Re ECF Project: 2007-04

Project Title: Stock and Ecological Status of Sea Urchins in Hong Kong: Evaluation of the Effectiveness of Marine Protected Areas Using Sea Urchins as Model Organisms

Applicant: The University of Hong Kong (Dr. Tak-cheung WAI)

Total Approved Grant: $392,620

Duration: 01/04/2008 to 31/03/2010

Project Status/Remarks: Completed

Scope:
The objectives of the study are

  1. to conduct a comprehensive literature review of the diversity, abundance, distribution and habitat preference of echinoderm species in the Hong Kong marine environment;
  2. to conduct underwater surveys to investigate the diversity, abundance, distribution and habitat preference of commercially exploited species (Anthocidaris crassispina), and other urchin species in rocky, coral and sandy habitats; and
  3. to conduct an ecological study to test the hypothesis that the number of size classes (i.e. size range) and abundance of urchin populations within MPAs are higher than those unprotected outside MPAs.

Summary of the Findings/Outcomes:
A series of quantitative surveys were conducted to study the diversity and distribution of sea urchins. The abundance of the commercially exploited species, Anthocidaris crassispina, was significantly lower in the north-east region than east and south-east regions; the abundance of Diadema setosum and Salmacis sphaeroides, in contrast, were the highest in the north-east area. This pattern can be explained by the observed, higher fishing pressure of Anthocidaris in the north-east area and the limited foraging range of the fishermen from Mainland China to the south-east region using P4 boats.

Among all the rocky sites, the highest abundance and size range of Anthocidaris were found in certain sites in the Ping Chau Marine Park (PCMP) and Cape d’ Aguilar Marine Reserve (CDMR) than sites outside the MPAs, indicating the significant effect of reduced fishing pressure on the enhancement of Anthocidaris population. Among the Marine Protected Areas (MPAs), new recruits of Anthocidaris were, however, only found in PCMP and CDMR, indicating that the low abundance of Anthocidaris in Hoi Ha Wan Marine Park and Yan Chau Tong Marine Park was likely due to a shortage of larval supply in these enclosed areas.

The 20 rocky sites were classified into 3 major substrate groups CCA, BRW and MIX by cluster analyses, representing rock surface dominated by crustose coralline algae, brown algae and a mixture of patches of various sessile groups, respectively. The distribution of these substrate groups was found to correlate to the total density of sea urchins. However, the distribution pattern was spatially variable with regions (north-east, east and south-east). In general, our results modelled that the intermediate urchin density in each region (~7 to 9 indiv. m-2) was likely to be a critical point, beyond this point, the stable substrate state would shift (i.e. MIX < > BRW in the north-east and east regions; CCA < > MIX in the south-east region). Further experimental studies can be conducted to test this hypothesis. Regardless of the intensity of fishing pressure, the sea urchin (Anthocidaris) inhabited substrate groups MIX and BRW produced higher quantity and quality of gonad that urchin in CCA. To manage the urchin fisheries in MPAs in order to (1) maintain a high complexity/diversity of sessile groups on rocky substrate and (2) maximize the gonad production of sea urchins, we proposed the total urchin density can be kept at the proposed intermediate urchin density to avoid the dominance of a particular substrate group in a particular region (e.g. the coralline barren ground in CCA in the south- east rocky reefs.