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Giant kelp (Macrocystis pyrifera) response under climate change scenarios: A case study on the Santa Barbara Channel

Davison, Giovanna LU (2026) In Student thesis series INES NGEM21 20261
Department of Earth and Environmental Sciences (MGeo)
Abstract
The rise in sea surface temperature (SST) is one of the most substantial impacts of climate change, as ocean warming is predicted to increase by 0.86-2.89˚C by 2100. Giant kelp (Macrocystis pyrifera) forests in Southern California are sensitive to changes in ocean temperatures, with a thermal threshold of 18–25˚C. They are ecologically significant because they provide many ecosystem services and serve as a foundation species for trophic interactions with purple sea urchins (Strongylocentrotus purpuratus) and southern sea otters (Enhydra lutris nereis). This thesis investigates the response of giant kelp biomass to SST changes in the Santa Barbara Channel using modelling to explore the ecological outcomes from... (More)
The rise in sea surface temperature (SST) is one of the most substantial impacts of climate change, as ocean warming is predicted to increase by 0.86-2.89˚C by 2100. Giant kelp (Macrocystis pyrifera) forests in Southern California are sensitive to changes in ocean temperatures, with a thermal threshold of 18–25˚C. They are ecologically significant because they provide many ecosystem services and serve as a foundation species for trophic interactions with purple sea urchins (Strongylocentrotus purpuratus) and southern sea otters (Enhydra lutris nereis). This thesis investigates the response of giant kelp biomass to SST changes in the Santa Barbara Channel using modelling to explore the ecological outcomes from 1850-2100. The model used an ensemble of three CMIP6 climate models (CMCC-CM2-SR5, HadGEM3-GC31-LL, and MCM-UA-1-0) under three different emission scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). This study found a negative correlation (r=-0.59, p<0.001) between observed annual maximum SST and giant kelp biomass. Kelp biomass declines were projected under three Shared Socioeconomic Pathways (SSPs), with a kelp population of zero projected by approximately 2060 under SSP5-8.5. These findings expand upon previous literature by projecting kelp decline under future warming, which emphasize the trophic cascade impacts on sea urchin and sea otter populations, and highlight the importance of active restoration techniques, such as the “green gravel” method and transplantation, to support giant kelp forests through 2100. (Less)
Popular Abstract
The rise in sea surface temperature (SST) is one of the most substantial impacts of climate change, as ocean warming is predicted to increase by 0.86-2.89˚C (1.55-5.20˚F) by 2100. Giant kelp (Macrocystis pyrifera) forests in Southern California are sensitive to changes in ocean temperatures, with a thermal threshold of 18-25˚C (64.4-77˚F). They are ecologically significant because they provide many ecosystem services, such as coastal erosion control and biofuel. Giant kelp also serve as a foundation species for trophic interactions, which describes how energy moves through an ecosystem, with purple sea urchins (Strongylocentrotus purpuratus) and southern sea otters (Enhydra lutris nereis). This thesis investigates the... (More)
The rise in sea surface temperature (SST) is one of the most substantial impacts of climate change, as ocean warming is predicted to increase by 0.86-2.89˚C (1.55-5.20˚F) by 2100. Giant kelp (Macrocystis pyrifera) forests in Southern California are sensitive to changes in ocean temperatures, with a thermal threshold of 18-25˚C (64.4-77˚F). They are ecologically significant because they provide many ecosystem services, such as coastal erosion control and biofuel. Giant kelp also serve as a foundation species for trophic interactions, which describes how energy moves through an ecosystem, with purple sea urchins (Strongylocentrotus purpuratus) and southern sea otters (Enhydra lutris nereis). This thesis investigates the response of giant kelp biomass to SST changes in the Santa Barbara Channel, located off the coast of Southern California in the United States, using modelling to explore the ecological outcomes from 1850-2100. Three climate models were combined and run under three potential emission scenarios (best case, most likely, and worst case) to project giant kelp biomass decline. This study found a negative correlation between observed annual maximum SST and giant kelp biomass, with a kelp population of zero projected by approximately 2060 under the worst case scenario. These findings expand upon previous literature by projecting kelp decline under future warming. This emphasizes the trophic cascade impacts on sea urchin and sea otter populations, which undermine the ecosystem balance within the giant kelp forest. This study highlights the importance of active restoration techniques, such as generating kelp via laboratory cultures for site seedings and transplantation, to support giant kelp forests through 2100. (Less)
Please use this url to cite or link to this publication:
author
Davison, Giovanna LU
supervisor
organization
course
NGEM21 20261
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Physical Geography, sea surface temperature, climate change, ocean warming, giant kelp, Macrocystis pyrifera, trophic cascades, Santa Barbara Channel
publication/series
Student thesis series INES
report number
765
language
English
id
9242724
date added to LUP
2026-06-23 10:19:55
date last changed
2026-06-23 10:19:55
@misc{9242724,
  abstract     = {{The rise in sea surface temperature (SST) is one of the most substantial impacts of climate change, as ocean warming is predicted to increase by 0.86-2.89˚C by 2100. Giant kelp ([i]Macrocystis pyrifera[/i]) forests in Southern California are sensitive to changes in ocean temperatures, with a thermal threshold of 18–25˚C. They are ecologically significant because they provide many ecosystem services and serve as a foundation species for trophic interactions with purple sea urchins ([i]Strongylocentrotus purpuratus[/i]) and southern sea otters ([i]Enhydra lutris nereis[/i]). This thesis investigates the response of giant kelp biomass to SST changes in the Santa Barbara Channel using modelling to explore the ecological outcomes from 1850-2100. The model used an ensemble of three CMIP6 climate models (CMCC-CM2-SR5, HadGEM3-GC31-LL, and MCM-UA-1-0) under three different emission scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). This study found a negative correlation (r=-0.59, p<0.001) between observed annual maximum SST and giant kelp biomass. Kelp biomass declines were projected under three Shared Socioeconomic Pathways (SSPs), with a kelp population of zero projected by approximately 2060 under SSP5-8.5. These findings expand upon previous literature by projecting kelp decline under future warming, which emphasize the trophic cascade impacts on sea urchin and sea otter populations, and highlight the importance of active restoration techniques, such as the “green gravel” method and transplantation, to support giant kelp forests through 2100.}},
  author       = {{Davison, Giovanna}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Student thesis series INES}},
  title        = {{Giant kelp (Macrocystis pyrifera) response under climate change scenarios: A case study on the Santa Barbara Channel}},
  year         = {{2026}},
}