Population variability and spatial-pattern of sea urchin Anthocidaris crassispina in Hong Kong

Hong Kong has a long and indented coast-line, featured by its complex hydrography. Of the twenty-one recorded sea urchin species in Hong Kong, the purple sea urchin Anthocidaris crassispina is the only species of commercial importance in which its gonads are considered a delicacy regionally. Over the years this species has retained the attention of researchers on its role as a dominant grazer in the regulation and maintenance of algae assemblages in distinct coastal habitats of Hong Kong. However, there is hitherto a paucity of studies examining the densities and frequency-distribution of size of individuals between contrasting local habitats. Moreover, there is no updated information available on sea urchin stocks to guide fisheries management decisions. With the environmental gradient of Hong Kong waters which provides an excellent research location for testing the hypothesis of the importance of morphological plasticity and resource allocation in response to food limitation and hyposalinity of sea urchin, a study was initiated on the sea urchins species, A. crassispina . Findings of a laboratorial experiment concur with field observation that both stressors had a significant negative effect on various aspects including test diameter, total weight, test weight, gonad weight and gonad index. It is revealed that A. crassispina has substantial adaptability to food limitation and hyposalinity, and such adaptation can have important consequences in resource allocation and body allometry. In response to hyposalinity, this species reduces test weight, thereby increasing the relative weight of the lantern. Alternatively, this species appears to allocate energy to body maintenance, rather than to increasing the relative size of the lantern in response to food limitation, which is considered a very different strategy employed by other sea urchins. Besides, marine protected areas in Hong Kong, for example the Cape d’Aguilar Marine Reserve, are effective management measures in protecting sedentary species such as sea urchins. Lau et al. (2011) showed that A. crassispina populations in nonprotected sites suffered from a higher mortality rate than the sea urchin population in Cape d’Aguilar. Although sea urchins in the reserve grew slower, likely due to a higher population density, the size at maturity was reached within two years. The high abundance of mature urchins may enhance their fertilization success, and promote a potential spillover effect to surrounding fished areas. Therefore, even small no-take reserves in highly disturbed coastal areas such as south China are important refugia for at least sedentary species like sea urchins. Copyright © 2014 Nova Science Publishers, Inc.