Molecular and morphological diversity of Narragansett Bay (RI, USA) Ulva (Ulvales, Chlorophyta) populations

Abstract

Macroalgal bloom-forming species occur in coastal systems worldwide. However, due to overlapping morphologies in some taxa, accurate taxonomic assessment and classification of these species can be quite challenging. We investigated the molecular and morphological characteristics of 153 specimens of bloom-forming Ulva located in and around Narragansett Bay, RI, USA. We analyzed sequences of the nuclear internal transcribed spacer 1 region (ITS1) and the chloroplast-encoded rbcL; based on the ITS1 data, we grouped the specimens into nine operational taxonomic units (OTUs). Eight of these OTUs have been previously reported to exist, while one is novel. Of the eight OTUs, all shared sequence identity with previously published sequences or differed by less than 1.5% sequence divergence for two molecular markers. Previously, 10 species names were reported for Ulva in Rhode Island (one blade and nine tube-forming species) based upon morphological classification alone. Of our nine OTUs, three contained blade-forming specimens (U. lactuca, U. compressa, U. rigida), one OTU had a blade with a tubular stipe, and six contained unbranched and/or branched tubular morphologies (one of these six, U. compressa, had both a blade and a tube morphology). While the three blade-forming OTUs in Narragansett Bay can frequently be distinguished by careful observations of morphological characteristics, and spatial/temporal distribution, it is much more difficult to distinguish among the tube-forming specimens based upon morphology or distribution alone. Our data support the molecular species concept for Ulva, and indicate that molecular-based classifications of Ulva species are critical for proper species identification, and subsequent ecological assessment or mitigation of Ulva blooms.

Differentiation between some Ulva spp. by morphological, genetic and biochemical analyses

“…7) showed that the most closely species are U. lactuca and U. compressa (Guidone et al, 2013). However, U. fasciata (Pasad et al, 2009) is showed to be far from both U. lactuca and U. compressa.…”

Re-evaluation of green tide-forming species in the Yellow Sea

“…We conclude that the green tide-forming species is not U. prolifera, but U. linza. According to recent studies from New Zealand, Australia, and the USA, U. prolifera is monophyletic regardless of the genes (Heesch et al 2009, Kraft et al 2010, Guidone et al 2013, Kirkendale et al 2013. Several Ulva spp.…”

<i>Ulva partita</i> sp. nov., a Novel <i>Enteromorpha</i>-Like <i>Ulva</i> Species from Japanese Coastal Areas

“…1 was also described producing many branches mainly confined at the basal part (Ogawa et al 2013), and the branching manner coincided with U. partita. There are many field surveys of Ulva based on morphological and molecular phylogeny in Europe (Mareš et al 2011, Wolf et al 2012, Oceania (Kraft et al 2010, Kirkendale et al 2013, Micronesia (O Kelly et al 2010), North America (Guidone et al 2013), and Asia (Duan et al 2012, Bast et al 2014. However, U. partita has only been collected from the Japanese seashore.…”