URI, Salve Researchers Study Harmful Seaweed Blooms

Macroalgal blooms cover a Rhode Island beach on Greenwich Bay. As the massive green mats wash up on beaches and take over shallow areas, they block needed light and deplete oxygen in the water column. (URI Thornber lab)

Macroalgal blooms cover a Rhode Island beach on Greenwich Bay. As the massive green mats wash up on beaches and take over shallow areas, they block needed light and deplete oxygen in the water column. (URI Thornber lab)

By ecoRI News staff

Much like the sudden onslaught of weeds overtaking your garden, algal blooms can rapidly transform from coastal nuisance to massive ecosystem threat. Research by scientists at the University of Rhode Island and Salve Regina University reveals new details about the life cycle of these macroalgal blooms that will aid in better management and protection of important coastal resources.

The report’s findings detail two separate life-history phases of Ulva compressa and Ulva rigida — two common species of seaweed or sea lettuce in Narragansett Bay — present during harmful bloom episodes.

“If you are trying to figure out how to control algal blooms, you need to know what part of the life cycle is causing problems,” said Carol Thornber, URI associate professor of biological sciences and the principal investigator for the Rhode Island Experimental Program to Stimulate Competitive Research (EPSCoR). “This gives us a much better understanding of how these blooms reproduce.”

In 2008, in one of the most prominent global outbreaks, a massive green tide deemed the world’s largest macroalgal bloom choked the Chinese coast of Qingdao, the host city for the Olympic sailing competition. The episode demonstrated the devastating effect macroalgal blooms can have on coastal health and marine ecosystems, with economic reverberations that ripple well beyond local and state boundaries.

In addition to making coastal waters impassable for beachgoers, boaters and fishermen, Thornber said the massive blooms wreak havoc on the ecosystem when they die. As the massive green mats wash up on beaches and take over shallow areas, they block needed sunlight and deplete oxygen in the water column, setting off a chain reaction that kills sea life and forms dead zones, she said.

Thornber, an ecologist, collaborated on the project with geneticist and developmental biologist J.D. Swanson, associate professor at Salve Regina University. With seed funding for their project from the Rhode Island Science and Technology Advisory Council, the team included URI graduate student Elaine Potter and URI and Salve undergraduates.

Data collected from sites in Greenwich Bay, which has been monitored monthly since 2005, indicated the location and spread of the blooms throughout the growth cycle. Genetic analysis by Swanson and Potter defined the life stages of the alga.

The researchers found that both species of Ulva spend periods of time in one of two phases, either haploid, with one copy of its genome, or diploid, with two copies. During the summer months, the two species presented both life phases, but in different abundance.

Ulva compressa was found to be prevalent throughout June, July and August. For Ulva rigida, gametophytes figured predominantly throughout the June to August bloom season.

The next step lies in designing DNA markers to track individual blooms. Even though the work is confined to the two Ulva species, the results are applicable to a broader field, according to the researchers.