Numerical simulations of barnacle larval dispersion coupled with field observations on larval abundance, settlement and recruitment in a tropical monsoon influenced coastal marine environment

Abstract

Observations were carried out to monitor the larval abundance, settlement and recruitment of barnacles on a regular basis for a period of two years. The results were then compared with the numerical modelling studies carried out along the west coast of India. Field observations of larval abundance showed temporal variations. The least abundance of larvae was mostly observed during the monsoon and the peak in abundance during the pre-monsoon. Numerical simulations also showed a seasonal change in larval dispersion and retention patterns. During pre-monsoon the larval movement was mostly found towards south and the larvae released from the northern release sites contributed to larval abundance within the estuaries, whereas during the monsoon the larval movement was mostly found towards north and the larvae released from southern release sites contributed to larval abundance within the estuary. During post-monsoon, the larval movement was found towards the north in the beginning of the season and is shifted towards the south at the end of the season, but the movement was mostly restricted near to the release sites. Larval supply from the adjacent rocky sites to the estuaries was higher during the premonsoon season and the retention of larvae released from different sites within the estuaries was found to be highest during the late post-monsoon and early pre-monsoon. Maximum larval supply and retention during the pre-monsoon coincided with maximum larval abundance, settlement and recruitment of barnacles observed in the field studies. These observations showed that the pattern of larval dispersion and retention in the region is predominantly driven by local hydrodynamics operating in the vicinity. Linking larval dispersion and retention with settlement and recruitment of barnacles indicated that the processes are mainly influenced by wind and resultant current patterns. These findings facilitate unravelling the processes operating in the region and to understand the distribution pattern of the intertidal organisms in general in this tropical environment influenced by monsoons.