Pores are among the dominant morphological features characterizing benthic foraminiferal tests. The presence, arrangement, and size of these pores vary greatly, likely in response to environmental conditions on the sea floor.
In this study, surface pores of deep-sea taxa from a number of locations with different bottom water oxygen conditions (Sulu Sea, California Borderlands, North Atlantic) are studied and show distinct patterns. Infaunal species, such as Chilostomella, Globobulimina, Pullenia, and Melonis spp., have pores widely distributed over most of the test surface, previously suggested to be in response to low oxygen levels in the pore waters.
Biconvex forms considered to live within the upper centimeter of sediments, such as Hoeglundina elegans and Oridorsalis umbonatus, have abundant small pores over most of the test, which may reflect low oxygen within the sediments, as well. Taxa living at the surface in well-oxygenated bottom waters, such as Planulina wuellerstorfi, have large pores on the spiral side, which are useful for streaming of protoplasm to attach the organism to hard substrates, and pores absent on the umbilical side. In contrast, specimens of P. wuellerstorfi from low oxygen locations, such as the California Borderlands and Sulu Sea, have pores over the entire test and are suggested to be advantageous in obtaining sufficient oxygen. The umbilical side can be evenly covered with pores, or pores can be restricted to the later, larger chambers, indicating ontogenetic differences. These observations indicate that the presence or absence of pores, their distribution, and abundance are ecophenotypic variations, in response to oxygen conditions overlying or within surficial sediments, in addition to being important for substrate attachment for some taxa.
If pore characteristics do reflect ecophenotypic variability, these findings suggest that pore patterns of epifaunal species, such as P. wuellerstorfi, will vary as a function of dissolved oxygen levels and have the potential of qualitatively reconstructing oxygen levels in the deep ocean from the fossil record.