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Abundance of a recently discovered Alaskan rhodolith bed in a shallow, seagrass-dominated lagoon

April 12, 2021

Rhodoliths are important foundation species of the benthic photic zone but are poorly known and rarely studied in Alaska. A bed of Lithothamnion soriferum rhodoliths was discovered in 2008 in Kinzarof Lagoon, Alaska, a shallow-water embayment dominated by eelgrass (Zostera marina). Rhodolith presence and biomass were estimated to assess trends and environmental factors that may influence rhodolith distribution and abundance during 4 years spread over a 12-year period (2008–2010, and 2019). Rhodolith presence and biomass were positively associated with percent seaweed cover, as most rhodoliths and seaweeds occurred in subtidal areas, and negatively associated with percent eelgrass cover. Rhodoliths occurred in two primary areas of the lagoon, a 182-ha core area in a shallow water (mean tide depth of -0.03 m MLLW) tidal channel with low eelgrass density, and a 22-ha outlying area at shallower water depths (>0.2 m MLLW) with moderate to high eelgrass cover. There was no apparent trend in rhodolith biomass over the study period despite wide variation in mean annual estimates. This study establishes a baseline for continued investigations and monitoring of this important benthic resource in Alaska.

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