2.6 Environmental issues in coastal lagoons

As probably the most densely populated areas in the world (Papayannis and Salathe, 1999), the Mediterranean coastal zones exemplify the conflict between the human exploitation of water resources and the ecological needs of aquatic ecosystems (Thompson and Flower, 2008).

In such a context, coastal lagoons have become a matter of concern due to the detrimental impact of several human activities over recent decades. The close relationship of lagoons with terrestrial ecosystem boundaries make these environments very vulnerable to hydrological modifications (freshwater diversions or drainage discharges), water pollution and habitat loss (Gamito et al., 2005; Perez Ruzafa et al., 2000, 2002, 2005b), which deeply change the structure of the lagoons’ ecological dynamics.

Aerial view of the lagoon area, bay of Cadiz (Spain), photo ©J.C. Macias, 2011

Coastal lagoons undoubtedly play a major role in regional economies, but increasing human pressure brings about ecological disturbances that could limit or suppress the economic and ecological services provided by these ecosystems (Troussellier and Gattuso, 2007). The degradation of the lagoon environment affects not only fishing activities, but also those related to recreation and ecotourism (see paragraphs 2.4.3 and 2.5.4), creating damages for the entire coastal community.

2.6.1 Deterioration of land surrounding lagoons

Some changes in the lagoons’ environment are historically related to the use of the surrounding land. The intensification of urbanization and litoralization, with a shift of many industrial activities to the coastal zones, as well as the increase of interventions aimed at implementing tourism-related facilities and agriculture practices have a strong impact on the lagoons’ ecosystem. For example, agriculture activities in the watershed often imply agricultural wastes and nutrient input into the lagoons as well as wastewater that may be contaminated with pesticides and contaminants, especially in those areas with intensive agriculture or industrial activities. Frequently, lagoons have even been considered as dumping areas for urban and industrial wastes (De Wit et al., 2011).
At present, great efforts and
investments are made to process

The deltaic lagoons of Egypt are the most polluted areas of the country, as they receive great amounts of untreated industrial, municipal and agricultural wastewater (Egypt country report). The Porto
Marghera industrial zone, in the Venice lagoon, is also well known: in the early 1920s, a harbour
along with many industries was built and industrial activities have carried out in the proximity of the
lagoon borders for more than fourty years
(Comune di Venezia, 2012).
industrial and urban wastewater before it enters the lagoons or their surrounding areas, in order to maintain lagoon waters in safe and adequate conditions and to support the fishing activities. For example, in the Orbetello lagoon, a glue and fertilizers factory was closed in 1992 (Lenzi, pers. comm.) and the most polluted section of the lagoon was isolated in order to keep chemicals and industrial residues inside a restricted area.

 

2.6.2 Eutrophication, changes in hydrology and salinity

Severe and widespread environmental problems experienced in many coastal zones are associated with an excess of nutrients. Eutrophication is a common phenomenon observed in many Mediterranean coastal lagoons. When this nutrient enrichment reaches unsustainable levels, it triggers anoxia and widespread die-offs of organisms, with serious impacts on the environment of the lagoon and therefore on its economic activities (Magni et al., 2009). The constant risk of eutrophication events in lagoons imposes the need of adopting measures that often require high energy and costs but are able to prevent and limit efficiently lagoon dystrophic crises (see paragraph 2.5.3).
In addition, water salinity increase and the salinization of lagoons surrounding areas often occur, mostly in the heavily populated semiarid coastal zones of the southern Mediterranean. In these areas, coastal lagoons are located downstream of inland drainage systems, and hence are particularly sensitive to changes in freshwater inflows as a result of water management. In North Africa, where freshwater resources are generally scarce, the growing demand of water for agriculture and industry and to serve an expanding population have placed coastal lagoon management requirements in direct competition with other human activities.

