Full stomachs at empty tides: tidal cycle affects feeding activity and diet of the sandy beach gastropod Olivella minuta

Abstract

Olivella minuta is an abundant neogastropod on sandy beaches from Texas (USA) to southern Brazil. This study aimed to characterize and compare the feeding activity and diet of a Brazilian population of O. minuta in different tidal zones (intertidal and subtidal), and different tidal levels (high and low tides), with three combinations of tidal zone and level being studied (intertidal during low tide, intertidal during high tide and subtidal). The results showed that diet composition was generally similar among tidal conditions, with O. minuta being a generalist, feeding on 45 different food items. Feeding activity, however, was higher in the intertidal during low tide, whereas the richness and diversity of food items were higher in the intertidal during high tide. The higher feeding activity of O. minuta during low tide may be linked to a lower risk of predation; at low tide organisms may be able to feed for a longer time, and this may be particularly true on beaches with fine sand, where water retention is higher than that on beaches with coarse sand. The higher diversity of food items consumed in the intertidal during high tide is likely related to the increased prevalence of planktonic food during high tide. Our results indicate that tidal zone and level may strongly influence the feeding activity of coastal soft-bottom species and that species may show higher feeding activity during low tide. Given the current loss of intertidal habitats due to anthropogenic activity and climate-change associated factors, our study has important implications, highlighting the importance of intertidal areas for the ecology and conservation of sandy beach species.

Prey preferences of juvenile whelk <i>Neptunea arthritica</i> (Gastropoda: Buccinidae) in Hakodate Bay, Hokkaido, Japan

“…In the field, researchers usually observe intertidal animals at low tide and only get a "snapshot" of predation at that time (Fairweather & Underwood 1983). Yet predator foraging behavior may depend on tidal conditions (Menge 1974, Checon et al 2020. Prey-handling times also differ among prey species (Fairweather & Underwood 1983, Carroll & Wethey 1990, Creswell & Mclay 1990, Soto et al 2004, Yamamoto 2004, López et al 2010, Meirelles & Matthews-Cascon 2016, Song et al 2019, because prey with more defensive morphologies require longer handling times, which in turn can bias field observations (Fairweather & Underwood 1983).…”