Foraminifers as hard substrates: an example from the Washington (USA) continental shelf of smaller foraminifers attached to larger, agglutinate foraminifers

This study from the continental shelf offshore from Washington, USA, describes an occurrence of attached foraminifers using other, larger foraminifers as their hard substrate. Isolated instances of such associations have been illustrated in a few publications; however, the example documented here is of an extensive relationship between smaller attached foraminifers and their substrate species. Host foraminifers were unusually large (4 mm to 5 cm) specimens of the agglutinate species Ammodiscus pacificus, Haplophragmoides canariensis, Rhabdammina linearis and Bathysiphon filiformis. The attached foraminifers were Cibicides pseudoungerianus, Tritaxis fusca and Cibicides refulgens. In addition to the attached foraminiferal tests, several attachment scars were evident, some of which can be attributed to epibiont foraminifers that became detached from the host.

There are several possible reasons these smaller foraminifers colonized the larger ones in this area. Most likely, the host foraminifers provided a stable platform for feeding. In addition, if the host was living, its motility could have prevented the smaller foraminifers from being smothered in this high sediment accumulation setting. Thus, these larger foraminifers act as convenient “benthic islands” (Taylor and Wilson, 2003) for their epibionts.