Nematode assemblage response to fish-farm impact in vegetated (Posidonia oceanica) and non‑vegetated habitats

Abstract

We investigated the impact of fish farming on the benthic biota of 2 habitats (seagrass meadows of Posidonia oceanica and non-vegetated soft bottoms), by examining in detail the nematode assemblages, and the effects of organic enrichment on their abundance, diversity (species richness and trophic diversity), community structure and individual size. All investigated faunal variables differed significantly between impact and control sediments, except for individual nematode biomass. Nematodes displayed reduced biodiversity beneath the investigated fish farms in both vegetated and non-vegetated habitats. The nematode genera Richtersia, Desmoscolex and Halalaimus were highly sensitive to biodeposition and disappeared almost completely in farm sediments, whereas other genera such as Daptonema and Prochromadorella largely increased their relative abundance. The impact of biodeposition was investigated also in terms of K-dominance curves and functional variables (life strategies as maturity index, and functional [i.e. trophic] diversity) which showed that nematodes are very sensitive to this kind of environmental disturbance. Our results indicate that the analysis of nematode assemblage composition, the life traits of the dominant species and the presence/disappearance of certain nematode species represent a reliable tool for monitoring the quality state of marine sediments exposed to fish-farm organic wastes.

A review of Italian research on free-living marine nematodes and the future perspectives on their use as Ecological Indicators (EcoInds)

“…Other studies found that the analysis of nematode assemblages at the genus level represents the most informative tool in relation to the EcoQ: in the study of Losi et al (2013a) the analysis of the nematode assemblage at the level of genus revealed the best connection between environmental status and biological response, and in Losi et al (2012) only the genera analysis brought to light early changes in the community due to the touristic pressure. The same results are reported by Vezzulli et al (2008) and Mirto et al (2014) in relation to the fish farm impact and by Schratzberger et al (2009) in relation to physical stress.…”

“…In a good portion of the reported study cases, MI responded to the stressors, proving to have the potential as quality status indicator (Mirto et al, 2002(Mirto et al, , 2014Semprucci et al 2010aSemprucci et al , 2013a. In agreement with those results, Moreno et al (2011), evaluating several nematode indices for EcoQ assessment, found that c-p composition and MI were among the best tools to evaluate the EcoQ.…”

“…Trophic classification has been, in fact, largely revised and modified in the last decade (Moens & Vincx, 1997), but the use of this more recent classification is hampered by the low number of species reclassified making its use in ecological surveys impossible. Mirto et al (2014) investigated the impact of fish farming on the meiobenthic and more specifically the nematode assemblages of Posidonia oceanica seagrass meadows and unvegetated soft bottoms (Pachino Bay, Sicily). Among the faunal parameters analysed, MI decreased significantly in the impacted sites in all habitats and regions, while diversity indices did not show a significant impact of the fish-farm.…”

“…There have only been four investigation procedures that have focused on nematode assemblages on the Italian coastal systems: three of them have been carried out in the Tyrrhenian Sea (Gulf of Gaeta and Vibo Marina) (La Rosa et al, 2001;Mirto et al, 2002;Vezzulli et al, 2008) and one in the Ionian Sea (Sicily) (Mirto et al, 2014) (Fig. 1).…”

Bridging the Gap Between Policy and Science in Assessing the Health Status of Marine Ecosystems

“…Current instruments that can analyze chlorophyll-a from in situ sampling can ground-truth satellite image analysis for monitoring of phyto-pigments concentrations in surface waters (Cristina et al, 2014(Cristina et al, , 2016 or assess aquaculture impacts (Mirto et al, 2010(Mirto et al, , 2014Luna et al, 2013;Bengil and Bizsel, 2014). In addition, pigment color analysis (particularly in situ flow cytometry) can provide insights on phytoplankton biodiversity , estimate and calculate time series of annual gross primary production, and support MSFD implementation .…”