2.6.3 Alien species

The introduction of allochthonous (or alien) species in the aquatic environment can be due to several reasons: they can be accidentally introduced by human activities, e.g. through vectors such as ship hulls and shells, or voluntary introduced in the environment, e.g. for farming purposes. The spreading of alien species in the aquatic ecosystems in various regions of the world is also recognized as a consequence of global climate change which affects the species distribution and resource dynamics in aquatic ecosystems (Occhipinti-Ambrogi, 2000; 2007). In general, alien species can have different (negative) impacts on their new environment: i) they can actively compete with autochthonous species (and in some cases eradicate them); ii) they can be a vector for viruses and germs and favour epidemies, iii) they can become invasive and create environmental problems.
In the Mediterranean lagoon environment, alien species that have often been voluntarily introduced have sometimes replaced autochthonous ones; nevertheless, besides this negative ecological impact, some beneficial effects of these new species have been claimed, since they have sometimes significantly contributed to the increase in fisheries production. For example, the oyster Ostrea edulis has been replaced by the Asian Crassostrea gigas (Thunberg, 1973) and the Japanese carpet shell, Ruditapes philippinarum, introduced in 1983 from south-eastern Asia in some Italian coastal lagoons, has displaced the local grooved carpet shell, R. decussates, in several areas (see paragraph. 2.4.1). Indeed R. philippinarum has proved to be more resistant to temperature and salinity changes, to adapt to a greater variety of substrates, and to show a faster growth rate.
In Egypt, the freshwater crayfish Procambarus clarkii used to be imported by a private
company for aquaculture purposes but has soon been released in the wild as the sale of this species on the Egyptian market failed. The species grew and reproduced in the Nile river and in its tributaries and invaded all the freshwater bodies from southern to northern coastal lakes, causing serious environmental problems such as the weakening of river and canal banks due to its burrowing behaviour and the destruction of tilapia (Oreochromis niloticus) nests due to its voraciousness. At present, scientists and public authorities are still trying to eradicate this alien species (Egypt country report).
The controlled introduction of allochthonous species for aquaculture purposes can lead to a parallel introduction of other undesirable alien species. In the Thau lagoon, in France, 20 percent of macroalgae are alien species and some of them have become invasive and modified the local biodiversity patterns. These macroalgae, originating from Japanese coastal zones (Boudouresque et al., 2011), have been probably introduced by means of alien oysters. In Egypt, the shrimp Penaeus indicus was introduced in 2011 from Thailand in the north-western area of the Manzala lagoon, for fishing purposes and strict measures to prevent the introduction of viral or bacterial pathologies were adopted (Egypt country report).

Lagoon fishers in Egypt, photo ©S.H. Abdel-Rahman, 2011

Another alien species that was accidentally introduced, possibly from Australia (transported on ships hulls or on commercial mollusc shells), is Ficopomatus enigmaticu, a 4?25 mm long worm (Polychaeta) that builds and lives in a carbonate tube. The accumulation of the carbonate tubings results in recifs of several tens of meters height, comparable to coral-like encrustations (Grillas et al., 2006), causing many problems in Mediterranean lagoons.
Local climate variations can also be responsible for the invasion of unusual species in lagoons: for example, the presence of the jellyfish Aurelia aurita and Rhizostoma pulmo has been reported in many Mediterranean coastal lagoons, such as in the lagoon of Varano and in the Sabaudia coastal lake (Italy country report). It is difficult to understand clearly the blooms of these organisms; these are probably due to various factors such as low rainfalls, high temperatures, high atmospheric pressure and increased nutrients. Species that have been sporadically present in lagoons may suddenly show a significant increase in number, or newly introduced species can find local conditions extremely favourable, creating an uncontrolled population explosion. These blooms may affect tourism-related activities and have a potential impact on fishing activities in lagoons, hampering capture operations and reducing the efficiency of fishing gear, or even have an effect on the fish commercial value (Molinero et al., 2009).

2.6.4 Ichthyophagous birds

Ichtyophagous birds can create environmental issues in the environment of lagoons since their voracious fish

hunting behavior often generates conflicts with fisheries and aquaculture, and in several cases (e.g. in the northern Adriatic valli), as a consequence of the impact of birds on fish stocks, fish farmers have abandoned extensive aquaculture activities.
In particular, the great cormorant (Phalacrocorax carbo) can eat 400?600 g of fish/day, i.e. more than 300 000 tonnes of fish captured from European waters every year. The cormorant issue has been thoroughly reviewed by Kindermann (2008) who pointed out that “the total population of great cormorants has grown twenty-fold over the last 25 years and is now estimated to comprise at least 1.7 to 1.8 million birds.
Cormorants have caused proven permanent damage to aquaculture undertakings and stocks of many wild fish species in the inland waterways and along sea coasts in many member States of the European Union. As the cormorant is not included in the lists of species whose hunting is permitted by the Wild Birds Directive, regular hunting is impossible [...]. However in recent years there have been various examples […] of derogation
In the Mar Menor (Spain), the great cormorant has become the dominant species together with crebes and Eurasian coots (Fulica atra) (Aymerich and Cedran, 2011). In Sardinian lagoons, ichthyophagous birds have a density of 5 specimen/ha, for a consumption of 111 t/year in the Cabras, Maerceddi and S. Ena lagoons (Marino et al, 2009). In Egypt, more than 6 percent of fish production was predated in the 1989/90 winter in the Bardawil Lagoon where up to 30 000 specimens of great cormorants are estimated to winter (Khalil and Shaltout; 2006 Egypt country report).

