the importance of refuges

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Experiments 1-2 were carried out indoor. 31 Coris julis to simulate high predation pressure of. Marine Reserve. 1. Shelter effect of matte on recruits. 2. Shelter ...
Role of predation in determining sea urchin size structure in seagrass meadows:

the importance of refuges

S. Farina, F. Tomas, P. Prado, J. Romero, T. Alcoverro

Complexity of habitat in an ecosystem has strong effects on behaviours of predators and preys . (Savino & Stein 1982; 1989; Werner et al. 1983; Eklov and Diehl 1994).

introduction

Paracentrotus lividus in Mediterranean Sea Recruits and middle-size urchins use crevices, holes, algae assemblages and boulders as permanent refuge. (Sala et al. 1998b; Hereu et al., 2004; Guidetti et al., 2004).

Adult urchins attain a partial refuge in their own size. (Tegner and Dyton 1981; Guidetti 2004).

Predation is practiced basically on juvenile populations (Tegner and Dayton, 1981; McClanahan and Muthiga, 1989; Sala 1997; Lopez at al., 1998)

it decreases with increasing of rocky bottom complexity space: “shelter Coris julis

effect ” (Sala et al. 1998b; Hereu et al., 2004; Guidetti et al., 2004)

Diplodus sargus Diplodus vulgaris

introduction

Structural complexity of vegetation may be a very efficient habitat, resource and shelter.. Leaf shelter indirectly provides protection from natural enemies

and predation in vegetated habitats is efficiently lower than in unvegetated ones (Crowder & Cooper, 1982; Summerson & Peterson, 1984; Tonn et al., 1989)…

? introduction

….but both in terrestrial and in marine ecosystems, vegetation like herbaceous plants is altered constantly in form and phenology by herbivores (Huntly 1991).

In Posidonia oceanica ecosystem

Sarpa salpa

Low herbivore pressure

High herbivore pressure Paracentrotus lividus

introduction

Does Posidonia oceanica increase sheltering possibilities for recruits and middle-size individuals of Paracentrotus lividus? Can Sarpa salpa, the main grazer of Posidonia oceanica, reduce these possibilities by modifying leaf length?

objectives

The mechanism of predation in relation to potential sheltering in Posidonia oceanica

length of the leaves’ canopy experiment 2 (recruits) experiment 3 (middle-size)

3 2 1

mat experiment 1 (recruits)

objectives

Recruits are too little to be observed in the field. Experiments 1-2 were carried out indoor.

31 Coris julis to simulate high predation pressure of Marine Reserve

1. Shelter effect of matte on recruits 2. Shelter effect of leaf length on recruits

Middle-size urchins are big enough to be marked and observed in the field. Experiment 3 was carried out in the field: high predation pressure of Marine Reserve. 3. Shelter effect of leaf length on middle-size urchins

Materials & methods

Experiments on recruits (0.2