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First freshwater coralline alga and the role of local features in a major biome transition.

ABSTRACT: Coralline red algae are significant components of sea bottom and up to now considered as exclusively marine species. Here we present the first coralline alga from a freshwater environment, found in the Cetina River (Adriatic Sea watershed). The alga is fully adapted to freshwater, as attested by reproductive structures, sporelings, and an inability to survive brackish conditions. Morphological and molecular phylogenetic analyses reveal the species belongs to Pneophyllum and is described as P. cetinaensis sp. nov. The marine-freshwater transition most probably occurred during the last glaciation. The brackish-water ancestor was preadapted to osmotic stress and rapid changes in water salinity and temperature. The particular characteristics of the karst Cetina River, such as hard water enriched with dissolved calcium carbonate and a pH similar to the marine environment, favoured colonization of the river by a marine species. The upstream advance and dispersal is facilitated by exceptionally pronounced zoochory by freshwater gastropods. Pneophyllum cetinaensis defies the paradigm of Corallinales as an exclusively marine group.

SUBMITTER: Zuljevic A

PROVIDER: S-EPMC4726424 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature

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First freshwater coralline alga and the role of local features in a major biome transition.

Žuljević A A Kaleb S S Peña V V Despalatović M M Cvitković I I De Clerck O O Le Gall L L Falace A A Vita F F Braga Juan C JC Antolić B B

Scientific reports 20160121

Coralline red algae are significant components of sea bottom and up to now considered as exclusively marine species. Here we present the first coralline alga from a freshwater environment, found in the Cetina River (Adriatic Sea watershed). The alga is fully adapted to freshwater, as attested by reproductive structures, sporelings, and an inability to survive brackish conditions. Morphological and molecular phylogenetic analyses reveal the species belongs to Pneophyllum and is described as P. ce ...[more]

PMID: 26791421

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Project description:Ocean acidification (OA) has important implications for the persistence of coral reef ecosystems, due to potentially negative effects on biomineralization. Many coral reefs are dynamic with respect to carbonate chemistry, and experience fluctuations in pCO₂ that exceed OA projections for the near future. To understand the influence of dynamic pCO₂ on an important reef calcifier, we tested the response of the crustose coralline alga Porolithon onkodes to oscillating pCO₂. Individuals were exposed to ambient (400 µatm), high (660 µatm), or variable pCO₂ (oscillating between 400/660 µatm) treatments for 14 days. To explore the potential for coralline acclimatization, we collected individuals from low and high pCO₂ variability sites (upstream and downstream respectively) on a back reef characterized by unidirectional water flow in Moorea, French Polynesia. We quantified the effects of treatment on algal calcification by measuring the change in buoyant weight, and on algal metabolism by conducting sealed incubations to measure rates of photosynthesis and respiration. Net photosynthesis was higher in the ambient treatment than the variable treatment, regardless of habitat origin, and there was no effect on respiration or gross photosynthesis. Exposure to high pCO₂ decreased P. onkodes calcification by >70%, regardless of the original habitat. In the variable treatment, corallines from the high variability habitat calcified 42% more than corallines from the low variability habitat. The significance of the original habitat for the coralline calcification response to variable, high pCO₂ indicates that individuals existing in dynamic pCO₂ habitats may be acclimatized to OA within the scope of in situ variability. These results highlight the importance of accounting for natural pCO₂ variability in OA manipulations, and provide insight into the potential for plasticity in habitat and species-specific responses to changing ocean chemistry.

Project description:The presence of banding in the skeleton of coralline algae has been reported in many species, primarily from temperate and polar regions. Similar to tree rings, skeletal banding can provide information on growth rate, age, and longevity; as well as records of past environmental conditions and the coralline alga's growth responses to such changes. The aim of this study was to explore the presence and characterise the nature of banding in the tropical coralline alga Porolithon onkodes, an abundant and key reef-building species on the Great Barrier Reef (GBR) Australia, and the Indo-Pacific in general. To achieve this we employed various methods including X-ray diffraction (XRD) to determine seasonal mol% magnesium (Mg), mineralogy mapping to investigate changes in dominant mineral phases, scanning electron microscopy-electron dispersive spectroscopy (SEM-EDS), and micro-computed tomography (micro-CT) scanning to examine changes in cell size and density banding, and UV light to examine reproductive (conceptacle) banding. Seasonal variation in the Mg content of the skeleton did occur and followed previously recorded variations with the highest mol% MgCO3 in summer and lowest in winter, confirming the positive relationship between seawater temperature and mol% MgCO3. Rows of conceptacles viewed under UV light provided easily distinguishable bands that could be used to measure vertical growth rate (1.4 mm year-1) and age of the organism. Micro-CT scanning showed obvious banding patterns in relation to skeletal density, and mineralogical mapping revealed patterns of banding created by changes in Mg content. Thus, we present new evidence for seasonal banding patterns in the tropical coralline alga P. onkodes. This banding in the P. onkodes skeleton can provide valuable information into the present and past life history of this important reef-building species, and is essential to assess and predict the response of these organisms to future climate and environmental changes.

Dataset Information

First freshwater coralline alga and the role of local features in a major biome transition.

Publications

First freshwater coralline alga and the role of local features in a major biome transition.

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