Spatial variation in the nearshore distribution and phenotypic traits of reef fish larvae suggest condition-dependent larval retention

Reef fishes are often described as having a ‘bipartite life history’, with clear differentiation between pelagic larvae and older benthic stages. However, we routinely observe reef fish larvae of mixed ages shoaling on temperate reefs around New Zealand, and a large body of literature suggests that nearshore larval development may be common. These observations raise the following questions: Do reef fish larvae ever leave the reef? Is offshore advection and/or dispersal condition-dependent? Is onshore migration prior to settlement a punctuated event, or a saltatory process? To partially address these questions, we evaluated spatial variation in larval abundance and traits (size, condition, morphology, and age) for the common triplefin Forsterygion lapillum . We sampled larvae using replicate light traps stratified by depth (i.e. deployed either 1 m below the surface or 1 m above the benthos) and distance (0, 500, or 1000 m) from the reef. Larvae were generally concentrated near the reef and varied widely in age, but their relative abundance within a location also depended on depth: larvae were more commonly caught in shallow traps when closer to the reef, and in deeper traps at locations when further offshore. Body condition, morphology, and age also varied as a function of an interaction between depth and location. Collectively, these patterns suggest that (1) nearshore retention is a prevalent feature of larval development for common triplefin, (2) offshore advection of larvae may be condition-dependent, and/or (3) onshore ontogenetic migration appears to be age- and condition-dependent, and it resembles saltatory settlement.