Fish mitigate trophic depletion in marine cave ecosystems.

Dark marine habitats are often characterized by a food-limited condition. Peculiar dark habitats include marine caves, characterized by the absence of light and limited water flow, which lead to reduced fluxes of organic matter for cave-dwelling organisms. We investigated whether the most abundant and common cave-dwelling fish Apogon imberbis has the potential to play the role of trophic vector in Mediterranean marine caves. We first analysed stomach contents to check whether repletion changes according to a nycthemeral cycle. We then identified the prey items, to see whether they belong to species associated with cave habitats or not. Finally, we assessed whether A. imberbis moves outside marine caves at night to feed, by collecting visual census data on A. imberbis density both inside and outside caves, by day and by night. The stomach repletion of individuals sampled early in the morning was significantly higher than later in the day. Most prey were typical of habitats other than caves. A. imberbis was on average more abundant within caves during the day and outside during the night. Our study supports the hypothesis regarding the crucial trophic role of A. imberbis in connecting Mediterranean marine caves with external habitats.

An ecosystem-based approach to assess the status of Mediterranean algae-dominated shallow rocky reefs.

A conceptual model was constructed for the functioning the algae-dominated rocky reef ecosystem of the Mediterranean Sea. The Ecosystem-Based Quality Index (reef-EBQI) is based upon this model. This index meets the objectives of the EU Marine Strategy Framework Directive. It is based upon (i) the weighting of each compartment, according to its importance in the functioning of the ecosystem; (ii) biological parameters assessing the state of each compartment; (iii) the aggregation of these parameters, assessing the quality of the ecosystem functioning, for each site; (iv) and a Confidence Index measuring the reliability of the index, for each site. The reef-EBQI was used at 40 sites in the northwestern Mediterranean. It constitutes an efficient tool, because it is based upon a wide set of functional compartments, rather than upon just a few species; it is easy and inexpensive to implement, robust and not redundant with regard to already existing indices.

Conservation of Mediterranean seascapes: analyses of existing protection schemes.

Marine protected areas (MPAs) are aimed at managing and protecting marine environments. Their design, however, often disregards both a thorough knowledge of the distribution of habitats and assemblages and the use of proper experimental evaluations of the efficacy of MPAs by comparing protected vs. unprotected zones. About 200 MPAs have been recently instituted in the Mediterranean area, but the evidence of their efficacy is scant. The MPA of Torre Guaceto (Southern Adriatic Sea, Italy) is one of the rare cases of effective protection enforcement. The reserve was instituted more than 10 years ago, a period currently considered as sufficient to show responses by organisms to protection. The MPA is divided into a C zone, the general reserve, where many activities are permitted, a B zone, the partial reserve where restrictions increase and two A zones, the integral reserve where access is prohibited. The goals of the paper were to map the distribution of benthic assemblages to assess if they were properly represented in the differently protected zones, and to test the efficacy of protection by quantifying possible differences between the assemblages in two control areas and in the two A zones, where human impact is completely excluded. The analysis of habitat and assemblage distribution within the MPA showed that the zones with total protection do not include most valuable environmental types. Most of the considered variables (i.e. cover of substratum, number of taxa, and average abundance of the most common taxa) were not significantly different in and out of the A zones, at each time of sampling. Results, however, suggested a possible effect of protection in modifying patterns of abundance of sponges under Cystoseira canopy (more abundant in the fully protected zone). In the subtidal habitat, differences were found in the structure of the whole assemblage and in the abundance of encrusting coralline red algae (more abundant outside the fully protected area). Notwithstanding the correct general methodology employed in the study, a lack of statistical power could have a role in preventing the detection of ecologically relevant effects of protection. In some instances, data pooling allowed a discrimination between cases where there was clearly no effect of protection and cases where there might be. On this basis, the optimization of this experimental design should be considered in further studies. In any case, if the goals of MPAs have not been clearly stated, efficacy of protection might prove very difficult to test even with the use of sound experimental designs.

Fish assemblages of Mediterranean marine caves.

Fish assemblages associated with 14 marine caves and adjacent external rocky reefs were investigated at four Marine Protected Areas (MPAs) along the coasts of Italy. Within the caves sampling was carried out in different sub-habitats: walls, ceilings, bottoms and ends of caves. On the whole, 38 species were recorded inside the 14 caves investigated. Eighteen species were exclusively found inside the caves: they were mainly represented by speleophilic (i.e. species preferentially or exclusively inhabiting caves) gobids (e.g. Didogobius splechtnai) and nocturnal species (e.g. Conger conger). Forty-one species were censused outside, 20 of which were shared with cave habitats. Apogon imberbis was the most common fish found in all 14 caves investigated, followed by Thorogobius ephippiatus (recorded in 13 caves), and Diplodus vulgaris and Scorpaena notata (both censused in 12 caves). Distinct fish assemblages were found between external rocky reefs and the different cave sub-habitats. New data on the distribution of some speleophilic gobids were collected, showing the existence of a pool of species shared by marine caves on a large scale (i.e. hundreds of km). Considering the uniqueness of cave fishes (18 exclusive species and different assemblage structures), the inclusion of marine caves among the habitats routinely investigated for fish biodiversity monitoring could facilitate the achievement of more comprehensive inventories. Due to their contribution to local species diversity and the shelter they provide to species valuable for conservation, marine caves should be prioritized for their inclusion not only within future MPAs through the Mediterranean Sea, but also into larger management spatial planning.