Influence of mussel aquaculture on the distribution of vagile benthic macrofauna in îles de la Madeleine, eastern Canada

Abstract

We examined spatial variation in the abundance of 4 benthic vagile species in a lagoon with blue mussel Mytilus edulis aquaculture (inside vs. outside of the mussel lease; among areas with 1 yr old, 2 yr old and harvested mussels; and with distance from mussel lines). American lobster Homarus americanus, Atlantic rock crab Cancer irroratus, common starfish Asterias rubens and winter flounder Pseudopleuronectes americanus were all at least 3 times more abundant in the farm area with 2 yr old mussels, where mussel fall-off is more frequent, than in areas outside of the farm or other areas within the farm. A strong association of lobsters with mussel line structures was observed, where most individuals were observed directly under the mussel lines, close to anchor blocks, in the areas with 1 yr old, 2 yr old and harvested mussels (58, 42 and 57%, respectively). Mussel farms influence the distribution of benthic macrofauna at a number of spatial and temporal scales, and this may be due to a number of mechanisms, depending on the species. An in situ experiment was done to separate the influence of anchor blocks and mussel fall-off on the distribution of lobsters, crabs, starfish and flounders. Results of the manipulative experiment highlighted the importance of shelter structures over a short-term period for lobsters, but not for the other 3 species. Conclusions from the observations and the manipulative experiment suggest that lobster distribution is a function of both physical structure and feeding opportunities, whereas the distribution of the other species was mainly due to trophic effects.

Attraction and repulsion of mobile wild organisms to finfish and shellfish aquaculture: a review

“…An experimental study showed that American lobster ( Homarus americanus ) were attracted to the presence of cement anchor blocks used in mussel farms in eastern Canada rather than to mussel fall‐off per se (Drouin et al . ). In Washington, the abundance of transient fish and macroinvertebrates in geoduck ( Panopea generosa ) sites with outplanting structures was twice that observed in reference areas, suggesting that some groups were attracted to the physical structure provided, or to the organisms associated with it (Washington Sea Grant ).…”

“…For example, Drouin et al . () used observational and manipulative studies to describe spatial variation in the abundance of American lobster in and around a mussel farm in Canada. Spatial variation was attributed to lobster being attracted to anchor blocks that serve as refuges and to increased prey abundance, including both fallen mussels and crabs that feed on the mussels.…”

Quantifying habitat provisioning at macroalgal cultivation sites

“…122 Macroalgal cultivation may provide similar habitat value to epibenthic species via increased food availability from farm-derived nutrients and detritus (including epibiont cast-off) and the creation of a more heterogeneous habitat (via detritus accumulation or farm infrastructure such as mooring systems). 8,17,[123][124][125] At a small temperate kelp farm in Sweden however, no effect on benthic macrofauna was reported, 101 whereas in Tanzania, lower abundances of macrofaunal or increases in sea urchin species, that could threaten to graze on the cultivated seaweed, were found. 118 Differing effects on epifauna reflect the diverse nature of macroalgal cultivation sites worldwide and highlights the need to increase monitoring across different systems.…”

“…Wild kelp populations contribute on average US$48,600 to $141,000 ha −1 yr −1 to capture fisheries across the four major kelp genera globally, with nine of the top 10 valuable species being benthic invertebrates such as lobsters, abalone, urchins and gastropods 122 . Macroalgal cultivation may provide similar habitat value to epibenthic species via increased food availability from farm‐derived nutrients and detritus (including epibiont cast‐off) and the creation of a more heterogeneous habitat (via detritus accumulation or farm infrastructure such as mooring systems) 8,17,123–125 . At a small temperate kelp farm in Sweden however, no effect on benthic macrofauna was reported, 101 whereas in Tanzania, lower abundances of macrofaunal or increases in sea urchin species, that could threaten to graze on the cultivated seaweed, were found 118 .…”

Biodiversity–Ecosystem Functioning (BEF) approach to further understanding aquaculture–environment interactions with application to bivalve culture and benthic ecosystems

“…as a refuge from predators) or to the prey associated with the structure is unclear (Würsig & Gailey 2002) and is likely species‐specific. For example, Drouin et al (2015) showed that lobster Homarus americanus is more attracted by the shelter created by mussel farming anchors, whereas winter flounder Pseudopleuronectes americanus seems to benefit from a trophic effect induced by the farm.…”