Reduced physiological performance in a free-living coralline alga induced by salmon faeces deposition

E Legrand,V Husa,S Andersen,Sps Rastrick,T Kutti,Ev Gonzalez Casal

doi:10.3354/aei00403

E Legrand, V Husa + Show 4 more

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https://doi.org/10.3354/aei00403

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Abstract

Maerl beds are formed by the accumulation of free-living coralline algae and have considerable ecological signiﬁcance due to the high diversity of associated fauna and flora. The rapid expansion of the Atlantic salmon Salmo salar aquaculture industry in Norway may have major impacts on surrounding maerl beds through the release of effluents, including fish faeces. This study is the first to test the effects of salmon faeces and inorganic sediment deposition on the photosynthesis, respiration, calcification and pigment content of the coralline alga Lithothamnion soriferum. In a 6 wk laboratory experiment, inorganic sediment and salmon faeces deposition significantly reduced the amount of light reaching the surface of coralline algae. No impact of inorganic sediment deposition was detected on L. soriferum physiology, while salmon faeces deposition increased respiration rate and reduced net primary production and calcification. The accumulation of salmon faeces stimulates proliferation of bacteria, with adverse consequences on L. soriferum physiology due to the potential release of toxic compounds. Burial by salmon faeces deposition also affects the physiology of coralline algae due to the flocculation of sticky faeces particles, which may limit nutrient and gas exchanges in the vicinity of thalli. Carbon dioxide accumulation in the vicinity of L. soriferum may lead to a decline in pH and alter the calcification process in cell walls. In natural maerl beds, the negative effect of faeces deposition may be exacerbated by longer-term exposure and the presence of other chemicals released by fish farms.

Highlights

Since capture fishery production has been relatively static for the past 40 yr, aquaculture has been responsible for the impressive growth in the supply of fish for human consumption (FAO 2020)
The present study is the first to show that salmon faeces deposition has a strong negative impact on the physiological response of Lithothamnion soriferum, resulting in clearly reduced net photosynthesis and growth, and enhanced respiration rates
Our results showed that both inorganic sediment and salmon faeces deposition significantly reduced the light level reaching the surface of coralline algae

Summary

Introduction

Since capture fishery production has been relatively static for the past 40 yr, aquaculture has been responsible for the impressive growth in the supply of fish for human consumption (FAO 2020). The rapid expansion of the salmon aquaculture industry in Norway can have major impacts on surrounding benthic ecosystems due to the release of Publisher: Inter-Research · www.int-res.com. During the on-growth of Atlantic salmon Salmo salar L. in open net cages, a large amount of organic wastes (faeces and waste food pellets) is released, sinks to the seafloor and interacts with benthic ecosystems. Deposition rates up to 70 g DW m−2 d−1 were measured in the vicinity of a farm in a shallow location, with high production levels (Keeley et al 2019). A severe impact of intensive production farms is generally associated with poor currents and water circulation, which may drastically damage benthic ecosystems due to the lack of oxygen in the sediment (Soto & Norambuena 2004, Yakushev et al 2020). Current methods used for monitoring have been developed for deeper soft-sediment environments and may not be suitable to detect subtle and slowly evolving impacts on maerl beds

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