OceTHE OFFICIALa MAGAZINEn ogOF THE OCEANOGRAPHYra SOCIETYphy CITATION Grebmeier, J.M., B.A. Bluhm, L.W. Cooper, S.G. Denisenko, K. Iken, M. Kędra, and C. Serratos. 2015. Time-series benthic community composition and biomass and associated environmental characteristics in the Chukchi Sea during the RUSALCA 2004–2012 Program. Oceanography 28(3):116–133, http://dx.doi.org/10.5670/ oceanog.2015.61. DOI http://dx.doi.org/10.5670/oceanog.2015.61 COPYRIGHT This article has been published in Oceanography, Volume 28, Number 3, a quarterly journal of The Oceanography Society. Copyright 2015 by The Oceanography Society. All rights reserved. USAGE Permission is granted to copy this article for use in teaching and research. Republication, systematic reproduction, or collective redistribution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] or The Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. DOWNLOADED FROM HTTP://WWW.TOS.ORG/OCEANOGRAPHY RUSSIAN-AMERICAN LONG-TERM CENSUS OF THE ARCTIC Time-Series Benthic Community Composition and Biomass and Associated Environmental Characteristics in the Chukchi Sea During the RUSALCA 2004–2012 Program By Jacqueline M. Grebmeier, Bodil A. Bluhm, Lee W. Cooper, Stanislav G. Denisenko, Katrin Iken, Monika Kędra, and Carlos Serratos 116 Oceanography | Vol.28, No.3 Photo credit: Bodil Bluhm ABSTRACT. Benthic macrofaunal and epifaunal composition and biomass and system in the Pacific Arctic will influence associated environmental drivers were evaluated for time-series stations occupied system-level ecological processes and during three cruises of the RUSALCA (Russian-American Long-term Census of the what the potential tipping points are in Arctic) program undertaken in August 2004, September 2009, and September 2012. biological community structure and bio- We focus on the benthic communities collected at repeat stations in the southern diversity (Moore and Stabeno, 2015). A Chukchi Sea and the key environmental characteristics that could influence benthic primary goal of our study was to inves- population structure and biomass. These characteristics included bottom water tigate the benthic ecological response to temperature, salinity, and chlorophyll a (chl a); integrated chl a; export production via these changing physical driving factors by sediment oxygen uptake rates as an indicator of food supply to the benthos; and surface evaluating time-series benthic collections sediment parameters that are known to influence benthic population community in the southern Chukchi Sea between the composition and biomass, such as grain size, carbon content, and chl a. Overall, both United States and Russia. the macrofaunal and epibenthic community composition at the time-series sites in the Using samples collected during three southern Chukchi Sea have remained relatively constant over the time period of this cruises of the Russian-American Long- study (2004–2012). However, some of the more sedentary macrofauna are showing term Census of the Arctic (RUSALCA) significant declines in biomass since 2004, particularly in the center of a macrobenthic in 2004, 2009, and 2012 by both Russian hotpot that has been persistent for decades in the southern Chukchi Sea. While and American scientists (Figure 1), we biomass estimates were more variable for the more motile epibenthic fauna, there was investigated key processes that influ- also an indication of declining epifaunal biomass since 2009. We highlight here as a ence the Pacific Arctic benthic ecosystem case study the benthic time-series efforts during RUSALCA that are also part of the (both macrofauna and epifauna). Over Distributed Biological Observatory (DBO) international network, which is tracking the observation period, the southern the status and trends of Arctic ecosystem response to the changing physical drivers in Chukchi Sea benthic habitat has increas- the southern Chukchi Sea. ingly been exposed to significantly longer open-water periods as seasonal sea ice INTRODUCTION and benthic processes is essential for has declined (Frey et al., 2014, 2015). We Changing seasonal sea ice conditions and tracking and forecasting ecosystem have collected and developed, with col- seawater temperatures strongly influence responses in the Pacific Arctic region, leagues, a large data set of benthic macro- biological processes and marine ecosys- where the greatest changes in Arctic sea- faunal, and to a limited degree epifaunal, tems at high latitudes (Grebmeier et al., sonal sea ice duration and extent have abundance and biomass in the eastern 2006a; Kędra et al., 2015). Understanding been observed (Grebmeier et al., 2010; Chukchi Sea over the last three decades the impacts of reduced seasonal sea ice Frey et al., 2015). Two important ques- (Feder et al., 2005, 2007; Grebmeier and warming seawater on water column tions concern how the developing new et al., 2006a, 2015 and references therein; FIGURE 1. Distribution