Kelp Forests Contain Wealth of Genetic Diversity and Potential

Saccharina latissima, or sugar kelp, is one of the dominant species in Maine’s kelp forests, providing food, habitat, and clean water to support a rich marine ecosystem. It is also the bedrock of the state’s burgeoning kelp aquaculture industry, which relies on the annual harvest of reproductive tissue from the wild.

A new study led by researchers at Bigelow Laboratory for Ocean Sciences provides the most comprehensive assessment to date of the genetic diversity and population structure of sugar kelp along Maine’s coast. The team found moderate levels of diversity within each study site and identified four distinct populations, shaped by the oceanography of a complex and dynamic coastline.

Previous work has shown that genetic diversity like this can bolster resilience to marine heat waves; it also provides critical raw material for an aquaculture industry that is the largest of its kind in the country. The findings, recently published in the Journal of Phycology, highlight the importance of regional management strategies to protect and leverage this genetic resource.

“There’s clearly a wealth of genetic variation along the coast that needs to be considered in management and restoration and that holds great potential for innovation in aquaculture,” said Senior Research Scientist Doug Rasher, the study’s senior author.

Rasher’s team has published several studies showing how warming is driving the steady decline of Maine’s kelp forests. This loss has cascading impacts on coastal ecosystems and is compromising the wild resource that the aquaculture industry depends on. Responding to that loss requires understanding the complex structure and potential genetic barriers of remaining kelp forests.

The team collected genetic material from sugar kelp at 11 sites spanning Maine’s “outer coast.” These areas are far enough out to be subject to oceanographic forces that affect the whole coastline but close enough to shore to be potential sites of industry sourcing in the future, the authors say.

They identified at least four distinct populations across study sites. The evidence suggests that genetic mixing readily occurs between sites within each population, presumably driven by currents dispersing kelp spores during their early life stage. However, kelp are mobile for only a very short window of time before settling on the seafloor for most of their life cycle. Even with strong currents, spores seemingly do not get very far, and there appears to be little gene transfer between populations.

“Having distinct populations means there are different genetic signatures along our coast, and some populations could have individuals that are more or less suited to thrive in varied environments,” said the study’s lead author, Rene Francolini, a former University of Maine PhD student in Rasher’s lab. “That’s important for restoration work or when we think about farmers who might collect reproductive tissue in one location and outplant seed in another.”

Earlier studies have asked these questions at both a larger scale, across all of New England, and a very fine scale between adjacent bays. In contrast, this is the first study to focus on the Maine coast as a holistic unit.

“We wanted to explore questions of genetic diversity within the state of Maine because that’s the spatial scale that’s relevant to managing wild kelp forests, developing effective restoration programs, and establishing best practices in aquaculture,” Rasher said. “We brought it down to the scale that really matters from a management perspective.”

This study was made possible, in part, by the publication by another team last year of the first complete sugar kelp genome. That resource enabled the researchers to map these genetically distinct populations. It also made it possible to begin identifying specific genes unique to each population that might help kelp forests adapt or be useful in an industry setting in the future.

“With a complete genome available, we can actually identify genes of interest and examine whether any of these genes are uniquely expressed in a given population,” Francolini said. “We have yet to be able to connect these genes to a specific function, but when we do, we will be able to pinpoint kelp variants that are uniquely strong candidates for improving kelp conservation, restoration, and aquaculture outcomes.”

This study was supported by the NSF Established Program to Stimulate Competitive Research (Grant #OIA-1849227), the Louise H. & David S. Ingalls Foundation, Maine Sea Grant, and the Nature Conservancy. Co-authors include Research Scientist Robin Sleith, as well as Kristina Cammen and Damian Brady from the University of Maine.

Photo Captions

Photo 1: Fishermen harvest skinny kelp from lines off Chebeague Island (Credit: Atlantic Sea Farms and New England Ocean Cluster).

Photo 2: Shane Farrell (left) and Dara Yiu (right), former University of Maine PhD students in Doug Rasher's lab, prepare for a dive survey to collect samples (Credit: Rene Francolini).

Photo 3: Rene Francolini poses with kelp during a dive survey near Allen Island (Credit: Bigelow Laboratory).