Effects of Fish-Farms on Marine Biodiversity Along the Mediterra-nean Coast

The expansion and growth of offshore mariculture is a growing business. The environmental effects of this industry are of particular concern because of the impacts they have on marine habitats and biodiversity<!–[if supportFields]>XE “biodiversity”<![endif]–><!–[if supportFields]><![endif]–>. Mirto et al. (2010) investigated the effects that fish farms have on the metazoan meiofaunal communities existing in areas exposed to fish farms along the coast of the Mediterranean Sea. The potential effects of fish farm effluents on the abundance and community composition of meiofauna were analyzed by comparing two different habitats in four different regions with different background trophic<!–[if supportFields]> XE “trophic” <![endif]–><!–[if supportFields]><![endif]–> conditions. It was found that there are conflicts between aquaculture<!–[if supportFields]> XE “aquaculture” <![endif]–><!–[if supportFields]><![endif]–> and the conservation of marine habitats and benthic primary producers. The organic enrichment of sediments falls beneath the sea cages used by fish farms. This sedimentation of particulate waste products from the fish farm has a direct effect on the local habitat. The continuous deposition of feces and food pellets from fish cages can alter the quantity as well as biochemical composition of sediment organic matter. The extent to which these areas are affected differs in different regions/habitats. Investigating meiofaunal assemblages in different regions of the Mediterranean Sea identifies the changes that are caused by aquaculture on benthic ecosystems and can provide insight to what is going on in these marine communities. —Lauren Lambert
 Mirto, S., Silvia B., Cristina G., Maja K., Antonio P., Mariaspina S., Marianne H., and Perry R.I., Ommer RE., Barange M., Werner F. 2010. The challenge of adapting marine social-ecological systems to the additional stress of climate change. Current Opinion in Environmental Sustainability 2,  356–363.

Mirto et al. (2010) hypothesized that fish farms influence the meiofaunal assemblages of existing habitats. This includes abundance, community structure, and diversity. Four regions along the Mediterranean Coastal zones were selected in order to provide a variety of different environmental conditions. Two different habitats were selected, meadows of seagrass vs. soft non-vegetated bottoms. Control sites were also chosen to match conditions and environmental features found at the bottom of fish farm cages. These sites were located at a distance of at least 1000m upstream from the fish farms to be certain that this habitat would not be affected. The sediment protein, carbohydrate, and lipid contentents were determined. The amount of meiofauna was determined by sieving through 1000 mm sieve for macrobenthos and macroalgae, and 32 mm sieve to retain smaller meiofauna. The differences between control and impact sediments were calculated using three-way-analysis-of-variance (ANOVA<!–[if supportFields]> XE “ANOVA”<![endif]–><!–[if supportFields]><![endif]–>). When significant differences were observed between the two groups, a post-hoc Student-Newman-Kuels test (SNK) was also used to assess this information.
The observations of the study showed differences between impacted and control sites as well as in the four geographical areas. SNK tests revealed a consistent increase in biopolymeric C concentrations in farm-impacted vegetated sediments in Cyprus, both habitats in Greece, and in non-vegetated sediments in Italy. Protein to carbohydrate ratio increased in both habitats in Italy and non-vegetated sediments in Spain. A decrease in impact sediments was observed in both habitats of Greece. The SNK test indicated a significant increase of meiofaunal abundance in impacted sites with vegetated sediments in Cyprus, in non-vegetated sediments in Italy, but no difference between control groups in other regions. In summary, Mirto et al. found that the differences between control and sites impacted by fish farms varied depending on the region.
Differences between impact and control sites in the meiofaunal community composition were only significant in non-vegetated sediments in Cyprus or Greece. Nematodes and Copepods were the most dominant taxa followed by polychaetes, ostracods, turbellarians, oligochaetes, gastrotrichs, and all other taxa. The richness of meiofaunal taxa decreased significantly in impacted sites in non-vegetated sediments but no significant differences between impact and control sites were observed in sea grass sediments. The taxa that disappeared beneath the cages varied throughout the sites, but always compromised the rare taxa which make up  <1% of total meiofaunal abundance.
Fish farms typically have an effect on the attributes of the benthic environment beneath cages and show a significant amount of modifications in the abundance, biomass, species composition, and evenness of meio and macrofauna.  However these observed changes associated with the presence of fish farm effluents are often not consistent because meiofaunal abundance may increase or decrease beneath the cage depending on characteristics of the site or farm. The abundance of meiofauna was generally higher in fish farm sediments, which could be a result of limited organic enrichment in the sediments beneath the cages. There is a clear and consistent meiofaunal response to the fish farm deposition in sea grass sediments. Posidonia oceanica<!–[if supportFields]> XE “Posidonia oceanica” <![endif]–><!–[if supportFields]><![endif]–> is the sea grass existing on the sites that plays a key ecological role for many of the organisms and assemblages by preserving biodiversity<!–[if supportFields]>XE “biodiversity”<![endif]–><!–[if supportFields]><![endif]–>. It is difficult to detect effects of fish farm biodeposition on sea grass meadows because the grass masks the changes in organic composition. The presence of a large number of filter feeders and detritus feeders within sea grass beds can also act as a buffer for the organic enrichment because of the amount of biodeposits that they consume.

Actual changes are difficult to know because of these supplemental factors. However in the long term, the increased sedimentation and waste particles that result from these farms does lead to the deterioration of the sea grass system and will eventually result in disruption of the ecosystem in place. Fish farm biodeposition in the Mediterranean Sea can provoke changes in meiofaunal abundance, community structure, and biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>. Because of the amount of variation between the sites, it is important to use indicators of fish farm impact in vegetated and non-vegetated systems in the future. 

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