Sea urchins of Peninsular Malaysia: Spatial distribution and species-habitat association

Abstract

Sea urchins are keystone herbivores in coral reefs that can prevent coral-algae phase shifts and promote coral resilience in the Caribbean. However, knowledge of sea urchin populations in the Indo-Pacific region is less extensive and their role in marine ecosystems remains uncertain. To fill this knowledge gap, this study examined the spatial distribution and species-habitat association of sea urchins in Peninsular Malaysia as a first step in exploring their potential for promoting reef resilience. Firstly, geographical information on the population characteristics of sea urchins in Peninsular Malaysia (Sunda Shelf and Malacca Strait Marine Ecoregions) was gathered. Using literature, questionnaire, and field surveys, ten species of sea urchins from six families were identified in the species record for Peninsular Malaysia. Prionocidaris bispinosa represents the first record for Malaysia, documented in the intertidal seagrass meadow at Tanjung Kupang, Johor. Combining density data from literature and field surveys, sea urchin density for Peninsular Malaysia was estimated to be 46.94 ± 66 individuals/100 m2. Secondly, the species-habitat association of Diadema setosum and Echinothrix calamaris were determined in belt-transect surveys (n=57), with transects laid parallel to shore at Pulau Rawa, Johor. Multivariate regression analysis identified D. setosum to be more associated with live coral cover and coral growth form, while E. calamaris distribution was driven by habitat rugosity, water depth and live coral cover. These findings suggest contrasting species-habitat associations for the two co-existing species. 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, deepening our knowledge of sea urchin distribution and the importance of habitat in shaping that distribution. This baseline data serves as valuable information in the planning and management of natural habitats for biodiversity and conservation in Malaysia’s marine ecosystem.