FINICKY FORAMS: HETEROGENEITIES IN RECRUITMENT ON EXPERIMENTAL SUBSTRATES, ROSS SEA, ANTARCTICA

Benthic recruitment is essential for structuring ecological communities, from the deep sea to tropical regions. In those regions, forams (foraminiferan protists) may comprise a major component of the benthic ecosystem, as they have in ancient ecosystems, extending to the Cambrian. However, very little is known about benthic foram recruitment in polar regions, and this is especially true for Antarctica. In the Ross Sea, invertebrate recruitment is thought to occur over decades, and in subantarctic regions, invertebrate recruitment occurs within two years in seasonally warmer waters. In previous studies, non-local, inorganic recruitment panels were deployed, but how might those non-organic substrates affect benthic recruitment, especially if larvae or propagules may be selective?

Here, we show that recruitment of benthic forams differ between experimental arrays composed of two treatments: inorganic calcite (in mesh bags of 0.1mm² opening) and natural calcite from the Antarctic scallop, Adamussium colbecki (in mesh bags of 1.0 mm² opening). The arrays were deployed at 9 m (30 ft) by ice divers at the Herbertson Glacier site of McMurdo Sound, Ross Sea, Antarctica. After two years on the seafloor, the arrays were retrieved, and for each mesh bag and substrate, the forams were identified and counted. If foraminiferal propagules were not selective of substrate type, we would expect that similar recruitment would occur on both treatment, but we found that recruitment was significantly higher on natural substrates than unnatural substrates (t-test, P < 0.01). Additionally, variance in recruitment was significantly higher on A. colbecki substrates and mesh bags than those of inorganic calcite (F-test, P < 0.01), indicating patchiness in recruitment. Our findings suggest that foraminiferal propagules are significantly more likely to recruit to natural substrates than to inorganic substrates. Therefore, utilizing natural substrates in taphonomic and paleoecologic studies may provide more accurate data to understand recruitment, community structure and dispersal capabilities of encrusting forams.