Addressing Key Challenges in Green Sea Urchin Aquaculture

The following approaches have been employed for objective 1, and will be employed for objectives 2 and 3 

Objective 1: Determining the ideal stocking density and size classes of sea urchins for shellfish integration. (In progress)  

This was conducted as a field experiment at the Casco Bay Mooring Farm located in Casco Bay, near Falmouth, Maine. The farm typically uses 5-tiered 50 cm diameter lantern nets in a range of mesh sizes, suspended on horizontal long lines which are 7 feet below the sea water surface. Each lantern net had approximately 6 feet of line, which placed the top of each lantern net approximately 2m below the surface. The trial ran for 3.5 months from late summer to early Fall.The trial comprised of 5 treatments:  

1. Control (no GSUs);  
2. Medium sized GSUs (35-43 mm TD) at a density of 8 GSUs per lantern net tier; 
3. Medium sized GSUs (35-43 mm TD) at a density of 10 GSUs per tier; 
4. Large sized GSUs (44 - 52 mm) at a density of 8 GSUs per tier; 
5. Large sized GSUs (44 - 52 mm) at a density of 10 GSUs per tier. 

Trials were conducted in 9mm mesh size lantern nets described above. Each treatment was held in a single lantern net tier, and replicated across five separate lantern net cages. Within each lantern net cage, the treatment tier location was randomized to account for light and depth influence (Sterling et al. 2016). These GSU size classes were chosen to build from previous trials (described in the Project Focus section). The size classes of GSUs are realistic sizes for rapid growing juveniles in a hatchery setting, and for GSUs at different sizes when grown on the farm.  

Sea scallops were maintained in all lantern net tiers at a density of 20-30% lantern net tier bottom coverage, which at the (approx. 2”) size used equated to 25 scallops per lantern net tier. For this trial, GSUs were sourced from the University of Maine's Center for Cooperative Aquaculture Research (CCAR) hatchery in Franklin, Maine and transported to Casco Bay Mooring Farm in coolers. Atlantic sea scallops were sourced from the Darling Marine Center (DMC) in Walpole, Maine, farm stock.  

5 HOBO onset data loggers (64k pendant loggers) were deployed with the experiment to measure and record seawater temperature every 30 minutes at the farm location. 

Objective 2: Determine whether GSU's can be reared on the outside of gear to reduce external net biofouling. (Expected start: March 2026) 

This trial was originally going to be conducted in parallel with Objective 1, at the Casco Bay Mooring farm site using 13” pearl nets with 9mm mesh size, but was delayed due to wanting to learn from Obj. 1 on how successful biofouling reduction was and help inform this objective’s refinement of methods. Our collaborator Stewart Hunt also stepped down from his aquaculture business meaning we could no longer conduct this work at his farm, creating further delays in finding an alternative suitable location. This trial will now be conducted at the Darling Marine Center in Walpole Maine, a marine research facility run by the University of Maine. There is an experimental aquaculture lease just offshore from the facility, where scallop and urchin work is permitted. We originally proposed to trial the use of enclosing GSUs onto the external surface of pearl nets, enclosing the urchins using a predator exclusion mesh net to prevent the urchins from escaping. However, given the success of Objective 1 in reducing biofouling, and having discussions with stakeholders and researchers, a priority focus was identified to better understand the importance of gear mesh size in relation to urchin efficacy on accessing and controlling biofouling on external net surfaces, which will be implemented in 2026. This was favored over the potential logistics and effort associated with trying to cover lantern nets with an exclusion mesh and ensuring GSUs remain secured within this. This updated approach still strongly aligns with the aim and objective of the work, which is to reduce biofouling using GSUs, allowing us to react to and adapt to the positive results and information we can gain to help inform industry. 

This trial will be carried out in pearl nets, gear used by some sectors of the scallop aquaculture industry. The effect of mesh size and urchin size will be tested as follows, and builds from the Obj. 1 results: 

1. A sea urchin control in 6mm pearl nets which only contains scallops and no GSUs; 
2. A sea urchin control in 9mm pearl nets which only contains scallops and no GSUs; 
3. 5 GSUs (medium urchins, 20-30mm) in 6mm pearl nets; 
4. 5 GSUs (large urchins, 30-40mm) in 6mm pearl nets; 
5. 5 GSUs (medium urchins, 20-30mm) in 9mm pearl nets; 
6. 5 GSUs (medium urchins, 30-40mm) in 9mm pearl nets 

All pearl nets will be stocked with 2” scallops at 20-30% lantern net bottom coverage (approx. 10 scallops per pearl net) following the same practices and sources of scallops (and GSUs) as Objective 1 for comparability. Gear mesh sizes were chosen to represent the mesh sizes used in Obj. 1, where biofouling reduction was evident, and from previous pilot trials which used 5-6mm mesh and showed less pronounced biofouling reduction. Urchin sizes and densities are also based on comparable sizes and densities used across both trials. 

