Site selection and carrying capacity in Mediterranean ... - FAO Sipam

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5.2 Environmental aspects for site selection in coastal areas
In European waters, cage aquaculture has been developed in coastal bays, fjords, and lochs. Because
of the potential environmental impact and user conflicts in a limited space, aquaculture has recently
received attention with respect to identification of new sites for grow-out production. Therefore,
before selecting a location for marine aquaculture, it is important to take into account several
ecological aspects.
Water quality for use by the farmed species e.g. in terms of oxygen level or absence of algal blooms,
is more likely to be high in exposed and offshore sites as opposed to coastal and sheltered sites. In the
Mediterranean, most of the production is carried out in relatively exposed sites (as opposed to Scottish
lochs, for instance) but not so often in offshore sites. Regulation is also diverse in the Mediterranean:
some countries (e.g. Cyprus, Malta etc) have for several years adopted a distance limit (from the shore
and between different farms) for fish farm sites. Turkey has also introduced this. Greece has adopted a
gradual adaptation scheme, allowing expansion of production only in offshore sites and imposing
reduction or stability for farms in coastal shallow sites.
The environmental effects of aquaculture depend a lot on the exposure and water depth of the site,
which are rather intercorrelated. Deep, offshore, exposed sites will, for example, not affect seagrass
habitats (if located beyond the 50m isobath), and will have less effects on benthic communities (if
carefully placed outside maerl beds, which tend to occur in deep waters) i.e. without causing anoxic
zones and outgassing. This will be also the case with the water column variables and the necessary
dilution of the solute wastes which will be rapidly taken up by the plankton and microbial food web.
Moving offshore will also greatly help reducing conflicts with other users of the coastal zone,
particularly tourism and artisanal fisheries. However, not all aspects are positive. In offshore and
exposed sites, the cost of the cage moorings and general construction at the farm increases and
follows an increased risk of physical damage to the installation. On the other hand, the safety of
personnel is put in higher risk in case of sudden storms, and some diving operations become more
dangerous with increased water depth. Finally an increase in distance from the shore for siting the
farm imposes a higher cost for the transport of personnel, the fish feed, and the harvested fish. From
the above it is evident that there are divergent interests in the site selection process that need to be
considered in the specific context of each particular site.
Furthermore, future changes may considerably affect the priorities in the balance of the above
requirements. For instance, the availability of fuel and energy may affect the decisions for site
selection towards the coast, or the emergence of a disease or parasite may impose a much more
pressing need to move offshore. Proximity to major transport routes is also an issue of importance
affecting site selection at a “macro” scale, i.e. there are regions, islands etc which are more preferable
for investment due to easier and faster transport of the aquaculture products to the main markets.
5.2.1 Organic discharge
The capacity of a water mass to assimilate an external input of organic matter will be very different
depending on the several ecological and oceanographic features. For coastal aquaculture, major
concerns come from the discharge of wastes in form of uneaten food and fish excretions, which will
especially have an effect on the benthos and species that are particularly sensitive to an increase in
input of organic matter. Organic matter input is closely dependent on species, production, culture
method, hydrography, feed type and management (Wu, 1995).
Organic waste is particulate and will sediment, in a high proportion, causing a change in the
properties of sediment in the vicinity of the farm, leading to modification of the sediment chemistry
and macrofaunal community structure (Karakassis et al. 2000), and favouring the proliferation of
opportunistic species and an increased abundance of opportunistic scavengers. Aquaculture increases
carbon and nutrient inputs to the sediment, mainly, nitrogen and phosphorus, which will accumulate
in the sediments and will lead to an higher oxygen demand, production of anoxic sediments and,
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