William L. Locke

Growth line deposition and variability in growth of two circumpolar bivalves (Serripes groenlandicus, and Clinocardium ciliatum)

Growth patterns of two common circumpolar bivalves, the Greenland cockle (Serripes groenlandicus), and the hairy cockle (Clinocardium ciliatum) have been used in previous studies to reconstruct environmental conditions in the arctic. To date, there has been no direct determination that growth lines in either species are deposited periodically, and there has been no examination of factors affecting growth. We placed calcein-marked individuals of both species on oceanographic moorings in two fjords (Rijpfjord and Kongsfjord) in the Svalbard archipelago for one and two (Kongsfjord only) years. Growth patterns were compared with concurrent in situ temperature and fluorescence data in order to assess environmental controls on growth. Dark growth lines are evident on the outer shell surface and internally in shell cross section in both S. groenlandicus and C. ciliatum, and both species deposited only one line per year, unequivocally confirming that internal lines are deposited annually. Growth line deposition in both species began in late summer to early fall, before the seasonal decline in temperature. There was no difference in growth of S. groenlandicus between the two fjords despite differences in water temperature (3°C), fluorescence (nearly threefold) and the onset and duration of the winter season. C. ciliatum, however, grew approximately 2.8 times faster in the warmer, more food-rich Kongsfjord than in Rijpfjord. Subannual lines were counted in two individuals of each species from each fjord, but deposition of these lines was not clearly related to number of growing days estimated by temperature and fluorescence.

Bivalve shell horizons in seafloor pockmarks of the last glacial‐interglacial transition: a thousand years of methane emissions in the Arctic Ocean

We studied discrete bivalve shell horizons in two gravity cores from seafloor pockmarks on the Vestnesa Ridge (∼1200 m water depth) and western Svalbard (79°00′ N, 06°55′ W) to provide insight into the temporal and spatial dynamics of seabed methane seeps. The shell beds, dominated by two genera of the family Vesicomyidae: Phreagena s.l. and Isorropodon sp., were 20–30 cm thick and centered at 250–400 cm deep in the cores. The carbon isotope composition of inorganic (δ13C from −13.02‰ to +2.36‰) and organic (δ13C from −29.28‰ to −21.33‰) shell material and a two-end member mixing model indicate that these taxa derived between 8% and 43% of their nutrition from chemosynthetic bacteria. In addition, negative δ13C values for planktonic foraminifera (−6.7‰ to −3.1‰), concretions identified as methane-derived authigenic carbonates, and pyrite-encrusted fossil worm tubes at the shell horizons indicate a sustained paleo-methane seep environment. Combining sedimentation rates with 14C ages for bivalve material from the shell horizons, we estimate the horizons persisted for about 1000 years between approximately 17,707 and 16,680 years B.P. (corrected). The seepage event over a 1000 year time interval was most likely associated with regional stress-related faulting and the subsequent release of overpressurized fluids.

Biological effects of mechanically and chemically dispersed oil on the Icelandic scallop (Chlamys islandica)

This study aimed to simulate conditions in which dispersant (Dasic NS) might be used to combat an oil spill in coastal sub-Arctic water of limited depth and water exchange in order to produce input data for Net Environmental Benefit Analysis (NEBA) of Arctic and sub-Arctic coastal areas. Concentration dependent differences in acute responses and long-term effects of a 48h acute exposure to dispersed oil, with and without the application of a chemical dispersant, were assessed on the Arctic filter feeding bivalve Chlamys islandica. Icelandic scallops were exposed for 48h to a range of spiked concentrations of mechanically and chemically dispersed oil. Short-term effects were assessed in terms of lysosomal membrane stability, superoxide dismutase, catalase, gluthatione S-transferases, glutathione peroxidases, glutathione reductase, glutathione, total oxyradical scavenging capacity, lipid peroxidation and peroxisomal proliferation. Post-exposure survival, growth and reproductive investment were followed for 2 months to evaluate any long-term consequence. Generally, similar effects were observed in scallops exposed to mechanically and chemically dispersed oil. Limited short-term effects were observed after 48h, suggesting that a different timing would be required for measuring the possible onset of such effects. There was a concentration dependent increase in cumulative post-exposure mortality, but long-term effects on gonadosomatic index, somatic growth/condition factor did not differ among treatments.

