FORAMINIFERAL POPULATION DYNAMICS ON ELEVATED SUBSTRATES AND IN SEDIMENTS AT 4,000M IN THE EASTERN PACIFIC (Invited Presentation)

After two years on the seafloor, four SEA3S (Seafloor Epibenthic Attachment Cubes) were recovered from 4000 m water depth at Station M in the Pacific Ocean. Significant, colonizing populations of foraminifera (Cibicidoides wuellerstorfi var lobotulus, Pyrgo sp., and an arborescent species) dominated these hard, elevated substrates, including the mesh on the cubes as well as plastic welding and fiberglass rods that extended upward from the SEA3. About 240 individual foraminifera were removed from the various plastic rods attached to SEA3s. Relatively equal numbers of individual foraminifera colonized the plastic (55 on ABS and 36 on PVC) and fiberglass (51 and 44 individuals on 2 rods) substrates. Other rods yielded appreciably fewer colonizing foraminifera with a total of only 16 individuals on all 4 rods. Within nearby sediments, Rose Bengal stained Nodosinum, Reophax, Paratrochammina, and other agglutinated foraminifera dominated the two push cores examined. Some Nodosinum specimens reached sizes from 4 to 15 mm. Total abundances in the two cores examined were relatively low (~150 to 20 individuals per 50cc). Globobulimina affinis was prevalent deeper within the core and made up the majority of calcareous fauna. Long-term records at Station M and the presence of intact radiolaria and planktonic foraminifera illustrate the connection with surface productivity in this abyssal locality.

It is noteworthy that foraminiferal populations colonizing the cubes differ appreciably from those in surrounding sediments. Available data suggest that epifaunal populations may not have been sourced from surrounding sediments, but may have colonized from propagules possibly distributed from nearby elevated substrates such as glass sponges. Likewise, colonizing epifauna do not seem to have appreciably influenced nearby sediment populations. These results provide clues about foraminiferal species substrate preferences and colonization patterns provide further evidence that substrate plays an important role in deep-sea meiofaunal heterogeneity and foraminiferal population dynamics. Observed differences between colonizing epifaunal foraminifera and sediment populations raise intriguing questions about colonization processes in deep bathyal and abyssal habitats.