Abstract
Fish farming in net cages is considered as an alternative to food production in response to elevated population growth, and zooplankton is an important resource to the development of this economic activity. We (i) compared microcrustacean composition in eutrophic and oligotrophic habitats under net tank influence, (ii) investigated changes in species distributions in these habitats, and (iii) indicated which chlorophyll-a concentrations presented thresholds that alter community structure. We expected different responses of species to changes in chlorophyll-a concentration due to net cage management, as chlorophyll-a represents an estimate of food availability. Microcrustacean samplings and chlorophyll-a estimation were made upstream, downstream and close to the net cages, during 120 days, in the Rosana Reservoir (Brazil). Species composition differed significantly (p<0.05) among habitats where in the eutrophic environment was found the largest number of species. However, only in the eutrophic habitats did frequency of occurrence and relative abundance of some species change with chlorophyll-a variation. Thus, net cage management influenced species distribution only in the most productive habitat. These responses can affect ecosystem processes related to trophic dynamics as secondary productivity and nutrient cycling.
Highlights
Net cage fish farming in reservoirs is considered as a promising alternative to meet the increasing need for food of the world population (Alves & Baccarin 2005, Dias et al 2011, Tiburcio et al 2015)
Admitting that threshold prediction brings benefits to ecosystem services and goods (Martin et al 2009) and that the identification of potential thresholds is an important aspect to the management of ecological systems, we aimed to i) compare microcrustacean species composition in eutrophic and oligotrophic habitats under net tank influence in a neotropical reservoir, (ii) determine changes in frequency of occurrence and relative abundance of species that occur in these habitats, and (iii) evaluate how chlorophyll-a concentration presents thresholds that alter community structure for these microcrustaceans
Species composition differed significantly between the studied habitats, but only in the eutrophic habitat changes in species frequency and abundance were attributed to chlorophyll-a concentration
Summary
Net cage fish farming in reservoirs is considered as a promising alternative to meet the increasing need for food of the world population (Alves & Baccarin 2005, Dias et al 2011, Tiburcio et al 2015) The increase of this activity is related to the exploitation of available reservoirs and lakes, high efficiency in management, readiness of fish removal and continuous water flow that would theoretically improve the water quality inside the cages and reduce the production costs (Cyrino & Kubtiza 1996, Furlaneto et al 2006, Halwart et al 2007). Fish farming employs a considerable volume of food input to fish production in reduced space and at high density, with consequent release of food remains and metabolites directly in the environment. This characterizes fish farming as a potential source of environmental impact (Beveridge 2004). Changes in nutrient loads in these systems due to food input
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