Lack of match between nutrient-enriched marine seafoam and intertidal abundance of long-lived invertebrate larvae

Abstract

Since most marine benthic species experience a pelagic larval phase, scales of dispersal are key determinants of population dynamics. Biologically derived marine foam has been suggested to increase chances of fertilisation and reduce dispersal of larvae of short-live duration (hours), thus maintaining localised intertidal populations. The present study examined the role sea-foam plays as a mechanism of physical retention/accumulation for long lived (weeks) invertebrate larvae that are relatively long-lived (weeks). Larvae were collected using a submersible pump at two sites along the south-east coast of South Africa, where intertidal assemblages are dominated by beds of mussels and barnacles. Sampling took place on six occasions in 2015–2016, during events of high sea-foam production and periods of no foam accumulation. Foam/water was collected from the surface and bottom of tidal channels. There was no difference in abundance of larvae of any of the invertebrate taxa examined, whether foam was present or absent. Regardless of foam state, barnacle and polychaete larvae were mostly associated with the surface of the short water column at the tidal channels. This study highlights how the very nearshore environment may play a key role in limiting scales of larval dispersal, but especially how the effects of physical processes can be taxon-specific, depending on the larval duration and characteristics.