Gaya sand invertebrates project

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A Preliminary Investigation on the Intertidal Macro-benthic Community at Padang Point, Pulau (Island) Gaya, Sabah

Wang, Mohd Ridwan, A.R., UNIMAS (Sarawak) & Wang, H. Chak, UBD (Brunei)

Figure 1: Shore profile at Padang Point, PulauGaya
Figure 2: Cluster Dendogram of Community Pattern; showing 3 large clusters
Figure 3: Principal Component Analysis of Community Pattern

Padang Point is located south of Pulau Gaya which consists of a sheltered sandy beach guarded by rocky shores on both sides. A beach-shore profile at Padang Point was drawn (see figure 1) and the distribution of macro-benthic intertidal communities was sampled using ‘standard’ line transect – 60m and 0.25 sq m quadrat techniques. Collected substrates were washed using sieve basket before sorting those living organisms to its order level. Both qualitative and quantitative data were recorded; and further analyzed using Cluster Dendrogram (CD) and Principle Component Analysis (PCA). Three intertidal community clusters were observed for both CD (dissimilarity index=10; see figure 2) and PCA bi-plot (see figure 3). These clusters were consistent to our hypothesis, whereby intertidal communities are not randomly distributed through space. In fact, a rather static horizontal zonation existed even though the community structures of an intertidal ecosystem is bound by a dynamic set of biotic and abiotic interactions. Our study showed a normal distribution curve, with intralittoral zone being the most diverse in taxa representative. Still, the distribution patterns was very much localized; whereby grazing gastropods have a propensity to dominate the upper reaches of the intralittoral zone while marine worms mostly occupied the lower reaches of intralittoral zone. It is hypothesized that the upper limit (or supralittoral zone) distribution of an organism is determined by its capacity to withstand desiccation, whereas its lower limit (or sublittoral zone) is determined strongly through biological interactions such as greater predator-prey stress association. Again, this distribution may be associated with the microhabitat conditions, which include both biotic i.e. density ratio of macro algae and predator; and abiotic factors such as the number of sheltered rock crevices for protection against the strong wave actions, and the the amount of dead organic matter available. Other factors that may also play a role in zonation include behavioral and physiological response to potential stresses.