Mesopelagic zooplankton feeding ecology and effects on particle repackaging and carbon transport in the subtropical and subarctic North Pacific Ocean

• Main Author: Wilson, Stephanie E.
• Format: Text
• Language: English
• Published: W&M ScholarWorks 2008
• Subjects: Marine Biology; Oceanography; Pacific; Subarctic
• Online Access: https://scholarworks.wm.edu/etd/1539616907; https://doi.org/10.25773/v5-8jmb-vw33; https://scholarworks.wm.edu/context/etd/article/2474/viewcontent/3340958.pdf

Differences in zooplankton community structure and diet within the mesopelagic zone (base of euphotic zone to 1000 m) play a key role in affecting the efficiency by which organic matter is exported to depth, but how the structure of mesopelagic food webs change with depth or location is poorly known. I examined how mesopelagic zooplankton affect particle export in an oligotrophic (Hawaii Ocean Time-series site ALOHA) compared to a mesotrophic (Japanese time series site K2) open-ocean system. In the first part of the study, I investigated how fecal pellet characteristics change with depth in order to quantify the extent of particle repackaging by mesopelagic zooplankton. There was significant evidence of mesozooplankton repackaging of sinking particles in the mesopelagic zone, as indicated by presence of new fecal pellet types (as different size, color, or shape) occurring at different depths. Fecal pellets reflected the disparate zooplankton community structure at the two sites, and larger pellets at K2 likely increased transfer efficiency of POC there compared to ALOHA. In the second portion of this study, I analyzed fatty acids (FA) in zooplankton and particles to characterize zooplankton diet and large (>51mum) particles in the mesopelagic zone of these two contrasting regions. Total FA concentration was higher in zooplankton tissue at K2, largely due to FA storage by ontogenetic vertical migrating species there. FA biomarkers that were indicative of particle feeding were also evident at both sites. Finally, I quantified cyanobacteria and small eukaryotic phytoplankton in the guts of mesopelagic zooplankton using light and epifluorescence microscopy to determine if mesopelagic zooplankton mediate the export of small phytoplankton to the deep sea. Cyanobacteria and small, eukaryotic phytoplankton occurred in the guts of nearly all target species sampled from the surface to 1000 m, indicating mesozooplankton grazing on aggregates is a pathway by which export of carbon and picoplankton can be enhanced. Guts ...