Ecological shifts in Mediterranean coralligenous assemblages related to gorgonian forest loss

PLoS One. 2014 Jul 23;9(7):e102782. doi: 10.1371/journal.pone.0102782. eCollection 2014.

Abstract

Mediterranean gorgonian forests are threatened by several human activities and are affected by climatic anomalies that have led to mass mortality events in recent decades. The ecological role of these habitats and the possible consequence of their loss are poorly understood. Effects of gorgonians on the recruitment of epibenthic organisms were investigated by manipulating presence of gorgonians on experimental panels at 24 m depth, for Eunicella cavolinii, and at 40 m depth, for Paramuricea clavata, at two sites: Tavolara Island (Tyrrhenian Sea) and Portofino Promontory (Ligurian Sea). After 4 months, the most abundant taxa on the panels were encrusting green algae, erect red algae and crustose coralline algae at 24 m depth and encrusting brown algae and erect red algae at 40 m depth. Assemblages on the panels were significantly affected by the presence of the gorgonians, although effects varied across sites and between gorgonian species. Species diversity and evenness were lower on panels with gorgonian branches. Growth of erect algae and recruitment of serpulid polychaetes were also affected by the presence of the gorgonians, primarily at Tavolara. Crustose coralline algae and erect sponges were more abundant on E. cavolinii panels at 24 m depth, while encrusting bryozoans were more abundant on P. clavata panels at 40 m depth. Effects of gorgonians on recruited assemblages could be due to microscale modification of hydrodynamics and sediment deposition rate, or by a shading effect reducing light intensity. Gorgonians may also intercept settling propagules, compete for food with the filter-feeders and/or for space by producing allelochemicals. Presence of gorgonians mainly limits the growth of erect algae and enhances the abundance of encrusting algae and sessile invertebrates. Therefore, the gorgonian disappearances may cause a shift from assemblages characterised by crustose coralline algae to filamentous algae assemblages, decreasing complexity and resilience of coralligenous bioconstructions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anthozoa / classification
  • Anthozoa / physiology*
  • Chlorophyta / physiology
  • Conservation of Natural Resources / methods*
  • Ecological and Environmental Phenomena*
  • Ecosystem*
  • Geography
  • Humans
  • Mediterranean Sea
  • Phaeophyceae / physiology
  • Rhodophyta / physiology
  • Seawater / chemistry
  • Seawater / microbiology

Grants and funding

This work has been partially funded by University funds to CC and has been co-funded by the Italian Ministry of Education, Universities and Research within the Flagship Project RITMARE “The Italian Research for the Sea” (belonging to the National Research Program 2012-2016 and coordinated by the Italian National Research Council), and within the scientific research program of national interest “Coastal bioconstructions: structures, functions, and management” (2010-11 PRIN prot. 2010Z8HJ5M_003). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.