Complexity of the prey spectrum of Agaronia propatula (Caenogastropoda: Olividae), a dominant predator in sandy beach ecosystems of Pacific Central America.

Nathan J Robinson,Winfried S Peters

doi:10.7717/peerj.4714

Nathan J Robinson, Winfried S Peters

Open Access

https://doi.org/10.7717/peerj.4714

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Abstract

Olivid gastropods of the genus Agaronia are dominant predators within invertebrate communities on sandy beaches throughout Pacific Central America. At Playa Grande, on the Pacific Coast of Costa Rica, we observed 327 natural predation events by Agaronia propatula. For each predation event, we documented prey taxa and body size of both predator and prey. The relationship between predator and prey size differed for each of the four main prey taxa: bivalves, crustaceans, heterospecific gastropods, and conspecific gastropods (representing cannibalism). For bivalve prey, there was increased variance in prey size with increasing predator size. Crustaceans were likely subdued only if injured or otherwise incapacitated. Heterospecific gastropods (mostly Olivella semistriata) constituted half of all prey items, but were only captured by small and intermediately sized A. propatula. Large O. semistriata appeared capable of avoiding predation by A. propatula. Cannibalism was more prevalent among large A. propatula than previously estimated. Our findings suggested ontogenetic niche shifts in A. propatula and a significant role of cannibalism in its population dynamics. Also indicated were size-dependent defensive behavior in some prey taxa and a dynamic, fine-scale zonation of the beach. The unexpected complexity of the trophic relations of A. propatula was only revealed though analysis of individual predation events. This highlights the need for detailed investigations into the trophic ecology of marine invertebrates to understand the factors driving ecosystem structuring in sandy beaches.

Highlights

Beaches on macrotidal coasts are highly dynamic habitats controlled by physical factors (McLachlan & Brown, 2006)
Predator size distribution The largest and smallest A. propatula we ever measured on Playa Grande had shell lengths of 60.1 and 13.2 mm, respectively, but such extreme sizes were rare
The subset of 327 A. propatula found with prey in their pouches, which is analyzed in the present study, ranged from 18.0 to 57.4 mm, with intermediate sizes from 25 to 37 mm representing a large majority (76%; Fig. 2)

Summary

Introduction

Beaches on macrotidal coasts are highly dynamic habitats controlled by physical factors (McLachlan & Brown, 2006). Inhabitants of sandy beaches, and especially those found in the intertidal zone, show specific morphological, physiological, and behavioral adaptations to the range of physical forces that dominate their ecosystem (Newell, 1979). How to cite this article Robinson and Peters (2018), Complexity of the prey spectrum of Agaronia propatula (Caenogastropoda: Olividae), a dominant predator in sandy beach ecosystems of Pacific Central America. Beaches worldwide are under immense pressure due to development, tourism, sea-level changes, and pollution of the coastal environment (Defeo et al, 2009; Schlacher et al, 2008; Pilkey et al, 2011). Studying sandy beach ecosystems does promote our knowledge of fundamental biological processes, but can provide the foundation for more efficient conservation measures

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