Strongholds of Ostrea edulis populations in estuaries in Essex, SE England and their association with traditional oyster aquaculture: evidence to support a MPA designation

Abstract

The flat oyster Ostrea edulis has declined significantly in European waters since the 1850s as a result of anthropogenic activity. Ostrea edulis was designated a UK Biodiversity Action Plan Species and Habitat in 1995, and as a Feature of Conservation Importance (FOCI) within the UK Marine & Coastal Access Act 2009. To promote the recovery of oyster beds, a greater understanding of its abundance and distribution is required. Distribution of O. edulis across the proposed Blackwater, Crouch, Roach and Colne MCZ in Essex was determined between 2008 and 2012. Ostrea edulis were present in four estuary zones; with highest sample abundance in the Blackwater and Ray Sand zones. Size structure of populations varied, with the Ray Sand and Colne zones showing a significant lack of individuals with shell height <39 mm. Ostrea edulis occurred in highest number on shell substratum, followed by silty sediments. There were no significant associations between O. edulis abundance or size structure with water column Chl a, suspended solids, oxygen, nitrate or ammonium concentrations, temperature or pH. Highest abundance and most equitable population shell-size distribution for O. edulis were located within, or adjacent to, actively managed aquaculture zones. This suggests that traditional seabed management contributed to the maintenance or recovery of the species of conservation concern. Demonstration that the Essex estuaries were a stronghold for Ostrea edulis in the southern North sea area led to the designation of the Blackwater, Crouch, Roach and Colne estuaries Marine Conservation Zone in 2013.

Forty questions of importance to the policy and practice of native oyster reef restoration in Europe

“…In the case of O. edulis in Europe, reference sites that may provide a baseline for assessing the progress of restoration efforts are absent from much of the range. Moreover, sites that still contain populations are generally modified as a result of a history of oyster production, dredging and other fishing activities, or modified via shifts in the dominant biotic community (Allison, Hardy, Hayward, Cameron, & Underwood, 2019; Helmer et al, 2019; Preston et al, 2020). As such, establishing reasonable baselines to inform adaptive management of restoration efforts where O. edulis habitats are currently absent is a key priority.…”

“…For example, a recent study in Essex, UK found little explanatory power of abiotic variables such as temperature and pH in explaining the occurrence of O. edulis . Occurrence and abundance were instead predominantly determined by the presence of shell (Allison et al, 2019). Given that O. edulis is largely extirpated from much of its range, there is a significant role to be played by habitat suitability models in identifying suitable locations if appropriate input data can be improved (see Gormley, Porter, Bell, Hull, & Sanderson, 2013).…”

From individual vital rates to population dynamics: An integral projection model for European native oysters in a marine protected area

“…While not yet common in oyster restoration in Europe there is also a long history of restoration and conservation interventions for restoring traditional shellfish fisheries (Allison, Hardy, Hayward, Cameron, & Underwood, 2020).…”

“…These range from potential biodiversity benefits from the presence of flat oyster beds or reefs (Lown, 2019; Pogoda, 2019) to potential filtration benefits resulting in increased water quality (Rodriguez‐Perez et al, 2019; Wilson, 1983). While not yet common in oyster restoration in Europe there is also a long history of restoration and conservation interventions for restoring traditional shellfish fisheries (Allison, Hardy, Hayward, Cameron, & Underwood, 2020).…”

“…Local oystermen are one of the biggest champions of oyster restoration in Essex and have successfully restored the species over the last 35 years to about 8.27 km 2 of the 284 km 2 MCZ (i.e. the Tollesbury & Mersea private several order – Allison et al, 2020). The MCZ management group is charged with recovery of native oysters to ‘good ecological status’ throughout the rest of the MCZ and with an associated management aim of permitted sustainable harvesting of the oyster for local aquaculture once this status has been achieved (KEIFCA, 2019a; KEIFCA, 2019b).…”