Progress report for FNE24-082
Project Information
The objective of the project is to measure the success of rearing oysters and urchins together -- will farming urchins and oysters together result in better survivorship within either or both species? Are they particularly effected by environmental fluctuations in temperature or salinity? Which type of grow out gear, bottom or surface, is most user-friendly for the farmer to grow urchins and oysters together? Does either type of grow out equipment result in better survival and/or growth? Are urchins able to reduce biofouling on either type of grow out gear or on oyster shells and if so, is there a noticeable effect on oyster growth or measurable reduction in farming effort? Another key part of the study is to see if urchins and oysters can survive the annual overwintering/hibernation process that begins for oysters in November and ends in April.
Aquaculture is a growing industry along the Maine coast but a small number of farms are multi-species farms. The grow out gear, equipment, and process is very specific for each species--creating monoculture sea farms. However, urchins carry the potential to be farmed alongside oysters in a mutually beneficial way. Urchins primarily eat algae and kelp that naturally occur as biofouling on oyster farms as well as encrusting animals that are competing filter feeders and pests. Prior studies have shown success in growing urchins and shellfish such as oysters together-- with urchins reducing biofouling by as much as 50% (e.g. McBride, 2005; Harris, 2014). The need to clean biofouling of oyster gear throughout the season in order to maintain the water flow that promotes oyster growth is one of the reasons farming oysters is so incredibly labor intensive. At a minimum, we spend 50% of our time or 100 hours each week pressure washing or brushing bags, flipping cages to prevent biofouling, or scraping barnacles, jingle shells, and other pests that fix to oyster shells and gear. If urchins can provide at least 50% reduction in biofouling, this has the potential to save up approximately $1,000 per week in labor and gas costs. Their potential on the farm would also not only be limited to mitigating biofouling. They could also provide a secondary market product for oyster farmers--not only making the oyster farming process more efficient, but increasing the financial viability of farms. A 2.8 oz. tray of Maine-grown uni (harvested from roughly 4-5 market size urchins) currently retails for $35 (SOPO Seafood 2023).
The potential for farming urchins is especially interesting due to their reduction in number from overfishing in the 1990's and other ecological changes since (Hunter, 2022). Restoring populations via aquaculture could help build a farmed market for the Northeast's high quality uni. With Maine's growing number of oyster farms, this project would investigate the potential benefits for growing urchins as a companion species on existing shellfish farms. I would be looking at the effects of urchins on oyster growth and biofouling, test out the success of rearing urchins in two different types of existing aquaculture gear used for shellfish production, and explore the results of urchin and oyster cohabitation at various temperatures, densities, and depths.
Any noticeable biofouling mitigation by urchins would assist growers in the shellfish industry to reduce manual labor and potentially create a better growing environment for oysters. Farming these species side-by-side utilizing existing farm equipment could add a valuable secondary crop to already functioning farm operations. A multi-species farm not only has added value--it is also a more sustainable and resilient farm. If an investigation like this can help promote the production of several complementary species at once, it is a benefit to the overall marine ecosystems in which those farms exist. Drawing growers' attention to polyculture and even multi-trophic farming practices, using a variety of depths at their sites to create a vertical farming system, could help create additional environmental benefits for lease sites up and down the coast.
Cooperators
- (Researcher)
- - Technical Advisor
Research
The project compared urchin and oyster grow out on two different existing permitted farm sites: my standard lease (CIPL) located in a protected inlet with shallower depths and warmer temperatures and one of my limited purpose lease sites (LGRA316) exposed to colder offshore water with greater depth. At each site two varieties of equipment were placed: tiered bottom cages and surface cages each containing oysters and urchins. In the early summer, oysters from the 2022 year class were measured with a flat ruler to select those between 1.5-2" in length. Two liters of 1.5-2" length oysters were placed in each 9mm mesh oyster bag along with 2 green sea urchins approximately 1.5" in width with spines obtained from the project's key collaborator, Luz Kogson, at the Maine Center for Cooperative Aquaculture Research. Three bottom cages and three surface cages were placed at each site and stocked with 36 grow out bags containing identical amounts of oysters and urchins. We attached HOBO loggers to a surface cage at each site in order to collect daily temperature and salinity data. In addition we collected weekly temperature and salinity data manually with a thermometer and refractometer. Temperature data was recorded both at the surface of the water and the bottom using a digital thermometer with wired probe. Sites were visited weekly in a 19' Carolina work skiff with Electradyne hauling motor. At each weekly visit to the inner and outer sites, a random selection of 3 oysters were pulled from a grow out bag in a surface cage and a bottom cage to collect length, width, height, and new growth measurements. The length was measured from hinge to center of beak, width measured from side to side at the oyster's widest point, height measured with calipers from bottom shell to highest point on the top shell, and new growth measured the widest section of flakey somewhat transparent and brittle edge lining the oyster's beak. At each visit urchins were also removed from the selected bag to check for survival. At this time we measured urchin total width with spines using calipers. All data was collected in a WetNotes notebook and later transferred to a spreadsheet document. Data was collected from July 12th to November 18th. At the final visit to each site, every bag was removed from the grow out equipment. Oysters and urchins from each bag were emptied in to a fish basket to note overall survival. Urchins were counted. Empty shells of oysters were noted in categories of zero (good), 1-2, 2-3, or 3-4. Photos were collected noting biofouling inside and outside grow out bags.
