Nursery value of Cystoseira forests for Mediterranean rocky reef fishes

The canopy-forming fucoid Cystoseira spp. provide biogenic structure, food and shelter for many organisms including fishes on Mediterranean nearshore rocky reefs. Infralittoral Cystoseira forests have declined or disappeared from many Mediterranean locales, leading to a severe transformation of the habitat and the loss of its tri-dimensional structure. Here we assess the nursery value of Cystoseira forests and the consequences of this habitat transformation on the recruitment of rocky reef fish assemblages. Densities of several reef fish juveniles—particularly Symphodus spp.—were 9 to 12 folds greater in Cystoseira forests than in other erect and turf algal assemblages. Experimental habitat manipulation mimicking the alteration of a Cystoseira canopy showed greater abundances of Symphodus spp. juveniles on artificially forested substratum than on bare substratum. Our study quantified for the first time the nursery value and functional importance of Cystoseira forests canopies suggesting that their loss may strongly affect the recruitment of littoral fishes in the Mediterranean Sea.

► We demonstrate the high nursery value of Cystoseira forests for coastal fish.
► Refuge availability seemed to be the main driver of Cystoseira nursery value.
► Depletion of these forests may strongly affect the recruitment of littoral fishes.
► The use of artificial Cystoseira thalli was an accurate method to manipulate habitat.