Sampling, data collection and analysis for Objectives 1 and 2 

Objective 1 data analyses are almost completed, and objective 2 has not been started yet. 

PI Elba visited the farm with Grower Hunt at the 10 week mark of the Objective 1 experiment to check the progress of the trials. During these visits the following was observed and recorded: the condition of the gear, the level of biofouling (photographed, see methods below), species survival, and all of the GSUs and a subsample of 5 scallops from each treatment replicate will be weighed, measured and photographed for size and shellfish biofouling (see methods below). During the project start and end (and bimonthly subsamples as appropriate), all shellfish will be measured for their shell length and mass and all sea urchins were weighed and measured for the test diameters using a combination of vernier calipers and digital photography against a stationary ruler for scale for digital measurements using ImageJ (Shindelin et al 2012). Urchins and shellfish at the experimental start were grouped by similar sizes to ensure homogeneity before being set out on the farm.  

Similarly, all nets and scallops were photographed against a scale to qualitatively rank the level of biofouling (e.g. Rare: <20% coverage per scallop, Frequent: 20–50% coverage per scallop, and Abundant: +50% organisms per scallop), following Ross et al. (2004), and identify biofouling species on nets and shellfish. All previously mentioned methods will be replicated in the Objective 2 experiment, with the addition of recording weights of the individual nets, as different gear (pearl nets) will be used. 

Baseline and end of experiment samples of shellfish (n = 10 per replicate tier) and all sea urchins were dissected. Shellfish wet tissue mass and sea urchin gonad mass was weighed to determine impacts on market meat of the species. Following international reporting protocols, sea urchin gonad weight was divided by the whole animal wet mass and expressed as a percentage. Gonad color was compared against a sea urchin color card to qualitatively assess whether gonads were marketable in color (bright orange to yellow color) or not (dark brown, gray to black color; Suckling et al. 2011).  

All data were stored on Microsoft Excel (version 16.101.1) and statistical analysis was carried out using R Statistical Software (v4.1.5; R Core Team, 2025). After data met the assumptions for normality (Shapiro-Wilks test) and homogeneity (Levene’s test; p > 0.05), data were analyzed using either an ANOVA nested with treatment replicate (TD, whole animal mass, size, adductor muscle mass,  GI, and net and shell biofouling) or a One Way ANOVA (survival). Where significant differences occurred (p < 0.05), a post hoc analysis was conducted using Tukey’s for balanced data sets or Bonferroni’s for unbalanced data sets to determine where treatment difference occurred (Underwood, 1996). Ranked data (mesh openings and gear biofouling) were analyzed using Fishers Exact tests, and a Benjamini - Hochberg correction was conducted due to reduce errors arising from multiple comparisons (Dytham, 2022; McDonald, 2014; Sokal & Rohlf, 1969). Proportional data (survival, GI) were arcsine transformed before analysis in order to improve normality, following approaches outlined by Dytham, (2022) and Sokal & Rholf (1969). 

Similar statistical analysis will be utilized for objective 2 as applicable. 

Objective 3: Increase awareness and grower uptake of green sea urchin aquaculture. (In progress) 

Key updates will be generated from results from the above objectives collated, analyzed, interpreted, and discussed across the whole project team through email communications and team update meetings throughout the project duration. After agreeing on the interpretation of the data and the technical guidance production information to be disseminated to stakeholders, this information will be collectively used to promote awareness of and technology transferred to regional industry via the GSU aquaculture interest email list (Managed by Advisor Suckling and collaborator Eddy), the NOAA Sea Grant extension network via my previous role as a Sea Grant Community Engagement and Communications Fellow, and via talks at events such as the Northeastern Aquaculture Conference (NACE), the Department of Marine Resources annual green sea urchin research forum (initiated in 2023 and often live streamed online to the broader region) and the Sea Urchin Zone Council (Project collaborator Eddy is the Aquaculture representative) which is attended by our targeted stakeholders such as fishers, shellfish and seaweed growers, processors, harvesters and permitters. In conjunction, it will be embedded into education at the University of Rhode Island where many aquaculture and fisheries students end up working in regional industry as growers and eventually as farm owners. More details on the outreach plans have been provided in the outreach plan section of the proposal below. To measure the impact of these outreach efforts, we will quantify the number of talks, attendees, and email/network recipients, and for effectiveness the number of new growers requesting to join the GSU aquaculture interest email list, seed requests and new GSU uptake by growers to via collaborator Eddy.