by Priya Shukla
In the past few years, multiple subsequent oceanographic events have decimated global kelp forest populations, having cascading effects on critical species living within them and economies that rely on them. Perhaps these charismatic systems’ sensitivity to their ambient environment may serve as ecological indicators of things yet to come.
A southern California kelp forest with fishes, algae, and surfgrass. Photo Credit: M. Ward
I was introduced to kelp forests as a system within which top-down processes can be easily observed (Estes & Palmisano 1974) and altered by humans (Estes et al. 1998). The influence that humans wield over this complex system intrigued me and I was determined to understand how human-induced climate change influenced the earliest and most vulnerable life stages of the Giant Kelp, Macrocystis pyrifera* (Shukla & Edwards 2017). I studied this incredible ecosystem during the Warm Blob of 2014 (Bond et al. 2015) and the El Niño of 2015 (Walsh et al. 2018) and was astonished by the extent to which human activity had shaped this seemingly aloof ecosystem.
Kelps are renowned for their rapid growth rates (Brown et al. 1997), immense capacity for phenotypic plasticity (Demes et al. 2009), and viscous alginates found in many household products (Kovalenko et al. 2011). Their three-dimensional structure harbors numerous flora and fauna (Steneck et al. 2002) – even the holdfasts that anchor them to the seafloor are teeming with life (Hauser et al. 2006)! The dense forests that kelps form underwater influence hydrodynamic conditions (Rosman et al. 2007) and entrain life-sustaining nutrients (Zimmerman and Kremer 1984). Their resilience and recovery in the aftermath of sea otter extirpations (Estes et al. 1989) and sewage pollution (Tegner et al. 1995) suggest that kelp forests may be inured to the impacts of anthropogenic climate change. Yet, it seems the opposite is true; these charismatic organisms may instead serve as harbingers of impending change in the coastal oceans.
Kelp forests are known to exist in temperate regions, where the waters are cold and nutrient-rich (Hernández-Carmona et al. 2001). The Giant Kelp’s longevity is unknown, as its dense aggregations are ripped from the seafloor during fierce storms every winter and during even more ferocious storms caused by El Niño events every four to seven years (Seymour et al. 1989). The warm, nutrient-depleted waters that El Niño events bring cause kelp forests to degrade and portend the impacts of climate change (Edwards 2004). Whatever kelp remains is consumed by sea urchins, which form “barrens” in these formerly kelp-dominated areas (Lawrence 1975). Kelp forests and urchin barrens have long been considered alternative stable states in the ecological literature (Mann 1977), yet this terminology does not feel appropriate in this moment. For, in the clearings devoid of kelp, non-native species that arrive by transoceanic ships take hold – species whose rapid life histories permit them to tolerate and/or capitalize upon the stressors that humans impose upon the ocean (Sullaway et al. in prep). It seems that we are no longer shifting between different phases of a single ecosystem. Rather, we are observing the emergence of a new ecosystem altogether – one inadvertently created by humans.
To ameliorate the impacts of human-derived change, there are efforts underway to perform managed relocations of kelp (Ford and Meaux 2010) and remove grazing urchins (Barboza 2013). Yet, these strategies alone cannot mitigate rising temperatures and CO2 levels, nor do we fully understand how well they will withstand changing oceanographic conditions or coups by non-native species. Given that the disappearance of kelps heralds the onset of an entirely new era of unprecedented events**, it is not only valuable, but necessary to consider their transience when evaluating their potential for being preserved (Dayton et al. 1998, Krumhansl et al. 2016). As we fight to conserve kelp forest ecosystems, we should also use their distinct susceptibility to warm waters as an indicator of not only climate change (Reed et al. 2016), but large-scale ocean change.
* My knowledge of kelp forest dynamics was cultivated in San Diego, California where the Giant Kelp is king and all other kelps in the region (except for the deepwater Elk Kelp – Pelagophycus porra, which is not nearly as well-studied) are shorter in stature and occupy the “understory”. When I think about human impacts on the kelp forest, I am envisioning the loss of these globally distributed charismatic megaflora. However, there are numerous other kelp species whose responses to environmental change may deviate from those that I describe here.
** Because Northern California kelp forests failed to rebound after the Warm Blob and El Niño in 2014-2015, the red abalone fishery was closed in 2017 to prevent the extinction of this culturally and ecologically important species (Callahan 2017).
Author Biography: Priya Shukla is an ocean and climate scientist at UC Davis’ Bodega Marine Laboratory. She received her undergraduate degree in Environmental Science and Management at UC Davis and earned her Master’s in Ecology from San Diego State University. Priya is a technician with UC Davis’ Bodega Ocean Acidification Research (BOAR) group, where she works on several projects to better understand and prepare for the effects of climate change on our coastal oceans. Priya uses science communication to bridge issues concerning social justice, rapid environmental change, and the scientific community. Connect with Priya @priyology and on her blog The Prosaic Mosaic.