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Midwater research

Deep-water salps in Monterey Bay
Project Manager/Lead Scientist: Larry Madin 

Investigation of pelagic tunicates in Monterey Bay has so far focused on appendicularians and, more recently, doliolids. The salps present appear to be mainly species found in the California Current or further offshore, which come into the Bay during the fall, but are not found at other times of the year. As filter feeders, salps are epipelagic or diel migrators, but no known species is wholly mesopelagic. This is in contrast to species of appendicularians (e.g. Bathochordaeus spp.), pyrosomes and doliolids (Doliopsis spp.) that occur in the midwater zone in Monterey Bay and elsewhere. As these are also filter feeders, using mechanisms similar to those of salps, it is surprising that no midwater salps have been reported.

This situation may now have changed. During an ROV dive in March 2001, Bruce Robison and I collected several specimens of a salp, both solitary and aggregate generations, which appeared to be limited to midwater depths. Although never identified, the salp had been seen on many previous dives by Robison and his research team and always seemed to occur in midwater. The salps were exceptionally delicate and transparent; they did not match any described species (there are about 40 species) and may well be a new species and/or genus. This would be the first new salp species found in many years, and possibly the first one restricted to midwater.

I propose to investigate the identity, occurrence and ecology of this salp in Monterey Bay, using the ROV Ventana for collection and observation, and the MBARI video library for records of occurrence. Working with Robisonís midwater group, I will use Ventana to collect additional specimens for detailed examination and laboratory experiments. This work will include a species description (if appropriate), and measurements of respiration, excretion, feeding rate, swimming speed and temperature tolerance. I will attempt to examine gut contents to see whether there is evidence of feeding in epipelagic or mesopelagic waters. Depending on success in keeping these salps alive at MBARI, it may also be possible to measure growth and reproductive rates. If this is truly a midwater species, it is likely to have a lower metabolic rate and food requirement than epipelagic forms. Comparative data are available for most other salp species (Madin & Deibel, 1998), and results from this species would be an interesting complement to work I am conducting on two other species (Thalia democratica and Salpa aspera) in the NW Atlantic, with funding from the National Science Foundation. The discovery and characterization of a mesopelagic salp would certainly expand our knowledge of the ecology and evolution of pelagic tunicates and their adaptation to varied niches in the water column.