Mesozooplankton grazing during spring sea-ice conditions in the eastern Bering Sea

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• 作者：Robert G. Campbell^a ; ^{campbell@gso.uri.edu} ; Carin J. Ashjian^b ; Evelyn B. Sherr^c ; Barry F. Sherr^c ; Michael W Lomas^d ; Celia Ross^c ; Philip Alatalo^b ; Celia Gelfman^a ; Donna Van Keuren^a
• 关键词：Copepod ; Euphausiid ; Ingestion ; Diets ; Prey selection ; Grazing impact ; Spring bloom
• 刊名：Deep Sea Research Part II: Topical Studies in Oceanography
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：134
• 期：Complete
• 页码：157-172
• 全文大小：1301 K
• 卷排序：134

文摘

Mesozooplankton (copepods and euphausiids) grazing rates and prey preferences were determined during a series of three research cruises to the eastern Bering Sea in spring 2008, 2009, and 2010. Chlorophyll was dominated by large cells (>5 µm), especially at bloom locations where they usually comprised greater than 90% of the total chlorophyll biomass. The relative importance of microzooplankton to the prey field biomass decreased with increasing chlorophyll concentration, and was less than 10% of the total prey biomass in ice-edge bloom regions. Overall, microzooplankton was the preferred prey of the mesozooplankton, although phytoplankton/ice algae were the dominant component of the diet because of their much greater biomass, especially during blooms. There were differences between mesozooplankton species in their prey preferences: Metridia pacifica, Pseudocalanus spp. and Calanus spp. had the strongest preference for microzooplankton prey, while euphausiids (Thysanoessa spp.) and Neocalanus flemingeri/plumchrus appeared to feed non-selectively on all prey items. Mesozooplankton exhibited a saturating feeding response to chlorophyll concentration (Holling׳s type II) that could be modeled by Michaelis–Menten equations. Taxa-specific maximum ingestion rates generally followed allometric theory, with smaller zooplankton having higher feeding rates than larger zooplankton, and ranged from about 4–30% body carbon day−1. Trophic cascades during grazing experiments could result in a substantial underestimate of chlorophyll ingestion rates, especially for those taxa that had a strong preference for microzooplankton. Grazing impacts by mesozooplankton on the integrated chlorophyll biomass and primary production were 2.7±4.4 and 26±48% day−1, respectively. Impacts increased significantly with increasing mesozooplankton biomass, which increased from early to late spring. However, grazing impacts were extremely low in ice-edge bloom regions. Our findings suggest that even when grazing by microzooplankton is included in our grazing impact estimates, about 50% of the primary production in phytoplankton blooms during spring on the eastern Bering Sea shelf is not grazed and is available for direct export to the benthic community.