Comparative dispersal of larvae from demersal versus pelagic spawning fishes

We conducted ichthyoplankton surveys on the east coast of the South Island, New Zealand, to address 2 questions: (1) Are certain types of reef fish larvae more likely to be dispersed on an exposed temperate coast? (2) Is larval dispersal more strongly associated with taxa that have pelagic eggs? Analyses were based on 492 plankton net samples collected perpendicular to the shore (0.05, 2, 4 and 6 km offshore) and parallel to the shore (0.05, 0.1, 0.3. and 1 km alongshore) from a rocky reef environment. We caught 60 taxa belonging to 32 families, but 11 taxa accounted for 97 % of all larvae collected. Only these common taxa were considered further. Larvae from the 3 taxa with pelagic eggs (Sprattus spp., Aldrichetta forsteri and Rhombosolea plebeia) showed varying degrees of dispersal that ranged from increased abundance close to shore to no clear pattern with distance from shore or alongshore from a rocky reef environment. Larvae from the 1 viviparous taxon (unidentified scorpaenids) were more abundant close to shore. Larvae from the 2 taxa with freshwater demersal eggs (unidentified retropinnids and galaxiids) had disparate patterns of offshore and alongshore dispersal. Retropinnids occurred almost exclusively at the nearshore stations, but galaxiids were more abundant further from shore and were only found nearshore adjacent to a river mouth. Larvae from the 5 taxa that hatched from marine demersal eggs (unidentified tripterygiids, Forsterygion spp., Gilloblennius tripennis, Grahamina capito and Ruanoho decemdigitatus) were all more common further from shore, For the taxa in this study, we reject the hypothesis that reef fish larvae that hatch from non-pelagic eggs are retained mostly or exclusively near reefs on an exposed coast. Broad-scale dispersal of fish larvae may provide benefits in terms of predator avoidance, re-colonisation of habitats and risk-spreading, but it carries with it the increased risk of unfavourable advection that may delay or even prevent recruitment.