Seasonal water column stratification drives the ontogeny of pelagic tunicates in shallow shelf systems

Pelagic tunicates, including salps and doliolids, can substantially impact microbial processes, carbon cycling, and the fate of primary production in continental shelf systems. However, the mechanisms behind their capacity to form blooms remain unclear. The precise oceanographic conditions experienced by these animals and their vertical migrations throughout ontogeny are needed to resolve the environmental drivers of their location, patchiness, abundance, and transport. To fill this knowledge gap, an in-situ imaging system was deployed in the northern Gulf of Mexico (nGOM) during the fall and summer of 2015-2016. The nGOM undergoes a seasonal shift from highly stratified summer conditions to fully mixed waters by mid-fall, making this location ideal to examine the impacts of vertical water column structure on salp and doliolid distributions. Images from multiple transects were manually classified into different life stages, including doliolid gonozooids, phorozooids, and nurses, and individual salps, salp rings, and chains. In summer, salps were consistently located within and around the pycnocline, regardless of their life stage. In contrast, doliolid stages showed distinct vertical distribution, with gonozooids and phorozooids primarily found above the pycnocline, and most nurses deeper in hypoxic (<2 mg/L) bottom waters. Even in the well-mixed conditions in fall, doliolids preferred deeper waters further offshore, suggesting that their patchiness is influenced by factors beyond vertical oceanographic structure.

Presentation Preference: Poster

Primary Presenter: Laura Treible, Savannah State University (laura.treible@gmail.com)

Authors:

Laura Treible, Savannah State University  (laura.treible@gmail.com)

Luciano Chiaverano, Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP)  (lchiaverano@gmail.com)

MickiAnne Harris, Weber State University  (mickianne13@gmail.com)

Patrick Duffy, University of Georgia, Skidaway Institute of Oceanography  (patrick.duffy@skio.uga.edu)

Adam Greer, University of Georgia, Skidaway Institute of Oceanography  (atgreer@uga.edu)