Dispersal carries added costs for bryozoans

For organisms with complex life cycles, longer time spent in the plankton by dispersing propagules can cause reduced survival, growth and fecundity, which could alter interactions between neighbours in the post-dispersal environment. We compared post-settlement performance of bryozoan Watersipora subtorquata colonies that developed from larvae of different natural and experimental planktonic durations over ca. 15 wk of colony growth. Settlers were situated either near established adults of the ascidian Botrylloides leachii or without competition. Increased larval planktonic durations reduced colony growth in the absence of competition; colonies that developed from longer or delayed larval durations were 2 to 3 times smaller than those that developed from shorter durations. Colonies that developed from longer larval periods (natural or experimental) also experienced higher mortality (75 to 100%) than those that settled quickly (20 to 42%), but these effects varied between experiments and seasons. In winter, W. subtorquata colonies of longer larval planktonic durations experienced greater mortality when adjacent to established B. leachii, whereas differences in colony growth due to planktonic duration were reduced by adjacent B. leachii. The influence of B. leachii varied between experiments in different seasons, however, and did not alter colony performance in summer. Our findings demonstrate that while increased larval planktonic duration can be costly for post-dispersal growth and survival, some differences can be mediated by species inter- actions and environmental variability. This suggests that while connectivity among populations that take longer to disperse may be limited, it may also be influenced in complex ways by the post-recruitment environment and not simply dispersal duration.