A Global Overview of Restorative Shellfish Mariculture

Abstract

Farming of marine organisms (mariculture) represented 36% of global aquaculture, with mollusks representing 58.8% in live weight. Mollusk populations in some locations are, however, threatened by degradation of the ecosystems and/or over-fishing. This threat is increasingly being addressed through Restorative Shellfish Mariculture (RSM), as opposed to mariculture alone. There is no general consensus in the literature on what can and cannot be considered RSM. While maximization of benefits other than provisioning services is often considered a prerequisite, in other cases the maximization of fisheries yields is prioritized. Here we define RSM as the farming of marine shellfish, implying some form of intervention during the species life cycle, in order to address negative socio-ecological issues arising from the unsustainable use of marine ecosystems, independent of the final ownership regime of the resource. Strategies for developing RSM were reviewed and classified along a gradient from the most conservation-oriented (e.g., habitat restoration, reintroduction of locally extinct endangered species), to the most fisheries-oriented (including some forms of fisheries enhancement), and classified as Non-hatchery Dependent or Hatchery Dependent strategies. We reviewed the targeted species and strategies implemented across 584 individual projects developed in the last decades in North America, Europe, Asia, Oceania and South America. We found that some 48 species, including 34 bivalves and 15 gastropods were targets of RSM in 34 countries. US projects accounted for ca. three quarters of the total (N = 438), with Philippines, Japan and Australia also being home to a large number. More than 90% of the projects involved five species, namely the eastern oyster (Crassostrea virginica, N = 379), the giant clam (Tridacna gigas, N = 65), the Olympia oyster (Ostrea lurida, N = 25), the bay scallop (Argopecten irradians, N = 25) and the hard clam (Mercenaria mercenaria, N = 15). Of the RSM projects, 51% used Non-hatchery dependent methods, mostly habitat restoration providing substrata for settlement, whereas some 49% involved hatcheries. 3% of the projects combined both methods. This review provides an overview of the breadth, depth and aims of RSM globally, develops a broad definition of the activity, and proposes a structure for classifying RSM.

The changing role and definitions of aquaculture for environmental purposes

“…All forms of aquaculture need to be economically sustainable, or at least economically viable, to succeed over time. However, commercial aquaculture is primarily motivated by financial outcomes, focusing on maximizing production with few considerations for the status of the species in nature 27 . Commercial aquaculture can, and ideally should, contribute to reduced environmental harms and positive social outcomes.…”

Aquaculture and Nature-based Solutions: identifying synergies between sustainable development of coastal communities, aquaculture, and marine and coastal conservation

“…algae and certain bivalves, so-called extractive species by FAO, 2018) can have a positive impact on ES, by not only improving provisioning services but also providing regulating and supporting services and, potentially, cultural services. Recent work is highlighted to promote the approach of a 'restorative mariculture', associated to seaweeds or shellfish, in which the restoration of ecosystem services is targeted first (Carranza & Zu Ermgassen, 2020;Fitzsimons et al, 2020;Theuerkauf et al, 2019).…”

“…FAO (2018) now encourages the production of "extractive species" (non-fed through compounded feeds); such species include marine bivalves and seaweeds that benefit from the environment by assimilating waste materials, including waste from fed species, therefore removing these wastes, and lowering the nutrient load in the water. Recent work (Carranza & Zu Ermgassen, 2020;Fitzsimons et al, 2020;Theuerkauf et al, 2019) explores the way a shellfish restorative and enhancement mariculture can be deployed with the implantation of shellfish reefs, such as the recent SOAR project by oyster farmers in the USA. * However, while adapting Life Cycle Analysis (LCA) assessment tools to a shellfish cultivation case, Aubin et al (2018) were able to show the limits of such regulating service on a "bouchot"-grown mussel system in France.…”

“…The emerging concept of a restorative aquaculture (Theuerkauf et al, 2019) Restorative Shellfish Mariculture (RSM) (Carranza & Zu Ermgassen, 2020) 15 may be explored under this NbS framework, as more than 500 existing cases of RSM are recorded.…”

An Assessment of the Potential Value for Climate Remediation of Ocean Calcifiers in Sequestration of Atmospheric Carbon

“…Every tonne of live shellfish that is harvested today provides half a tonne of nutritious meat. When the corresponding half-tonne of dead shell is returned to the seabed to contribute immediately to a growing reef habitat that fosters biodiversity, shoreline stability and make its contribution to CaCO3 accumulation in ocean sediments [119][120][121][122]. In particular cases (oysters and giant clams, for example), such restoration repairs the losses caused by generations of overfishing.…”