Effects of Changing Environmental Conditions on Lagoon Ecology - Coastal Lagoons: Ecosystem Processes and Modeling for Sustainable Use and Development - page 214

Shortening
of food
chains

Increasing
competitive
weakness

Salinity 300%

FIGURE 5.9 Effects of increasing salinity on food chains and the competitive capability of
species. Under extreme environmental conditions food chains are shortened and competitive
weakness increases. (Adapted from Por, F.D., Mar. Ecol ., 1, 121, 1980. With permission.)

of chlorophyll a and high phytoplanktonic biomass ( see Figure 5.8) . In this kind of
lagoon, primary production mainly remains in phytoplankton assemblages, generally
characterized by Cyanophytes, and the benthic biomass is low.
Sedimentation is mainly organic, and the interstitial environment in sediment is
reductor. Faunal assemblages are mainly composed by detritivorous and some her-
bivorous crustaceans (belonging to genera such as Sphaeroma , Corophium , Idotea,
Gammarus , Microdeutopus ), grazer gastropods (e.g., Hydrobia ), carnivorous poly-
chaetes ( Nereis ), and detritivorous insect larvae (Chironomids). In hypersaline
lagoons, Artemia , Tricoptera, Oligochaeta, Odonates can easily be found on a veg-
etation stand of Potamogeton and Characeae (mainly in limnogenic waters). In
general, the communities of these lagoons are dominated by r -selected species,
characterized by a short generation time and a high reproductive effort, producing
many small offspring. The diversity is low and many ecological niches may remain
unoccupied because of lack of immigration and colonization. The top-down control
by predator-prey relationships is low or nonexistent.
In choked lagoons, which are only temporarily open to the sea (during storms,
for instance), the migration of marine organisms is intermittent and depends on
the temporary openings to the sea. 64,65 These marine organisms rely on the main-
tenance of marine conditions inside the lagoon for their subsistence. The presence
of marine organisms inside the lagoon can be temporary, and it may lead to a
situation where only few species survive throughout the year.
As pointed out previously, coastal lagoons are more productive than other eco-
systems in terms of fisheries yield. 120 They are important in the life cycles of many