Marine community ecology: importance of trait-mediated effects propagating to through complex life cycles

Present theory of marine community structure includes the effect of environmental factors that act upon larval survival on distribution and abundance of benthic adults. The theory assumes that pre-settlement environmental factors produce a direct effect at the population level, determining the abundance of individuals that enter the benthic habitat. These are density effects that propagate from the larval to the benthic phase (abbreviated here as DEMPHs). However, recent information suggests that pre-settlement factors may also produce an effect on population abundance, mediated by changes in traits of settlers. For instance, larvae experiencing food stress may give rise to juveniles with reduced energy reserves, growth rate, and in consequence with a low life expectancy. Thus, such trait-mediated (e.g. life historical, physiological) effects propagate through different life phases of the complex life cycles of benthic invertebrates, ultimately affecting juvenile survival. In this paper, I discuss the potential role of this special kind of trait-mediated effect (abbreviated here as DELPHIs) on benthic communities. I show that DELPHIs may affect the shape of the stock-settlement function leading to an erroneous interpretation of the role of post-settlement factors on benthic communities. Mortality due to DELPHIs is the consequence of pre-settlement factors but may be confounded with mortality due to post-settlement factors. In this regard, I conclude that the only solution to avoid this error is to incorporate measurements of traits of individuals in settlement and recruitment studies. Besides, DELPHIs may allow for complex interactions between pre- and post-settlement processes, suggesting that dichotomous views about the role of pre- and post-settlement processes are not appropriate. Finally, I suggest that future field research in benthic communities should incorporate an estimation of DELPHIs as a tool to expand, and thus improve, marine community theory.