Regional variation in larval retention and dispersal drives recruitment patterns in a temperate reef fish

Abstract

Although there is wide appreciation for the influence of variable larval transport on recruitment, few studies have investigated the relationship between recruitment intensity and the origin(s) of recruits. We evaluate this relationship for the common triplefin Forsterygion lapillum in Wellington Harbour (a semi-enclosed bay) and the adjacent open coast of North Island, New Zealand. As the harbour is productive, with many F. lapillum adults, we predicted the harbour would be an important source of recruitment for both regions. We estimated larval origins and dispersal histories using embryonic and larval otolith chemistry, respectively, with differences in otolith elemental composition consistent with birth and/or development in either harbour or open ocean waters. In the harbour, recruitment was greatest when locally spawned larvae were retained. Although large recruitment pulses to the open coast were comprised mostly of larvae originating from the open coast, 72 % of all recruits to the south coast were actually spawned in the harbour. Dispersal of larvae from the harbour was frequent, but in low numbers, and was unrelated to opportunities for transport from the harbour. Given recent evidence for differences in larval growth between regions, we suggest that (1) faster larval growth combined with nearshore larval distributions result in high recruitment to the harbour and moderate, but demograph-ically important, dispersal from the harbour to the open coast. In contrast, we suggest that (2) the combination of strong tidal currents in Cook Strait and slower larval growth result in lower recruitment and greater transport of larvae among open coast populations. The mechanisms that underlie such context-dependent dispersal have important implications for patterns of connectivity. © Inter-Research 2010.