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The influence of canopy algae on vertical patterns of distribution of low-shore assemblages on rocky coasts in the northwest Mediterranean

The influence of canopy algae on vertical patterns of distribution of low-shore assemblages on rocky coasts in the northwest Mediterranean
The influence of canopy algae on vertical patterns of distribution of low-shore assemblages on rocky coasts in the northwest Mediterranean
Canopy-forming algae have been shown to play a fundamental role in the maintenance of understorey assemblages on rocky shores. In the Mediterranean, low-shore habitats are often monopolised by canopy algae of the genus Cystoseira and, in particular, by the species Cystoseira amentacea var. stricta. Alternatively, low-shore habitats are dominated by turf-forming algae and/or mussels. Previous studies showed that loss of Cystoseira, by natural or anthropogenic disturbances, resulted in the increase of turfing algae. Here, we propose that turf-forming algae may act as colonisers from nearby habitats, specifically from lower portions of the shore. The following hypotheses were tested to investigate this proposition: (1) in presence of Cystoseira, the assemblage living under its canopy will be distinct, in terms of composition and structure, from that found lower on the shore, (2) if the canopy of Cystoseira was removed, the differences between the two assemblages would decrease or disappear, (3) the effects of the canopy would be more important than other causes of variability at the spatial scale investigated (hundreds to thousands of metres), and (4) that effects of removal of the canopy would be consistent through time. These hypotheses were tested by means of a canopy removal experiment, involving several spatial and temporal repetitions of the manipulation.

The assemblage underneath the canopy of Cystoseira was distinct from that found immediately lower on the shore, but when the canopy was removed there were no differences between the two. The effects of the canopy were consistent at the spatial and temporal scales investigated. Several species living under the canopy disappeared and were replaced by turf-forming species, resulting in a homogenisation of the two habitats and in a drastic loss of habitat diversity. This study shows that Cystoseira can be considered a habitat-forming species, responsible for the maintenance of two distinct low-shore assemblages. In this light, its importance should be taken into account by policies aiming to preserve biodiversity on rocky shores.
Rocky shores, Canopy algae, Cystoseira, Habitat-formers, Habitat homogenisation, Conservation of biodiversity
0022-0981
89-106
Bulleri, Fabio
bcd65a86-a185-4b29-8068-12918b1329e5
Benedetti-Cecchi, Lisandro
73993387-813b-4258-84de-49e6ed0b455c
Acunto, Stefano
089fa880-6727-4e27-a6ea-ce8ab33457e2
Cinelli, Francesco
004418e0-4b87-453b-9fde-f5781efc39fa
Hawkins, Stephen J.
758fe1c1-30cd-4ed1-bb65-2471dc7c11fa
Bulleri, Fabio
bcd65a86-a185-4b29-8068-12918b1329e5
Benedetti-Cecchi, Lisandro
73993387-813b-4258-84de-49e6ed0b455c
Acunto, Stefano
089fa880-6727-4e27-a6ea-ce8ab33457e2
Cinelli, Francesco
004418e0-4b87-453b-9fde-f5781efc39fa
Hawkins, Stephen J.
758fe1c1-30cd-4ed1-bb65-2471dc7c11fa

Bulleri, Fabio, Benedetti-Cecchi, Lisandro, Acunto, Stefano, Cinelli, Francesco and Hawkins, Stephen J. (2002) The influence of canopy algae on vertical patterns of distribution of low-shore assemblages on rocky coasts in the northwest Mediterranean. Journal of Experimental Marine Biology and Ecology, 267 (1), 89-106. (doi:10.1016/S0022-0981(01)00361-6).

Record type: Article

Abstract

Canopy-forming algae have been shown to play a fundamental role in the maintenance of understorey assemblages on rocky shores. In the Mediterranean, low-shore habitats are often monopolised by canopy algae of the genus Cystoseira and, in particular, by the species Cystoseira amentacea var. stricta. Alternatively, low-shore habitats are dominated by turf-forming algae and/or mussels. Previous studies showed that loss of Cystoseira, by natural or anthropogenic disturbances, resulted in the increase of turfing algae. Here, we propose that turf-forming algae may act as colonisers from nearby habitats, specifically from lower portions of the shore. The following hypotheses were tested to investigate this proposition: (1) in presence of Cystoseira, the assemblage living under its canopy will be distinct, in terms of composition and structure, from that found lower on the shore, (2) if the canopy of Cystoseira was removed, the differences between the two assemblages would decrease or disappear, (3) the effects of the canopy would be more important than other causes of variability at the spatial scale investigated (hundreds to thousands of metres), and (4) that effects of removal of the canopy would be consistent through time. These hypotheses were tested by means of a canopy removal experiment, involving several spatial and temporal repetitions of the manipulation.

The assemblage underneath the canopy of Cystoseira was distinct from that found immediately lower on the shore, but when the canopy was removed there were no differences between the two. The effects of the canopy were consistent at the spatial and temporal scales investigated. Several species living under the canopy disappeared and were replaced by turf-forming species, resulting in a homogenisation of the two habitats and in a drastic loss of habitat diversity. This study shows that Cystoseira can be considered a habitat-forming species, responsible for the maintenance of two distinct low-shore assemblages. In this light, its importance should be taken into account by policies aiming to preserve biodiversity on rocky shores.

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More information

Published date: 2002
Keywords: Rocky shores, Canopy algae, Cystoseira, Habitat-formers, Habitat homogenisation, Conservation of biodiversity

Identifiers

Local EPrints ID: 188429
URI: http://eprints.soton.ac.uk/id/eprint/188429
ISSN: 0022-0981
PURE UUID: bf00958a-89c2-48ec-945a-988f45c4b354

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Date deposited: 24 May 2011 15:42
Last modified: 16 Jul 2019 23:32

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