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Macroalgal forests dominate shallow hard bottom areas along the northern portion of the Western Antarctic Peninsula (WAP). Macroalgal biomass and diversity are known to be dramatically lower in the southern WAP and at similar latitudes around Antarctica, but few reports detail the distributions of macroalgae or associated macroinvertebrates in the central WAP. We used satellite imagery to identify 14 sites differing in sea ice coverage but similar in terms of turbidity along the central WAP. Fleshy macroalgal cover was strongly, negatively correlated with ice concentration, but there was no significant correlation between macroinvertebrate cover and sea ice. Overall community (all organisms) diversity correlated negatively with sea ice concentration and positively with fleshy macroalgal cover, which ranged from around zero at high ice sites to 80% at the lowest ice sites. Nonparametric, multivariate analyses resulted in clustering of macroalgal assemblages across most of the northern sites of the study area, although they differed greatly with respect to macroalgal percent cover and diversity. Analyses of the overall communities resulted in three site clusters corresponding to high, medium, and low fleshy macroalgal cover. At most northern sites, macroalgal cover was similar across depths, but macroalgal and macroinvertebrate distributions suggested increasing effects of ice scour in shallower depths towards the south. Hindcast projections based on correlations of ice and macroalgal cover data suggest that macroalgal cover at many sites could have been varying substantially over the past 40 years. Similarly, based on predicted likely sea ice decreases by 2100, projected increases in macroalgal cover at sites that currently have high ice cover and low macroalgal cover are substantial, often with only a future 15% decrease in sea ice. Such changes would have important ramifications to future benthic communities and to understanding how Antarctic macroalgae may contribute to future blue carbon sequestration.
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This content will become publicly available on April 30, 2026
Substantial short-term increases in brown macroalgal cover and total macroalgal biomass with decreased sea ice on the Western Antarctic Peninsula
There are numerous reports of macroalgal abundance along the northern portion of the Western Antarctic Peninsula (WAP) but little information about short-term variation in macroalgal abundance or in community structure. Here, we video-recorded replicate vertical transects between 5 and 40 m at 4 sites separated by <30 km near Anvers Island in 2019 and 2023, with 2 of the sites also recorded in 2020. Total macroalgal cover increased between 2019 and 2023 in all individual transects sampled in both years, with substantial increases in perennial brown overstory macroalgal cover. Nonparametric multivariate analyses of the communities identified significant differences in the macroalgal assemblages among all sites, and between 2019 and 2023 at 3 of the sites, but there were no significant differences in the macroinvertebrate assemblages across sites or years. Combined percent cover and destructive biomass quadrat sampling of a limited number of quadrats enabled estimations of macroalgal biomass changes from the video data. Although the absolute magnitudes reported here should be treated as preliminary estimates, biomass increases between 2019 and 2023 were clearly substantial because they were primarily from increases in the large overstory brown macroalgae. Sea ice concentrations were decreasing substantially across this time interval and were likely a causal factor in the increased macroalgal cover and biomass.
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- PAR ID:
- 10591326
- Publisher / Repository:
- Inter-Research
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 759
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 17 to 34
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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