England Wilder Humber – Remote Larval Setting and Intertidal Deployment of Ostrea edulis

A Scalable Approach for Native Oyster Restoration in the UK

The aim of this demonstraton was to address the bottleneck in Ostrea edulis restoration of producing reliable and cost-effective seed at scale; a key bottleneck to restoration efforts. Remote setting of spaton- shell offers a promising solution, enabling early-stage deployment while addressing biosecurity and supply constraints. As part of the Wilder Humber project, Yorkshire Wildlife Trust (YWT), in collaboration with The Nature Conservancy (TNC) and The Oyster Restoration Company (TORC), delivered the UK’s first demonstration of remote native oyster larval setting for and the first trial onto granite.

What is remote setting?

Remote setting involves taking oyster larvae and cooling them to below 8°C to halt metabolism for safe transport over several days to a restoration site. Once there, the larvae are rewarmed and introduced to setting tanks to settle on substrate—unlike direct setting, where larvae are added directly to tanks at the hatchery without cooling or transport. This method reduces the high cost of shipping individual mature oysters.

Methods

Two 2.7m3 circular tanks with scallop shell substrate and two 0.6m3 rectangle tanks with granite rock were used to compare the settlement rate on different substrates. The final swimming larval stage, eyed pediveliger larvae, were added in two batches: on 1 September 2024 (342,000 total, <1% settlement, batch discarded) and on 4 September 2024 (170,000 total, with 147,330 in shell tanks and 22,670 in rock tanks). After two weeks these were placed onto our trestle system.

Results

Achieved settlement rate: 18% (SE ±4.3%), close to target of 20%. (Comparable to hatchery set rate.)

Survival Post-Deployment:

4-week survival post-deployment:	9-month survival post-deployment
– Rock: 35% (SE ±8.7%)	– Rock – no oysters present
– Shell: 28% (SE ±7.5%)	– Shell – oysters still present

Lessons learnt

The first larval batch was lost due to early ice melt during transport; the second batch, shipped with additional ice packs, arrived in good condition—demonstrating a cost-effective and improved delivery method. Spat settlement on granite was difficult to assess due to the mottled surface, suggesting a need to allow longer growth in tanks to improve visibility and counting accuracy. Holding spat on substrate for extended periods pre-deployment may also improve outcomes. The setup we initially trialled involved transporting large water volumes across beach terrain, posing logistical challenges due to tidal restrictions, improved access or on-site water treatment may be beneficial in future trials.

*Photo by Cate Holborn*
*Remote setting tanks,* *Spurn Field Station*.

*Photo by Laura Welton*
*Submerged granite in tank with settled oyster larvae.*

Photo by Cate Holborn
Submerged scallop shells in tank with settled oyster larvae.

Photo by Finn Varney
Oyster spat on shell under a microscope.

*Photo by Laura Welton*
*Oyster spat on granite*.

What we are doing now – Greedy Gut Experiment

Building on these results, we are now running an intertidal restoration trial over the next five years, comparing the performance of juvenile oysters on shell versus mature, re-laid oysters. Three different oyster treatments are being assessed on fifteen 25m2 plots at Spurn Point: clustered and evenly distributed spat-on-shell provided by The Oyster Restoration Company (TORC), and evenly distributed mature oysters cultivated within the Humber.

Distribution Treatment	Total number of oysters	Oysters per plot	Oysters per m2
Evenly distributed adults	2,250	750	30
Evenly distributed spat-on-shell	Approx. 20,000 (1.3 rapid reef bags)	Approx. 6,666	266
Clustered spat on shell	Approx 10,000 (0.6 rapid reef bags)	Approx. 3,333	133
Bare cultch (cockle shell)	0	0	0
Bare sediment	0	0	0

Table: Minimum numbers of oysters for restoration trial

Over a two-year period, the project will evaluate oyster survivability, adaptability, recruitment, impact on biodiversity, alongside a cost-benefit analysis comparing juvenile oysters to mature oysters for intertidal restoration. This research aims to inform scalable, evidence-based strategies for native oyster recovery and broader marine habitat restoration across UK coastal waters. In addition, seasonal sub-sampling of live oysters will assess metabolic rates, and nutrient
and particulate fluxes by placing oysters from each treatment into incubation chambers to gain a better understanding of the biology of the oysters in this location.