In situ observations of giant appendicularians in Monterey Bay

Giant appendicularians (Bathochordaeus sp., Urochordata, Appendicularia) were observed in midwater in Monterey Canyon, Monterey Bay, California, from manned submersibles, Deep Rover, Alvin and MIR I, and with video from a ROV. Bathochordaeus utilizes secreted mucus structures to feed, but these structures and the orientation of the animal to the feeding-filter differ significantly from those of other genera in the Family Oikopleuridae. A continuously secreted sheet of mucus (unlike the episodically produced structured houses of other appendicularians) envelops both the body and the feeding-filter, protecting the animal from predators and scavenging large particles from the water feeding-filter, protecting the animal from sheet is occasionally up to 2 m in diameter, and large amounts of particulate material accumulate on this surface over time. We calculate that an individual can maintain the mucus sheet at specific depth horizons for as long as 30 days, collecting and impeding the downward flux of particulates. Eventually the sheet is disturbed or separates from the animal and feeding-filter due to its sediment burden, and collapses into a compacted mass which sinks rapidly (±800 m day⁻ to the sea bed to depths of at least 3500 m. The obvious importance of these often common, large, filter-feeding appendicularians in water column ecology and vertical flux will require further investigation.