The findings, published in the Journal of Phycology, come at a pivotal moment. Sugar kelp is one of the dominant species in Maine’s kelp forests, providing food, habitat, and clean water that support a rich marine ecosystem. It is also the biological bedrock of the state’s burgeoning kelp aquaculture industry, the largest of its kind in the United States, which relies on the annual harvest of reproductive tissue from wild kelp populations. As ocean warming continues to drive the steady decline of these forests, understanding the genetic architecture of what remains has become an urgent scientific and economic priority.

Senior Research Scientist Doug Rasher, the study’s senior author, and his team have published several previous studies documenting how rising water temperatures are eroding Maine’s kelp forests. That loss has cascading impacts on coastal ecosystems and threatens the wild resource upon which the aquaculture industry depends. Responding effectively, the researchers argue, requires a detailed map of the structure and potential genetic barriers among the remaining forests.

“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.”

To build that map, the team collected genetic material from sugar kelp at 11 sites spanning Maine’s “outer coast.” These locations were chosen deliberately: they are far enough offshore to be subject to the oceanographic forces that influence the entire coastline, yet close enough to shore to be plausible future sources of reproductive tissue for the aquaculture industry. The analysis revealed moderate levels of genetic diversity within each study site and identified at least four distinct populations distributed along the coast.

The evidence suggests that genetic mixing occurs readily between sites within each population, presumably driven by currents dispersing kelp spores during their early life stage. But kelp are mobile for only a very brief window of time before settling on the seafloor for the remainder of their life cycle. Even with the strong currents that characterize the Gulf of Maine, spores seemingly do not travel far, and there appears to be little gene transfer between the four 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 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.”

That distinction carries real-world consequences. Previous research has shown that genetic diversity can bolster resilience to marine heat waves, providing populations with the raw material to adapt as conditions shift. It also supplies critical variation for selective breeding in aquaculture, where traits such as growth rate, thermal tolerance, and morphology can determine the success of a farm. If farmers harvest reproductive tissue from one genetically distinct population and deploy the resulting seed string in waters dominated by another, they could inadvertently disrupt local adaptation—or, conversely, miss an opportunity to match the best-suited genotypes to the right environments.

Earlier studies had examined kelp population genetics at both a much larger scale, across all of New England, and at a very fine scale between adjacent bays. This study is the first to treat the Maine coast as a holistic unit, filling a critical gap between those extremes. “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,” Rasher said.

A technological breakthrough made the study possible. Last year, another research team published the first complete sugar kelp genome—a reference resource that enabled Rasher’s group to map genetically distinct populations with far greater precision than previous marker-based approaches. The genome also opens the door to identifying specific genes unique to each population, genes that might help wild kelp forests adapt to warming waters or prove valuable in an industry setting.

“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.”

The implications extend well beyond Maine. Kelp forests worldwide are retreating in the face of marine heat waves, and restoration practitioners are increasingly turning to genetics to guide their efforts—selecting donor populations that harbor heat-tolerant variants, avoiding outplanting genotypes poorly matched to local conditions, and preserving the evolutionary potential of fragmented populations. Maine’s sugar kelp, with its newly resolved population structure and a complete genome to work from, offers a template for how such efforts might proceed elsewhere.

For the aquaculture industry, the study arrives as the sector matures. Maine’s kelp farmers have built a regenerative ocean farming economy on the annual wild harvest of sorus tissue—the reproductive material from which farm seed is propagated. The new findings suggest that sourcing decisions, long made largely on geography and convenience, could be refined with genetic information: matching seed sources to outplanting sites within the same population, or deliberately drawing on genotypes from populations whose unique gene variants confer advantages in particular environments.

The research 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 of Bigelow Laboratory, as well as Kristina Cammen and Damian Brady of the University of Maine.

As warming continues to reshape the Gulf of Maine, the genetic diversity cataloged in this study represents both a warning and an opportunity—a reservoir of variation that, if managed wisely at the regional scale the researchers advocate, could help kelp forests endure and even thrive in the decades ahead.

Kelp forests are complex marine ecosystems found worldwide, particularly thriving in temperate coastal waters such as those off the Pacific coast of North America, the United Kingdom, South Africa, and Australia. These underwater forests serve as crucial habitats for numerous marine species, supporting biodiversity and providing economic value through fisheries. Additionally, kelp forests play an essential role in carbon sequestration, absorbing CO2 and helping mitigate global climate change. Acting as natural coastal buffers, they also protect shorelines from erosion by dissipating wave energy, underscoring their ecological and socioeconomic importance.

However, escalating marine heatwaves—exacerbated by anthropogenic climate change—have inflicted catastrophic damage on kelp forests, especially along the West Coast of North America. The 2014–2016 North Pacific marine heatwave, dubbed “the Blob,” caused unprecedented warming of ocean waters, resulting in widespread kelp mortality. Compounding this thermal stress is the surge in sea urchin populations, which have proliferated following sharp declines in predatory sea stars. These overgrazing urchins effectively devastate kelp habitats, hindering natural recovery processes and threatening the long-term stability of these ecosystems.

