Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens

Rogers‐Bennett, Laura; Catton, Cynthia A.

doi:10.1038/s41598-019-51114-y

Cited by 282 publications

(329 citation statements)

References 64 publications

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“…This is contrary to many regions of the world that are experiencing transitions from kelp forests to urchin barrens (e.g. Tasmania, Eastern Australia, Norway, Northern California; [12,50,51]. In many regions, the loss of fish or invertebrate predators can result in urchin barren formation [52] but this is unlikely to explain the lack of barrens in southern Argentina as the fish community is made up of smaller species that are unlikely to control urchins through predation.…”

Section: Discussionmentioning

confidence: 88%

“…Globally, there is concern for the future of kelps (Laminariales) as temperate nearshore systems are increasingly impacted by both local stressors such as sedimentation, pollution, overfishing and direct harvest as well as global stressors related to climate change such as marine heatwaves [5][6][7][8][9][10][11]. Marine heatwaves in particular are predicted to increase and have been shown to have dramatic negative effects on kelps [9,12]. Despite a plethora of recent scientific studies and popular media headlines showing dramatic losses of kelp forests, often marked by sharp transitions to low diversity urchin barrens or turf algae, a comprehensive global analysis showed that kelp loss is not uniform, but rather highly spatially variable in both magnitude and direction of change [10].…”

Section: Introductionmentioning

confidence: 99%

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Kelp forests at the end of the earth: 45 years later

et al. 2020

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The kelp forests of southern South America are some of the least disturbed on the planet. The remoteness of this region has, until recently, spared it from many of the direct anthropogenic stressors that have negatively affected these ecosystems elsewhere. Re-surveys of 11 locations at the easternmost extent of Tierra del Fuego originally conducted in 1973 showed no significant differences in the densities of adult and juvenile Macrocystis pyrifera kelp or kelp holdfast diameter between the two survey periods. Additionally, sea urchin assemblage structure at the same sites were not significantly different between the two time periods, with the dominant species Loxechinus albus accounting for 66.3% of total sea urchin abundance in 2018 and 61.1% in 1973. Time series of Landsat imagery of the region from 1998 to 2018 showed no long-term trends in kelp canopy over the past 20 years. However,~4-year oscillations in canopy fraction were observed and were strongly and negatively correlated with the NOAA Multivariate ENSO index and sea surface temperature. More extensive surveying in 2018 showed significant differences in benthic community structure between exposed and sheltered locations. Fish species endemic to the Magellanic Province accounted for 73% of all nearshore species observed and from 98-100% of the numerical abundance enumerated at sites. Fish assemblage structure varied significantly among locations and wave exposures. The recent creation of the Yaganes Marine Park is an important step in protecting this unique and biologically rich region; however, the nearshore waters of the region are currently not included in this protection. There is a general lack of information on changes in kelp forests over long time periods, making a global assessment difficult. A complete picture of how these ecosystems are responding to human pressures must also include remote locations and locations with little to no impact.

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Section: Discussionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Kelp forests at the end of the earth: 45 years later

et al. 2020

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“…In northern California, the recreational red abalone fishery is valued in the tens of millions of dollars (Reid et al ). The California Fish and Game Commission closed the abalone fishery in 2018 for a minimum of three seasons, citing negative effects on abalone populations due to “extreme environmental condition” which broadly included the loss of the only key urchin predator to disease, massive increases in urchin barrens, and widespread losses of kelp (Rogers‐Bennett and Catton ). This is an example of how cascading ecological effects can reverberate through lower trophic levels resulting in devastating environmental effects that require drastic management actions that ultimately have profound economic consequences.…”

Section: Discussionmentioning

confidence: 99%

Trophic redundancy and predator size class structure drive differences in kelp forest ecosystem dynamics

Eisaguirre

Davis

et al. 2020

Ecology

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Ecosystems are changing at alarming rates because of climate change and a wide variety of other anthropogenic stressors. These stressors have the potential to cause phase shifts to less productive ecosystems. A major challenge for ecologists is to identify ecosystem attributes that enhance resilience and can buffer systems from shifts to less desirable alternative states. In this study, we used the Northern Channel Islands, California, as a model kelp forest ecosystem that had been perturbed from the loss of an important sea star predator due to a sea star wasting disease. To determine the mechanisms that prevent phase shifts from productive kelp forests to less productive urchin barrens, we compared pre-and postdisease predator assemblages as predictors of purple urchin densities. We found that prior to the onset of the disease outbreak, the sunflower sea star exerted strong predation pressures and was able to suppress purple urchin populations effectively. After the disease outbreak, which functionally extirpated the sunflower star, we found that the ecosystem response-urchin and algal abundances-depended on the abundance and/or size of remaining predator species. Inside Marine Protected Areas (MPAs), the large numbers and sizes of other urchin predators suppressed purple urchin populations resulting in kelp and understory algal growth. Outside of the MPAs, where these alternative urchin predators are fished, less abundant, and smaller, urchin populations grew dramatically in the absence of sunflower stars resulting in less kelp at these locations. Our results demonstrate that protected trophic redundancy inside MPAs creates a net of stability that could limit kelp forest ecosystem phase shifts to less desirable, alternative states when perturbed. This highlights the importance of harboring diversity and managing predator guilds.

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“…Human recreational activities, capture during spawning, and coastal development activities can interfere with the critical portion of their life cycle during reproduction by scaring away spawning fish and interrupting or stopping runs that depend on tidal timing [15,25,26]. California grunion are important in the marine ecosystem and food web [17,34], although No runs above W3 have been reported on Oceanside beaches in recent years. By comparison, between 2016-2018 across southern California, large runs (W4 or 5) occurred for 10% of the reports, on many different beaches.…”

Section: Discussionmentioning

confidence: 99%

Effects of Repeated Sand Replenishment Projects on Runs of a Beach-Spawning Fish, the California Grunion

Martin

Adams

2020

JMSE

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Beach habitats are diminishing globally, particularly in urban areas, as sea-level rise, erosion, and shoreline hardening, along with reduced sediment inputs, combine to squeeze the coast. In California, USA an endemic marine fish, the California grunion, spawns on sandy beaches during late-night spring tides. Its unique recreational fishery is managed by the California Department of Fish and Wildlife. The City of Oceanside, CA contracts for annual harbor dredging and, after testing, places the sandy sediment on its public beach. The effects on local beach wildlife from this annual sand replenishment are not known. We examined the effect of this repeated activity as a case study over three years on the spawning runs of the California grunion. Some spawning runs occurred in all three years, but the fish avoided areas with high scarps in the intertidal zone that developed following sand placement activity. Grunion spawning runs have declined in the habitat range as a whole over the past two decades, and those in Oceanside have declined to an even greater extent. Increasing sandy beach habitat can be beneficial to wildlife, but the method of placement, timing of the project, and fate of the beach afterward can modulate or prevent beneficial effects. Frequent repetition of sand placement may accumulate impacts without allowing sufficient time for the ecosystem to recover. Rather than improving the habitat, these repeated projects in Oceanside may degrade the spawning habitat for the grunion. Alternative discharge methods and locations, slope and elevation designs, sediment volumes, and greater care in beach fill practices should be implemented to reduce future impacts.

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Marine heat wave and multiple stressors tip bull kelp forest to sea urchin barrens

Cited by 282 publications

References 64 publications

Kelp forests at the end of the earth: 45 years later

Kelp forests at the end of the earth: 45 years later

Trophic redundancy and predator size class structure drive differences in kelp forest ecosystem dynamics

Effects of Repeated Sand Replenishment Projects on Runs of a Beach-Spawning Fish, the California Grunion

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