Gulf of Alaska | Ecosystem Perspectives
100 years of change in southeast Alaska canopy kelp Presenter: Jordan Hollarsmith , jordan.hollarsmith@noaa.gov, NOAA AFSC Emily Evenson , emily.evenson@wsu.edu, Washington State University
Kelp forests are highly spatially and temporally variable, though long-term declines have been observed in many parts of the world, driven by climate change and other anthropogenic factors. The complex and extensive coastline of Southeast Alaska has precluded regular surveys of canopy kelp extent that would allow for the detection of long-term changes. To begin to fill this critical knowledge gap, we drew upon historical and modern surveys to understand change in spatial coverage and species composition of canopy kelp between two time points captured in surveys conducted in 1913 (Cameron 1915) and from 2004 to 2010 (Shorezone Alaska). We georeferenced the Cameron maps and traced the linear extent of all kelp beds. We then compared species composition and bed length (modified based on thickness) to the Shorezone surveys, focusing on differences across physical exposure gradients and latitude. Species composition was categorized as single-species canopy of giant, bull, or dragon kelps ( Macrocystis pyrifera , Nereocystis luetkeana , or Eualaria fstulosa , respectively) or mixed-species. Overall, we did not find dramatic differences between the two datasets - canopy kelp was observed throughout Southeast Alaska in both surveys with no evidence of widespread regional extirpation, such has been observed in other canopy kelp ecosystems. The linear extent of canopy kelp was significantly greater in the Shorezone surveys, and this difference was most notable in southern Southeast Alaska, and in highly-exposed areas (p < 0.001). More beds of M. pyrifera were observed in north and central Southeast Alaska in the Shorezone surveys than in the Cameron surveys. No major changes in N. luetkeana bed size or numbers were observed between the two datasets, despite large-scale reductions in N. luetkeana beds observed in regions of California, Oregon, and Washington. Caution must be applied when comparing these two datasets due to extreme differences in available survey technology, and potential differences in season and tidal height. The Cameron maps were generated based on visual observations taken from motor- and rowboat across one season (May to September 1913), while the Shorezone data came from aerial video and photographic surveys that targeted low tides and were generated across multiple years. Considering these differences, we conclude that canopy kelp populations in Southeast Alaska have been quite stable over the past century.
Alaska Marine Science Symposium 2023 167
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