2 Monitoring of Marine Aquaculture
63
of different levels of taxonomic resolution (Karakassis and Hatziyanni 2000) and
the use of various levels of taxonomic resolution, sieve mesh size and sample size
(Lampadariou et al. 2005) can also be used as a basis for cost-effective monitoring
protocols for the assessment of the state of the benthic environment in the vicinity
of fish farms.
An alternative method for monitoring the effects on the benthic environment
would be to focus on some geochemical variables that reflect the organic content
of the sediment, such as total organic carbon (TOC) or organic matter, usually
measured by means of the loss on ignition method (LOI) which provides straightforward results. Hyland et al. (2005) have shown that TOC can be used as an indicator of the quality of the benthic environment since it can predict quite reliably
macrofaunal diversity. On the other hand, studies on the recovery process do not
show good relationships between TOC and the benthic fauna community, but
instead correlate with oxygen demand, indicating that it is the labile pool of TOC
controlling faunal distribution (Pereira et al. 2004). It is also worth noting that TOC
or LOI values in samples taken beneath fish farms could be misleading since their
concentrations at the surface layer could remain fairly constant although the depth of
the farm sediment measured through sediment profiles could change remarkably
with season (Karakassis et al. 1998). Also, pools in the surface layer may show
significant seasonal variation, as has been found in a Danish farm, where the TOC
pools in the surface layer correlated with the seasonal changes in fish production
(Holmer and Kristensen 1992). At larger spatial scales, the effects of fish farms on
macrofauna are rather negligible and particularly so in the case of coarse sediment
sites and, therefore, it could be expected that those effects are unlikely to disturb
other (remotely located) uses of the coastal zone. In both Norway and Canada
monitoring systems have been constructed with more detailed analysis of the sediments,
but based on relatively simple measuring techniques, which allow the fish farmer
himself to follow the benthic impacts at the farms (Hangen et al. 2001; Brooks and
Mahnken 2003), but in Norway the authorities require that the monitoring is performed by an independent firm or institute. In Scotland, the authorities are implementing benthic monitoring along with modelling, which strengthens the field
sampling (Cromey and Black 2005). If the sampling and models deviate, field conditions are up for a more detailed examination. Monitoring in both Norway and
Scotland operates within different zones around the farms, where sites at increasing
distance from the farms are allowed different degrees of benthic impact (Ervik et al.
1997; Cromey and Black 2005).
The effects on water quality are probably those causing more concern regarding
the quality of the marine environment. It is well known that fish farms release large
quantities of dissolved nutrients in the ambient water, particularly nitrogen and
phosphorus (Holby and Hall 1991; Hall et al. 1992). Furthermore, these nutrients
are mainly released during the summer period when light availability is high and
therefore it could be expected that phytoplankton blooms are likely to occur in the
vicinity of fish farms. However, numerous studies (Pitta et al. 1999, 2006; La Rosa
et al. 2002; Soto and Norambuena 2004) have failed to detect significant changes
in chlorophyll a or particulate organic carbon (POC) in the water column in the
63
of different levels of taxonomic resolution (Karakassis and Hatziyanni 2000) and
the use of various levels of taxonomic resolution, sieve mesh size and sample size
(Lampadariou et al. 2005) can also be used as a basis for cost-effective monitoring
protocols for the assessment of the state of the benthic environment in the vicinity
of fish farms.
An alternative method for monitoring the effects on the benthic environment
would be to focus on some geochemical variables that reflect the organic content
of the sediment, such as total organic carbon (TOC) or organic matter, usually
measured by means of the loss on ignition method (LOI) which provides straightforward results. Hyland et al. (2005) have shown that TOC can be used as an indicator of the quality of the benthic environment since it can predict quite reliably
macrofaunal diversity. On the other hand, studies on the recovery process do not
show good relationships between TOC and the benthic fauna community, but
instead correlate with oxygen demand, indicating that it is the labile pool of TOC
controlling faunal distribution (Pereira et al. 2004). It is also worth noting that TOC
or LOI values in samples taken beneath fish farms could be misleading since their
concentrations at the surface layer could remain fairly constant although the depth of
the farm sediment measured through sediment profiles could change remarkably
with season (Karakassis et al. 1998). Also, pools in the surface layer may show
significant seasonal variation, as has been found in a Danish farm, where the TOC
pools in the surface layer correlated with the seasonal changes in fish production
(Holmer and Kristensen 1992). At larger spatial scales, the effects of fish farms on
macrofauna are rather negligible and particularly so in the case of coarse sediment
sites and, therefore, it could be expected that those effects are unlikely to disturb
other (remotely located) uses of the coastal zone. In both Norway and Canada
monitoring systems have been constructed with more detailed analysis of the sediments,
but based on relatively simple measuring techniques, which allow the fish farmer
himself to follow the benthic impacts at the farms (Hangen et al. 2001; Brooks and
Mahnken 2003), but in Norway the authorities require that the monitoring is performed by an independent firm or institute. In Scotland, the authorities are implementing benthic monitoring along with modelling, which strengthens the field
sampling (Cromey and Black 2005). If the sampling and models deviate, field conditions are up for a more detailed examination. Monitoring in both Norway and
Scotland operates within different zones around the farms, where sites at increasing
distance from the farms are allowed different degrees of benthic impact (Ervik et al.
1997; Cromey and Black 2005).
The effects on water quality are probably those causing more concern regarding
the quality of the marine environment. It is well known that fish farms release large
quantities of dissolved nutrients in the ambient water, particularly nitrogen and
phosphorus (Holby and Hall 1991; Hall et al. 1992). Furthermore, these nutrients
are mainly released during the summer period when light availability is high and
therefore it could be expected that phytoplankton blooms are likely to occur in the
vicinity of fish farms. However, numerous studies (Pitta et al. 1999, 2006; La Rosa
et al. 2002; Soto and Norambuena 2004) have failed to detect significant changes
in chlorophyll a or particulate organic carbon (POC) in the water column in the