3 Aquaculture and Coastal Space Management
105
species, such as Capitella cf capitata. Western Mediterranean fish farms, located in
open areas, reduce the number of families of macrofauna and diversity compared
with control areas (Maldonado 2005). However, the spatial extent of these impacts
is limited. For Mediterranean fish farms, Karakassis et al. (2000) found a consistent
spatial pattern where the benthic community approaches its normal characteristics
at 25 m from the core of the fish farm. Wildish and Pohle (2005) reviewed a range
of studies and found that most effects on the benthos were local or footprint-limited
(0.05–0.5 km
2
), even though fish farm wastes may spread over a greater range from
the farm (e.g., up to 1 km: Sara et al. 2003, 2006).
Regions where seagrass meadows are present are more susceptible to significant changes in biodiversity than regions where sandy habitats prevail. Several
studies around the Mediterranean Sea show that fish farms affect seagrass meadows, modifying habitat structure (content of organic matter on sediments) in the
surrounding meadows at a scale of hundreds of meters (Ruiz et al. 2001; Marba
et al. 2006). Changes to shoot morphology, shoot density, biomass, rhizome
growth, nutrient and soluble sugar concentrations are possible impacts of fish
farm activities near seagrass meadows (e.g., Dimech et al. 2002). Even after
several years of cessation of the impact, the decline of seagrasses continues
(Delgado et al. 1999). The results of a study on vertical growth of Posidonia
oceanica suggest that these effects begin soon after the initiation of farming
activities, hence suggesting a low resistance of seagrass meadows to fish farm
impacts (Marba et al. 2006).
Fish farm activities may also impact other types of seagrass meadows, as has
been recorded from Cymodocea nodosa meadows in the Canary Islands (Tuya
et al. 2005), which can lead to a cascading effect on seagrass-associated fauna.
Cymodocea nodosa seagrass meadows throughout the Canary Islands have been
degraded by fish farming. Some fish species are strongly associated to this
meadow, such as Diplodus annularis, Spondyliosoma cantharus or Mullus surmuletus (Tuya et al. 2005). In combination with the strong fishing pressure that exists
in the Canary Islands, degradation of C. nodosa meadows may accelerate the
reduction of these fish populations, increasing the problem of overfishing and
stock depletion.
To avoid impacting seagrass meadows, aquaculture facilities are deployed in
deeper waters and are recommended to be sited a minimum of 800 m from Posidonia
beds in the Mediterranean Sea (EU project MEDVEG: Effects of nutrient release
from Mediterranean fish farms on benthic vegetation in coastal ecosystems; www.
medveg.dk). A problem generated by shifting the spatial arrangement of farms in
the coastal zone is that other important biotic communities can be affected if management does not account for them. For example, mäerl beds occur worldwide and
are formed by an accumulation of unattached calcareous red algae, growing in a
superficial living layer on sediments within the photic zone (Fig. 3.8, Barberá et al.
2003). It is, as for Posidonia beds, a protected habitat under European legislation.
Decreases in water quality affect the survival of mäerl beds; consequently, locating
aquaculture facilities on mäerl grounds also entails negative consequences for
marine biodiversity.
105
species, such as Capitella cf capitata. Western Mediterranean fish farms, located in
open areas, reduce the number of families of macrofauna and diversity compared
with control areas (Maldonado 2005). However, the spatial extent of these impacts
is limited. For Mediterranean fish farms, Karakassis et al. (2000) found a consistent
spatial pattern where the benthic community approaches its normal characteristics
at 25 m from the core of the fish farm. Wildish and Pohle (2005) reviewed a range
of studies and found that most effects on the benthos were local or footprint-limited
(0.05–0.5 km
2
), even though fish farm wastes may spread over a greater range from
the farm (e.g., up to 1 km: Sara et al. 2003, 2006).
Regions where seagrass meadows are present are more susceptible to significant changes in biodiversity than regions where sandy habitats prevail. Several
studies around the Mediterranean Sea show that fish farms affect seagrass meadows, modifying habitat structure (content of organic matter on sediments) in the
surrounding meadows at a scale of hundreds of meters (Ruiz et al. 2001; Marba
et al. 2006). Changes to shoot morphology, shoot density, biomass, rhizome
growth, nutrient and soluble sugar concentrations are possible impacts of fish
farm activities near seagrass meadows (e.g., Dimech et al. 2002). Even after
several years of cessation of the impact, the decline of seagrasses continues
(Delgado et al. 1999). The results of a study on vertical growth of Posidonia
oceanica suggest that these effects begin soon after the initiation of farming
activities, hence suggesting a low resistance of seagrass meadows to fish farm
impacts (Marba et al. 2006).
Fish farm activities may also impact other types of seagrass meadows, as has
been recorded from Cymodocea nodosa meadows in the Canary Islands (Tuya
et al. 2005), which can lead to a cascading effect on seagrass-associated fauna.
Cymodocea nodosa seagrass meadows throughout the Canary Islands have been
degraded by fish farming. Some fish species are strongly associated to this
meadow, such as Diplodus annularis, Spondyliosoma cantharus or Mullus surmuletus (Tuya et al. 2005). In combination with the strong fishing pressure that exists
in the Canary Islands, degradation of C. nodosa meadows may accelerate the
reduction of these fish populations, increasing the problem of overfishing and
stock depletion.
To avoid impacting seagrass meadows, aquaculture facilities are deployed in
deeper waters and are recommended to be sited a minimum of 800 m from Posidonia
beds in the Mediterranean Sea (EU project MEDVEG: Effects of nutrient release
from Mediterranean fish farms on benthic vegetation in coastal ecosystems; www.
medveg.dk). A problem generated by shifting the spatial arrangement of farms in
the coastal zone is that other important biotic communities can be affected if management does not account for them. For example, mäerl beds occur worldwide and
are formed by an accumulation of unattached calcareous red algae, growing in a
superficial living layer on sediments within the photic zone (Fig. 3.8, Barberá et al.
2003). It is, as for Posidonia beds, a protected habitat under European legislation.
Decreases in water quality affect the survival of mäerl beds; consequently, locating
aquaculture facilities on mäerl grounds also entails negative consequences for
marine biodiversity.