Three macroalgal species belonging to Chlorophyta (Ulva rigida), Rhodophyta (Ellisolandia elongata) and Phaeophyceae (Heterokontophyta; Cystoseira tamariscifolia), naturally growing at the same shore level and representing 3 morpho-functional groups, were exposed to short-term changes in temperature under different carbon and nitrogen regimes. Experiments were conducted in outdoor tanks at 4 combinations of carbon and nitrogen levels under reduced solar radiation. In vivo chl a fluorescence parameters and pigment contents were monitored to assess diurnal physiological responses and potential for recovery. Strong fluctuations in chl a fluorescence parameters, but not in chl a content, were observed in response to diurnal variation in solar radiation and light climate within the tanks; sensitivity varied between algal species and, in some cases, depended on the carbon and nitrogen regime. Nitrogen uptake was similarly high in U. rigida and E. elongata and lowest in C. tamariscifolia. In U. rigida and E. elongata, chl a concentrations decreased after high-carbon treatments. Effective photosystem II quantum efficiency was reduced in all species at noon, and lowest in C. tamariscifolia. The results highlight the complexity of physiological short-term acclimations which were most likely linked to biochemical changes at the cellular level. Long-term experiments are required in future for more comprehensive investigation of the observed interactive effects of the different environmental parameters

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The red seaweed Asparagopsis taxiformis embodies five cryptic mitochondrial lineages (lineage 1-5) introduced worldwide as a consequence of human mediated transport and climate change. We compared globally collected mitochondrial cox2-3 intergenic spacer sequences with sequences produced from multiple Australian locations and South Korea to identify Asparagopsis lineages and to reveal cryptic introductions. We report A. taxiformis lineage 4 from Cocos (Keeling) Islands, Australia, and the highly invasive Indo-Pacific Mediterranean lineage 2 from South Korea and Lord Howe Island, Australia. Phylogeographic analysis showed a clear haplotype and geographic separation between western Australian and Great Barrier Reef (GBR) isolates belonging to the recently described lineage 5. The same lineage, however, was characterized by a substantial genetic and geographic break between the majority of Australian specimens and Asparagopsis collections from South Solitary Island, Southern GBR, Lord Howe Island, Kermadec Islands, Norfolk Island, New Caledonia and French Polynesia. The disjunct geographic distribution and sequence divergence between these two groups supports the recognition of a sixth cryptic A. taxiformis mitochondrial lineage. As climatic changes accelerate the relocation of biota and offer novel niches for colonization, periodic surveys for early detection of cryptic invasive seaweeds will be critical in determining whether eradication or effective containment of the aliens are feasible.