2.2 Ecological issues and features of lagoons

An exhaustive and formal ecological assessment of Mediterranean coastal lagoons, of their structure and functioning, is beyond the purpose of this review. Several research and scientist networks have worked and keep working on the ecological aspects of lagoons. A few highlights that may be useful to discuss future prospects for Mediterranean coastal lagoon management are presented here, while paragraph 2.3 is dedicated to the complex biodiversity that sustains fisheries activities in lagoons.

According to Barnes (1980), coastal lagoon science is relatively young, but nowadays only tropical lagoons can be considered as poorly studied (Esteves et al., 2008). For the Mediterranean region, there is a vast quantity of information available on basic ecology, living resources, environmental issues or management, although Perez-Ruzafa et al. (2010) point out that research towards understanding coastal lagoon ecological processes in the Mediterranean region has been discontinued over time.
The need to monitor many coastal ecosystems has stemmed from the necessity to document environmental quality, to follow restoration, to detect management interventions or to address specific requirements. Many research frameworks exist in most Mediterranean countries; projects have been launched and are still ongoing to tackle the multiple aspects of coastal lagoon science in Europe, North Africa and in the western Mediterranean Sea (Thompson and Flower, 2009). Apart from past contributions within the framework of the FAO-GFCM (see paragraph 1.1), the extensive review of literature and an analysis of the information gathered in this document show that the volume of data obtained from monitoring frameworks and scientific knowledge on different aspects of lagoon ecology that derives from it are extremely high; many Mediterranean coastal lagoons have been studied over the last 30 years, although the amount of information and the level of scientific knowledge differ among the different countries and lagoons.

Notwithstanding their differences in size, location, climate and management regimes, Mediterranean coastal lagoons share many features such as shallowness, connections with the sea through channels and inlets, coastal barriers and strong physical and ecological gradients (Unesco, 1981); as anywhere else in the world, they feature a high productivity and a large variety of habitat interfaces within a complex ecological stability. If these general characteristics are largely recognized, the question is “What  are the factors that determine the structure

Some lagoons have been extensively studied and monitored in their main ecological components. In the Orbetello lagoon (central Italy), several studies have been carried out between the late 1990s and 2000 due to the need to document environmental conditions and to monitor the outcomes of human interventions in the lagoon (Innamorati, 1998; Innamorati and Melillo, 2004; Italy country report).
The lagoon of Venice, the second largest lagoon of the Mediterranean after the deltaic lagoons of Egypt, is the most studied lagoon: intensive monitoring programmes are constantly carried out and ongoing in order to provide information regarding the protection, control, surveillance and monitoring of the lagoon system with a view to preserving the city of Venice (Italy country report). The Venice lagoon has been subject to the most important land and water management interventions in time. In this large lagoon, there is a wide array of land and water uses, which have strongly influenced the lagoon ecosystem.
and functioning of ecosystems with such characteristics?” (Carrada and Fresi, 1988). Distinct criteria such as salinity, substrate type, formation, isolation, size, morphology, etc.
(Barnes, 1980; Guelorget and Perthuisot, 1983) have been summoned in order to describe the functioning of coastal lagoon ecosystems. Salinity has been usually considered as the essential parameter to explain observed gradients in density, biomass, species richness or diversity (Por, 1972; 1980). In the early 1980s, Guelorget and Perthuisot (1983) proposed that zonation patterns and species distribution in the lagoons be determined by confinement, i.e. the degree of separation from the marine domain. Later, Perez-Ruzafa and Marcos (1992, 1993) suggested that the colonization rate by marine species was the main factor shaping the lagoon assemblage structure in a confinement gradient, and that the species composition in each lagoon resulted from competition between marine and lagoon species (Perez Ruzafa et al., 2007). Mariani (2001) confirmed that fish community in lagoons appeared to be consistent with current salinity trends. In any case, the majority of biological assemblage characteristics, including community structure and productivity still relate to the geomorphologic characteristics of lagoons (Perez-Ruzafa et al., 2007) and are conditioned by environmental stress (Gamito et al., 2005).

Coastal lagoons in the Bay of Cadiz (Spain), photo ©J.C. Macias, 2011