Marine Invertebrate diversity along a reef gradient at Tunku Abdul Rahman Marine Park

Transcription

1 Marine Invertebrate diversity along a reef gradient at Tunku Abdul Rahman Marine Park Eka Fatmawati, Subekti Sulistyawati, Megan Bartlett, Toh Kok Ben, Ian McFadden & Ruchira Somaweera ABSTRACT We compared diversity of marine invertebrates along mid-reef, reef crest and reef slope regions in the coral reef at Tunku Abdul Rahman marine sanctuary at Gaya Island in Sabah, Malaysia. 12 plots were placed in 4 replications in each marine zonation. The most diversity in marine invertebrates was found in the reef crest area, possibly because this region contained the most coral cover, providing the most invertebrate microhabitats. INTRODUCTION Coral reef ecosystems are the most diverse and complex aquatic communities (Karlson et al, 2004). Although they are diverse as a whole this diversity is not evenly distributed among habitat types within the reef (Karlson et al, 2004). For a keystone species, the corals, diversity was found to be greatest on reef slopes, mid-level on crests and lowest on reef flats in a study in the region (Karlson et al, 2004). Although many studies of coral reef diversity focus on coral, fewer focus on the other invertebrates inhabiting this complex structural mosaic. A terrestrial parallel might be drawn between marine invertebrates and rainforest insects, because both groups inhabit key structural, sessile organisms within the community upon which they are closely specialized. Recent work by Novotony et al (2002) indicates that insect diversity might be less related to specialization and more to the diversity of plants present to specialize on. This might have a similar effect in marine invertebrates in that their diversity may be influenced by the diversity and abundance of the coral on which they occur. To understand patterns of invertebrate diversity between different parts of the reef, with differing levels of coral cover, we studied a section of coral reef at Tunku Abdul Rahman marine sanctuary at Gaya Island off the coast of Kota Kinabalu in Malaysian Borneo. MATERIALS AND METHODS Field sampling We sampled the marine invertebrate assemblages in 12 plots, four in each the mid reef (~im deep and 5-10m land-wards from the reef edge), reef crest (~1-2m deep and at reef crest) and the reef slope (~2-3m deep) at the Tunku Abdul Rahman marine park at Pulau Gaya on 7 August The sampling session began at 11:30 with two groups of three working separately. The method included two observers placing a 1x1m plastic quadrat on the bottom and actively looking for invertebrates while the other recorded the data. The number of specimens found in the respective invertebrate group were recorded separately on a underwater slate. Statistical analysis We entered data using OpenOffice Calc and performed statistical analyses using the program R Clustering dendrogram and MDS analysis were used to determine the similarity between plots. Shanon Wiener diversity indexes of each location were calculated and ANOVA was done for each taxa between locations.

2 RESULTS - Sampling yielded at total of ten taxonomic groups. The most abundant were the urchins and the bivalves (figure 3). Clustering dendrograms and MDS show no relationship between habitat type and taxon (figure 2) Shannon-Weiner diversity indexes were calculated for each habitat type (reef slope, reef crest, and mid-reef) and the highest diversity was found along the reef crest (H = 1.34). The second highest diversity was on the reef slop (1.16) (figure 1). ANOVA analysis found no significant differences between distribution of taxa among habitats. DISCUSSION The reef crest showed the highest diversity of invertebrates, possibly because of the higher abundance of potential micro habitats due to the higher coral cover. The reef slope had the second highest level of diversity. The diversity in this area may actually have been underrepresented due to the sampling methods. On the reef slop the water is deeper and in order to closely observe the corals deeper dives were needed. This meant that less time was spent doing the checking and organisms may have been missed. Bivalves contributed for most of the mollusks encountered. They are usually borrowers and are attached to a substrate. The higher abundance of stable substrates in mid reef and reef crest might have accounted for their higher abundance in the two regions. Furthermore, members of the bivalve genus Tridacna maintain a symbiotic relationship with zooxanthellae (Allen & Steene 2003). Hence the higher availability of sunlight in the two regions may have also contributed to the high number of bivalves. Being sessile filter feeders, crinoids and sponges mostly depend on the water currents and waves to find food (Allen & Steene 2003). Thus their higher abundance in the reef slope may be due to the higher availability of food due to the nutrients brought by currents. The preference of sponges for slopes is also shown by Wood and Aw (2002). The low numbers in some taxonomic groups are probably due to the random sampling followed, and might not represent a pattern. Most of the marine invertebrates are cryptic and some are nocturnal, thus the actual diversity would be larger that encountered. ACKNOWLEDGMENTS Our sincere gratitude goes to the organizers of the Biodiversity of Borneo Harvard Field Course 2007, especially Dr. Cam Webb for the opportunity to participate; Min Sheng Khoo for assistance with data analysis; and the staff of Tunku Abdul Rahman Marine Park. REFERENCES (1) Allen, G.R. & Steene, R. (2003). Indo-Pacific coral reef field guide. Tropical reef research. (2) Karlson, R. H., Cornell, H. V. & Hughes, T. P. (2004), Coral communities are regionally enriched along an oceanic biodiversity gradient., Nature 429(6994):

3 (3) Novotony et al 2002 (LOOK UP REFERENC) (4) Wood, E. & Aw, M. (2002) Reef fishes, corals and invertebrates of Malaysia and the South China Sea. New Holland Publishrs, UK. APPENDIX A B C D FIGURE 1: Shanon Wiener Diversity Indexes for the three regions.

4 FIGURE 2. MDS Plot showing the relationship between taxon groups and the plots.

5 FIGURE 3. The mean number of invertebrates recorded in the three locations.