Bivalve Growth Rate and Isotopic Variability Across the Barents Sea Polar Front Michael L. Carroll Akvaplan-niva, Tromsø Norway William Ambrose, William Locke, Stuart Ryan, Beverly Johnson Bates College, Lewiston ME, USA International Sclerochronology Conference: Caernarfon, Wales May 2013

NESSAR - Norwegian Component of the Ecosystem Studies of Subarctic and Arctic Regions (Norwegian IPY ) Led by Ken Drinkwater, Institute of Marine Research Goal: quantify the impact of the Polar Front on the structure and function of Arctic marine ecosystems of the Barents sea in order to predict the ecosystem response to possible future climate change Physical Structure and Processes Ecosystem Structure Ecosystem Function

Objective Compare growth rates and temporal growth patterns of bivalve populations in close proximity but with different water masses Compare growth rates and temporal growth patterns of bivalve populations in close proximity but with different water masses Assess dietary sources from tissue stable tissue isotopes to explain growth differences Assess dietary sources from tissue stable tissue isotopes to explain growth differences Identify relationships between growth patterns and environmental drivers Identify relationships between growth patterns and environmental drivers Assess the influence of water masses (and Polar Front) in regulating benthic ecological function over extended time scales

Clinocardium ciliatum 50+ year max age 50+ year max age Soft-sediment dweller Soft-sediment dweller Suspension feeder Suspension feeder

Unique Elements of the Barents Sea System Water mass structure Water mass structure - Arctic Water, Atlantic Water, well-defined Polar Front Complex bathymetry Complex bathymetry Sea ice as a factor (spatially and temporally variable) Sea ice as a factor (spatially and temporally variable)

Arctic Water : B26 – 100 m B27 – 120 m Polar Front: B28 – 140 m B29 – 160 m Atlantic Water: B30 – 180 m Physical Setting and Sampling Locations Sampling in May and Sept Total transect length – 60km

Water Mass Properties May September

Overall Shell Growth Rates Growth rates LOWEST at the Polar Front B C A P<0.01

Stable Isotopes in Food Web Studies Consumer tissues are enriched in heavy Nitrogen isotopes compared to their diet Consumer tissues are enriched in heavy Nitrogen isotopes compared to their diet - 15 N/ 14 N generally increases (3–4 ‰) with trophic position. For Carbon, there is little fractionation with trophic position ( <1 ‰ ) For Carbon, there is little fractionation with trophic position ( <1 ‰ ) - 13 C/ 12 C can thus be used to trace carbon sources in systems where two isotopically distinct carbon sources are present “YOU ARE WHAT YOU EAT!”

Tissue Stable Isotopic Trends 2.1 ‰ 1.3 ‰

Seasonality in Food Supply Food source Carbon seasonally consistent; heavier in Atlantic and PF Nitrogen seasonally variable; more so at Polar Front and Atlantic

Summary Overall growth rates are highest in the Atlantic domain and lowest at the Polar Front in the Barents Sea Overall growth rates are highest in the Atlantic domain and lowest at the Polar Front in the Barents Sea Tissue stable isotope signatures reveal different food sources but consistent seasonality patterns among water masses Tissue stable isotope signatures reveal different food sources but consistent seasonality patterns among water masses - Atlantic: more refractory isotopic signature suggests degradation prior to ingestion, but also higher primary productivity - Arctic water – high-benthic pelagic coupling - Polar Front – more isotopically similar to Atlantic

Interannual Growth Patterns (SGI) Raw growth increments Standardized Growth Index Detrend for ontogenetic changes

Environmental Drivers (time series) Atmospheric (large-scale) Atmospheric (large-scale) - NAO, AO, AMO, Arctic Climatic Regime Index (ACRI) Oceanographic Time Series Oceanographic Time Series - Sea Temp. (Kola Time Series, West Spitsbergen Current), Sea Ice Cover Meteorological Variables Meteorological Variables - Air Temp., Pressure, Precipitation

Environmental Relationships

Statistical Model GLM, Multiple regression (Forward Stepwise) GLM, Multiple regression (Forward Stepwise) Arctic Polar Front Atlantic Ice Free Days - - * - - AMO * NAO - - * Kola Sea Temp. - Bjørnøya Precip Total Variability Explained (R 2 )

Is cold good for benthos? Why? Indirect food web interactions mediating food availability to the benthos Indirect food web interactions mediating food availability to the benthos - NAO+ = warm zooplankton dominated food web lower benthic food quality (Ottersen & Stenseth (2001; Witbaard et al. 2003) - Bering Sea benthic biomass increased in cold periods due to restriction of predatory demersal fish (Coyle et al. 2007) - Fram Strait POC flux greater in years with more sea ice (Lalande et al, 2012) Metabolic demand is reduced in cold water Metabolic demand is reduced in cold water

Summary Overall growth rates are highest in the Atlantic domain and lowest at the Polar Front in the Barents Sea Overall growth rates are highest in the Atlantic domain and lowest at the Polar Front in the Barents Sea Tissue stable isotope signatures reveal different food sources but consistent seasonality patterns among water masses Tissue stable isotope signatures reveal different food sources but consistent seasonality patterns among water masses - Atlantic: more refractory isotopic signature suggests degradation prior to ingestion, but also higher primary productivity - Arctic water – high-benthic pelagic coupling - Polar Front – more isotopically similar to Atlantic Interannual growth patterns reflect variation in cyclic oscillatory climatic modes and sea ice Interannual growth patterns reflect variation in cyclic oscillatory climatic modes and sea ice - Atlantic populations appear more sensitive to environmental variability - Periods with colder conditions were associated with enhanced growth Continued Arctic warming and sea ice attenuation could lead to poorer performance of benthos Continued Arctic warming and sea ice attenuation could lead to poorer performance of benthos

Acknowledgements Funding Provided by: Norwegian Research Council IPY, NESSAR U.S. National Science Foundation Hughes Foundation (Bates College)

Food Sources for Bivalve Growth Phytoplankton Phytoplankton δ 13 C -24, δ 15 N 4.0 δ 13 C -24, δ 15 N 4.0 Ice Algae Ice Algae δ 13 C -20, δ 15 N 1.8 δ 13 C -20, δ 15 N 1.8 Søreide et al Søreide et al Tamelander et al Tamelander et al Trophic Step: δ 13 C = 0.6 ‰ δ 15 N = 3.4 ‰ Søreide et al. Under review