Modern epiphytic foraminifera have been reported on seagrasses from different areas, but little is known about those living on macroalgae. This study on reefal environments of New Caledonia is the first to inventory epiphytic foraminifera on a large number of well-identified macroalgae. Its objective is to learn more about epiphytal foraminiferal ecology and its use for environmental and paleoenvironmental interpretations. A total of 152 species of epiphytic foraminifera were identified on 81 substratal phyta that include 55 species of macroalgae. This study confirms the complexity of the distribution of foraminiferal communities on phytal substrata at a micro-scale, and shows that temporal availability of the substratum might play a role. It also reveals that some foraminiferal species might have quite different life modes between environments and regions. The structural characteristics of the macroalgae explain part of the differences in epiphytic foraminiferal assemblage composition. The only strong relationship established between macroalgae and foraminifera is the presence of spinose rotaliids, soritids, and Amphistegina in filamentous thalli and three-dimensional mats. However, macroalgal species that have a wide bathymetric range might harbor completely different communities at different depths, in which case the nature of the substratum might be overshadowed by other parameters such as light, depth, and hydrodynamics. These results call for prudence when interpreting paleoenvironmental data, and show that long-term monitoring is needed to define population dynamics that could be applied in paleoenvironment and paleoclimate reconstructions.

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