RI researchers yield new clues in harmful seaweed blooms

Much like the sudden onslaught of weeds overtaking your garden, algal blooms can transform seemingly out of nowhere from coastal nuisance to massive ecosystem threat.

Groundbreaking research from a Rhode Island team of scientists now reveals critical new details about the life cycle of these macroalgal blooms that will aid in better management and protection of important coastal resources.

Ulva blooms
A macroalgal bloom mat covers a beach in Greenwich Bay.

Reported in PLOS ONE Friday, Feb. 26, the findings detail two, separate life history phases of Ulva compressa and Ulva rigida — two common species of seaweed or sea lettuce in Rhode Island’s 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,” says Carol Thornber, University of Rhode Island associate professor and Rhode Island NSF EPSCoR principal investigator. “This gives us a much better understanding of how these blooms reproduce, which gives us insight to blooms in other parts of the world.”

3. URI student_samples
Working with the Thornber lab, a University of Rhode Island student collects macroalgal bloom samples.

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 put on full display 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 recreational and commercial fishermen, Thornber says, 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 light and deplete oxygen in the water column, setting off a chain reaction that kills sea life and forms dead zones.

Thornber, an ecologist, collaborated on the project with J.D. Swanson, Salve Regina University associate professor, a geneticist and developmental biologist. With seed funding for their project from a Rhode Island Science and Technology Advisory Council (STAC) collaborative research grant, the team included URI master’s student Elaine Potter, lead author on the journal article, and URI and SRU undergraduates. A key piece of RI EPSCoR equipment — a flow cytometer — helped tease out the different genetic phases of the blooms.

Data collected by the Thornber lab from sites in Greenwich Bay, monitored on a monthly basis since 2005, indicated the location and spread of the blooms throughout the growth cycle. With his genetics expertise, Swanson helped guide Potter in the effort with the flow cytometer to define the life stages.

Part of the importance of gaining this understanding is grounded in better management of the environmental and economic threat. On the flip side, the genomic work reveals the molecular mechanisms taking place; details that shed light on factors that cause the blooms.

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. The flow cytometer can distinguish cell by cell which phase the algae is in, at different times during the bloom-forming season. The team found that during the summer months, the two species presented the two life phases, but in different abundance.

The researchers found Ulva compressa prevalent throughout June, July, and August with a predominance of gametophytes, the haploid phase, during the waxing and waning months of June and August. Heading into the height of bloom season in July, gametophytes and sporophytes, the diploid phase, appeared in equal abundance.

For the Ulva rigida, gametophytes figured predominantly throughout the June to August bloom season.

Ulva blooms on the beach
Macroalgal blooms smother a Greenwich Bay beach during the summer season.

Potter, who completed the monthly surveys and collected the Ulva samples, says that at the outset the team had no idea what it might find since very few studies focused on ploidy (the number of sets of chromosomes in a cell) in macroalgal blooms. And, none of those studies took place in Narragansett Bay.

She says she ran her first successful samples through the flow cytometer and saw some contained about double the amount of fluorescence as the others: “I thought, ‘Does this mean that some samples are haploid and some are diploid?’ It turned out that was the case.”

Swanson, who presented the team’s findings at a November 2015 conference in China, where he was the only molecular talk at the event, says the Rhode Island team has accumulated an advanced data set on Ulva.

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. For example, if there is an edible species that you want to encourage to grow, the team’s genetic work identifies the pathways to fire up development.

By Amy Dunkle | Photos by the Thornber lab