Co-culturing green sea urchins with European flat oysters to control biofouling in oyster cages
This is a suggestion for a Degree Project for Bachelor's and Master's levels at the Department of Marine Sciences. Degree projects at the Department of Marine Sciences are done independently and must be written and assessed individually.
Subject: Marine Biology
Start: Autumn 2026
Level: Bachelor or Master’s thesis 30 - 60 hp, suitable for students in marine biology, ecology, or environmental science
Supervisor: Susanne Lindegarth, Nadjejda Espinel Velasco
Location: Tjärnö Marine Laboratory
Background
Oyster aquaculture, particularly in suspended cages or trays, is highly susceptible to biofouling. Fouling organisms (e.g., tunicates, barnacles, mussels, algae) compete for food, increase gear weight, reduce water flow, and increase handling time, leading to significant economic losses.
The European flat oyster (Ostrea edulis) is a species of significant ecological and commercial value. A major problem for all aquaculture operations at sea is biofouling by unwanted organisms on the farming equipment. One method to control biofouling is to use sea urchins in the farm cages, which graze upon all types of newly settled organisms, hence prevent growth of unwanted species. However, O. edulis is generally considered more sensitive to environmental stressors and handling compared to other oyster species such as the Pacific oyster (Magallana gigas).
Therefore, the use of a biological control method like co-culturing with sea urchins must be carefully evaluated to ensure it does not negatively impact growth and survival of the flat oysters.
Project Description
This experiment - based on Sterling et al. (2016) - aims to use the grazing activity of green sea urchins (Strongylocentrotus droebachiensis) to biologically control biofouling within oyster cages and to determine the optimal urchin density that balances biofouling mitigation with the health and growth of the oysters. This approach could offer an environmentally benign method that also provides a secondary marketable product – ripe sea urchins.
Main research questions:
- Can green sea urchins effectively control biofouling on and within O. edulis cages without negative harm to the oysters?
- What urchin stocking density achieves optimal biofouling control without negatively impacting oyster growth or survival?
- How does urchin stocking density affect urchin growth (somatic and gonad) and survival in co-culture system?
Requirements
The work will be done at Tjärnö marine laboratory in collaboration with Ostrea AB at Sydkoster. Infrastructure to test effects of sea urchins on biofouling will be set up at multiple sites around Tjärnö and Kosterhavet.
Some experience from fieldwork at sea is required, such as small boat operations.