measures […] restricted in space or time: e.g. shooting permits for certain areas (Italy), for certain periods or for fixed quotas (France and Slovenia); in particular cases approval has also been granted for intervention in breeding colonies (felling of nesting trees, rendering eggs infertile)”.
In fact, suspending physical barriers has proved to be effective to prevent predation by cormorants only above intensive small culture fish ponds, since these structures cannot be applied to larger surfaces such as those dedicated to extensive aquaculture systems (Kindermann, 2008). In the Mediterranean, some fishers have thus considered hunting practices as the only mean to contrast the negative environmental impacts of birds on their activities and, in some cases, controlled hunting has contributed to preserve wetlands and, indirectly, biodiversity.

Figure 3. Logo of the “Save the fish” campaign promoted by Italian fishers

The debate between conservation and hunting is still open although the prevailing position of the public opinion is to consider the conservation of birds as a priority and to contemplate lagoons as protected areas to preserve wildlife.

2.6.5 Climate change

Lagoon environmental features such as depth, connections with the sea, sediment dynamics, size, as well as water temperatures and productivity, shall all be affected by global climate change and the rise of sea level (Bianchi and Morri, 2004; de Wit, 2011; Nicholls et al., 2007). Although there is a continuous debate about the consistency and potential impacts of climate change worldwide and in particular in the Mediterranean area, it will certainly (directly or indirectly) affect the region and some economic activities such as agriculture and the exploitation of natural resources in the marine domain and in coastal lagoons. Climate change will probably cause variations of the physical and chemical parameters of water (e.g. temperature, pH, salinity), increase erosion, air temperature and UV radiation, the latter two being predicted to increase of about 3°C and 20 percent respectively in 2100 with respect to the present situation (Brochier and Ramieri, 2001; Coll et al., 2004).
Altogether, these environmental changes could contribute to the degradation and loss of critical habitats in lagoons (e.g. nursery areas and seagrass meadows) due to the intensification of eutrophication processes and to frequent algal blooms. Changes in water temperature and salinity may increase the spread of allochthonous species, alterate interspecies relations and the ecological balance of lagoons’ ecosystems as well as modify the distribution patterns of living resources. For example, the seagrass Zostera marina has its southern distribution limit in the Mediterranean Sea, and an increase in mean water temperature could bring about the
rarefaction and disappearance of this species from the Mediterranean coastal lagoons, with potential dramatic impacts on biodiversity. All these effects could be even more marked in shallow lagoons, with important consequences on the pelagic food web (Vidussi et al., 2011).

Cabras lagoon in Sardinia (Italy), photo ©I. Viale, 2011
One of the more evident effects of climate change, in particular for an enclosed basin such as the Mediterranean Sea, is the sea level rise, the current rate of which is already much faster than that observed over geological time (Brochier and Ramieri, 2001). In fact, coastal lagoons have formed during periods of transgression under sea level rise, but the natural processes that have shaped lagoons and conditioned their lifetime are currently being accelerated and exasperated by the increased rate of sea level rise. Sea level rise could jeopardize the ultimate existence of Mediterranean coastal lagoons, in particular the deltaic lagoons of Egypt, France and Northern Italy. It is difficult to predict in which direction the lagoon fate shall evolve. Rising sea levels and increasing erosion of sand spits (lido) and barrier islands may hasten the disappearance of lagoons at the land and seascape level, as they may be converted to open bays. Moreover, the lido and waterbody of lagoons may move inward, leaving the possibility for a lagoon setting; in fact inward moving of lagoons is a natural phenomenon during periods of seawater level rise (de Wit, 2011). This possibility depends on the geomorphological and physical conditions of the land and seascape. One can suppose that in many coastal areas of the Mediterranean, an inward moving trend shall be hampered by shoreline urbanization, due to increased demographic load and litoralization, or hindered by man-made structures built to protect the land from erosion and/or flooding.
Finally, another important effect of global climate change is ocean acidification; seawater has usually a mean pH of 8.2, which has currently decreased to 8.1 and is expected to further decrease to 7.9 (Fowler, 2008; de Wit, 2011). Such a pH shift may have important consequences on marine ecology, as acidification is detrimental for calcifying organisms like phytoplankton (e.g. coccolithophorids) and shell-forming bivalves (Orr et al., 2005). However, it can be assumed that many coastal lagoons could have the capacity to buffer acidification owing to the presence of calcareous sediments.

