The marine bivalve species, Arctica islandica, was reared under experimental conditions for 29 weeks in the Gulf of Maine in order to determine the relationship between the carbon isotope composition of shell carbonate (delta C-13(S)) and ambient seawater dissolved inorganic carbon (delta C-13(DIC)), as well as to approximate the metabolic contribution (C-M) to shell material. Three experimental environments were compared: two flow-through tanks (one at ambient seawater conditions, one with a supplemental food source) and an in situ cage. Each environment contained 50 juveniles and 30 adults. Both juvenile (2-3 years) and adult (19-64 years) specimens displayed average percent C-M of less than or equal to 10% when using three different proxies of respired carbon: digestive gland, adductor muscle and sediment. Hence, the primary control on delta C-13(S) values is ambient DIC. The relationship between delta C-13(DIC) and delta C-13(S) for 114 individuals used in the study was:delta C-13(DIC) = delta C-13(S) - 1.0 parts per thousand (+/- 0.3 parts per thousand)No ontogenetic effect on delta C-13(S) was observed, and growth rates did not generally impact delta C-13(S) values. Based on the results of this study, shell material derived from the long-lived ocean quahog (A. islandica) constitutes a viable proxy for paleo-DIC from the extratropical Atlantic Ocean. (C) 2012 Elsevier Ltd. All rights reserved.

The production of cultured Eastern oysters (Crassostrea virginica) in the northern New England states and Canadian Maritime Provinces is hampered by a short growing season, relatively cold water temperatures, and outbreaks of Roseovarius Oyster Disease (ROD). A breeding program at the University of Maine has produced the University of Maine Flowers Select (UMFS) line by selecting for oysters with improved cold water growth performance and resistance to ROD. We conducted two grow-out trials comparing the survival, size, and yield for the UMFS line to two other genetically improved lines of Eastern oysters to assess the suitability of this line outside of the Damariscotta River, where it was developed. In the first trial, oysters were deployed in August just prior to when ROD outbreaks typically occur in Maine among small, seed oysters. We observed substantial differences in yield in this field trial, particularly at study sites located on the Damariscotta River. These differences were due to variation in line-specific survival. The second field trial was deployed in June when ROD has less of an impact on seed oysters. Mortality in this second trial was lower than in the first trial and there was a corresponding higher dependence of line-specific yield on variation in growth. However, there was no line which consistently grew better and had higher yield at all sites. Based on our results, we suggest that breeding programs for Eastern oysters may benefit from focusing on the additive nature of survival variation among lines and placing less emphasis on the relatively subtle variation in line-specific growth.

To further evaluate the potential use of Mg/Ca and Sr/Ca ratios as a paleothermometer in the shell carbonate of the blue mussel Mytilus edulis, we grew juvenile mussels (∼15 mm shell height; <2 years old) collected from Maine, USA, in controlled environments for 4 months. The four-by-three factorial design consisted of four circulating temperature baths (7, 11, 15 and 19°C), and three salinity ranges (23, 28, and 32). During the experiment, water Mg/Ca and Sr/Ca molar ratios were monitored weekly, and showed little variation across all salinity and temperature ranges. Data from sampled shells including all salinity treatments yielded relatively poor relationships between shell elemental chemistry and water temperatures. However, if only the low salinity treatment data (23) are used, the relationships between shell elemental chemistry and water temperature improve moderately. Based on the data presented here, it may be possible to use Mg/Ca and Sr/Ca ratios from the shell carbonate of juvenile M. edulis to reconstruct paleotemperatures in estuarine settings (salinity below 24) with a corresponding RMSE (root mean squared error; 95% confidence interval) of ±2.4°C and ±2.8°C, respectively. In order for this methodology to be statistically meaningful, water temperature changes must be rather large, as the errors associated with using Mg/Ca and Sr/Ca ratios from the shell material of M. edulis are substantial. Further work is required to determine if the findings presented here can be duplicated, and if the potential salinity effect is pervasive.

