Biodiversity of Coastal Lagoon Ecosystems and Their Vulnerability to Global Change

Abstract

In this chapter we define coastal lagoons according the definition proposed by Kjerfve (1994) as “shallow water bodies separated from the ocean by a barrier, connected at least intermittently to the ocean by one or more restricted inlets, and usually oriented shoreparallel”. This definition is given in an introduction chapter of a multiauthor book edited by Kjerfve (1994). Nevertheless, in the scientific literature the term coastal lagoon is not always used. For example, in the North American ecological literature the term estuary has often been used rather than coastal lagoon for systems including “Laguna Madre”, “Lake Pontchartrain” and “Waquoit Bay”. In contrast, in the socio-historical context of Southwestern Europe, lagoons are well recognised and distinguished from estuaries as is shown by the vernacular languages that contain specific words for the coastal lagoons, their barriers and inlets. Thus, coastal lagoons are named “laguna” in Spanish and Italian, “lagoa” in Portuguese and “lagune” in French. However, the Spanish word “laguna” also refers to a relatively shallow freshwater lake system, and coastal lagoons are referred to as “lagunas costeras”. In French, the word “lagon” refers to a marine water body that is separated from the open sea by a coral reef. Therefore, one has to be aware of possible confusions and different perceptions of coastal lagoons by different communities. Lagoon science is relatively young and had some difficulty of getting from the ground as was earlier highlighted in the classical book by Barnes (1980) titled “Coastal Lagoons; the natural history of a neglected habitat”. Actually still today coastal lagoons in the tropical world have been poorly studied so far (Esteves et al., 2008). In Europe, nowadays a thriving community of lagoon scientists exists that joins together in biannual meetings since 2003 (European Coastal Lagoons Symposium, Eurolag), the latest (2011) has taken place in Aveiro, Portugal. Coastal lagoon ecosystems are a particular type of estuarine systems where seawater mixes with fresh water from their continental catchments. These systems occupy about 12 % of the world coastlines (see Fig. 1). Salinities have been used since 1958 to classify the lagoons and other brackish or estuarine waters according the Venice system. Accordingly, a lagoon with salinities below 5 ppt is oligohaline; mesohaline waters have salinities between 5 and 18 ppt and polyhaline between 18 and 30 ppt. Lagoons with salinities above 30 ppt but below that of seawater are termed mixoeuhaline. Connections with the sea can be temporary or