Initially, we weren't able to pickup the urchins from the Center for Cooperative Aquaculture Research until later in the spring than we'd planned--delaying the start of our data collection until early July as opposed to June.
On average the outer site on bottom and inner site on surface produced the largest oysters. All oysters measured between 2.9 and 3.14 in in length--showing substantial growth from the 1.5-2" length that they were stocked at. All sites had good survival of oysters and urchins with no major die-offs. Temperature differences between the two sites were greatest during the warmer months with 2 degrees separating the surface temperatures (depending on tide). As temperatures cooled the differences in water temperature between the two sites narrowed.
Neither surface or bottom cages at either site contained oysters that grew as large as the control: a site that contained oysters stocked at the same length and density and flipped weekly to control biofouling. These oysters on average were 1/4-1/2" longer than the oysters grown with urchins.
The following graphs display temperature and salinity gathered by the HOBO loggers deployed at the two different sites:
By growing oysters and urchins together as companion species, we hoped to observe symbiotic effects on both species including the enhancement of oyster growth due to the reduction of biofouling on grow out bags as well as the parallel growth of urchins. We did not see any oyster or urchin loss due to their combined growing space and therefore concluded that they did not harm one another. Initially we worried that urchins would potentially kill smaller oysters with weaker shells. We were also worried that the urchins would potentially not have enough food through biofouling alone and would die. Neither urchins nor oysters were effected in these ways. The urchins did not harm the 1.5-2" oysters initially set in the bags. The urchins were able to survive the growing season without additional food (kelp) other than the biofouling algae within the bag. Because urchins cannot be exposed out of water for prolonged lengths of time, we were not able to use the sun drying feature of the grow out gear to kill off excessive biofouling. While this was known before the experiment began, what became apparent while it was underway was that the urchins could not counter the level of biofouling effectively. Over time, the inside of the 9mm mesh bags were overcome with sea squirts--a problem that we do not normally see in such severity in our regularly flipped surface cages. The sea squirts appeared to be especially prevalent in the 2024 growing season and they clogged up the 9mm mesh bags reducing the waterflow and growing space and caused the bags to become so heavy that they were hard to collect and handle. In the future, because urchins cannot be exposed out of water, they would either have to be collected before the flipping/drying process or the bags and cages they were placed in would require additional manual cleaning--defeating the purpose of growing urchins and oysters as companion species. An improvement based on the results here could require that they be grown in bottom trays and cages only or free-range on a bottom culture site (although they would then be subject to predation). Because the sea squirts were so packed within the grow out bags, they will likely effect the survival of both oysters and urchins overwintered in them.
Education & Outreach Activities and Participation Summary
Participation Summary:
Throughout the summer, we hosted 3 different tours with private parties where we walked through our ongoing urchin/oyster grow-out experiment. The tours were informal run-throughs for more formal tours that we are arranging for 2025 season--where we will hire out a 36-passenger boat to visit the farm throughout the summer months. We also plan to publish photos and results of the process on our social media and website.
Learning Outcomes
While the study is still underway, the learning benefits are among our farmers specifically. The study has been so beneficial for our farmers--the time to gather data on temperature and salinity and make general observations weekly. We look forward to sharing our results with the greater aquaculture community.
Project Outcomes
With the project still in progress we cannot yet report on outcomes. However, we are looking forward to seeing the project's completion this spring. We already have recommendations for improvements to the work accomplished in 2024--including some potential new trials growing urchins and oysters together in bottom trays.
Looking back, we would revise the stocking density and number of bags included in the trial. Because our methods set out that we stock oysters between 1.5-2" with three surface cages and three bottom cages at each site, we needed to stock more than 70 9mm bags for grow out. While we initially thought the number of bags would provide an adequate sample size and therefore more accurate results, the process of hand measuring oysters to that specific length was incredibly time consuming and delayed the start of the grow out.