Feeding of Aulacomya atra Under Different Organic Matter Sources (Autochthonous and Allochthonous) in a Chilean Patagonia Fjord Ecosystem

Paulina Montero,Giovanni Daneri,Federico Betti,Giorgio Bavestrello,Martina Coppari

doi:10.3389/fmars.2021.612406

Abstract

Aulacomya atra is an active suspension feeder, spatially dominant in the shallow-water hard-bottom benthic communities of the Chilean Patagonia fjords. In this region, the vertical flux of autochthonous organic matter (OM) reaching the benthos is augmented by allochthonous OM both from a terrestrial origin and from intensive salmon farming. This mixed pool of OM represents a potential source of food for a variety of benthic consumers, but to date little is known about the degree of utilization of these materials by filter feeders organisms. In this context, feeding experiments on A. atra in Puyuhuapi Fjord, Chilean Patagonia, were conducted during summer and winter 2018–2019. These experiments were designed to determine ingestion rates (IR) of A. atra fed with autochthonous (bacterial and microplanktonic community) and allochthonous (salmon food pellet) OM. Additionally, samples of A. atra tissues and suspended particulate organic matter (SPOM) were taken from the study area for stable isotope analysis. Data from laboratory experiments indicated that A. atra can feed on both autochthonous and allochthonous OM, but higher IR were detected in individuals fed with salmon food pellets. Because the IR is sensitive to food particle density rather than specific type of food, diet preferences of A. atra in feeding experiments could not be determined. Stable isotope analyses indicate that A. atra in natural environment preferentially exploits food with an isotopic signal corresponding to autochthonous OM, highlighting the primary role of phytoplankton carbon in their diet. Extensive utilization of terrestrially derived OM is therefore unlikely, although utilization of OM derived from salmon farming is not precluded because of the overlap in isotopic signal between food pellets and marine plankton.

Highlights

In aquatic ecosystems, animals that feed on particles suspended in the water are collectively known as filter feeders (Jørgensen, 1990)
The aim of the present study was to determine the capacity of A. atra to assimilate and ingest organic matter (OM) derived both from salmon feed, and from a phytoplankton and bacterial origin by means of stable isotope analysis and experimental feeding studies conducted in Puyuhuapi Fjord, Chilean Patagonia, during summer and winter periods between 2018 and 2019
The study was conducted in Puyuhuapi Fjord which extends for about 90 km between 44◦19 S and 44◦57 S in northern Chilean Patagonia (Figure 1), and runs in a N–NE direction, connecting directly to the open sea via the Moraleda Channel at its mouth, and through the Jacaf Channel near the head (Schneider et al, 2014)

Summary

Introduction

Animals that feed on particles suspended in the water are collectively known as filter feeders (Jørgensen, 1990). By filtering water to satisfy their nutritional demands, these organisms remove substantial quantities of microscopic particles from seston, such as bacteria, phytoplankton, detritus, and suspended sediments (Wright et al, 1982; Langdon and Newell, 1996; Prins et al, 1998; Kreeger and Newell, 2000; Cranford et al, 2011). These bottom dwelling organisms process large amounts of suspended organic matter (OM) and are often major agents of pelagic-benthic coupling and nutrient cycling (Norkko et al, 2001). Several studies have indicated that bivalves growing adjacent to salmon farming areas remove OM advected from cages by increasing their growth rates (Lander et al, 2004; Peharda et al, 2007; Sarà et al, 2009) and helping to reduce the negative ecological impacts of the salmon industry (Lefebvre et al, 2000; MacDonald et al, 2011) such as the increase in load of OM in the water column and seafloor (Quiñones et al, 2019)

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