Marine Threat: Kelp



Recent dramatic declines in kelp forests globally have been linked to warming oceans caused by a changing climate.

Kelps (Order Laminariales) are brown algae that occupy 43 percent of the world’s marine ecoregions living along coastlines of all continents except Antarctica (Spalding et al. 2012). They are among the highest primary producers in any environment with extraordinarily high rates of growth and productivity. Kelps are vital to a bio-abundant marine ecosystem due to their role as ‘foundation’ or habitat-forming species, maintaining ecologically diverse communities commonly termed kelp forests. Kelps, and the kelp forest communities that they support, provide a range of critical ecosystem services, including nutrient cycling, biodiversity support, shoreline protection, and fisheries, collectively valued in billions of dollars annually across the globe (Bennet et al. 2016). Kelps are also a source of alginates (thickeners used in many products) and are increasingly being viewed as food sources for humans.

Warming ocean temperatures, caused by global climate change, is causing widespread declines in kelp abundance around the world, in locations as diverse as Norway, New Zealand, southern Australia, and more recently, along the west coast of the United States (Krumhansl et al. 2016). As a result, biodiversity and ecosystem services that kelp forests support are diminishing as well.

It is unknown exactly why kelps are unable to recover and rebound from disturbances, specifically during extended periods of unusually warm waters (Reed et al. 2016). What is known is that kelp forest die-offs are not ubiquitous. An analysis of global patterns of kelp forest change conducted by Krumhansl et al in 2016 found significant regional variations, with some populations declining, some increasing, and some maintaining kelp biomass. Specifically, a few locations in Fjordland, New Zealand, Southern California Bight, and Gulf of Alaska showed increases in kelp abundance over the past several decades, although no explanation of this trend can be found in the existing scientific literature. Importantly, this analysis concluded that more monitoring of kelp forests is essential for understanding the scale of the problem and discovering how unique regional characteristics drive kelp forest abundance.

Beyond the impacts of climate change, the near shore and shallow waters in which kelps grow exposes them to a diverse array of human activities that impact the coastal zone, including harvesting, pollution, sedimentation, and recreation. These localized stressors have documented effects altering fish and invertebrate community composition and causing localized declines in kelp abundance. However, these stressors have not, to date, produced the large geographical scale and rapid complete loss of kelp forests that have recently been observed as an ecological effect of climate-induced changing ocean conditions (Steneck et al. 2002).

California Kelp Context

Since 2014, more than 90 percent of the bull kelp canopy area north of San Francisco to the Oregon border has been lost due to a combination of oceanographic and ecological stressors. Concurrently, populations of sea urchins have exploded due to the widespread loss of their primary predator, the sunflower star due to sea star wasting syndrome (SSWS). A global analysis of trends has shown a decline in the aerial extent of kelp in this region (and extending north) since the mid-1970’s (Krumhansl et al. 2016). Central California kelp forests have also been depleted from overgrazing by urchins but, not to the same extent. Recent studies of kelp forests in central California also show a pattern of large losses of kelp every winter, due to high wave disturbance, (Reed et al. 2011). Giant kelp (Macrocystis pyrifera) in Southern California faces a different suite of potential drivers of change than in northern and central California kelp forests. Historically, poor water quality and sedimentation also have negatively affected kelp in this region although long term trends of kelp biomass have remained stable or shown slight increases (Krumhansl et al. 2016).



Traditional conservation measures (harvest control and protected areas) have had limited, local success in reversing kelp forest declines.

Similar to coral reefs, kelp forest conservation and restoration efforts have been focused on maintaining not just the kelps themselves, but also the complex and diverse communities that comprise kelp forest ecosystems. These ecosystems support a vast array of commercial fisheries as well as important ecosystem services. All of these contribute to the high prioritization of conservation and restoration of kelp systems. While conventional conservation measures, including limiting pollution inputs from land, establishing protected areas, or altering fishery regulations have had some reported localized success, the regional and global outcomes for kelp conservation are not as hopeful (Strain et al. 2015).

