Springtime renewal of zooplankton populations in the Chukchi Sea
Introduction
The Chukchi Sea has long been recognized as a flow through system, with multiple lines of evidence demonstrating replacement of water and intrinsic plankton on time scales of order months for most of the region (e.g., Berline et al., 2008, Hopcroft et al., 2010, Wassmann et al., 2015, Stabeno et al., 2018, Woodgate, 2018). Given the relatively short turnover time of the Chukchi Sea (less than a year), it is clear that most if not all zooplankton populations are transient. However, because most previous descriptions of the zooplankton community have been conducted during the summer, only the summertime characteristics have been comprehensively described and there has been little information available from other times of the year to describe the seasonal evolution of the community composition or to track the advective progression of zooplankton through the Chukchi Sea.
Three main pathways carry water northwards through the Chukchi Sea from Bering Strait: through Hope Valley and Herald Canyon in the west, through the Central Channel to the east of Herald Shoal, and in the east along the western coast of Alaska and exiting through Barrow Canyon (Coachman et al., 1975, Weingartner et al., 1998, Weingartner et al., 2005, Woodgate et al., 2005). The circulation is somewhat complex, as both the western and central pathways branch or bifurcate at points along their pathways. Particularly relevant to the present study is the branching of the Central Channel pathway to the east just north of Herald Shoal and along the southern flank of Hanna Shoal (Pickart et al., 2016, Lin et al., 2019). Much of the outflow from the Chukchi Sea occurs through Barrow Canyon (Fig. 1). Upon exiting the canyon, a portion of the flow turns eastward to feed the Beaufort Shelfbreak Jet (Nikolopoulos et al., 2008), while a larger portion turns westward to form the Chukchi Slope Current (Corlett and Pickart, 2017; Li et al., 2019). The outflow from Herald Canyon feeds the eastward-flowing Chukchi Shelfbreak Jet (Linders et al., 2017).
Different water masses are associated with each of the main advective pathways (Coachman et al., 1975, Gong and Pickart, 2015). Generally, Anadyr Water enters Bering Strait in the west, following the western pathway through the Chukchi Sea. Alaskan Coastal Water enters the eastern side of Bering Strait in summer and is advected in the Alaskan Coastal Current along the eastern pathway to exit the shelf through Barrow Canyon. North of Bering Strait, Anadyr and Bering Shelf Water mix to form what is known as Bering Summer Water (Pisareva et al., 2015), which mostly follows the central pathway northward through the Central Channel, turning to the east north of Hanna Shoal, with several eastward divergences along the way.
Each of these water masses has been associated with characteristic zooplankton communities in recent studies (Wassmann et al., 2015 and references therein; Ershova et al., 2015, Pinchuk and Eisner, 2017, Spear et al., 2019, Xu et al., 2018). Most of the studies have further partitioned the water mass associated species groups into spatially distinct distributions. Furthermore, different nomenclatures for the water masses (e.g., Bering Summer Water vs. Chukchi Summer Water) somewhat complicates the synthesis. However, some generalities for each water mass can be described. Overall, the Bering Summer Water/Chukchi Summer Water (hereafter referred to as Bering Summer Water) is marked by Calanus glacialis, Pacific copepod species such as C. marshallae, Neocalanus spp. and Eucalanus bungii bungii (herein E. bungii) and meroplankton, with the abundances of Pacific species decreasing to the north. Lower abundances of Pacific species and meroplankton and more abundant euphausiids are typical of the Anadyr Water. The Alaskan Coastal Water generally carries more inshore, euryhaline smaller species such as Acartia hudsonica and Centropages abdominalis and is distinct from the neighboring Bering Summer Water. A fourth zooplankton community, dominated by Arctic endemics such as C. hyperboreus, is found along the northern edge of the Chukchi Sea and sometimes extending south through Barrow Canyon after reversal of the prevailing poleward flow there (Pinchuk and Eisner, 2017). While some overlap exists in terms of presence or absence between the water mass types, within a given study the zooplankton communities are distinct. Studies with a broader geographical coverage (e.g., Matsuno et al., 2011; Eisner et al., 2013, Ershova et al., 2015, Pinchuk and Eisner, 2017, Xu et al., 2018) also note both northern-southern and eastern-western transitions, both of which are likely related to the advective pathways, distance from the Bering Sea source, and seasonal evolution of the populations and communities.
Because most of the characterizations of the zooplankton communities have been conducted during summer, relatively little is known about those communities during other seasons or how the communities change throughout the year, driven by the phenology of the zooplankton themselves and how that phenology is linked to zooplankton advection through the Chukchi Sea. The congeneric large bodied copepods Calanus glacialis and C. marshallae are of particular interest, since they feature prominently in the zooplankton community and their populations may require re-establishment each year after being flushed out to the north over the winter (Wassmann et al., 2015). These species also are a critical link in the Arctic food chain as prey for planktivorous fish such as arctic cod (Walkusz et al., 2011, Rand et al., 2013).
The objectives of the present study are to describe the abundances and distributions of the copepods C. glacialis and C. marshallae (copepodid and adult life stages) and of large bodied zooplankton relative to the distribution of water masses and advective pathways during late spring in the northeastern Chukchi Sea. Because C. glacialis and C. marshallae are extremely difficult to differentiate taxonomically, and because C. marshallae is relatively rare, those species were not separated and are herein designated as C. glacialis (Plourde et al., 2005, Campbell et al., 2009, Nelson et al., 2009). The work presented here was conducted opportunistically during a cruise to the region that focused on hydrography, sea ice, and primary productivity of the Chukchi Sea in late spring (Arrigo et al., 2017). The goal was to establish information on the zooplankton community of the Chukchi Sea at that time of year and to gain insight into the population dynamics of the copepod C. glacialis, a key member of the mesozooplanton community. This is the first description of these associations and distributions during late spring when the zooplankton community is undergoing a seasonal evolution. It is also the first survey to capture both the overwintering and early summer zooplankton composition of the Chukchi Sea.
