analysis based on their high abundance within the reef: the Western King Wrasse (Coris auricularis), Brown-spotted Wrasse (Notolabrus parilus) and Western Stripped Trumpeter (Pelates octolineatus). As a consequence of the reef’s proximity to anthropogenic development and activity, and its ease of access by the public, the area is deemed worth conservational efforts. The reef spans 4.4km north to south, and extends offshore 1.5km to the edge of the Cottesloe Fringing Bank (http://www.mesa.edu.au/friends/seashores/images/australia_dist.gif). Cottesloe Reef was of ecological interest for this study in the attempt to obtain greater understanding of the spatial patterns existing in the fish populations of a local Perth reef system.

Methods Student groups working in the three habitat zones carried out data collection for this study, although data collection in the field occurred across several years through University of Western Australia. However for the validation of the proposed hypothesis, data collected by 2013 Marine Science (SCIE2204) students was primarily analysed. The results were then compared to data from 2011 and 2012, which was collected using the same methodology. The 2013 fish data was collected by student snorkeler groups working in either the northern or southern half of the FHPA (Figure 1). Groups of four snorkelled in each allocated habitat zone (Figure 2) laying down a 10m transect on the sea floor. Two snorkelers moved side by side along the transect line with one counting fish 5m to the left of the line and one counting fish 5m to the right. Both the number and species of fish sighted were recorded at the end of the 10m transect swim on a waterproof data table. In each zone we repeated the 10m transect swim four times in different locations throughout each of the three zones (a total of twelve replicates per group). Five student groups performed transect measurements throughout the habitat zones, performing a total of sixty replicate transects.

The raw data collected by the various student groups was compiled in a Microsoft Excel spread sheet for analysis. We took the average of the replicates of each group (average fish count per zone) and calculated standard error between the group averages. Finally, an average of species abundance per zone was calculated by compiling the data of all groups. This data processing was likewise performed for measures of fish species diversity, represented by number of species observed.


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Figure 1 Aerial photo showing division of north and south study regions at Cottesloe. Regions extended to 200m from shore and were each 60m wide.

Figure 2 Aerial photo showing division of three habitat zones at Cottesloe Reef. The lagoon zone extends to 50m offshore, the flat reef extends from 50 to 100m offshore and broken reef extends from 100 to 200m offshore.


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Results

In 2013 the average number of fish (of all species) increased with increasing distance from shore (Figure 3). The lagoon held the lowest fish abundance, with an average of 23 fish sighted, while the flat reef held an average of 83 and the broken reef an average of 84. The two zones furthest from shore contained a very similar average fish count.

Figure 3. Graph of 2013 average fish abundance across three habitat zones at Cottesloe Reef. Values represent the average number of fish counted by all student groups. Fish of 31 species were included in the counts (see Appendix). Error bars represent standard error of the mean abundances from the five student groups.

In the southern area of Cottesloe Reef the total individual fish count increased with increasing distance from shore (Figure 4). The southern area, throughout all habitat zones, had a lower abundance of fish (of all species). In the northern data collection area, the flat reef, rather than the broken reef, had greater total abundance of fish.

Figure 4. Graph of 2013 average fish abundance across three habitat zones between north and south reef regions at Cottesloe Reef. Values represent the average number of fish counted by all student groups. Fish of 31 species were included in the counts (see Appendix). Error bars were produced using standard error of the mean abundances from the five student groups.

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In 2013 species diversity increased with increasing distance from shore (Figure 5). Of the 31 fish species examined in this study 12.3% were present in the lagoon zone, 23.2% were present in the flat reef zone and 29.7% were present in the broken reef zone.

Figure 5. Graph of 2013 average species diversity across three habitat zones at Cottesloe Reef. Values represent the average number of species counted by all student groups, out of the total 31 species (see Appendix). Error bars were produced using standard error of means from the five student groups.

In 2012 species diversity also increased with increasing distance from shore (Figure 6), with 18.5% of the 31 species present in the lagoon zone, 27.7% present in the flat reef zone and 30.8% present in the broken reef zone. Overall, these results were highly similar to those of 2013 (Figure 5).

Figure 6. Graph of 2012 average species diversity across three habitat zones at Cottesloe Reef. Values represent the average number of species counted by all student groups, out of the total 31 species (see Appendix). Error bars were produced using standard error of means from the five student groups.

