Distribution, habitat association, and movement patterns of Sea Urchins (Diadematidae) in coral reefs, Peninsular Malaysia / Mok Man Ying

Mok , Man Ying (2023) Distribution, habitat association, and movement patterns of Sea Urchins (Diadematidae) in coral reefs, Peninsular Malaysia / Mok Man Ying. Masters thesis, Universiti Malaya.

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Abstract

Sea urchins are keystone herbivores in coral reefs as they prevent coral-algae phase shift and promote coral resilience in the Caribbean. However, the knowledge of sea urchins in the Indo-Pacific region is not extensive and their role in marine ecosystems remains unidentified. To fill this knowledge gap, this study aimed to examine the population ecology of sea urchins in Peninsular Malaysia, and their relationship with the tropical coral reefs habitat, as the first step to explore their potential in promoting reef resilience. Firstly, geographical information on the density, diversity, and distribution of sea urchins in Peninsular Malaysia (The Sunda Shelf and Malacca Strait Marine Ecoregion) were collated using three approaches – literature, questionnaire and field surveys. From the field surveys, a total of seven species from five families with a mean density of 41.6 ± 52.98 individuals/100 m² were documented. When combined with the literature and questionnaire surveys, 10 species of sea urchins from six families can be found within Peninsular Malaysia. The first record of Prionocidaris bispinosa for Malaysia was documented at the intertidal seagrass meadow in Tanjung Kupang, Johor. The species composition of sea urchins between the ecoregions was similar but differed significantly between coral reefs and seagrass meadows. With the data gathered, species lists and maps illustrating the density, species richness and diversity hotspots of sea urchins were produced. Secondly, coral reef habitat association patterns for Diadema setosum and Echinothrix calamaris were determined in belt-transect surveys (n = 57), with transects laid parallel to shore at different depths at Pulau Rawa, Johor. Multivariate regression analysis identified D. setosum to be more associated with live coral cover and coral growth form; in contrast, the distribution of E. calamaris that was driven by habitat rugosity, water depth and live coral cover. These findings suggest contrasting species-habitat associations for the two co-existing species. Finally, the movement patterns of D. setosum— a key species on tropical coral reefs that is endemic in the Indo-Pacific region was documented. By tracking 25 tagged sea urchins over twenty-four hours in Pulau Rawa, the total travel distance (18.91 ± 11.56 m), movement speed (0.79 ± 0.5 m/hour), 24-h displacement (5.87 ± 6.32 m) and home range (8.24 ± 6.52 m) of D. setosum were documented, and to date are novel findings especially for nocturnal sea urchin movements. The absence of homing and aggregation behaviour that are commonly displayed by other sea urchin species as predator avoidance strategies, suggests that predation pressure on the studied reef is low. Given the limited information about sea urchins in Malaysia, this study appears to be the first in-depth study of its kind in the country, investigating their distribution and the importance of habitat in shaping their density distributions and movement patterns. The baseline data serve as valuable information in the planning and management of natural habitats for biodiversity and conservation in Malaysia’s marine ecosystem. Explicitly, this knowledge provides important insight for incorporating sea urchins in coral rehabilitation interventions to enhance the resilience of coral reefs on the brink of degradation.

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