Innovations Research Updates: Gretchen Grebe

SEANET Innovations Theme Fellow, Gretchen Grebe, is a PhD candidate in the Aquaculture and Aquatic Resources program of the School of Marine Sciences at the University of Maine. Gretchen is working with her graduate advisors, Dr. Carrie Byron (UNE) and Dr. Damian Brady (UMaine), to better understand both the source of nutrients in nearshore Casco and Saco Bays and also how these nutrients support the growth of kelp. Additionally, Grebe’s research helps to identify patterns between the growth of cultivated Sugar kelp and nutrient dynamics, which is important because many kelp growers have little information about the timing and amount of nutrients present at their sites.

Gretchen Grebe out collecting samples in Saco Bay

Grebe is in the middle of her fourth field season, collecting environmental observations and Sugar kelp tissue samples. She started sampling in December of this year and will continue until the kelp is harvested from growing sites in May. When sampling,  Grebe and her helpers measure the amount of light available to the kelp on that day by lowering a LI-COR Spherical Quantum Sensor to the depth of the longline (2 meters). They also collect water samples on the water’s surface and at the depth of the longline. Kelp tissue samples are collected from multiple spots along the longline. This winter, tilt current meters from Lowell Instruments were suspended at two of Grebe’s sampling sites to better measure the change in ocean current direction and magnitude throughout the growing season.

Back in the lab, Grebe analyzes the collected water samples for nitrate nitrogen and phosphate concentration, pH, and salinity. The kelp tissue samples are measured using a suite of growth parameters including blade length, width, stipe length, and total weight. A subset of these samples are prepared for tissue analysis which quantifies the amount of total nitrogen, total carbon, nitrogen isotopes, and carbon isotopes in the kelp tissue. Some of this tissue is also be used in assays to quantify the amount of enzyme-driven nitrate assimilation in specific kelp blades. Grebe is working on statistical analyses comparing the observed environmental parameters to growth and tissue composition of the collected kelp. She is comparing data across seasons and sites so that she can provide recommendations regarding future siting and management of kelp aquaculture.

Grebe recently presented research updates at the Northeast Aquaculture Conference and Expo (NACE) and at the World Aquaculture Society (WAS) meeting. She is currently making revisions to a manuscript that takes a higher-level look at the human and natural systems supporting kelp aquaculture in Maine and makes recommendations to ensure the sustainable development of kelp aquaculture in the Americas and Europe. The paper will be published in an open-access journal this summer to ensure that the findings are accessible to all stakeholders.