A comparison of foraminiferal infaunal distributions in field and experimental samples from 550-m depth in the Bay of Biscay

In three successive laboratory experiments the infaunal distribution of benthic foraminifera from the same collection site in the Bay of Biscay was studied and compared to field data. Over a period of 3 years, on three separate occasions, a total of 24 cores containing live foraminifera were collected and used for different experiments. After initial mixing of the sediment, species distribution was similarly restored in all experiments and species composition remained unaltered. For a comprehensive summary and statistical evaluation of the vertical distribution patterns of the six dominant species Erlang distributions were used. The infaunal distribution patterns of individual species varied with time in the field and showed more variation compared to the three experiments. However, the vertical succession of species in cores from the same date or experiment was very similar. A significant correlation exists between optima of taxa that share a similar range of optimum depths. Shallow-living species positively correlate with intermediate species, which in turn also positively correlate with deep-living species. Conversely, no significant correlation exists between the shallow and deep optimum species. The vertical distribution patterns show more variation in the field cores, where the oxygen-penetration depth also shows more variation. Less variation is observed in the oxygen profiles and foraminiferal distribution patterns in the experimental cores. This difference in variation of the position of the oxic/anoxic boundary and of the vertical distribution of benthic foraminifera between the experimental and field cores points to a correlation between sediment geochemistry and the optimum foraminiferal occurrence. This study further shows that experiments with bathyal benthic foraminifera are replicable under laboratory conditions and that the habitat preferences of foraminifera are not altered in an experimental setting or after mixing of sediments. These results support the great potential of culture experiments with natural substrates and differentiated infaunal habitats to establish relationships between environmental parameters and foraminiferal test chemistry as proxies for past conditions.