MEPS 585:143-154 (2017)  -  DOI: https://doi.org/10.3354/meps12386

ABSTRACT: Spatial distributions of organisms result from a complex interplay of processes, including habitat selection as well as species interactions, and it remains a continual challenge to disentangle the relative importance of such effects. I investigated how habitat variation and conspecific interactions influence the abundance and distribution of different life history stages of the intertidal fish Oligocottus snyderi. I first examined the role of priority recruitment effects and found that prior recruitment had no effect on subsequent O. snyderi recruitment. I then examined how habitat variation influences adult and recruit abundances by manipulating surfgrass Phyllospadix spp. cover in tide pools, a habitat attribute that positively covaries with both O. snyderi life history stages. Surprisingly, whereas O. snyderi adults showed the expected negative response to surfgrass removal, the recruit response was positive. Additional experiments investigated whether these contrasting results were due to an ontogenetic change in habitat preference or to negative interactions between adults and recruits. Direct manipulation of adult abundance in the field determined that O. snyderi recruit abundance increases when adult abundance decreases. Laboratory studies indicated that although O. snyderi recruits have little to no preference for surfgrass cover, they do exhibit a strong negative reaction to conspecific adults and adjust their distributions accordingly. This combination of field and laboratory studies suggests that the ontogenetic habitat shift of O. snyderi is actually a result of negative interactions between size classes, such that recruits settle into sub-optimal tide pools in order to avoid interacting with adults.

KEY WORDS: Habitat variation · Conspecific interactions · Intraspecific competition · Aggregation · Recruitment · Oligocottus snyderi