Oysters, bivalve mollusks, perform key Services: they are filter feeders (filtering 140 l of water per day) contributing to keep the water clean; they build underwater structures, the ‘oyster beds’ or ‘oyster reef’ that are actually barriers helping to increase the substrate complexity. Such structures are especially important in harbor areas where they provide space for organisms to settle and hide and also representing real physical barriers that protect the coast from the sea. Oysters, similarly to Mytilus sp., are ‘carbon sinks’ thus they are able to use the carbon in the water to build their shells.

Among the different species of oysters, Ostrea edulis, known as the flat oyster (Figure 1), is a native species of Europe originally building extensive beds along the continent coastline and playing a crucial role in the economies of coastal populations and in maintaining the richness of marine ecosystems. Nowadays, the species is highly endangered and at risk of extinction according to the Convention for the Protection of the Marine Environment of the Northeast Atlantic (OSPAR). Thus, actions aimed a its restoration and repopulation are becoming a priority.

Figure 1. Ostrea edulis shells

The flat oyster in the Gulf of La Spezia has been reported from late 1800s, however, strong direct anthropogenic impacts, such as coastal urbanization, the development of military and commercial harbor, the subsequent pollution of water and seabed, together with indirect impacts, such as the loss of marine habitats, substrate depletion and modification, altered sedimentation rates, and climate change, have all severely threaten O. edulis local population. Nonetheless, O. edulis is still present in some areas of the Gulf of La Spezia, including harbor sites, where can be found growing on ropes, submerged metal objects (chains, anchors), piers and artificial structures. The changes of the seafloor (i.e., muddy bottoms) are such that the flat oyster is not able to settle and grow forming ‘oyster beds’, but the persistence of the species despite the impacts is a sign of the resilience of the local population.

Within the context of PNRR RAISE project (Ecosystem of Innovation for Liguria Region, National Program for Research and Resilience), an activity on the regeneration of port areas through circular approaches and nature-based solutions (NBS) has been designed by ENEA, together with the Cooperativa di Mitilicoltori Associati, IMC Foundation and the PhD program in Marine Sciences and Management at the University of Milano Bicocca. This activity will aim at regenerating St. Teresa Bay through ecosystem restoration, including O. edulis beds.

Launched during the Oyster Fest held May 10-12 in La Spezia, the activity will be carried out by two PhD and a master students (University of Milan Bicocca and the University of Bologna). At present, structures for catching the oyster larvae – consisting on ‘Chinese hats’ (Figure 2A) and oyster shells positioned in nets made of natural fibers such as hemp (Figure 2B)(provided by Reeco) – are in preparation. They will be positioned in 3 sites within the Gulf and monitored over 12 months to check the settlement and the growth of oysters.

A                                                                         B

Figure 2. Larvae catchers- Chinese hat (A) and hemp nets with oyster shells (B)

In addition, growth and metabolic measurements (respiration and calcification) of individuals of O. edulis characterizing the resident population of the Gulf (Figure 3) will be performed in order to monitor their health status through time. The biological measurements will be coupled with environmental monitoring – through Smart Bay S. Teresa empowered observatory – that will include high resolution physico chemical data acquisition and transmission from seven stations and that will be fully deployed in the coming months (funding: PNRR-RI EMBRC-UP).

Figure 3. Individuals of Ostrea edulis population positioned in the ‘oyster lantern’ used for oyster rearing

Written by: Erica Gabrielli and Sofia Lorenzini


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