A Demonstration of DNA Barcoding-Based Identification of Blade-Form Ulva (Ulvophyceae, Chlorophyta) Species from Three Site in the San Juan Islands, Washington, USA

Marine macroalgae are foundation species that play a critical ecological role in coastal communities as primary producers. The macroalgal genus Ulva is vital in intertidal communities, serving as a food source and shelter for organisms, but these species also form environment-damaging nuisance blooms. This project aimed to demonstrate the utility of DNA barcoding for determining the diversity of Ulva species in the San Juan Islands (Washington, DC, USA). Blade-form Ulva (Ulvophyceae) specimens were collected from the lower, mid, and upper intertidal zones at three sites experiencing different levels of wave exposure. Sequences of plastid-encoded tufA were generated for each specimen and cluster analyses revealed the presence of four species at the collection sites. Two species were positively identified as Ulva expansa and Ulva fenestrata based on their sharing identical tufA sequences with those of the holotype specimens. Sequences of plastid-encoded rbcL and the nuclear-encoded ribosomal ITS regions of representative specimens were used to identify the other two species as Ulva prolifera and Ulva californica based on their similarity to epitype and topotype specimen sequences, respectively. Additional types of specimen sequencing efforts are needed to increase the number of Ulva species that can be accurately identified and realize their true biodiversity.

Automated summary

This study aimed to determine the diversity of Ulva species in the San Juan Islands using DNA barcoding. Four species were identified through sequencing and cluster analysis, and their identities were confirmed using holotype and topotype specimens. Additional sequencing efforts are needed to accurately identify more Ulva species and understand their true biodiversity.