Habitat and mutualism affect the distribution and abundance of a shrimp-associated goby

To elucidate factors that affect patterns of habitat use by a goby, Ctenogobiops feroculus, which interacts mutualistically with an alpheid shrimp, Alpheus djeddensis, goby density and habitat type were surveyed along the north shore of Moorea, French Polynesia. Although linear and quadratic multiple regression models both described the relationship between goby density and habitat as being statistically significant, more than twice the variation was accounted for by the quadratic model compared with the linear model. Further evaluation using univariate scatter plots confirmed that goby density correlated non-linearly with habitat as maximal goby density occurred in locations with approximately 71% sand and 29% rubble. Next, an aquarium-based, habitat choice experiment demonstrated that shrimp prefer to burrow in sand - rubble compared with pure sand, and that shrimp are unable to build tunnels in pure sand because burrows collapse in this substrate. This research shows that habitat choice by one organism ( e. g. a shrimp) can, because of positive interactions, affect the distribution of another species ( e. g. a goby). In addition, it highlights the importance of assessing non-linear relationships in studies of habitat use and, when appropriate, using statistical methods that do not rely on linear assumptions.