Regions such as Western Australia and the west coast of the U.S. have experienced almost a complete extirpation of kelp in a single summer season. The predominant outcome of these events is the transition to what is often referred to as an ‘alternative stable state’ or “phase change” to sea urchin barrens and/or turf dominated reefs (Filbee-Dexter et al. 2018; Ling et al. 2014; Filbee-Dexter et al. 2014). In these instances, conventional efforts to restore sea urchin barrens back to kelp forest ecosystems have reported very limited and localized success. In locations including Tasmania, Western Australia, and Southern California, more restrictive fishery protections for urchin predators such as lobster, in combination with protected area designations, have resulted in some local kelp forest regrowth (Strain et al. 2015; Kriegisch et al. 2016; Bates et al. 2017). While very limited in geographic scope, traditional restoration approaches (such as kelp re-planting) have also seen some success in encouraging the re-establishment of associated fish and invertebrate communities. However, locally restored kelp forests remain threatened by warming ocean temperatures.

In summary, the approaches dominating kelp forest conservation include classic restoration and resource management/population control measures, implemented almost entirely by local and regional governing agencies. Private sector engagement, where it exists, is led almost entirely by local fishery/harvest interests, and in California, has been motivated by the recognition of ocean acidification as a worrisome stressor on commercial shellfish. New research suggests that primary producers such as kelp and seagrasses may play an important localized role in mitigating acidification effects on nearby shellfish beds.

Driven initially by commercial rather than traditional conservation goals, new research suggest that on both local and global scales kelps and seagrasses may ameliorate the impacts of ocean acidification and further may play a role in mitigating the impacts of greenhouse gas emissions by sequestering and storing carbon (Krause-Jensen et al. 2016; Chung et al. 2011; Duarte et al. 2013). Research in these fields is nascent and frequently limited by the current short duration of observational time series data. Evidence is fast accumulating for the role of seagrasses in ameliorating the impacts of ocean change and this warrants further research to illuminate biotechnology potential. By comparison, as discussed below, kelp contributions to climate change mitigation are most often considered in the context of aquaculture and biofuels production, and thus divorced from their role as foundational species of complex and important ecosystems. (Please see our section on market alternatives for more information on aquaculture and biofuels.)



Increasing evidence suggests a role for kelps and seagrasses in climate mitigation and in ameliorating impacts of changing ocean conditions. Genomic insights and pilot projects may accelerate progress in this area.

Genomic understanding of kelps is hampered by the sheer size and inherent complexity of kelp genomes. Only a single kelp species has been sequenced to date, but this study, in combination with the transcriptome and metabolome, is providing new insights into the genetic regulation of growth and physiology as well as the impacts of changing temperature or ocean chemistry parameters (Ye et al. 2015; Konotchick et al. 2013).

Currently, genomics is being applied and used in kelp forest conservation primarily as an informational input to evaluate and prioritize among traditional conservation or management options. There is an accumulating body of knowledge revealing genetic differences through the geographic range of giant kelp that indicates adaptation to local environmental conditions (Wernberg et al. 2018). Similarly, genetic data has been used to inform the structure and characteristics of fishery regulations but not to promote production, unlike  terrestrial agriculture (Bernatchez et al. 2017).

Similar to approaches used in terrestrial forest conservation, there may be opportunities to develop  genetic interventions for  other species that maintain the kelp community.  For example, a tiered strategy could be implemented that mixes relatively labor intensive manual control approaches (such as the urchin harvest days sponsored by California Department of Fish and Wildlife Marine Region) with a “repressible lethal” genetic approach to diminish the reproductive capacity of urchins. Another approach would be to facilitate adaptation through genetic intervention for sea star wasting disease. This would have the benefit of maintaining sea star populations at levels that naturally control the prevalence of urchins.

Note: The genetic control of invasive and/or irruptive species like urchin is described in more detail in a subsequent section of this report.



For kelp forest ecosystems, there are very few examples of research collaborations between marine conservation ecologists and the ‘-omics’ fields of study; at least in so far as evidenced in the literature. This lack of transdisciplinary research presents a barrier to rapid progress, but creative convening of thought-leaders in the respective fields of study could provide a path forward.

Lack of genetic and genomic data inherently limits the insights that become possible through comparative genomics applications or derivative research trajectories (e.g., transcriptomics, metabolomics) that begin to link genetic information to functional consequences.



Jenn Caselle, University of California Santa Barbara, Marine Science Institute

Dan Reed, University of California Santa Barbara, Marine Science Institute

Mike Graham, Moss Landing Marine Laboratory

Craig Johnson, University of Tasmania


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