Exhaustive reanalysis of barcode sequences from public repositories
highlights ongoing misidentifications and impacts taxa diversity and
distribution: a case study of the Sea Lettuce.
Sea Lettuce (Ulva spp.; Ulvophyceae, Ulvales, Ulvaceae) is an
important ecological and economical entity, with a worldwide
distribution and is a well-known source of near-shore blooms blighting
many coastlines. Species of Ulva are frequently misidentified in
public repositories, including herbaria and gene banks, making species
identification based on traditional barcoding hazardous. We investigated
the species distribution of 295 individual distromatic foliose strains
from the North East Atlantic by traditional barcoding or next generation
sequencing. We found seven distinct species, and compared our results
with all worldwide Ulva spp sequences present in the NCBI
database for the three barcodes rbcL, tufA and the ITS1.
Our results demonstrate a large degree of species misidentification in
the NCBI database. We estimate that 21% of the entries pertaining to
foliose species are misannotated. In the extreme case of U.
lactuca, 65% of the entries are erroneously labelled specimens of
another Ulva species, typically U. fenestrata. In
addition, 30% of U. rigida entries are misannotated, U.
rigida being relatively rare and often misannotated U.
laetevirens. Furthermore, U. armoricana and U.
scandinavica present as being synonymous to U. laetevirens. An
analysis of the global distribution of registered samples from foliose
species also indicates possible geographical isolation for some species,
and the absence of U. lactuca from Northern Europe. Altogether,
exhaustive taxonomic clarification by aggregation of a library of
barcode sequences highlights misannotations, and delivers an improved
representation of Ulva species diversity and distribution. This
approach could be easily adapted to other taxa.