In this context, MPAs have emerged as a promising tool to enhance ecological resilience. MPAs are designated sections of the ocean where human activity, particularly fishing, is regulated or restricted to protect habitats and marine biodiversity. However, the level of protection varies widely among MPAs, ranging from fully no-take reserves to areas permitting considerable extractive activities, including destructive fishing practices like bottom trawling. The UCLA study has focused on MPAs with explicit restrictions on fishing, providing a clearer understanding of how such regulatory measures impact kelp forest dynamics.

By analyzing 54 MPAs and their corresponding reference sites along California’s coast, researchers compared kelp forest cover from 1984 to 2022 using satellite imagery. This rigorous comparative approach allowed them to isolate the effects of MPAs on kelp resilience to heat stress, distinguishing between resistance (avoiding loss) and recovery (regaining cover) after marine heatwaves. The study confirms that kelp within MPAs demonstrated greater post-heatwave recovery relative to unprotected sites, especially notable in southern California, where heat stress and ecological pressures are often more severe.

The mechanisms behind this enhanced recovery appear linked to the protection of key predator species within MPAs. Species such as lobsters and sheephead fish, which prey upon herbivorous invertebrates like sea urchins, help control urchin populations and reduce overgrazing. In the absence of these predators, unchecked urchin populations can decimate kelp stands. Thus, MPAs indirectly support kelp regeneration by maintaining the integrity of trophic interactions critical to ecosystem balance. This trophic cascade demonstrates the intricate connections between species that underlie ecosystem resilience.

Despite these encouraging findings, the researchers caution that the protective effect of MPAs is not uniform across all sites. Variability in environmental conditions, MPA management quality, enforcement efficacy, and local oceanographic features influence outcomes. For example, areas characterized by localized upwelling tend to be cooler and nutrient-rich, fostering kelp populations with greater thermal tolerance, thereby naturally enhancing resilience. Strategically situating MPAs in such dynamic environments could maximize conservation effectiveness.

Moreover, the study highlights the importance of integrating kelp forest monitoring into long-term conservation strategies and global biodiversity frameworks. The Kunming-Montreal Global Biodiversity Framework, adopted at COP15 in 2022, sets ambitious targets to safeguard at least 30% of marine and terrestrial habitats by 2030. This research underscores the utility of kelp forests as bioindicators that reflect ecological health and climate resilience in marine protected systems, thereby providing valuable feedback for adaptive management and policy formulation.

Co-author Emelly Ortiz-Villa, a PhD researcher at UCLA’s Department of Geography, emphasizes that MPAs help buffer kelp against climate-induced disturbances, offering ecosystem services beyond just conservation. The study’s evidence suggests that MPAs not only support biodiversity preservation but also bolster ecosystem functions critical to human well-being, such as carbon sequestration and coastal protection. This multifaceted benefit strengthens the case for expanding and effectively managing MPAs in a warming world.

Senior author Professor Kyle Cavanaugh adds that the results have significant implications for conservation planning. MPAs should be prioritized in regions poised to exhibit natural resilience—such as areas with frequent upwelling events or kelp populations adapted to warmer temperatures—to optimize the return on investment in ocean conservation. Understanding spatial and ecological nuances will be critical to designing MPAs that can withstand escalating climate threats and foster robust marine ecosystems.

The study also draws attention to the pitfalls of designating MPAs without enforcing adequate protections. Many so-called MPAs globally permit activities detrimental to ecosystem health, diminishing their potential to contribute to resilience. Robust enforcement, clearly defined management regulations, and community engagement are necessary components of successful MPAs that can mitigate the increasing frequency and intensity of marine heatwaves.

Looking ahead, the research team advocates for further investigation into the drivers of uneven MPA effectiveness. Identifying the interplay of biological, physical, and managerial factors will equip stakeholders with knowledge to tailor conservation efforts adapted to local environmental realities. Such adaptive management is essential as climate change accelerates and marine ecosystems face unprecedented threats.

This landmark study vividly illustrates the critical role of spatial management in safeguarding the future of kelp forests, ecosystems integral to marine biodiversity and carbon cycling. As the ocean continues to warm, strategies that integrate MPAs with broader climate mitigation efforts offer a beacon of hope for protecting these vibrant underwater forests and the myriad species and communities that depend on them.

Subject of Research: Not applicable
Article Title: Marine protected areas enhance climate resilience to severe marine heatwaves for kelp forests
News Publication Date: 19-Aug-2025
Web References: http://dx.doi.org/10.1111/1365-2664.70112
Image Credits: Ortiz-Villa et al.
Keywords: Marine ecology, Marine conservation, Marine ecosystems, Climate change