INFLUENCE OF SALINITY AND TEMPERATURE ON GROWTH AND SURVIVAL OF THE PLANKTONIC LARVAE OF MARENZELLERIA-VIRIDIS (POLYCHAETA, SPIONIDAE)

In a series of experiments, the planktonic larvae of Marenzelleria vir idis (Verrill, 1873) were exposed to various combinations of salinity (S = 0.6, 2.5. 5.0, 10 and 20 parts per thousand and temperature (T = 5, 10 and 20 degrees C) from the 1-setiger stage to the onset of metam orphosis (16- to 17-setiger stage). One-setiger larvae were unable to complete their development to metamorphosis at salinities below 5 part s per thousand. Metamorphosis was successful at salinities of 10 and 2 0 parts per thousand, when the animals adopted a benthic life mode. La rval development was more rapid at 10 parts per thousand than at 20 pa rts per thousand, and was positively affected by higher temperatures. Larvae exposed to a salinity of 3.5 parts per thousand at the 4- to 5- setiger stage developed and completed metamorphosis to benthic juvenil es despite the low salinity. These larvae developed most rapidly at a temperature of 10 degrees C. The salinity tolerances (LC(50)) of M. vi ridis larvae (t = 48 h),juveniles and adults (r = 72 h in each case) w ere determined at 10 degrees C. The results showed that all developmen t stages can tolerate salinities <1 parts per thousand. The importance of constraints on development and tolerance to low salinities for the successful colonization of oligohaline regions is shown and discussed in connection with other brackish-water organisms.