Application of a new protocol to evaluate the benthic impacts of aquaculture: Colonization of experimental units for monitoring by polychaeta
Graphical abstract
Introduction
The effects of aquaculture activities on benthic environments are well documented (Holmer et al., 2005, Martinez-Garcia et al., 2013, Tomassetti et al., 2016), and the greatest effects are typically due to organic enrichment, derived from an accumulation of uneaten food and fish excretions (Borja et al., 2009, Mirto et al., 2010, Martinez-Garcia et al., 2015). Over the last two decades. It has been developed various environmental indices to define Environmental Quality Standards for assessing the environmental impact of marine aquaculture (Pearson and Rosenberg, 1978, Odum, 1985, Borja et al., 2009, Karakassis et al., 2013, Aguado-Giménez et al., 2015). Macrobenthic species are often used as biological indicators to monitor the environmental impact caused by organic enrichment (Pearson and Rosenberg, 1978, Carvalho et al., 2006). Among all macrobenthic groups, polychaetes are remarkably well represented in every benthic habitat (Beesley et al., 2000) and their identification represents a useful tool for detecting changes in the benthos caused by fish farming activities (Lampadariou et al., 2005, Dean, 2008, Martinez-Garcia et al., 2013). Diverse groups of polychaetes are present at different organic enrichment levels, from pristine to heavily disturbed areas (Giangrande et al., 2005); their composition and relative abundances can be transformed to a numerical index (Borja et al., 2000), or analysed by multivariate parameters to assess the quality of the benthic environmental (Aguado-Giménez et al., 2007). One of the main problems in the use of these indicators is the spatial variability in the complex and heterogeneous habitats, due to natural processes or geochemical changes associated with the presence of fish-farm effluents (Holmer et al., 2008, Mirto et al., 2010). Moreover, latitudinal changes, depths, different types of underlying sediment (Kalantzi and Karakassis, 2006, Fernandez-Gonzalez et al., 2013), patchy substrata (Longdill et al., 2007) and different sampling approaches (Tataranni and Lardicci, 2009) could affect to results from a monitoring program. It is also a problem for the development of reference conditions, primarily because they are chosen randomly and could vary from the fish farm conditions (Forchino et al., 2011) due to similar reason as above. Results from different sediments such as sand, mud, meadow, pebbles or shell-hash are difficult to compare. Moreover, the bottom is sometimes covered with hard substrata (including mussel detritus or rubbish from aquaculture), which prevents the usage of drags or cores.
Thus, it is not always easy to conduct management studies and to compare levels of pollution among facilities placed in different regions, or in impact versus control assessments, because of the interaction between natural spatial variability of the habitat and patchy effects of aquaculture. In addition, if the sampling is expensive or should be done quickly due to security reason, the number of replicates could be reduced, which could have a strong effect on the power analysis, potentially leading to the misunderstanding of statistical results (Colquhoum, 2014).
A tool to avoid this problem could be the usage of experimental units for monitoring (EUMs), in which all of the initial physical, chemical and biological conditions are known. The philosophy of this approach is to avoid natural variability of marine habitats, deploying EUMs underneath the fish farm facility and control locations for a defined time period and then recovered. Once back in the laboratory, geochemical changes in the sediment and recolonization processes can be studied over a standardise sediment. Recolonization experiments in different sediment types have previously been carried out under stress conditions produced by anthropogenic impacts (Guerra-García and García-Gómez, 2006, Lu and Wu, 2007, Guerra-García and García-Gómez, 2009) and concretely under fish farm conditions (Lu and Wu, 1998, Fernandez-Gonzalez et al., 2016). The latter authors described the distribution and succession of benthic species, and how the accumulation of toxic metabolites can become a limiting factor in recolonization. In particular, sulphide concentration is a useful variable to represent stress levels in relation to organic matter degradation caused by fish farm activities (Hargrave et al., 2008, Keeley et al., 2012). However, we have found no studies that assessed the use of these recolonization experiments (using EUMs) as a tool for marine environmental impact management, particularly for aquaculture facilities.
Therefore, the general aim of this paper is to assess the feasibility of EUMs using polychaeta species as bioindicators, for the evaluation of the environmental impact of fish farming aquaculture, so that they could be applied to monitoring programs, additionally to typical sampling methodology. The objectives were: 1) to test the effectiveness of EUMs as an instrument to evaluate environmental quality by studying changes on polychaetes assemblage structure at species level and to define the most important species that reflect changes in assemblage structure; 2) to compare different sediments (sand and mud) in order to observe if the EUM could be use in a wide range of benthic habitats were normally aquaculture is located; 3) to compare the detection of environmental impacts due to fish farming using different indices based on Pearson and Rosenberg (1978) and multivariate analyses in EUMs, and 4) to evaluate the potential use EUM as an alternative tool for monitoring programs.
Section snippets
Material and methods
Study area
Experiments were carried out at Guardamar del Segura (Fig. 1) in the southeast of Spain (38°5′45.88″N; 0°36′15.84″W). The study period was between June and August 2010, and was characterised by intensive fish feeding and high water temperature. Guardamar del Segura bay hosts three fish farm facilities in water ranging from 23 to 30 m depth; the finfish species were European sea bass (Dicentrarchus labrax-Linnaeus 1758) and gilthead sea bream (Sparus aurata-Linnaeus 1758). These
Results
After one month, granulometric characteristics and organic matter did not show significant changes comparing impact and control locations (Fig. 2). However, there was an increase in TFS under the fish farms in sandy sediments, and to a lesser extent, in muddy sediments too (Fig. 2). In sandy sediments under fish farms there were differences in TFS concentration between locations (Table 1). Values of total abundance, S, AMBI, H′ and J are represented in Fig. 3. Polychaeta total abundance was
Discussion
After only one month of deployment, the biotic index calculated using the polychaetes that colonized the EUMs could detect the effects of fish farming, specially AMBI and multivariate analysis. Accurate information on the status of the environment was provided by both the indices based on Pearson and Rosenberg (1978), and multivariate analyses of polychaete assemblage in recolonization processes with sulphide concentration measures. The use of EUMs could therefore, complement traditional
Agreements
We are grateful to Agustin Ríos and the staff of CULMAR fish farms that gave us access and help in the study. We also thank our colleagues: V. Fernandez-Gonzalez, P. Arechavala-Lopez, K. Toledo-Guedes, D. Izquierdo-Gomez, M. Vázquez- Luis, L.M. Ferrero-Vicente, I. Aragones and A. Loya-Fernández for their invaluable cooperation during the sampling work. We also thank to Joaquin Moreno for his statistical advice. This project has been supported by Planes Nacionales de Acuicultura (JACUMAR) from
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