Age class interactions in a marine goby, Elacatinus prochilos (Böhlke and Robins, 1968)

Abstract

Many reef fishes settle monthly throughout the year, so multiple cohorts generally occur together. Yet, much research has focused on a single age class (i.e., settlers) and has ignored age class interactions. The focus of this work was to quantify within and between age class interactions of new settlers and older fish of a marine goby, Elacatinus prochilos. All age classes of this species co-occur on live coral substrate. Thus, all age classes experience and interact with all other age classes. In addition, previous work in this system has shown that post-settlement processes varied over space and drove spatial variation in habitat quality (i.e. post-settlement survival of fishes varied among coral heads at a common density of fishes). Therefore, I also explored how variation in habitat quality may modify interactions between age classes. I found that both inter- and intra-cohort interactions were similar (each age class had similar per capita effects on one another and each other). However, there was evidence for older fish being less affected by settlers than settlers were by other settlers. There was also an indication that variation in habitat quality affected the two age classes differently. This work highlights that in order to extrapolate longer-term dynamics (i.e., multiple generations) over larger spatial and temporal scales, we must consider how different age classes or stages interact with one another, and, if appropriate, explore reef fish dynamics using a stage-structured approach.