Mollusk Shell Debris Accumulation in the Seabed Derived from Coastal Fish Farming

Lotte Krüger,Nuria Casado-Coy,Pablo Sanchez-Jerez,Carlos Sanz-Lazaro,Carlos Valle

doi:10.3390/jmse7100335

Lotte Krüger, Nuria Casado-Coy + Show 3 more

Open Access

https://doi.org/10.3390/jmse7100335

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Abstract

Fish farm facilities become colonized by biofouling, and in situ cleaning activities may increase the accumulation of biofouling, mostly shell-hash, on the sediment. However, there is a lack of knowledge about the effect of fish farming on this process. We evaluated the effect of fish farming on shell-hash accumulation on sediments in three fish farms in the Western Mediterranean in Spain. On the one hand, coverage of non-degraded shell on the seabed was estimated using an underwater camera attached to a frame of 1 × 1 m. On the other hand, superficial sediment samples were taken by a Van-Veen grab, and from a subsample, shell-hash was sorted at the laboratory, dried, and weighted. A significant increase of shells on sediment was detected under fish farms compared with the other treatments, with average values of 53 g kg-1, and 1.12% of cover. Shell-hash at zones close to the fish farm cages (Zone of Influence located between 40 to 60 m from the closest cage) did not show statistical differences compared to the reference zones, 300–500 m away from the concession limits, but the shell cover showed statistical differences. Fish farming activities produce a local increase in the sedimentation rate of shells under the cages. The derived ecological consequences of this accumulation need to be further studied.

Highlights

Surfaces immersed in the marine environment become colonized by marine organisms from macromolecules to larger algae and sessile invertebrates such as mussels, ascidians, and hydroids, through a successional process known as biofouling [1]
The physical structures associated with marine aquaculture such as fish farming, include lines, anchors, nets, floating rings, etc., which introduce a new habitat in the pelagic environment that is colonized by biofouling
Marine sediments should be influenced by sediment grain size [5], physical changes due to debris accumulation from biofouling have not been sufficiently studied in the Mediterranean Sea

Summary

Introduction

Surfaces immersed in the marine environment become colonized by marine organisms from macromolecules to larger algae and sessile invertebrates such as mussels, ascidians, and hydroids, through a successional process known as biofouling [1]. The physical structures associated with marine aquaculture such as fish farming, include lines, anchors, nets, floating rings, etc., which introduce a new habitat in the pelagic environment that is colonized by biofouling. This process is a complex and recurring problem in all sectors of the marine aquaculture industry [2]. Fish farming, using floating net pens, is a growing activity across the oceans, especially in the Mediterranean Sea [3] The development of this activity has been accompanied by the assessment of the interactions with the environment, in particular the impact of sedimentation of organic matter on surrounding benthic habitats [4]. We hypothesized that fish farming might increase the quantity of shell-hash on sediments, having reduced impact in near locations (50 m far away from the cages) due to the rapid sedimentation of the biofouling fragment

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