Demography of Nebalia sp. (Crustacea: Leptostraca) determined by carrion bait trapping in Lobster Bay, Cape d'Aguilar Marine Reserve, Hong Kong

摘要

The feeding ecology of leptostracans is not well-known. In the present study, species of Nebalia (Crustacea: Leptostraca) were captured every month for 1 year from Lobster Bay, Hong Kong, using baited traps. Captured individuals fell into a size range of 0.36-3.64 mm and 0.95-5.52 mm in carapace and total lengths, respectively. They were divided into different reproductive stages based on the morphology of the second pair of antennae and thoracopods. Sexual dimorphism becomes apparent between 0.7-1.5 mm (CL) and 1.4-3.2 mm (TL). Most individuals collected were sexually differentiated, but immature (79.7% of the captured individuals), followed by post-ovigerous (11.4%) and ovigerous (8.9%) females. Sexually undif-ferentiated juveniles were rare (3.9%). The sex ratio of the immature individuals approached 1:1 with a propensity towards male dominance. Not one mature male was captured. Although females with setose thoracopod endopods, indicating that they were ovigerous, were captured frequently, only two were carrying eggs. The two brooding females had clutch sizes of 11 and 17 eggs. Alternate peaks in relative abundance of ovigerous and post-ovigerous females were identified, the latter following the former. Reproductive activities occurred mainly in April-May and October-December, indicating that two cohorts are recruited. Catches using baited traps could be explained by the reproductive season of Nebalia sp. High catches were usually associated with the months of highest reproductive activity, low catches with peaks in post-ovigerous females. It is therefore concluded that not all individuals at various reproductive stages are attracted to carrion and hence adopt a scavenging feeding mode. Catches of Nebalia sp. in Hong Kong possibly reflect their annual cycle of reproductive activity.