Shellfish culture: a complex driver of planktonic communities

Abstract

This review features recent updates on planktonic community alteration attributed to shellfish farming across three major drivers: predation, nutrient availability and the hydrodynamic environment. The grazing pressure generated by filter‐feeder communities (shellfish and epibionts) constitutes a ‘top‐down’ control of planktonic communities in aquaculture areas, inducing a significant depletion of planktonic organism concentration. By selecting larger cells during the filtration process, shellfish also favour smaller organisms in the water column, leading to the dominance of the latter. Direct excretion and the benthic alteration process tend to fertilise the water column and significantly stimulate primary production. The associated epibiont community particularly contributes to this regeneration process. The expected consequence of increasing nutrient availability is generally a planktonic shift in favour of small planktonic species. However, investigation on the relationship between planktonic structure and nutrient conditions has revealed a wide complexity and variability. Finally, all structures used in shellfish farming activities interact with water currents and tend to significantly increase the residence time of planktonic organisms inside shellfish farming areas. In grazing‐dominated systems, an increase in residence time tends to increase the exposure time of planktonic populations to detrimental conditions, reducing biomass and production. The general consequences of shellfish farming are a decrease in primary production in farming ecosystems, and a possible alteration of structure and functioning of planktonic communities. The implications of shellfish farming also appear to be quite different from other aquaculture activities such as fish farming, which tend to promote primary production leading to eutrophication process.

Evaluation on feasibility of two probiotics as microalgae substitutes for Ruditapes philippinarum spat cultured in shrimp aquaculture wastewater

“…In fact, filter‐feeding shellfish, biofilters for species in integrated aquaculture system, play an important role in wastewater remediation. Filtration of shellfish feeds, biological disturbance and excretion may affect the ecological process of water body (Hulot et al, 2018; Lukwambe et al, 2020). The top‐down control of microalgae, bacteria and organic debris in wastewater has a restoration effect (Lukwambe et al, 2019; Petersen et al, 2019).…”

Offshore longline mussel farms: a review of oceanographic and ecological interactions to inform future research needs, policy and management

“…The spatial distribution of such flow changes is not simple as there are areas for instance, around the corners of a farm and beneath, where the disturbed flow accelerates (Stevens et al 2008). Currents within the suspended canopy have been found to be as little as 25% those of the outside water flow with water speed reductions reaching up to 90% in extreme cases (Plew 2013;Lin et al 2016;Hulot et al 2018). A study of an inshore but highly hydrodynamic mussel farm in Cobscook Bay (USA) used hydrodynamic and material transport models to show how flow is diverted around the farm with velocities increasing outside the structure while flow attenuation is up to 50% at the centre (O'Donncha et al 2016).…”

“…Due to their extensive filtration activity and grazing (Spencer 2002), large numbers of bivalve filter feeders like Mytilus sp. lead to ecosystem changes as they remove large quantities of phytoplankton and nutrients from the water column enhancing a 'topdown' control of planktonic communities within aquaculture areas (Prins et al 1997;Lehane & Davenport 2002Petersen 2004;Hulot et al 2018;Grant & Pastres 2019). Shape and composition of particles play a role in the shaping of the mesoplankton community.…”

“…As the farm interacts with water currents reducing flows, the residence time of planktonic organisms increases, increasing their exposure to consumption, which can reduce both the biomass and production of plankton, described to be one of the main drivers of planktonic variability (Ferreira et al 2007;Hulot et al 2018). In a bay where the drag of an offshore mussel farm raft amplified water residence times, an increase in seston depletion was seen (Newell & Richardson 2014).…”

Regional Integrated Multi-Trophic Aquaculture (RIMTA): Spatially separated, ecologically linked

“…As regards bivalves, they need to be cultivated on appropriate densities, depending on the oceanographic conditions such as depth or current intensity to avoid environmental drawbacks in the benthos due to the release of particulate waste (Dumbauld et al, 2009;Fabi et al, 2009). Additionally, extensive bivalve cultures can lead to the depletion of planktonic organisms (Hulot et al, 2018). Thus, oceanographic variables related to potential benthic environmental drawbacks, such as current intensity or depth, as well as carrying capacities, should be taken into account in the location where the culture will be deployed (McKindsey, 2012).…”