A new set of N isotopic reference values for monitoring Ulva green tides in coral reef ecosystems.

Green tides occurrence has increased in coral reefs, yet few reference values have been documented to support bloom management in these ecosystems. Here, we took advantage of recent Ulva green tides that occurred in New Caledonia to (i) identify the elements limiting the growth of Ulva spp. during these blooms; and (ii) validate the use of isotopic markers for identifying sources of nutrients that generated blooms. N/P ratios highlighted a stronger limitation of algae by phosphorus than by nitrogen on sites under oceanic influence, while the proportions of N and P were optimal for algal growth at sites where green tides occurred. Macroalgae highly exposed to sewage water was characterized by higher δ15N than macroalgae collected in areas exposed to synthetic inorganic fertilizers. From these results, we established a new set of threshold values for using δ15N in Ulva species as an indicator of nitrogen source type in coral reefs.

Historical biogeographical analysis of the Udoteaceae (Bryopsidales, Chlorophyta) elucidates origins of high species diversity in the Central Indo-Pacific, Western Indian Ocean and Greater Caribbean regions.

There is a growing interest in elucidating the biogeographical processes underlying biodiversity patterns of seaweeds, with recent studies largely focusing on red and brown macroalgae. This study focuses on the siphonous green algal family Udoteaceae, which is diverse and globally distributed in tropical to warm-temperate seas, and includes species that form important components of tropical reefs. We explored the historical processes that have shaped current biodiversity patterns in the family by analyzing a comprehensive dataset of 568 specimens sampled across its geographical range, and including 45 species, corresponding to 59% of the known diversity. Historical biogeographical analysis was based on a three-locus time-calibrated phylogeny, and probabilistic modeling of geographical range evolution. Many species were found to have restricted ranges, indicative of low dispersal capacity. Our analysis points toward a Western Tethys origin and early diversification of the Udoteaceae in the Triassic period. Three centers of diversity were identified, which are, in order of highest species richness, the Central Indo-Pacific, the Western Indian Ocean, and the Greater Caribbean. Different drivers have likely played a role in shaping these diversity centres. Species richness in the Central Indo-Pacific likely resulted from speciation within the region, as well as recolonization from neighbouring regions, and overlap of some wider ranged species, corroborating the "biodiversity feedback" model. Species richness in the Western Indian Ocean can be explained by ancient and more recent diversification within the region, and dispersal from the Central Indo-Pacific. The Greater Caribbean region was colonized more recently, followed by diversification within the region.

Diversity and taxonomic revision of tribes Rhipileae and Rhipiliopsideae (Halimedaceae, Chlorophyta) based on molecular and morphological data.

Genera and species of the tribes Rhipileae and Rhipiliopsideae are abundant in most coral reef ecosystems worldwide. However, the group has been largely overlooked, and very little genetic data is available to accurately assess its diversity, phylogenetic relationships, and geographic distribution. Our study provided an in-depth reassessment of tribes Rhipileae and Rhipiliopsideae based on a species-rich dataset and the combination of molecular species delimitation, multilocus phylogenetic analyses (tufA, rbcL, and 18S rDNA), and morpho-anatomic observations. Our results revealed an unexpected diversity of 38 morphologically validated species hypotheses, including 20 new species, two of which are described in this paper and one resurrected species (Rhipilia diaphana). Based on our phylogenetic results we proposed to redefine the genera Rhipilia and Rhipiliopsis and described two new genera, Kraftalia gen. nov. (Rhipileae) and Rhipiliospina gen. nov. (Rhipiliopsideae). Finally, we validated Rhipiliella Kraft and included it in the tribe Rhipileae. Although Rhipilia and Rhipiliopsis have a pantropical distribution, none of the species studied here appeared cosmopolitan; instead, they have restricted distributions.

Exploring the Udoteaceae diversity (Bryopsidales, Chlorophyta) in the Caribbean region based on molecular and morphological data.

The Udoteaceae family (Bryopsidales, Chlorophyta) is known to be highly diverse morphologically in the Caribbean region, but only few studies have studied its genetic diversity. Using an integrative taxonomic approach, this study aimed at (1) exploring the Udoteaceae species diversity using a combination of five DNA-based species delimitation methods and morpho-anatomical data for confirmation; (2) estimating the discriminatory power of traditional diagnostic characters using a morphology-based clustering method and statistical analyses focused on the genus Udotea; and (3) reconstructing the phylogeny of the family based on a multilocus analysis (tufA, rbcL, 18S rDNA). Our results revealed strong congruence between species hypotheses across delimitation methods and markers. Morpho-anatomical characters proved essential to validate these hypotheses, to assign species names and to unveil new species. Morphological analyses led to relevant results for accurately discriminating Udotea morphospecies. Siphon features and cortication were key characters to define supra-specific groups and to revise the taxonomy of the genus Udotea. Phylogenetic analyses confirmed the polyphyly of Udotea, Rhipocephalus and Penicillus, which led us to propose a revised definition of Udotea sensu stricto based on both genetic and morphological data. Finally, our study emphasizes the importance of combining genetic and morphological data for the taxonomic revision of the Udoteaceae, but stresses the need of including more taxa from other geographical regions to better resolve taxonomic issues.