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The three individual fish species selected for analysis based on their high abundance also displayed differences in abundance across habitat zones (Figure 7). The Brown-spotted Wrasse (Notolabrus parilus) was present in all three zones. It was most abundant in the flat reef, followed by the broken reef zone and then lagoon zone with the lowest abundance. The other two selected species were present only in two zones each. The Western Striped Trumpeter (Pelates octolineatus) was present in the highest abundance in the lagoon zone followed by the flat reef zone. The Western King Wrasse (Coris auricularis) was present in the flat reef and the broken reef, with a higher abundance in the flat reef. These patterns of abundance in individual species across habitat zones differ from the pattern seen in Figure 3 when all 31 species were counted.

Figure 7. Graph of 2013 average fish abundance of three highly abundant fish species across three habitat zones at Cottesloe Reef. Values represent the average number of fish of each species counted by all student groups. Error bars were produced using standard error of means from the five student groups.

Discussion The results of our study support our predictions concerning fish abundance and diversity. The prediction that fish abundance would be lowest in near-shore habitat zones and greatest in offshore zones was reflected in 2013 data displayed in Figure 3. The prediction that fish species diversity would likewise increase with increasing distance from shore was reflected in both the 2012 and 2013 diversity data displayed in Figures 5 and 6. Hence the results of this study support the hypothesis that with increasing distance from shore, fish biodiversity and abundance increases. As the broken reef and flat reef showed greater topographic variation and vegetative seabed cover than that of the flat reef, our results show that habitats of greater variation in these respects hold greater value for the preservation of fish species abundance and diversity.

However, in the examination of three highly abundant fish species unexpected results arose in relation to the overall habitat gradient we observed. The abundance of Notolabrus parilus and Coris auricularis (Figure 7) suggests that the flat reef holds the ability to support a high number of this species, contrary to the trend seen in Figure 3. Yet the abundance of Pelates octolineatus supports our hypothesis, increasing from lagoon to flat reef zones. The variation in population structure between these selected species across the habitat zones shows that

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particular habitats hold the ability to support individual species to varying extents. One habitat zone, in which a given fish species thrives, is not necessarily the optimum spatial location for another species’ survival. Research has provided the understanding that distribution patterns of Notolabrus parilus and Coris auricularis in Western Australia, are influenced by the amount of trophic elements and red algae cover (Tuya et al., 2009), yet the variety of Cottesloe Reef fish species are likely to be influenced by other habitat factors as well. We propose that habitat value is dependent on a vast range of variables but ultimately depends upon the individual species utilising the specific habitat type. All habitat types and spatial locations across the Cottesloe Reef may hold value for a multitude of different species, and therefore must be regarded as important for protection and preservation regardless of the overall trend seen in this data suggesting that the broken reef is the most valuable habitat zone. However, as our hypothesis predicts, the lagoon zone showed the lowest species abundance and diversity across all Figures. Sloping reef platforms provide shelter for fragile invertebrate species, such as molluscs and echinoderms, as well as primary primary producers, which are a food source for the varying fish species in the zone furthest from shore. The lagoon zone lacks such habitat structure, and hence its overall productivity is likely to be low. Other studies have also shown the value of varying habitat types within an ecosystem for the support of varied and abundant fish life.

A 2003 study by Harman et al. in Hamelin Bay displayed both a higher abundance of fish, and greater species richness in high relief reef than low relief reef. The observations of our study reflected this same pattern, where the highest numbers of individuals and species diversity were both observed in the broken reef zone. Overhangs and ledges characterize the high relief reef, with high shelter availability for fish species. Rocky reefs also allow for the growth of algae. The presence of algal growth on limestone reef was shown to correlate with fish abundance and diversity in the Hamelin Bay studies.

A 2013 study by Wakefield et al. examined the effects of wave action and physical factors on fish abundance in a shallow sandy lagoon region of Cockburn Sound, finding a higher abundance and species diversity in rocky outcrops and seagrass than in a sand bed location. The reason behind the lower abundances and diversity was proposed to be a result of limited shelter and high wave action, reducing the suitability of this habitat type for fish reproduction, attaining of food and avoiding of predators. As this zone is highly homogenous the quantity of ecological niches is low in comparison to a highly heterogeneous environment (such as the broken reef observed at Cottesloe).

Our results show that the abundance of fish was greater in the northern area of Cottesloe Reef. These results are most likely related to the presence of the man-made stone groin at the northern end of the study area. The southern edge of the study area lacks any such rock structure, which provides not only shelter from predators but from wave action, surges and tidal influences as well. The results of the Cockburn Sound studies showed higher abundance of fish between limestone outcrops and human-introduced rock and that the man-made rock wall brings a different composition of species than that associated with natural limestone reefs (Wakefield et al. 2013). Our results in the northern area are an interesting insight into the ability of anthropogenic structures to benefit ecological communities by provision of habitats and protection from environmental factors. This study of Cottesloe Reef reflects a beneficial effect of rock structures artificially introduced into an established reef ecosystem. Potential


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for future rehabilitation of reef systems in the Perth metropolitan area exists based on this result.

