Abstract
ABSTRACTSurveys of the seaweed flora of the Falkland Islands and of Tierra del Fuego revealed the presence of a new species of brown alga. Dictyota falklandica sp. nov. inhabits the shallow rocky infralittoral in sheltered localities and the lower intertidal in more exposed sites. Dictyota falklandica has a regular to irregular habit of dichotomously branched blades, forming erect thalli composed of a single-layered cortex and medulla, with margins in the apical parts dotted with dormant apical cells. Sporangia occur in irregular groups or longitudinal lines on the thallus surface. Molecular phylogenies based on chloroplast psbA and rbcL and mitochondrial cox1 sequences showed that the species from the Falkland Islands is sister to a clade formed by D. korowai, recently described from New Zealand and D. kunthii known from both the Pacific coast of South America and New Zealand. Temperature tolerance experiments, showing mortality at 25 °C but survival at 20 °C, confirm the cold-temperate affinity of this taxon. Its relationship to other cold-temperate Southern Hemisphere species is discussed, with its closest relatives living in regions with sea surface temperatures of at least 7–10 °C higher.
Highlights
Dictyota species are common members of the benthic communities in warm-temperate and tropical seas, and the genus is widely considered to have warm-water affinities (Tronholm et al 2010)
Molecular phylogenies based on chloroplast psbA and rbcL and mitochondrial cox1 sequences showed that the species from the Falkland Islands is sister to a clade formed by D. korowai, recently described from New Zealand and D. kunthii known from both the Pacific coast of South America and New Zealand
We report on our recent observations and collections of Dictyota from the Falkland Islands, including a formal description as a new species, underpinned by temperature tolerance experiments with cultured isolates
Summary
Dictyota species are common members of the benthic communities in warm-temperate and tropical seas, and the genus is widely considered to have warm-water affinities (Tronholm et al 2010). Among the 97 Dictyota species currently recognized, 87 are described from warm-temperate and tropical seas (Guiry & Guiry 2019). Their effective chemical defense against grazing based on diterpenes (Hay et al 1987; Wiesemeier et al 2007) and high constitutive hydrogen peroxide release, likely for the control of bacterial biofilms (Küpper et al 2002), as well as their ability to propagate through fragmentation (Herren et al 2006), enables them to form sizeable populations even in localities under high grazing pressure such as Ascension Island (Tsiamis et al 2017). Defense against amphipods is inducible in Chilean Dictyota kunthii (C.Agardh) Greville (Macaya & Thiel 2008), which may be a more widespread feature in this genus.
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