Never Underestimate the Importance of a Stringy, Brown Mass

Sargassum, not to be confused with sarcasm, is a genus of large brown seaweed (a type of algae). An adornment of berry or grape-like structures (pneumatocysts) filled with air adds buoyancy to the plant, allowing it to spend its life in enviable fashion – floating along on the surface of the ocean. Granted the stringy, brown mass may be off-putting in appearance, it does serve an important purpose. While seemingly enjoying a life of leisure, great mats of the plants serve as vital feeding and breeding grounds for marine life and can stretch for miles. Fish, sea turtles, marine birds, crabs, shrimp, and more set sail on this floating habitat. In addition, it provides a nursery area for a variety of species, including mahi, tuna, and marlin. Even in its death, this indomitable plant continues to give of itself. Upon losing its buoyancy, it falls to the floor of the sea, providing energy in the form of carbon to fishes and invertebrates, making it an important part of the deep-sea food web.

Sargassum is prevalent in the Gulf Stream. One of the most fascinating phenomena in nature, the Gulf Stream is a warm and swift Atlantic Ocean current that originates in the Gulf of Mexico, stretches to the tip of Florida, and follows the eastern coastlines of the United States and Canada. It is an essential resource for North Carolina’s offshore fisheries due to its incredible biodiversity and pockets of productivity in an otherwise barren environment. The Stream is a major driver of global climate and an important vehicle for nutrient cycling and nitrogen fixation in the open ocean, or pelagic, environment because of the Sargassum communities found in its waters.

Nitrogen is a macro-nutrient required by all living things; however, atmospheric nitrogen needs to be “fixed” through a series of steps to become biologically available to organisms. Because it is the limiting nutrient in the pelagic environment, any process that delivers biologically available nitrogen to the system could increase primary productivity which cascades up the food chain. The microorganisms that live on Sargassum, known as the epiphytic community, are suspected to play a critical yet vastly underestimated role in the nitrogen fixation process.

The Gulf Stream is also a significant potential source of renewable power generation. The North Carolina Renewable Ocean Energy Program (NCROEP), a Coastal Studies Institute-led research initiative that attracts state and outside funding, conducts interdisciplinary research, development, and testing of hydro-kinetic energy harvesting strategies, with an emphasis on Gulf Stream power assessment and device siting.

What impact, if any, would measures and devices needed to harness the power of the Gulf Stream for grid-scale renewable energy have on the surrounding environment and offshore ecosystem?

Enter CSI research scientist and NCROEP Associate Director, Dr. Lindsay Dubbs, and UNC-Chapel Hill graduate student, Claire Johnson. Their team of scientists, students, interns and volunteer researchers is part of an ongoing study specifically interested in examining nutrient cycling and primary productivity within Sargassum and surrounding communities. They hope to better understand just how much nitrogen is being added to the environment by the epiphytic and planktonic communities associated with the Gulf Stream’s Sargassum patches. Their work involves a series of measurements and experimental procedures conducted in the field, lab, and through geospatial analysis.

This, and additional research conducted within the NCROEP Environmental and Regulatory Assessment, is essential to minimizing and mitigating any potential impacts that marine hydro-kinetic devices may have on offshore ecosystems. While utility-scale wave and current energy installations do not yet exist, ocean energy extraction has gained increasing attention as a viable component of the energy mix of the future. The Sargassum nutrient cycling and productivity research being conducted by CSI will be the most recent and thorough study ever conducted on this type of fixation, therefore providing valuable and novel insights to guide the future of renewable ocean energy development through the NCROEP.