Delayed effects of larval exposure to Cu in the bryozoan Watersipora subtorquata

Abstract

Larval experience affects early post-metamorphic performance of a range of marine invertebrates, and even brief events during the larval stage can be important. One of the important larval stresses for organisms living in urban coastal environments is exposure to toxicants. Larvae may pass through patches of toxicants in their dispersal stage with the potential to affect their postmetamorphic performance. However, most studies on embryonic or larval tolerance to pollutants end at, or before, metamorphosis, have little follow-up and almost all are done under laboratory conditions. In this study, we tested whether short-term larval exposure to copper has short-and long-term carry-over effects in the encrusting bryozoan Watersipora subtorquata by following settlement and metamorphosis in the laboratory, then transplanting colonies into the field, in 2 seasons and at 2 sites in SE Australia. Cu at 100 µg l -1 accelerated larval attachment in winter and summer, but inhibited metamorphosis. When transplanted to the field, juveniles survived and grew well, and effects on survival and growth did not appear until several weeks or months after settlement. Larval exposure to Cu reduced survival of colonies to about 2/3 that of control colonies in summer and at 1 site, reduced survival to about 20% that of controls in winter. The fall in survivorship occurred abruptly after 3 to 5 wk in summer and 14 wk in winter. The surviving colonies grew more slowly than the controls. In general, there was little temporal variation in Cu effects, but there was spatial variation in effects on survival and growth of colonies within and between sites.KEY WORDS: Cu · Carry-over effects · Attachment · Metamorphosis · Post-metamorphic survival · Post-metamorphic growth · Spatial variations · Temporal variations · Bryozoan Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 257: [77][78][79][80][81][82][83][84][85] 2003 competitive ability, time to reach reproductive maturity or fecundity. However, so far, laboratory studies on embryonic or larval tolerance to pollutants end at, or before, metamorphosis, have little follow-up and most are done under laboratory conditions. Even when carry-over effects of prolonged swimming or larval nutrition have been examined, they have generally not extended very far beyond the completion of metamorphosis, leaving open the possibility that some effects may only become apparent after a considerable time.In a previous study, we found there were impacts of brief larval exposure to Cu on performance of the arborescent bryozoan Bugula neritina (T. Y.-T. Ng & M. J. Keough unpubl. data). Larval photopositive behaviour was affected and the metamorphosis was delayed or inhibited. Post-metamorphic survival and growth of the colonies were reduced, although the actual combination of effects varied between different sites. Here, we extend this approach to another bryozoan and test whether brief larval stresses have effects on attachment and metamorphosis of larvae ...

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