Using a historical ecology approach to describe algal community change: Neushul revisited

Abstract

Marine macroalgae provide important ecosystem services that warrant attention. Shifting baselines across decadal time scales make it difficult to detect and understand long-term changes in macroalgal communities. Historical data can provide the basis for these long-term comparisons, but is sparse for benthic systems. This study aims to use one rare comprehensive survey of benthic macroalgae in the San Juan Islands, Washington published by Michael Neushul in 1967 as a historical baseline for surveys of the benthic macroalgal community along the Brown Island shoreline. By repeating dive surveys along three of Neushul’s original transects, using a DropCam to take still photos along ten transects, and conducting snorkel surveys along the shoreline edge of three transects, we make comparisons between the state of Brown Island algal communities in 1962/63’ and July of 2021. We found that the presence of the canopy forming kelp Nereocystis luetkeana, which was observed in Neushul’s original study, has reduced almost to nothing. Snorkel surveys along the shoreline and one dive survey showed the presence of the invasive brown seaweed Sargassum muticum that was not present in 1967. In general, subcanopy kelps and understory macroalgae are not a focus of recent studies of kelp distribution changes. This study provides a unique description of understory macroalgae communities with historical context. Further study of this area and a more thorough repetition of Nueshul’s original transects can provide deeper insight into long-term trends and the current state of the Brown Island macroalgal community.