The Structure of Mediterranean Rocky Reef Ecosystems across Environmental and Human Gradients, and Conservation Implications

Abstract

Historical exploitation of the Mediterranean Sea and the absence of rigorous baselines makes it difficult to evaluate the current health of the marine ecosystems and the efficacy of conservation actions at the ecosystem level. Here we establish the first current baseline and gradient of ecosystem structure of nearshore rocky reefs at the Mediterranean scale. We conducted underwater surveys in 14 marine protected areas and 18 open access sites across the Mediterranean, and across a 31-fold range of fish biomass (from 3.8 to 118 g m−2). Our data showed remarkable variation in the structure of rocky reef ecosystems. Multivariate analysis showed three alternative community states: (1) large fish biomass and reefs dominated by non-canopy algae, (2) lower fish biomass but abundant native algal canopies and suspension feeders, and (3) low fish biomass and extensive barrens, with areas covered by turf algae. Our results suggest that the healthiest shallow rocky reef ecosystems in the Mediterranean have both large fish and algal biomass. Protection level and primary production were the only variables significantly correlated to community biomass structure. Fish biomass was significantly larger in well-enforced no-take marine reserves, but there were no significant differences between multi-use marine protected areas (which allow some fishing) and open access areas at the regional scale. The gradients reported here represent a trajectory of degradation that can be used to assess the health of any similar habitat in the Mediterranean, and to evaluate the efficacy of marine protected areas.

Setting an ecological baseline prior to the bottom-up establishment of a marine protected area in Santorini island, Aegean Sea

“…Furthermore, an integrated assessment was performed at 5 and 15 m depth, jointly addressing structural aspects of fish assemblages and their associated benthic communities (e.g. Sala et al, 2012).…”

“…Fully protected marine areas are estimated to barely cover 0.04% of the Mediterranean Sea (PISCO & UNS, 2016). In reality, this percentage is even smaller, considering that even in many fully protected areas of the Mediterranean poaching and other illegal destructive activities still occur (Guidetti et al, 2008;Sala et al, 2012).…”

The application of genetics to marine management and conservation: examples from the Indo-Pacific

“…The design of marine protected areas (MPAs) has generally been based on a number of considerations, often not relevant to the biology of the species that they are supposed to protect (Sala et al 2012). The application of parentage and kinship analyses to our understanding of connectivity among reefs is still in its infancy, yet it has yielded some very promising results that are likely to inform managers as to the proper design of future MPAs.…”

Role of two co-occurring Mediterranean sea urchins in the formation of barren from Cystoseira canopy

“…Furthermore, anthropogenic stressors such as global warming and overfishing have also created this process. Overfishing of large sea urchin predator fish, especially Diplodus spp., can cause severe sea urchin outbreaks (Paracentrotus lividus and Arbacia lixula) and promote a shift in rocky benthic community structure (Hereu et al, 2008;Sala et al, 2012;Cardona et al, 2013). The variation in sea urchin grazing intensity may drive switches between one complex state, dominated by a stratified assemblage of several erect algae including the Cystoseira genus, to a simpler one, dominated by few encrusting algae, the so-called 'barren ground' (Shears and Babcock, 2002;Estes et al, 2011).…”