Addressing Key Challenges in Green Sea Urchin Aquaculture

The following approaches will be employed to address the previously described project objectives: 

Objective 1: Determining the ideal stocking density and size classes for shellfish integration. 

This will be 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 lantern net cages (15mm mesh size) suspended on horizontal long lines which are 7 feet below the sea water surface. Each lantern net has approximately 6 feet of line, which places the top of each lantern net approximately 13-15’ below the surface.

The trial will comprise 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 will be conducted in lantern net cages described above. Each treatment will be held in a single lantern net tier, and replicated across five separate lantern net cages. Within each lantern net cage the treatment tier location will be randomized to account for light and depth influence (Sterling et al. 2016; Table 1). These GSU size classes were chosen to build off of previous trials (described in the Project Focus section). The size classes of GSUs are realistic sizes for rapid growing juveniles that can be achieved in a hatchery setting, and for hatchery supplied GSU seed which have been grown on the farm. If mass produced in monoculture at the farm, the benefit of integrating larger size classes of farm grown GSUs with scallops would be to help boost gonad growth in preparation for the market (>52 mm size).

Sea scallops will be maintained in all lantern net tiers at a constant density of 30% lantern net tier bottom coverage, which at the (approx. 2”) size we will use will equate to 30 scallops per lantern net tier. For this trial, GSUs will be 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 will be sourced from Casco Bay Mooring’s farm stock. 

A HOBO onset data logger (Model U24-002-C) will be deployed with the experiment to measure and record seawater temperature and conductivity (salinity) every 15 minutes at the farm location. These are not monitored currently by the grower.  Having this data will allow us to connect any changes in conditions to shellfish and urchin performance and provide more information on their tolerances needed by the grower and by the broader GSU industry and can be shared in Objective 3.

Objective 2: Determine whether green sea urchins can be reared on the outside of gear to reduce external net biofouling. 

This trial will also be conducted in parallel with Objective 1, at the Casco Bay Mooring farm site and will use 13” pearl nets with 9mm mesh size. While pearl nets are not typically used at this farm, they are utilized in other scallop farms across the region (e.g. Vertical Bay Maine, Peter Andrews). Their small size and independent units provide an easy handling approach to carry out this important proof of concept study. 

This trial will apply the following treatments: 

1. A sea urchin control which only contains scallops and no GSUs;
2. A low stocking density of GSUs (6 per pearl net) on the external pearl net surface, enclosed using a 12.7 mm (½”) mesh size predator exclusion nylon mesh netting;
3. A high stocking density of GSUs (9 per pearl net) on the external pearl net surface, enclosed with netting;
4. A net control which only contains scallops,has  no GSUs and has the external netting to determine whether the presence of the netting alone influences biofouling on the external pearl net surface.

The GSU stocking densities and size (42 mm) have been adopted from the best performing results from Sterling et al. (2016) who enclosed GSUs onto mussel long lines using a net enclosure (described in Previous Work section) to allow us to determine how well these methods translate to alternative gear in aquaculture and enable study comparisons for performance. All pearl nets will be stocked with 2” scallops at 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. 

Sampling, data collection and analysis for Objectives 1 and 2

PI Elba will visit the farm with Grower Hunt every 2 months to check the progress of the trials. During these visits the following will be 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). This will allow the team to assess trial progress and act as a backup in case of unlikely losses of nets during the project.

During these visits, PI Elba will also download seawater parameter logger data, clean the logger of fouling, reset it, and as needed calibrated for continued measurements.

During the project start and end (and bimonthly subsamples as appropriate), all shellfish will be measured for their shell length, width and height and mass and all sea urchins will be 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 will be grouped by similar sizes to ensure homogeneity before being set out on the farm. 

Similarly, all nets and scallops will be photographed against a scale to qualitatively rank the level of biofouling (e.g. Rare: <2 organisms per scallop Frequent: 2–5 organisms per scallop Abundant: 5+ organisms per scallop), following Ross et al. (2004), and identify biofouling species on nets and shellfish. Fouling species and the nets will be weighed wet and dry to quantitatively determine biofouling presence. Additionally, to quantify fouling per tier in the first trial, a square of mesh of standard size will be randomly chosen and photographed to measure percentage of net occlusion (PNO) following methods of Sterling et al. (2016). 

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

Data will be analyzed using R Studio to determine the treatment effects (GSU size, stocking density, use of external net) on biofouling, survival, growth, wet tissue mass, gonad index and color for shellfish and sea urchins and environmental data (temperature and salinity) within the farm. Treatment differences will be analyzed using either Nested ANOVA via a General Linear Model or One-Way ANOVA after testing for normality and homogeneity of variance (p > 0.05). After significant ANOVA results, Tukey’s or Bonferroni’s Pairwise Comparisons will be utilized to determine which treatments differ for balanced and unbalanced data sets respectively. Non-parametric Kruskal Wallis tests will be carried out where heterogeneous residual variability remains after transforming data following Sokal and Rohlf (1995) or for qualitative data. The sample size in each trial will be sufficient for the proposed statistical testing.

Objective 3: Increase awareness and grower uptake of green sea urchin aquaculture.

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 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.