Seasonal abundance and vertical distribution of crab larvae from northern Patagonia (Argentina): implications for their transport in a biogeographic boundary region

Abstract

In species with meroplanktonic larval phases, some reproductive traits (i.e. seasonality and larval behaviour) interact with hydrographic features to determine larval transport. This work reports the seasonal, diel and ontogenetic changes in vertical distribution of crab larvae in the boundary region between the Argentine and the Magellanic biogeographic provinces of the Atlantic coast off northern Patagonia (Golfo Nuevo; 42.75°S, 65.00°W). Larval seasonality was studied from 47 plankton hauls taken from August 2004 to July 2005. Vertical distribution was studied from 45 stratified plankton hauls carried out in August 2005, December 2005 and April 2006. Crab larval stages were detected throughout the year, but abundance was higher from midwinter to midsummer. Species from southern regions – Munida gregaria, Peltarion spinosulum and Halicarcinus planatus – were abundant during winter and aggregated mainly near the surface, regardless of the hour of the day. In contrast, species from northern regions – Platyxanthus patagonicus, Ovalipes trimaculatus, Leucippa pentagona, Leurocyclus tuberculosus, Cyrtograpsus spp. and Pachycheles chubutensis – were abundant during spring and summer and were usually aggregated near the surface during the night and dispersed in subsurface layers during the day. Ontogenetic changes in vertical distribution were not observed. Residual currents reported in the area (3–6 km·day⁻¹) and duration of larval life (approximately 15–70 days) suggests a minimum potential transport on a 100-km scale. Biological information reported in this work could be explicitly incorporated in a circulation model to accurately predict larval transport and connectivity.

Key words:

• Decapod
• larvae
• vertical migrations
• dispersal
• Southwestern Atlantic

Acknowledgements

The authors wish to thank the technician staff of the National Patagonic Center, ‘Hormiga’ Díaz, ‘Bebo’ Vera, Fabián Quiroga and Néstor Ortiz and the Prefectura Naval Argentina. Thanks are also due to Rodrigo Carracedo, Gustavo Leal, Rodrigo Hernández-Moresino, Augusto Crespi, ‘Pinino’ Orri and Walter Helbling (Photobiology Station Playa Union), for their invaluable help with field work. This study was partially funded by project PICT 2010-2373 and project BID OC-AR 1728 PICT 14700, both from the Argentinean National Agency of Scientific and Technological Promotion (ANPCYT).