Climate Change and the European Water Dimension - Agri ...

IV.D.3. Expected effects related to changes in environmental factors
Temperature increase in coastal lagoons would
o influence organism metabolism and niche distribution
o affect species interactions and distribution
o modify structure of food web and biogeochemical cycles (e.g. N, C)
o change ecological processes, especially primary production and
decomposition
Temperature increase may have different effects. Species are adapted to specific
ranges of temperature. Temperatures exceeding these ranges will influence life
cycles, nutrient uptakes, growth rates, cellular division (e.g. heterotrophic bacteria,
phytoplankton), predation rates (e.g. ciliates, copepods), reproduction and
recruitment processes (e.g. zooplankton, mollusc), habitat colonization (e.g.
seagrasses) and finally the production (e.g. primary and secondary). Temperature
effects may include changes in ecosystem communities. For example, species
adapted to warmer temperatures - e.g. exotic species migrating from the Red Sea or
imported with commercial species - will take advantage from temperature rise, whilst
indigenous species will be out-competed. Species that are unable to migrate or
compete for resources may face an extinction risk.
Changes in community composition (e.g. food web) can alter energy transfer and
biogeochemical cycling (Viaroli et al., 1996). In turn, alteration of biogeochemical
processes can affect water quality and species adaptation/survival. Expected
increase in metabolism rates may also increase mineralization rates of organic
matter, which in turn may enhance nutrient availability and intensify the oxygen
disequilibrium already existing in Mediterranean coastal lagoons. A greater
availability of mineral nutrients is expected to favour spring macroalgal blooms
followed by an accentuation of summer dystrophic crises and harmful microalgal
blooms in the colder periods.
As far as commercial species are concerned (e.g., clams, oysters, mussels),
increase of water temperature and its duration will have effects on metabolism and
recruitment, increase of pathogen diffusion (Troussellier et al., 1998), risk of harmful
microalgal blooms that affect commercial value, increase of oxygen demand and
sulphide production.
Changes in precipitation patterns have important consequences for
o water balance of coastal ecosystems
o dissolved nutrient transport from the watershed to the coastal lagoon
o solid transport both from land-side and sea-side
Increases or decreases in precipitation and runoff may respectively increase the risk
of coastal flooding or drought. Increase of extreme events, namely flooding/drought
alternance like in Southern Europe in 2000-2003 can alter salinity and nutrient
balances within lagoons. Prolonged flooding determines submersion in the subsident
areas of the watershed and a decrease of salinity in the lagoon. This will affect
marine, and to a lesser extent brackish species. Salinity changes will influence
seagrasses, changing seed germination, propagule formation, growth and
photosynthetic rates (Short and Neckles, 1999). Many commercial species (e.g.
clams) may be negatively influenced. Prolonged drought causes a decrease in
freshwater discharge. On the landside, it causes increased costs (e.g. for irrigation)
and decreased vegetal production (as in 2003). In the lagoon side, less freshwater
discharge causes a decrease in nutrient discharge, which in turn lower phytoplankton
production and biomass with effects on clam and mussels crops. For example in the
112