RESUMEN

Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO3 and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ88/86 Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry. Coccolithophores were cultured within a temperature and a pCO2 range from 10 to 25°C and from 175 to 1,240 µatm, respectively. Both environmental drivers induced a significant linear increase in coccolith stable Sr isotope fractionation. The temperature correlation at constant pCO2 for Emiliania huxleyi and Coccolithus braarudii is expressed as Δ88/86 Sr = -7.611 × 10-3 T + 0.0061. The relation of Δ88/86 Sr to pCO2 was tested in Emiliania huxleyi at 10 and 20°C and resulted in Δ88/86 Sr = -5.394 × 10-5 pCO2 - 0.0920 and Δ88/86 Sr = -5.742 × 10-5 pCO2 - 0.1351, respectively. No consistent relationship was found between coccolith Δ88/86 Sr and cellular physiology impeding a direct application of fossil coccolith Δ88/86 Sr as coccolithophore productivity proxy. An overall significant correlation was detected between the elemental distribution coefficient (DSr ) and Δ88/86 Sr similar to inorganic calcite with a physiologically induced offset. Our observations indicate (i) that temperature and pCO2 induce specific effects on coccolith Δ88/86 Sr values and (ii) that strontium elemental ratios and stable isotope fractionation are mainly controlled by precipitation kinetics when embedded into the crystal lattice and subject to vital effects during the transmembrane transport from seawater to the site of calcification. These results provide an important step to develop a coccolith Δ88/86 Sr palaeoproxy complementing the existing toolbox of palaeoceanography.

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RESUMEN

Didemnum granulatum is a colonial fouling ascidian that lives in subtidal substrates, worldwide. It exhibits two morphotypes, orange and beige. In this study, we verified if the color morphotypes and/or the spatial distribution of specimens in different islands might be associated to patterns of genetic structure of a single species, or if they represent distinct cryptic species. Specimens were collected in four islands, along the coast of the Santa Catarina state. A segment of 490 bp from the mitochondrial gene cytochrome c oxidase subunit 1 (COI) was amplified from 45 samples. Twenty-one haplotypes were identified. The total haplotype diversity (0.912) and the total nucleotide diversity (0.044) were high. The global Fst of the populations analyzed was 0.97, with most of the variation occurring between orange and beige groups (82.19%). The variation found between populations within groups was 15.37%, and 2.45% within populations. Haplotype networks and the neighbor-joining tree showed clear genetic divergence between individuals of distinct colors, and between the islands. These evidences strongly support the presence of a complex of two cryptic species for D. granulatum occupying the studied area. Both species were also highly genetically structured between islands, suggesting that the conservation process of these populations is complex.(AU)

Didemnum granulatum é uma ascídia colonial incrustante de substratos consolidados infralitorâneos, e de ampla distribuição mundial. Variação na pigmentação é comum em invertebrados marinhos, e morfotipos de D. granulatum das cores laranja e bege foram detectados na região. Neste estudo, nós verificamos se os morfotipos de cor e/ou a distribuição espacial dos espécimens nas diferentes ilhas podem estar associados aos padrões de estruturação genética de uma única espécie, ou se eles representam espécies crípticas distintas. Os espécimens foram coletados em quatro ilhas ao longo da costa do estado de Santa Catarina. Um total de 45 amostras tiveram amplificados um segmento de 490pb do gene mitocondrial citocromo oxidase subunidade I (COI). Vinte e um haplótipos foram identificados. A diversidade haplotípica total (0.912) e a diversidade nucleotídica total (0.044) foram altas. O Fst global das populações analisadas foi 0.97, e a maior parte da variação ocorreu entre os grupos laranja e bege (82.19%). A variação encontrada entre as populações dentro dos grupos foi 15.37%, e 2.45% dentro das populações. A rede de haplótipos e a árvore de Neighbor-joining mostraram nítidas divergências genéticas entre os indivíduos de cores distintas, e entre as ilhas. Tais evidências sugerem a presença de um complexo de duas espécies crípticas de D. granulatum na região. Ambas as espécies foram fortemente estruturadas geneticamente entre as ilhas, o que reforça a necessidade de que tais atributos sejam considerados em medidas de conservação e proteção do ambiente marinho, mais especificamente nestas ilhas.(AU)

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RESUMEN

Didemnum granulatum is a colonial fouling ascidian that lives in subtidal substrates, worldwide. It exhibits two morphotypes, orange and beige. In this study, we verified if the color morphotypes and/or the spatial distribution of specimens in different islands might be associated to patterns of genetic structure of a single species, or if they represent distinct cryptic species. Specimens were collected in four islands, along the coast of the Santa Catarina state. A segment of 490 bp from the mitochondrial gene cytochrome c oxidase subunit 1 (COI) was amplified from 45 samples. Twenty-one haplotypes were identified. The total haplotype diversity (0.912) and the total nucleotide diversity (0.044) were high. The global Fst of the populations analyzed was 0.97, with most of the variation occurring between orange and beige groups (82.19%). The variation found between populations within groups was 15.37%, and 2.45% within populations. Haplotype networks and the neighbor-joining tree showed clear genetic divergence between individuals of distinct colors, and between the islands. These evidences strongly support the presence of a complex of two cryptic species for D. granulatum occupying the studied area. Both species were also highly genetically structured between islands, suggesting that the conservation process of these populations is complex.

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