of RUSALCA benthic sampling stations with HC49 KHR-73B HC46 SS3 sampling years color-coded: 2004 WN3 HC55 HC26-1 Beaufort HC52 HC22 HC21 Sea in green, 2009 in red, and 2012 in G8 SS4 WN2 Herald HC18 HC40 blue, and repeat time-series sites KHR-85B Canyon HC26 SS5 HC27 G11 for two of the years in yellow and WN1 KHR-62B KHR-58B Wrangel HC60 G12 all three years in purple. The circles East Siberian Is. 70° N Sea HC3 HC2 represent collections by US scien- CEN1a HC1 G13 LS3 KHR-106 KHR-107 HC14 tists and the squares by Russian S2 G14 LS1 Chukchi scientists. The general current flow CEN3 Sea Data Source (dotted and solid lines with arrows) X2 USA CEN5 S7 BSW D10 Russia is modified from Grebmeier et al. SCC CL3 CL2 CL1 CL4 KHR-22 Sample Year Cape Lisburne (2015). This paper focuses on X1 CL6 KHR-24 CS17 2004 the southern Chukchi Sea time- Point Hope 2009 CL8 AW CS13 series sites indicated by purple RUSSIA CL9 CS12 2012 CL10 CS8 dots along the CS (Chukchi South) 2009, 2012 CS7 ACW and CL (Cape Lisburne) lines. CS4 2004, 2009, 2012 ACW = Alaska Coastal Water. X26 Depth (m) X27 BSW = Bering Sea Water. 65° N 0 - 30 UNITED AW = Anadyr Water. 30 - 50 STATES SCC = Siberian Coastal Current. 50 - 80 80 - 200 0 80 160 > 200 nm 175° E 180° 175° W 170° W 165° W 160° W Oceanography | September 2015 117 Bluhm et al., 2009; Iken et al., 2010; US-Russian/Soviet programs such as (CL) transect lines (Figure 1), in con- Blanchard et al., 2013a; S. Denisenko BERPAC [Bering-Pacific studies]), as well junction with the Distributed Biological et al., 2015, in this issue). Other related as time-series studies in other regions of Observatory (DBO) program initiated studies have assessed carbon cycling in the Chukchi Sea continental shelf, have in 2010 (Grebmeier et al., 2010) that also general (reviewed in Grebmeier, 2012; identified “footprints” of persistent ben- includes a subset of stations on the CS line Mathis et al., 2014; Grebmeier et al., 2015). thic biomass, dominant fauna, and export (see Box 1). These time-series stations are However, there have been very limited of carbon to the sediments in the Pacific also part of the Circumpolar Biodiversity oceanographic and biological studies on Arctic region (Grebmeier et al., 2015). Monitoring Program (CBMP), which is the continental shelf regions of the west- The RUSALCA macrofaunal and part of the Conservation of Arctic Flora ern Chukchi Sea and East Siberian Sea, epibenthic studies have been under- and Fauna (CAFF) activity of the Arctic which were focus areas for the RUSALCA taken since 2004, specifically along the Council (CAFF, 2013). The international program. RUSALCA (and the previous Chukchi South (CS) and Cape Lisburne aspects of the RUSALCA program add BOX 1. TIME-SERIES BENTHIC BIOMASS ON THE RUSALCA DBO/CS LINE The RUSALCA time-series stations on the Chukchi South (CS) tran- (Akademik Koralev), in 1993 (Okean), in 1995 (Alpha Helix), and sect (Figure B1, left panel) have been incorporated into the interna- annually since 1998 during DBO cruises with international collab- tional Distributed Biological Observatory (DBO), which is tracking orators aboard CCGS Sir Wilfrid Laurier (only in US waters). the status and trends of benthic communities and environmen- Time-series data in the region indicate spatial and temporal tal conditions in the region. The RUSALCA data have been instru- variability in the benthic communities due to variable water mass mental in delineating the benthic biomass hotspot that extends dynamics and current velocities. The data overall (excluding the across the US-Russian border, thereby providing coordinates for hotspot stations UTN5 and CS8) indicate declining benthic bio- an enhanced suite of ecosystem observations in this region. Data mass since the 1970s, with a more rapid decline starting in the have been collected in this area not only by RUSALCA during the late 1990s (Figure B1, right). However, the high biomass UTN5 first decade of this century but also during prior Russian and US station on the CS line had increasing benthic biomass from 2000 cruises, including the joint Bering-Pacific cruises (BERPAC) in 1988 to 2010, with subsequent declines after that to 2012; this decline 120 Dominant Taxa Stations 100 UTN1 ) UTN2 –2 Bivalvia Others UTN3 Sipuncula Anthozoa Nemertea m 80 Polychaeta CrustaceaAscidiacea Echinoidea Ophiuroidea UTN4 60 UTN5 UTN6 East Siberian UTN7 Sea Beaufort 40 70° N Sea CS4 Wrangel biomass (gC CS8 Is. Macrofaunal benthic 20 CS12 CS17 Chukchi 0 Predicted Benthic Sea =DBO3 Stations CS-17 DBO3.1 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 Biomass United 2 UTN-7 States (gC/m ) CS-12 Year 0.01 – 10 UTN-5 UTN-6 CS-8 UTN-4 10 – 20 UTN-3 FIGURE B1. (left) Distribution of dominant benthic macrofaunal taxa 20 – 30 CS-4 UTN-2 30 – 40 DBO3.14 UTN-1 RUSSIA Russia type and total station biomass in the Chukchi Sea from 1973 to 2012 40 – 70 70 – 251 (updated from Grebmeier et al., 2006a).