Seasonality and biological characteristics of the shallow-water mysid Mesopodopsis orientalis (Crustacea: Mysida) on a tropical sandy beach, Malaysia

Abstract

The seasonality in abundance, population structure, and other biological aspects of the tropical shallow-water mysid Mesopodopsis orientalis were studied at an open sandy beach with fine sand on the southern coast of Penang Island, north-western Peninsular Malaysia, from December 2004 to August 2006. The monthly collections ranged from 0.7–534 indiv.m⁻², with an overall mean of 49 indiv.m⁻². The density, however, could reach as high as 8,656 indiv.m⁻². There were no correlations between the abundance of mysids and the temperature, salinity, or tidal cycle, and the wide range in the variations of catches was considered to be mainly due to their heterogeneous distribution. Moreover, no distinct pattern was found in abundance between day and night and again between shady and sunny areas. Males accounted for 33.3–56.5% (mean; 47.3%) of the monthly samples; females predominated over males in the entire shore population. Reproduction of M. orientalis in Penang waters is continuous throughout the year and seasonality in reproductive traits is non-existent or, if present, considerably reduced. The number of eggs/embryos carried by females exhibited a positive correlation with female size, and the maximum brood size was 24. The egg diameter ranged from 0.30–0.42 mm, with a mean of 0.37 mm, and was independent of female size. Thus, the clutch size of the Penang population of M. orientalis was more fecund than that observed in the estuarine counterpart, Mesopodopsis tenuipes, but the former was smaller in size than the latter during all stages in its life cycle.