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Communities

Photophilic algal communities

Photophilic algal communities develop within the first few metres of depth where light is abundant. These communities are fundamental for rocky ecosystems, due to their ecological role as primary producers and providers of shelter for a great diversity of associated species that live or feed within them.

In recent years, anthropogenic direct and indirect disturbances have caused serious modifications to algal communities in extensive areas of the Mediterranean. The main modifications have been a decrease in biodiversity, a reduction in total biomass, a reduction in spatial complexity, unbalance in bottom-up and top-down controls, and considerable loss of resilience.

The study of these disturbances from an interdisciplinary approach that includes taxonomy, physiology, population dynamics and modelling will enable us to attain more precise knowledge of the consequences of these perturbations, and will provide us with guidelines for eliminating or attenuating their effects, or even for considering the implementation of restoration methods.

 

 

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Deep-water Cystoseira spp. communities

In deep-water Mediterranean rocky coastal bottoms (>35–40 m depth) stands of Cystoseira spp. are found. The communities characteristically have high structural complexity (i.e. high diversity and species richness) and low dynamics (i.e. low productivity). For instance, deep-water Cystoseira spp. forms old-growth forests with individuals that are over 50 years old. Due to their slow demographic dynamics, these communities are highly sensitive to several perturbations, such as increases in water turbidity, eutrophisation, the erosive effects of anchoring and fishing nets, overgrazing by sea urchins as a consequence of overfishing, or the effects of introduced invasive species. Hence, they have already disappeared from several regions across the Mediterranean, although they still remain in some areas.

In spite of their interest, the composition, structure, dynamics and geographic distribution of these deep-water assemblages remain widely unknown, probably because it is difficult to study such deep habitats. The decline of these unique and fragile assemblages calls for their study and to establish management actions that will ensure their conservation.

 

 

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Coralligenous communities

Coralligenous communities have been defined as organogenous constructions formed principally by calcareous sciaphilic algae, mainly Lithophyllum, Lithothamnion, Mesophyllum, Neogoniolithon, Peyssonnelia, and Halimeda, which develop in dim light conditions (20–120 m depth). Such concretions of coralline algae form a complex structure which holds or shelters a high number of algal and animal species. This enhances coralligenous communities’ role as one of the most important ‘hot spots’ of species diversity in the Mediterranean. Furthermore, coralligenous assemblages are characterized by harbouring a great number of endangered species, which are long-lived organisms, whose slow growth and recruitment rates make them very sensitive to disturbances.

Unfortunately, coralligenous communities in the NW Mediterranean have been suffering the effects of several human related disturbances such as increases in water turbidity, eutrophisation, the erosive effects of anchoring and fishing nets. Likewise, more recently these communities are being affected by two major disturbances: mass mortality events linked to Mediterranean warming and the invasion of introduced species. The direct and combined effects of both of these disturbances could have severe consequences for the conservation of these precious coralligenous communities. Therefore, the acquisition of baseline data at community level is vital, to assess the impact of present and future disturbances and to anticipate future trends in communities.

 

 

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