Unveiling hidden relationships between biodiversity and ecosystem functioning in Mediterranean rocky reefsHI-BEF project

Progetto: Research project

Dettagli progetto

Description

4 - Research Project AbstractIn the Mediterranean, overfishing of large predatory fish, especially of Diplodus spp., can cause severe sea urchin outbreaks and promote a shift in benthiccommunities. The variation in sea urchin grazing intensity may drive switches between one complex state, dominated by a stratified assemblage of several erect algaeincluding those of Cystoseira genus (Erected Macroalgae Assemblage, EMA), to a simpler one, the barren, dominated by few encrusting algae (Encrusting Corallinesalgae Assemblages, ECA). ECA state is geographically widespread and can paradoxically persist for long periods also in marine protected areas (MPAs).Theoretically, the ban of extractive human activities usually leads to the recovery of key predators of sea urchins (fishes, lobsters, sea stars), which control urchinspopulations and allow the restoration of the erect macroalgal-dominated states. However, large barren areas can be found along the oldest Mediterranean MPAs. Inthese cases, recovery of the top predators is too slow, due to their initial over-exploitation, and sea urchins abundance may explode, due to the combined effect of lackof natural predators and human exploitation. EMA states and associated organisms are known to be highly productive compared to structurally simpler states, such asECA. EMAs transfer vast quantities of carbon, nitrogen and phosphorus to coastal food webs either through direct transfer of animal biomass (i.e. predation,movements of individuals) or out-welling of dissolved and particulate organic matter. On the contrary, ECA systems are assumed to be characterized by low diversityand productivity. There is indirect evidence that deforestation can negatively affect the productivity of individual species or groups of species, with effects that arelikely to propagate along food chains. However, recent studies conducted in the North Pacific indicated that, although ECA exhibits a low structural complexity, it canprovide a high number of microhabitats available for a wide variety of cryptic invertebrate species.ECA state areas are widespread in the Mediterranean, but the information on the associated biodiversity and functioning are still very scarce.The aims of this project are:(1) Assessing mechanisms involved in the transitions between EMA and ECA states;(2) Assessing the benthic biodiversity in EMA and ECA;(3) Assessing ecosystem functioning in EMA and ECA.A multidisciplinary approach (manipulative, descriptive, isotopic and of mass balance) will be adopted to achieve these aims.For (1) assessing mechanisms involved in the transitions between EMA and ECA states, a manipulative approach will be adopted. Our intention is to study, with arigorous, manipulative approach, the factors (abiotic and biotic) responsible for the creation, stability and transition between EMA and ECA present on the upperinfralittoral rocky shores of the Mediterranean Sea. Manipulative experiments will be employed to assess the relative role of total density and composition ofherbivore species, refuges availability for herbivores, disturbance and switches in herbivore feeding mode in triggering the shift from EMA to ECA and maintainingECA.For (2) Assessing the benthic biodiversity in EMA and ECA, and (3) Assessing ecosystem functioning in EMA and ECA, community structure and functionaldiversity of benthic assemblage, energy flow and trophic interactions will be defined in EMA and ECA states and compared at a mesoscale level.The structure of the food webs will be determined through the study of trophic guilds and stable isotopes (13C/1

Layman's description

In the Mediterranean, overfishing of large predatory fish, especially of Diplodus spp., can cause severe sea urchin outbreaks and promote a shift in benthiccommunities. The variation in sea urchin grazing intensity may drive switches between one complex state, dominated by a stratified assemblage of several erect algaeincluding those of Cystoseira genus (Erected Macroalgae Assemblage, EMA), to a simpler one, the barren, dominated by few encrusting algae (Encrusting Corallinesalgae Assemblages, ECA). Barrens are geographically widespread and can paradoxically persist for long periods also in marine protected areas (MPAs). Theoretically,the ban of extractive human activities usually leads to the recovery of key predators (fishes, lobsters, sea stars) controlling sea urchin populations and restoringmacroalgal-dominated habitats. However, large barren areas can be found along the oldest Mediterranean MPAs (i.e. in France at the Port-Cros National Park, theScandola Natural Reserve; in Spain some areas of the Islands Medes Marine Reserve, the Cabrera National Park the Cabo de Palos-lslas Hormigas marine Reserve;the Bouches de Bonifacio Intemational Marine Park; in Italy Asinara and Ustica Island). In these cases, recovery of the top predators is too slow, due to their initialover-exploitation, and sea urchins abundance may explode, due to the combined effect of lack of natural predators and human exploitation. Moreover, a growing bodyof evidence suggests that, once created, barrens can be maintained also by relatively low densities of sea urchins. Although encrusting macroalgae assemblages arewidespread in the Mediterranean, the information on the associated biodiversity and functioning are still very scarce. Recent studies, conducted in the North Pacific,indicated that, although encrusting algae exhibit a low structural complexity, they can provide a high number of microhabitats available for a wide variety of crypticinvertebrate species.Mediterranean barrens give us the opportunity to explore, with a multidisciplinary approach, the effect of erect algae assemblages' loss on biodiversity and functioningof rocky reef allowing to test the theories on the effect of biodiversity changes on the functioning of ecosystems.Within this context, the project HI-BEF aims to:1) Assessing mechanisms involved in the transitions between Erected Macroalgae Assemblage (EMA) and Encrusting Corallines algae Assemblages (ECA) states;2) Assessing the benthic biodiversity in EMA and ECA;3) Assessing ecosystem functioning in EMA and ECA.

Key findings

Ambiente e cambiamento climatico
StatoAttivo
Data di inizio/fine effettiva1/1/12 → …