Reproduction ofAmphiporus lactifloreus (Hoplonemertini) on tidal flats: implications for studies on the population biology of nemertines

The reproductive period and life-history parameters were investigated for the hoplonemertineAmphiporus lactifloreus found on the tidal flats of the island of Sylt in the northern Wadden Sea. Every six weeks 20 individuals were collected and then histologically examined to determine the development stage of their reproductive organs.A. lactifloreus reproduces in the late autumn, its peak reproduction being in the second half of November. Individuals from all size classes >20 mm body length produced gametes. Individuals of the cohorts that reproduced in the late autumn of 1992 persisted and grew until July 1993, indicating thatA. lactifloreus is an iteroparous species. The length of relaxed individuals was significantly correlated with their length under anaesthetized conditions, but the regression changed significantly after the reproductive period. Length under ‘relaxed’ conditions was significantly correlated with weight (wet weight, dry weight, and ash-free dry weight); these relationships did not vary significantly before or after the reproductive period. Our results show that important life-history data of intertidal nemertines can be obtained without time-consuming histological studies. On the basis of these findings, recommendations for future studies on the population biology of intertidal nemertines are given. Regular length measurements of nemertines under ‘relaxed’ conditions are proposed as a useful tool for tracking the growth and survival of annual cohorts of intertidal nemertines.