Ecological Shifts in Mediterranean Coralligenous Assemblages Related to Gorgonian Forest Loss

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.

Composition and abundance of octocorals in the Sea of Marmara, where the Mediterranean meets the Black Sea

“…Among them, some long-living species are considered as ''ecosystem engineers'' (Jones et al 1994, Ponti et al 2014 in Mediterranean marine hard-bottom communities, with significant effects on the structure, biomass and biodiversity of coralligenous communities (Ballesteros 2006). Although scientific studies and conservation efforts focus increasingly on octocorals and mainly gorgonians, our knowledge on their presence and distribution in the eastern Mediterranean is yet insufficient (Salomidi et al 2009).…”

Demographic responses to warming: reproductive maturity and sex influence vulnerability in an octocoral

“…This slow-growing octocoral plays an important role in the maintenance of biomass, diversity, and complexity of the Mediterranean coralligenous assemblages (True 1970;Ballesteros 2006;Ponti et al 2014). During the last decade, P. clavata has been widely impacted by mass mortality events (Cerrano et al 2000;Garrabou et al 2009) that have greatly affected its distribution, demography, and reproduction (see Linares et al 2005Linares et al , 2008aCerrano and Bavestrello 2008;Cupido et al 2008Cupido et al , 2009Linares and Doak 2010;Huete-Stauffer et al 2011).…”

Structure and biodiversity of coralligenous assemblages dominated by the precious red coral Corallium rubrum over broad spatial scales

“…Climate warming and the potential effects of ocean acidification are also major threats affecting populations12202122. It has been demonstrated that a decrease in the abundance of habitat-forming species leads to a rapid fragmentation in community structure and a loss of species benefiting from the structural complexity these species provide23242526. C. rubrum is a slow-growing, long-lived species, and plays a key role as a habitat forming species and in the functioning of coralligenous habitats mainly due to its trophic activity, biomass and perennial biogenic structure as other Mediterranean gorgonian species102427.…”