Quantifying spatiotemporal variability in mesozooplankton distribution and nutritional quality around seamounts within the Canadian Offshore Pacific Bioregion

Date

2024-01-04

Authors

Labbé, Daniel M.

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Abstract

Zooplankton are a diverse group of organisms that are the key link between primary producers and higher trophic levels in marine ecosystems. They are an important food source for many fish, marine mammal, and sea bird species, and are a major allochthonous energy source for seamounts. Therefore, zooplankton are an important indicator of ecosystem processes in the open ocean. The southern portion of the Canadian Offshore Pacific Bioregion (OPB), in the Northeast Pacific, is a seamount-rich environment that has recently been a target of conservation efforts by the Canadian Government via the proposal of the Tang.G̲wan - ḥačxwiqak - Tsig̲is (TḥT) Marine Protected Area (MPA). Oceanographic research expeditions (Northeast Pacific Deep-sea Exploration Project; NEPDEP) from 2015 to 2022 surveyed near seamounts to inform the monitoring and management of TḥT and other MPAs in the Canadian OPB. Part of this sampling program included oceanographic and zooplankton sampling. Marine monitoring typically only accounts for variability in zooplankton biomass and/or species abundance, overlooking potential variability in zooplankton nutritional quality. This thesis uses size fractionated zooplankton biomass samples to quantify the spatiotemporal variability in zooplankton biomass and nutritional quality (i.e., energy density, total lipids, and total proteins) in the Canadian OPB. The data presented in this thesis indicate that zooplankton distribution is driven primarily by mesoscale oceanographic processes and not by the presence of seamounts, per se. Interannual variability was the most significant driver of change in the zooplankton community, representing up to a 7-fold difference in biomass and up to a 2-fold difference in zooplankton nutritional quality, where generally warm (cool) water years had less (more) nutritious zooplankton communities. Spatially, there were distinct differences between zooplankton collected within offshore and continental slope regions, which influences the allochthonous energy provided to seamount ecosystems. This data was also used to identify key zooplankton taxa which appear to have a disproportionate effect on total zooplankton nutritional quality. Notably, Neocalanus spp. were associated with lipid-rich zooplankton samples, while gelatinous species (e.g., doliolids and salps) were associated with lower energy density. These data and analyses have important implications for the future monitoring and conservation of the Canadian OPB and provide important baseline characterization of the spatiotemporal variability of the zooplankton community around seamounts in this region.

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Keywords

Zooplankton, Seamount, Spatiotemporal variability, Nutritional quality, Lipids, Proteins, Energy density

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