Section snippets
Methods
Sampling was conducted from May 16 – June 20, 2014 during a cruise on the USCGC Healy to the Chukchi Sea as part of the SUBICE (Study of Under-ice Blooms in the Chukchi Ecosystem) program (Arrigo et al., 2017). The cruise track was centered in the eastern Central Chukchi Sea between Pt. Hope/Cape Lisburne and the Chukchi slope with most work conducted considerably offshore of the Alaskan coast (Fig. 2). The sampling scheme was designed to intercept known and hypothesized advective pathways (
Results
Twenty-three zooplankton types, including life stages of C. glacialis, euphausiids, and meroplankton, were differentiated (Table 2). Smaller copepods such as Oithona spp. and Pseudocalanus spp. were collected with the 500 µm mesh net and were ubiquitous in the study area but were not sampled quantitatively with that large mesh-size net and are not included in the present analysis. Both spatial and temporal variability in the abundances of different taxa were observed. Some types were
Discussion
Zooplankton abundances and composition and C. glacialis population structure together revealed that there were three zooplankton communities, corresponding to three of the station groups (Group 1-Group 3), present in the northeastern Chukchi Sea during May-June 2014, one each found in the northern and southern portion of the study region and one at the northernmost stations, all associated with different water mass characteristics and with their distributions impacted by the prevailing current
Concluding remarks
Although associations between zooplankton community compositions and abundances in the Chukchi Sea have been described previously, this is the first description of these associations and distributions during late spring when the zooplankton community is undergoing a seasonal evolution. It is also the first survey to capture both the overwintering and summer zooplankton composition offshore of the Alaskan coast. A conceptual model describing the evolution of C. glacialis populations in the
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Many thanks to the Captain, Officers, and Crew of the USCGC Healy for their support during the cruise, especially the bosun mates for their help with the net tows, and to all members of the science party, especially Kevin Arrigo for inviting C. Ashjian to join the cruise. Special thanks to back deck science teammates Moritz Schmitt and Tanja Schollmeier for good company and moral support during all of the almost unpredictable overnight stations and to computer lab teammates Toby Martin, Scott
References (51)
- et al.
Mesozooplankton abundance and distribution in association with hydrography on Hanna Shoal, NE Chukchi Sea, during August 2012 and 2013
Deep-Sea Res. II
(2017) - et al.
Mesozooplankton prey preference and grazing impact in the Western Arctic Ocean
Deep-Sea Res. II
(2009) - et al.
The Chukchi slope current
Prog. Oceanogr.
(2017) - et al.
Physical control of the distributions of a key Arctic copepod in the Northeast Chukchi Sea
Deep-Sea Res. II
(2017) - et al.
Summertime circulation in the eastern Chukchi Sea
Deep-Sea Res. II
(2015) - et al.
Ecosystem characteristics and processes facilitating persistent macrobenthic biomass hotspots and associated benthivory in the Pacific Arctic
Prog. Oceanogr.
(2015) - et al.
Zooplankton community patterns in the Chukchi Sea during summer 2004
Deep Sea Res. II
(2010) - et al.
Life history and biogeography of Calanus copepods in the Arctic Ocean: an individual-based modeling study
Prog. Oceanogr.
(2012) - et al.
Zooplankton distribution in the western Arctic during summer 2002: hydrographic habitats and implications for food chain dynamics
J. Mar. Syst.
(2008) - et al.
Circulation of the Chukchi Sea shelfbreak and slope from moored timeseries
Prog. Oceanogr.
(2019)
On the nature and origin of water masses in Herald Canyon, Chukchi Sea: synoptic surveys in summer 2004, 2008, and 2009
Prog. Oceanogr.
Circulation of winter water on the Chukchi shelf in early Summer
Deep Sea Res. II
Spatial heterogeneity in zooplankton summer distribution in the eastern Chukchi Sea in 2012–2013 as a result of large-scale interactions of water masses
Deep-Sea Res. II
On the nature of wind-forced upwelling in Barrow Canyon
Deep-Sea Res. II
Flow of Pacific water in the western Chukchi Sea: Results from the 2009 RUSALCA expedition
Deep-Sea Res. I
Seasonal and Regional Patterns in Egg Production of Calanus glacialis/marshallae in the Chukchi and Beaufort Seas during Spring and Summer, 2002
Deep-Sea Res. II
Seasonal and interannual variation in the planktonic communities of the northeastern Chukchi Sea during the summer and early fall
Continental Shelf Res.
Distribution and diet of larval and juvenile Arctic cod (Boreogadus saida) in the shallow Canadian Beaufort Sea
J. Mar. Syst.
The contiguous domains of Arctic Ocean advection: trails of life and death
Prog. Oceanogr.
Circulation on the North Central Chukchi Sea Shelf
Deep-Sea Res. II
Increases in the Pacific inflow to the Arctic from 1990 to 2015, and insights into seasonal trends and driving mechanisms from year-round Bering Strait mooring data
Prog. Oceanogr.
A year in the physical oceanography of the Chukchi Sea: moored measurements from autumn 1990–1991
Deep Sea Res. Part II
Late spring nitrate distributions beneath the ice-covered Chukchi shelf
Geophys. Res. Lett.: Biogeosci.
Climate induced variability in Calanus marshallae populations
J. Plankton Res.
Euphausiid transport in the Western Arctic Ocean
Mar. Ecol. Prog. Ser.
Cited by (1)
Geographic variation in population structure and grazing features of Calanus glacialis/marshallae in the Pacific Arctic Ocean
2023, Frontiers in Marine Science