Biology of the bottom-dwelling shrimp Nauticaris marionis Bate, 1888 at the sub-Antarctic Prince Edward Islands

Sub-Antarctic bottom-dwelling caridean shrimps Nauticaris marionis were collected in April/May between 1984 and 1997 over the shelf region of the Prince Edward Islands (37 °50′E, 46 °45′S). N. marionis is a partially protandric hermaphrodite. Hatching probably occurs just before April each year, but may persist until May. During the 1st year N. marionis seem to survive in undetected localities, moult into juveniles, and then settle amongst the benthos from the plankton beginning probably after November. Diel vertical migration then occurs up to an unknown larger size. The vast majority of juveniles develop into males, most of which transmutate into females by April/May of their 3rd year. Reproduction can occur before all male secondary characteristics have been lost. A minority of individuals develop directly into females without passing through a male phase. Individuals older than 5 years are undetectable using samples of the sizes analysed, but they may well persist in the population. The von Bertalanffy growth parameters for N. marionis are tentatively identified as k=0.2353/year, L ∞=12.6 mm, t 0=−0.2828 years and WW ∞=2.03 g. Sex-reversal in N. marionis at Marion Island may be affected by the changing environment as sexual differentiation is probably determined during the planktonic stage.