Characterization of algal community composition and structure from the nearshore environment, Lake Tahoe, (United States)
Periphyton assemblages from the nearshore environment of the west side of Lake Tahoe, California, were analyzed to determine their taxonomic composition and community structure across habitats and seasons. Lake Tahoe, an iconic oligotrophic subalpine lake, has experienced increases in nuisance algal blooms beginning in the 1960’s that have been attributed to anthropogenic stressors, and samplings spanning from November 2019-September 2020 provide useful snapshots against which older monitoring from the 1970’s and 1980’s may be contextualized. A voucher flora, complete with descriptions, photo-documentation and referencing to species concepts employed, was created as a method of providing reproducible identification and enumeration of algal species, and more seamless reconciliation of detailed taxonomic data with future monitoring projects. The eulittoral zone (0-2m) is dominated by elongate araphid (Synedra, Ulnaria) and stalked diatoms (Gomphonema, Cymbella, Encyonema) with strong seasonality. The sublittoral zone is dominated by a nitrogen-fixing Epithemia-cyanobacteria assemblage that showed less seasonal changes in dominance or composition, but did expand to impinge on the 2m depths of the eulittoral zone in the Fall. Sublittoral epipsammic samples, despite their proximity to rocks, had a very distinct diatom composition and high species dominance, similar to what was seen in the fall eulittoral samples, with high numbers of Staurosirella chains and small biraphid diatoms. The deeper samples at 30 and 50 m contained high numbers of live Epithemia, and indicates a thriving sublittoral assemblage at these greater depths, but with less biomass. The 2019-20 data show the same diatom taxa present in the 1970’s and 1980’s but with changes in species dominance. Notably, there was less of the green alga Mougeotia, when compared to the 1970’s data, and higher a dominance by Epithemia in the sublittoral zone, persisting year-round. These new data show roughly double the algal species biodiversity that had been documented previously in the Lake Tahoe nearshore, and is largely attributed to the methods employed. It is hoped that these methods will be adopted on a wider scale to make it easier to produce species level taxonomic work in this area, and to insure better harmonization between projects.