In the future, similar surveys of fish should be conducted on a larger scale, using longer transects and/or more replicates. Data from the Cottesloe FHPA should be compared to data from other temperate reefs to determine if a similar pattern of fish abundance and diversity along a habitat gradient is observed on other reef systems. In addition, if data were collected over a span of more than two days, this would control for the influence of daily and seasonal variations in weather, water temperature and visibility.

In conclusion, we recommend continued surveying of the habitat gradient observed in our study in future years for increased reliability of results, and in order to examine changes to fish diversity and abundance over a longer time scale. We propose that conservation efforts should be made, in particular, in the broken reef zone and flat reef zone due to high fish abundance and diversity. However, based on the results of three individual fish species, habitat types are valuable at an individual species level, with varying population structures in individual species relative to the general trend seen for all 31 species. The value of a habitat type is dependent on the particular species in question. Hence we conclude that at Cottesloe Reef all habitat types are of value for conservation efforts. We also suggest further research and analysis into the effect of anthropogenic artificial reef structures along the Perth coast, as potential may exist to increase fish abundance and diversity in established reef systems, or rehabilitate damaged reef areas. The students involved in this 2013 study found the results to be informative, interesting and valuable.


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Appendix

Fish species found in the Cottesloe FHPA

Scientific name Common Name

Anoplocapros amygdaloides Western Smooth Boxfish Apogon victoriae Red-Striped Cardinal Fish Arripis georgianus Australian Herring Caranx ignobilis Giant Trevally Chataedon assarius West Australian Butterflyfish Cheilodactylus rubrolabiatus Red-lipped Morowong Coris auricularis Western King Wrasse Enoplosus armatus Old Wife Epinephelus spp. Cod Halichoeres notospilus Banded Wrasse Kyphosus bigibbus Buffalo Bream Labridae Wrasse (other) Meuschenia spp. Leatherjacket Neatypus obliquus Footballer Sweep Nesogobius spp. Goby Notolabrus parilus Brown Spotted Wrasse Ophthalmolepis lineolatus Maori Wrasse Parapercis haackei Wavy Grubfish Paraplesiops meleagris Western Blue Devil Parma spp. Scalyfin Parupeneus spilurus Black-spotted Goatfish Pelates octolineatus Western Striped Trumpeter Phyllopteryx taeniolatus Weedy Seadragon Pseudolabrus biserialis Red-banded Wrasse Rhabdosargus sarba Tarwhine Scolopsis margaritifera Pearly Monocle Bream Scorpis georgianus Banded Sweep Siganus fuscescens Rabbitfish Sillago bassensis Whiting Torquigener pleurogramma Common Blowfish Unknown black striped lagoon fish


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References

Friedlander, AM and Parrish, JD 1998, ‘Habitat characteristics affecting fish assemblages on a Hawaiian coral reef’, Journal of Experimental Marine Biology and Ecology, vol. 224, pp. 1-30.

Harman, N et al. 2003, ‘Differences in fish assemblages from different reef habitats at Hamelin Bay, south-western Australia’, Marine and Freshwater Research, vol. 54, pp. 177-184.

Levin, P., Petrik, R. & Malone, J. 1997. Interactive effects of habitat selection, food supply and predation on recruitment of an estuarine fish. Oecologia, 112, 55-63.

Tuya, F et al. 2009, ‘Habitat structure affect abundances of labrid fishes across temperate reefs in south-western Australia’, Environmental Biology of Fishes, vol. 86, pp. 311-319.

Tuya, F., Wernberg, T. & Thomsen, M. S. 2009. Habitat structure affect abundances of labrid fishes across temperate reefs in south-western Australia. Environmental Biology of Fishes, 86, 311-319.

Wakefield, C et al. 2013, ‘Fish Assemblages Associated with Natural and Anthropogenically-Modified Habitats in a Marine Embankment: Comparison of Baited Videos and Opera-House Traps’, PLoS One, vol. 8, no. 3.

Wilson, SK, Babcock, RC, Fisher, R, Homes, TH, Moore, JAY and Thomson DP 2012, ‘Relative and combined effects of habitat and fishing on reef fishing communities across a limited fishing gradient at Ningaloo’, Marine Environmental Research, vol. 81, pp.1-11.

(No Author) 2001 ’Plan of Management for the Cottesloe Fish Habitat Protected Area’ Fisheries Management Paper No. 155.

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