The relationship between stable isotope composition (δ13C and δ18O) in seawater and in larval shell aragonite of the sea scallop, Placopecten magellanicus, was investigated in a controlled experiment to determine whether isotopes in larval shell aragonite can be used as a reliable proxy for environmental conditions. The linear relationship between δ13CDIC and δ13Caragonite (r2 = 0.97, p < 0.0001, RMSE = 0.18) was:δ13CDIC=1.15(±0.05)∗δ13Caragonite-0.85(±0.04)The relationship between δ13CDIC and δ13Caragonite described for P. magellanicus resulted in larval shell aragonite that was depleted on average by 1.82‰ (SD = 0.22‰, range = 1.1–2.1‰) from predicted equilibrium values based on the relationship calibrated for inorganic aragonite. The average contribution of metabolic carbon that resulted in this depletion was 5.4% (SD = 0.57%; range = 3.4–7.8%). Stable oxygen isotopes were deposited into the larval shell in equilibrium for most samples, and the linear relationship described by least squares regression between temperature and δ18Oaragonite–δ18Owater (r2 = 0.90, p < 0.0001, RMSE = 0.63) was:T(°C)=20.0(±0.4)-4.6(±0.3)∗(δ18Oaragonite-δ18Owater)However, larvae reared under "stressful" conditions were depleted from oxygen isotope equilibrium. Further studies are necessary to determine the variable contribution of metabolic carbon to the larval shell in field conditions, the potential effects of growth rate on carbon isotope composition, and the factors influencing oxygen isotope depletion in P. magellanicus larval shell before the isotope composition of larval shells can be used to reconstruct δ13CDIC or temperature of the seawater in which the larvae developed.

To investigate ocean variability during the last millennium in the Western Gulf of Maine (GOM), we collected a 142-year-old living bivalve (Arctica islandica L.) in 2004, and three fossil A. islandica shells (calibrated 14CAMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) for stable isotope and growth increment analysis. A statistically significant relationship exists between modern GOM temperature records [shell isotope-derived (30 m) (r = −0.79; P < 0.007), Prince 5 (50 m) (r = −0.72; P < 0.019), Boothbay Harbor SST (r = −0.76; P < 0.011)], and Labrador Current (LC) transport data from the Eastern Newfoundland Slope during 1993–2003. In all cases, as LC transport increased, GOM water temperatures decreased the following year. Decadal trends in the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) influence GOM water temperatures in the most recent period, with water temperatures decreasing during NAO and AMO negative modes most likely linked to LC transport and Gulf Stream interaction. Mean shell-derived isotopic changes (δ18Oc) during the last 1,000 years were +0.47‰ and likely reflect a 1–2°C cooling from 1000 ad to present. Based on these results, we suggest that observed cooling in the GOM during the last millennium was due to increased transport and/or cooling of the LC, and decreased Gulf Stream influence on the GOM.

To investigate environmental variability during the late Holocene in the western Gulf of Maine, USA, we collected a 142-year-old living bivalve (Arctica islandica) in 2004, and three fossil A. islandica shells of the Medieval Warm Period (MWP) and late MWP / Little Ice Age (LIA) period (corrected 14CAMS = 1030 ± 78 ad; 1320 ± 45 ad; 1357 ± 40 ad) in 1996. We compared the growth record of the modern shell with continuous plankton recorder (CPR) time-series (1961–2003) from the Gulf of Maine. A significant correlation (r 2 = 0.55; p < 0.0001) exists between the standardized annual growth index (SGI) of the modern shell and the relative abundance of zooplankton species Calanus finmarchicus. We therefore propose that SGI data from A. islandica is a valid proxy for paleo-productivity of at least one major zooplankton taxa. SGIs from these shells reveal significant periods of 2–6 years (NAO-like) based on wavelet analysis, multitaper method (MTM) analysis and singular spectrum analysis (SSA) during the late Holocene. Based on established physical oceanographic observation in the Gulf of Maine, we suggest that slope water variability coupled with North Atlantic Oscillation (NAO) dynamics is primarily responsible for the observed SGI variability.

