Taxonomic determination of the cryptogenic red alga, Chondria tumulosa sp. nov., (Rhodomelaceae, Rhodophyta) from Papahānaumokuākea Marine National Monument, Hawai‘i, USA: A new species displaying invasive characteristics

Abstract

Survey cruises by the National Oceanic and Atmospheric Administration (NOAA) in 2016 and 2019 yielded specimens of an undetermined red alga that rapidly attained alarming levels of benthic coverage at Pearl and Hermes Atoll, Papahānaumokuākea Marine National Monument, Hawaiʻi. By 2019 the seaweed had covered large expanses on the northeast side of the atoll with mat-like, extensive growth of entangled thalli. Specimens were analyzed using light microscopy and molecular analysis, and were compared to morphological descriptions in the literature for closely related taxa. Light microscopy demonstrated that the specimens likely belonged to the rhodomelacean genus Chondria , yet comparisons to taxonomic literature revealed no morphological match. DNA sequence analyses of the mitochondrial COI barcode marker, the plastidial rbc L gene, and the nuclear SSU gene confirmed its genus-level placement and demonstrated that this alga was unique compared to all other available sequences. Based on these data, this cryptogenic seaweed is here proposed as a new species: Chondria tumulosa A.R.Sherwood & J.M.Huisman sp. nov. Chondria tumulosa is distinct from all other species of Chondria based on its large, robust thalli, a mat-forming tendency, large axial diameter in mature branches (which decreases in diameter with subsequent orders of branching), terete axes, and bluntly rounded apices. Although C . tumulosa does not meet the criteria for the definition of an invasive species given that it has not been confirmed as introduced to Pearl and Hermes Atoll, this seaweed is not closely related to any known Hawaiian native species and is of particular concern given its sudden appearance and rapid increase in abundance in the Papahānaumokuākea Marine National Monument; an uninhabited, remote, and pristine island chain to the northwest of the Main Hawaiian Islands.

Phylogenomic analysis of pseudocryptic diversity reveals the new genus Deltalsia (Rhodomelaceae, Rhodophyta)

“…2017a, Sherwood et al. 2020, Piñeiro‐Corbeira et al. 2020a,b), highlighting the need to improve molecular datasets in this diverse red algal order for which only a small proportion of the diversity has been molecularly characterized.…”

Nitrogen stable isotopes (δ15N) and tissue nitrogen in shallow‐water and mesophotic macroalgae differ between the Main Hawaiian Islands and the Northwestern Hawaiian Islands

“…Because of this, we examined site‐specific differences at the level of island/atoll. Manawai was the most extensively surveyed atoll in August 2019 due to the discovery of the cryptogenic red alga C. tumulosa that displayed invasive traits across the reefs (Sherwood et al 2020). Understanding whether algal tissue nitrogen concentrations differ at various sites at Manawai could provide insight into processes that may increase the growth or occurrence of this cryptogenic alga.…”

“…With the exception of the recent discovery of the cryptogenic, invasive‐like alga Chondria tumulosa (Sherwood et al 2020), the Northwestern Hawaiian Islands do not contain invasive macroalgae. In comparison, the Main Hawaiian Islands contain several species of invasive Chlorophyta and Rhodophyta (Smith et al 2002; Foster et al 2019).…”

Long-term ecological monitoring of reefs on Hawai’i Island (2003-2020): Characterization of a common cryptic crust, Ramicrusta hawaiiensis (Peyssonneliales, Rhodophyta)

“…As climate change continues to affect coral reefs, reef communities may respond and shift-additional macroalgal species, which are rare or cryptic and were previously overlooked, may become more abundant. For example, the fleshy red alga, Chondria tumulosa may have been a sparse and cryptic species at Pearl and Hermes Atoll in the Northwestern Hawaiian Islands that increased in abundance and spread rapidly after changes in ecosystem conditions (Sherwood et al, 2020a). Changes in nutrient concentrations (Stimson, 2015), water temperature (Boudouresque and Verlaque, 2010;Dijkstra et al, 2019), and greenhouse gas concentrations (Fernańdez de la Hoz et al, 2019) have been linked to coral-macroalgal phase shifts on reefs, range shifts in macroalgal distribution, and changes in macroalgal abundances.…”