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Abstract. Sediment characteristics determining macrofauna communities were investigated on the continental shelf of Crete. The sedimentary environment of the outer continental shelf of Crete is characterized by a silty substrate with significant decrease in chlorophyll a and organic carbon concentration with depth. Redox potential values indicated an ample supply of oxygen at all depths. Values of most production-related parameters TOC, chlorophyll a , ATP were found at the low end of the range reported from the literature even though the sampling stations were very close to the coastline. Organic carbon to chlorophyll ratios in the sediments indicated that most of the organic material is of phytoplankton origin; the quality of the organic material in the outer shelf, however, seems to be of lower bioavailability. 相似文献
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A. Machias I. Karakassis M. Labropoulou S. Somarakis K. N. Papadopoulou C. Papaconstantinou 《Estuarine, Coastal and Shelf Science》2004,60(4):771-779
The species composition, abundance and diversity of demersal fish assemblages has been investigated in an oligotrophic coastal bay in the Aegean Sea which is a designated zone for the development of aquaculture. Samples were collected using experimental trawling, before the establishment of fish cages in the area during early June 1987 and after attaining the maximal production of the aquaculture zone in late May 2001. The overall abundance of the fish assemblage increased by a factor of 4 and the average trophic level of the fish community increased from 3.59 to 3.79. Traditional diversity indices showed an increase in dominance but the distinctness measures of biodiversity showed that the overall structure obtained after the establishment of fish farming was not phylogenetically impoverished. Multivariate analysis showed that the community differences between the two periods are quantitative rather than qualitative. Comparisons in length frequencies between the two periods indicated that specimens of the species compared were either similar or larger in the second period. The species favoured by the presence of aquaculture were not the ones normally feeding on the food pellets under the cages but those normally occurring in the fishing grounds of the study. It is concluded that the release of nutrients from fish farming in nutrient-poor systems can have a positive effect on local fisheries with no visible negative change in species composition or biodiversity. 相似文献
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Holmer M Argyrou M Dalsgaard T Danovaro R Diaz-Almela E Duarte CM Frederiksen M Grau A Karakassis I Marbà N Mirto S Pérez M Pusceddu A Tsapakis M 《Marine pollution bulletin》2008,56(9):1618-1629
This paper provides a synthesis of the EU project MedVeg addressing the fate of nutrients released from fish farming in the Mediterranean with particular focus on the endemic seagrass Posidonia oceanica habitat. The objectives were to identify the main drivers of seagrass decline linked to fish farming and to provide sensitive indicators of environmental change, which can be used for monitoring purposes. The sedimentation of waste particles in the farm vicinities emerges as the main driver of benthic deterioration, such as accumulation of organic matter, sediment anoxia as well as seagrass decline. The effects of fish farming on P. oceanica meadows are diverse and complex and detected through various metrics and indicators. A safety distance of 400 m is suggested for management of P. oceanica near fish farms followed by establishment of permanent seagrass plots revisited annually for monitoring the health of the meadows. 相似文献
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To investigate the combined effects of decreasing taxonomic resolution (i.e. species, family, phylum), the use of different mesh-size (1.0 mm and 0.5 mm) and the type of samplers used (van Veen vs. corers taken by divers) on the quality of data obtained, a comparative study was undertaken with the overall aim of identifying cost efficient methods for routinely monitoring the ecological change caused by Mediterranean fish farming. The results clearly showed that information loss was relatively low as data were aggregated at higher taxonomic levels, particularly up to the level of family or even order. It was also found that the extra information gained by sieving samples through a 0.5 mm sieve did not improve the ability to distinguish the potentially impacted sites from the control stations. Finally, it was found that a relatively large proportion of the available information concerning the community structure such as abundance, biomass or diversity is lost when sampling is carried out with corers. A cost/benefit ratio analysis for the two sampling and the two sieving methods showed minimal values for the van Veen samples (for both sieve fractions) at the family level, indicating that analysis at this level gives the best balance between precision of the results and decrease in taxonomic effort. However, if the time needed to sort the samples is included in the analysis, then samples taken with corers using a 0.5 mm sieve and identified to families seems like a good compromise between precision and cost. 相似文献
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Eugenia T. Apostolaki Núria Marbà Marianne Holmer Ioannis Karakassis 《Estuarine, Coastal and Shelf Science》2009,81(3):390-400
Fish farming impact on the seasonal biomass, carbon and nutrient (nitrogen and phosphorus) balance of the endemic Mediterranean seagrass Posidonia oceanica was assessed in the Aegean Sea (Greece) in order to detect changes in magnitude and fate of seagrass production and nutrient incorporation with organic loading of the meadows. Phosphorus concentration in the leaves, rhizomes and roots was enhanced under the cages throughout the study. Standing biomass was diminished by 64% and carbon, nitrogen and phosphorus standing stock by 64%, 61% and 48%, respectively, under the cages in relation to those at the control. Seagrass production decreased by 68% and element (C, N, P) incorporation by 67%, 58% and 58%, respectively, under the cages. Leaf shedding was reduced by 81% and loss of elements (C, N, and P) through shedding by 82%, 74% and 72%, respectively, under the cages. Leaf and element (C, N, P) residual loss rate, accounting for grazing and mechanical breakage of leaves, was decreased by 79%, 85%, 100% and 96%, respectively, at the control station. At the control station, 13.98 g C m?2 yr?1, 1.91 g N m?2 yr?1 and 0.05 g P m?2 yr?1 were produced in excess of export and loss. In contrast, under the cages 12.69 g C m?2 yr?1, 0.31 g N m?2 yr?1 and 0.04 g P m?2 yr?1 were released from the meadow. Organic loading due to fish farm discharges transformed the seagrass meadow under the cages from a typical sink to a source of organic carbon and nutrients. 相似文献
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The influence of caged mariculture on the early development of sublittoral fouling communities: a pan-European study 总被引：2，自引：0，他引：2
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Díaz-Almela E Marbà N Alvarez E Santiago R Holmer M Grau A Mirto S Danovaro R Petrou A Argyrou M Karakassis I Duarte CM 《Marine pollution bulletin》2008,56(7):1332-1342
Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities. 相似文献
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A number of 41 papers dealing with the benthic effects of fish farming were reviewed and the values of the variables studied were extracted to be used in a meta-analysis of effects. The papers used covered a wide range of farmed species, geographic regions, management practices and specific site characteristics (e.g., depth, exposure, and sediment type). Therefore, the total data-set may not be considered as biased towards a particular set of conditions as is often the case with data collected in a single study. More than 120 biological and geochemical variables were monitored, occasionally using different sampling and analytical protocols for the same variables. The rank correlation analysis between all possible pairs of variables in the data set showed a large number of significant positive or negative correlations, reflecting the response of these variables to benthic organic enrichment. The use of stepwise regression showed that most biological and geochemical variables are determined by a combination of distance from the farm with bottom depth and/or latitude. Results of stepwise regression, repeated separately for each type of sediment, showed that although the general pattern was similar among different types of sediments, the coefficients varied considerably indicating changes of the distance affected by settling particulate organic material for different sediment types. The overall conclusion is that the complicated interactions between variables and the lack of data, such as current speed, induce difficulties in setting common or uniform environmental quality standards for benthic effects of fish farming and these should take into account the existing considerable differences between geographic regions, depth zones and sediment types. 相似文献
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Karakassis I.; Tsapakis M.; Hatziyanni E.; Papadopoulou K.-N; Plaiti W. 《ICES Journal of Marine Science》2000,57(5):1462-1471