2.6.6 Effects of lagoon exploitation

Usually, management measures in response to fish yields decline in lagoons (see paragraph 2.4.2), regardless of the reason, consist of shifting the production towards culture-based activities. The intensification of these activities has often increased the pressure on lagoon ecosystems, introducing additional unbalancing factors such as biological and chemical effects on the environment. Recently, conservation agencies and projects have started to raise public administrations and NGOs’ awareness on coastal lagoons in order to include conservation issues within the management of fisheries in the lagoons.
For example, intentional restocking actions (see paragraph 2.5.2) to enhance lagoon production or accidental escapes from intensive culture facilities could generate genetic pollution in coastal lagoon fish communities. At present, restocking is often carried out with hatchery fry, often originated from broodstock of unknown origin; therefore, in this case, restocking introduces specimens that genetically differ from the local population.
The impact of land-based farms is certainly lower than that of culture cages due to the physical confinement of culture ponds from the lagoon. However, it is difficult to assess the genetic impact of aquaculture for a number of reasons such as the lack of basic genetic information on natural populations, the relatively low genetic structure of euryhaline fish species, the lack of traceability of many culture practices and, last but not least, non-compulsory declaration of restocking actions or escape events to public authorities in several countries (Svaasand et al., 2007).
Additionally, pathologies can easily spread from culture facilities to the wild by means of both contaminated waters and infected fish that escape and act as vectors. In the Orbetello lagoon (Italy) for instance, grey mullets have been affected by the germ Pasteurella spread from seabass and seabream intensive aquaculture farms located around the lagoon (Fisichella et al., 1991; Italy country report). Moreover, the introduction of allochthonous fish species for culture purposes can also unintentionally introduce allochthnous pathologies (see paragraph 2.6.4).
The changeover to non-indigenous species that has occurred, for instance, in shellfish farming has resulted in increased production capacity (due to better performance obtained with these new species) but has had several ecological impacts. As an example, the Venice lagoon has been totally altered by the use of dredges to harvest the introduced Japanese carpet shell (Ruditapes philippinarum), whereas the collection of the local clams used to be carried out before with artisanal means. The dredging practice has strongly affected the bottom and the water column as most of the sediments have been lifted by fishing gear, suspending and resettling in different parts of the lagoon; then, they have been partly transported to the sea through inlets, creating an overall increase of silting in the lagoon channels. It is estimated that Japanese carpet shell 34 harvesting has caused the loss of one billion cubic meters of sediments per year in the Venice lagoon. These direct effects on the sediments may have indirect effects on the aquatic organisms and ecosystems. Many studies (Pranovi and Giovanardi, 1994; Fontolan et al., 1995; Pranovi et al., 1998; Province of Venice, 1998) have reported that the action of gear used for clam harvesting has caused a general depletion of the number of species and total biomass in the benthic lagoon community.
However, it is also possible to observe positive relationships between aquaculture activities and the environment. For example, the management of northern Adriatic valli, in Italy, foresees a number of interventions, the aim of which is ultimately to preserve habitats and wildlife and to maintain the environmental and naturalistic value of this area, where hunting activities and extensive aquaculture have always been practised (Donati et al., 1999). In the valli, maintaining ecological conditions has been for centuries at the basis of long-term profitability (Ardizzone et al., 1988). At present, about 30 percent of maintenance works carried out in a valle are estimated to provide an ecological service preserving the environmental value of the area (Italy country report).

Flamingoes in Veta La Palma (Spain), photo ©M. Medialdea, 2011