Spatio-temporal heterogeneity of benthic harmful dinoflagellate assemblages at the fringing reefs of Rawa Island, Malaysia / Yong Hwa Lin

Yong, Hwa Lin (2017) Spatio-temporal heterogeneity of benthic harmful dinoflagellate assemblages at the fringing reefs of Rawa Island, Malaysia / Yong Hwa Lin. Masters thesis, University of Malaya.

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Abstract

Ciguatera Fish Poisoning (CFP) is regarded as the most common seafood intoxication in human, involving the neurotoxins produced by some species of epiphytic and benthic dinoflagellates found in coral reefs and inshore habitats of tropical and subtropical regions. The benthic harmful dinoflagellates, Gambierdiscus spp., Fukuyoa spp., Ostreopsis spp., Prorocentrum spp., Coolia spp. and Amphidinium spp. are predominantly epiphytic in nature, forming mucilaginous layers to attach onto macrophytes and epi-benthic layers of substratum. The phase shifts of coral-dominated reefs to algal dominated reefs may favor proliferation of these benthic dinoflagellate assemblages. The effects of bottom substrate complexity and host selectivity factors on host colonization by these benthic dinoflagellates are still unknown. This study aimed to investigate benthic harmful dinoflagellate assemblages in relation to reef microhabitats by adopting a non-destructive sampling technique. Rawa Island, Terengganu was selected based on healthy and unhealthy coral reefs at the study site. Hierarchical cluster analysis and non-metric multidimensional scaling (MDS) was adopted to define biologically distinct regions with respect to the reef microhabitats characters. A total of 115 artificial screen samples collectors were deployed underwater and successfully retrieved by SCUBA after 24 hours deployment period. Average daytime temperature and salinity of shallow sea surface water were recorded between 30 – 33 °C and 30 – 32 PSU respectively, with consistent daily light intensity in a range of 1000 – 2500 μmol m-2s-1 recorded. The resultant data of this study clearly indicated benthic dinoflagellate assemblages were prominently distributed in disturbed reef microhabitats and dispersed in a patchy distribution pattern among distinct habitat types. Ostreopsis was known as predominant species among other five benthic epiphytic genera and perennially present in all bottom microhabitats investigated at each sites. It was more tolerate to slightly shaken microhabitats rather than calm sheltered areas probably due to their abilities to secrete mucilage layers in order to associate with bottom substratum. Gambierdiscus population was likely attributed to the presence of filamentous turf algae population appeared on dead coral fragments in shallow sheltered reefs area (0.5 – 3 m). Tuft algal mat on dead coral fragments provides favorable dense and fine branches of adherent microhabitats for Gambierdiscus to overcome strong water movement, supporting larger surface area for cell attachment. Majority of Prorocentrum spp. and Amphidinium spp. were significantly higher at inshore sheltered associated with heavy sand sediments but less at macrophyte. The presence of Coolia spp. was scarce in almost all samples collected from sites. This phenomenon can be explained that sudden water disturbance may breakdown the close attachment between benthic dinoflagellates and bottom substratum, prompting to reintroduction of benthic dinoflagellates populations into water column. As a conclusion, data analyzed in this study indicated disturbed coral reefs environment could attribute to proliferation of benthic harmful dinoflagellate communities despite of possible circumstances of environmental variations. Preliminary investigation on host preference of benthic harmful dinoflagellates is important to discover their species diversity and distribution and their possible impacts on marine organisms as well as human intoxication risks.

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