Abundance of macrofauna in dense seagrass is due to habitat preference, not predation

Abstract

Two main hypotheses compete to explain why prey abundance decreases when seagrass density is reduced. One proposes that predators are more successful amongst seagrass of lower density; the other invokes habitat choice by prey. We reduced the density of seagrass in the presence, and in the absence, of predators in a field experiment to discriminate between these hypotheses. When seagrass was manipulated abundances of all six prey species decreased simultaneously both in the presence and in the absence of predators. We conclude that correlations of prey abundance and shoot density within a seagrass bed are proximately due to habitat preference of dense seagrass by prey. We report another experiment which supports this conclusion and shows that habitat preference is exercised at the earliest opportunity. However, the habitat preferences may have been selected by predation pressure.

Utilization of seagrass habitats by juvenile groupers and snappers in Banten Bay, Banten Province, Indonesia

“…2). This finding is in accordance with literature indicating the importance of vegetated areas, such as seagrass beds, for settlement and nursery of several species of grouper and snapper (Allen, 1985;Bell & Westoby, 1986;Bell et al, 1987;Bell & Pollard, 1989;Jory & Iversen, 1989;Chester & Thayer, 1990;Heemstra & Randall, 1993;Jenkins et al, 1997;Tolan et al, 1997). A reason for the seagrass preference of juvenile groupers and snappers is the diverse and abundant invertebrate fauna in this habitat, which is supported by the plants.…”

“…4, 5), which is in accordance with the selection by pelagic larvae of structurally complex microhabitats for their first settlement. Redistribution of juveniles only takes place within the selected seagrass bed, because crossing bare substrate increases the risk of predation (Bell & Westoby, 1986;Bell et al, 1997). Irlandi et al (1995) argue that rates of predation increase with increased fragmentation of the seagrass habitat.…”

Ichthyofauna associated with Cymodocea nodosa meadows in the Canarian Archipelago (central eastern Atlantic): Community structure and nursery role

“…Bell and Westoby (1986a) found a positive relationship between the density of the meadow and the abundance of small fish in terms of the presence/absence of predators, suggesting that fish are capable of discriminating between more or less dense meadows, or between meadows and adjacent bottoms lacking vegetation. In the present study no relationship was found between structural complexity and the richness and abundance of the associated ichthyofauna; this is probably due to the spatial scale of the study.…”

Zonación vertical del macrobentos de sustratos sólidos del estuario del río Massangana, Bahía de Suape, Pernambuco, Brasil

“…Aunque la distribución de las comunidades bentónicas en el ambiente sea regulada por procesos dinámicos abióticos, donde los organismos presentan afinidades por determinados hábitats, la estructura de las mismas es primariamente un reflejo de la complejidad del hábitat, donde las interacciones entre los organismos, sobretodo la competencia y la depredación, pueden estar íntimamente ligadas a el control de la densidad poblacional de la fauna asociada (Bell & Westoby 1986, Preston & Moore 1988. La intervención antropogénica puede promover alteraciones en el modelo esperado de composición y distribución espacial de los organismos bentónicos costeros, sobretodo en regiones portuarias, sujetas a las fuertes agresiones ambientales, provenientes de fuentes de polución como las cloacas domésticas, hospitalarias e industriales y a la recepción de especies exóticas transportadas por embarcaciones en viajes transoceánicos (Farrapeira 2006).…”