To study the effects of temperature, salinity, and life processes (growth rates, size, metabolic effects, and physiological/genetic effects) on newly precipitated bivalve carbonate, we quantified shell isotopic chemistry of adult and juvenile animals of the intertidal bivalveMytilus edulis(Blue mussel) collected alive from western Greenland and the central Gulf of Maine and cultured them under controlled conditions. Data for juvenile and adultM. edulisbivalves cultured in this study, and previously by Wanamaker et al. (2006), yielded statistically identical paleotemperature relationships. On the basis of these experiments we have developed a species‐specific paleotemperature equation for the bivalveM. edulis[T °C = 16.28 (±0.10) − 4.57 (±0.15) {δ18OcVPBD −δ18OwVSMOW} + 0.06 (±0.06) {δ18OcVPBD −δ18OwVSMOW}2; r2= 0.99; N = 323; p < 0.0001]. Compared to the Kim and O'Neil (1997) inorganic calcite equation,M. edulisdeposits its shell in isotope equilibrium (δ18Ocalcite) with ambient water. Carbon isotopes (δ13Ccalcite) from sampled shells were substantially more negative than predicted values, indicating an uptake of metabolic carbon into shell carbonate, andδ13Ccalcitedisequilibrium increased with increasing salinity. Sampled shells ofM. edulisshowed no significant trends inδ18Ocalcitebased on size, cultured growth rates, or geographic collection location, suggesting that vital effects do not affectδ18OcalciteinM. edulis. The broad modern and paleogeographic distribution of this bivalve, its abundance during the Holocene, and the lack of an intraspecies physiologic isotope effect demonstrated here make it an ideal nearshore paleoceanographic proxy throughout much of the North Atlantic Ocean.

To quantify species‐specific relationships between bivalve carbonate isotope geochemistry (δ 18 O c ) and water conditions (temperature and salinity, related to water isotopic composition [δ 18 O w ]), an aquaculture‐based methodology was developed and applied to Mytilus edulis (blue mussel). The four‐by‐three factorial design consisted of four circulating temperature baths (7, 11, 15, and 19°C) and three salinity ranges (23, 28, and 32 parts per thousand (ppt); monitored for δ 18 O w weekly). In mid‐July of 2003, 4800 juvenile mussels were collected in Salt Bay, Damariscotta, Maine, and were placed in each configuration. The size distribution of harvested mussels, based on 105 specimens, ranged from 10.9 mm to 29.5 mm with a mean size of 19.8 mm. The mussels were grown in controlled conditions for up to 8.5 months, and a paleotemperature relationship based on juvenile M. edulis from Maine was developed from animals harvested at months 4, 5, and 8.5. This relationship [T°C = 16.19 (±0.14) − 4.69 (±0.21) {δ 18 O c VPBD − δ 18 O w VSMOW} + 0.17 (±0.13) {δ 18 O c VPBD − δ 18 O w VSMOW} 2 ; r 2 = 0.99; N = 105; P < 0.0001] is nearly identical to the Kim and O'Neil (1997) abiogenic calcite equation over the entire temperature range (7–19°C), and it closely resembles the commonly used paleotemperature equations of Epstein et al. (1953) and Horibe and Oba (1972). Further, the comparison of the M. edulis paleotemperature equation with the Kim and O'Neil (1997) equilibrium‐based equation indicates that M. edulis specimens used in this study precipitated their shell in isotopic equilibrium with ambient water within the experimental uncertainties of both studies. The aquaculture‐based methodology described here allows similar species‐specific isotope paleothermometer calibrations to be performed with other bivalve species and thus provides improved quantitative paleoenvironmental reconstructions.