Deposition of annual growth lines in the apex of the common limpet (Patella vulgata) from Shetland Islands, UK and Norway: Evidence from field marking and shell mineral content of annual line deposition

The abundance, accessibility and value of limpets as a source of food and bait for coastal peoples have resulted in their high frequency in shell middens worldwide. The limpet Patella vulgata is found in middens from the Mediterranean to Norway, and morphometric and sclerochronological analyses of its shell can provide insight into harvesting patterns and paleoenvironmental variables valuable in reconstructing climate. Previous work with P. vulgata has relied on lines on the exterior of the shell, or on lines exiting on the shell surface in shell cross-section, as annual or sub-annual markers. Shell damage may compromise these lines and limit the use of some shells, but growth lines are also found in the better-preserved shell apex. We investigated whether the growth lines in the apex of P. vulgata from two locations in Northern Europe are annual using calcein-marking and recapture. Investigations were performed at one site in the Shetland Islands (UK) and at one site at the northern limit of P. vulgatas range in Northern Norway. We also used laser ablation to measure the concentration of minerals in the shells of two individuals from Shetland to determine if patterns of minerals suggested as bioproxies for temperature and productivity varied annually. All individuals deposited one growth line in the apex during their year in the field, and the lowest ratios of Sr/Ca and Ba/Ca and to a lesser extent Mg/Ca were coincident with annual lines on the shells from Shetland. Growth at both sites was modelled using the von Bertalanffy growth function, and apex growth was nearly five times faster in Shetland than in Norway, probably a result of differences in temperature between the two locations.

Lack of adult novel northern lineages of invasive green crab Carcinus maenas along much of the northern US Atlantic coast

Introduced over 200 yr ago to the east coast of North America, Carcinus maenas now ranges from New York to Newfoundland. In the 1980s, a secondary invasion of European lineages, termed northern haplotypes, occurred in Nova Scotia. Young-of-the-year sampled in 2007 revealed that northern haplotypes were present in low frequencies at several northwestern Atlantic sites as far south as New York; a model predicted an increase in their range and frequency over time. We collected samples in 2013 and 2014 to determine the haplotypes of adult crabs from New York to Nova Scotia. Six haplotypes, encompassing previously identified northern and southern haplotypes, 1 novel southern haplotype, and 1 Scandinavian haplotype, were identified in 275 crabs sampled at 11 sites. Northern haplotypes were only found in Nova Scotia, Beals Island (Maine), and Mount Desert Island (Maine) at a frequency of 60, 8, and 24%, respectively; remaining sites were predominantly composed of a previously identified southern haplotype. Northern haplotypes are limited in adult crabs to Mount Desert Island and north, indicating that the southern haplotype is selectively favored at some point during their life history, recruitment of northern larvae is limited south of Mount Desert Island, or entire year-classes post-2007 were lost. Our results do not support the predictions of an increase in the range and frequency of northern haplotypes, at least among adults, and indicate that a more complete knowledge of factors affecting C. maenas life stages is necessary to understand the current distribution of haplotypes.

Analysis of the Size, Shape, and Modeled Age of Common Limpets (Patella vulgata) from Late Norse Middens at Sandwick, Unst, Shetland Islands, UK: Evidence for Anthropogenic and Climatic Impacts

ABSTRACT Zooarchaeological faunal remains are commonly examined to investigate harvesting behavior. We determined limpet (Patella vulgata) shell size and shape, and estimated shell age from several middens at the Late Norse Sandwick South Site, Unst, Shetland, UK, whose strata represent distinct occupational phases (Phase 1: AD 1100–1200, Phase 2: AD 1200–1250, Phase 3: AD 1250–1350). Our goal was to determine if the many limpets found there could provide insight into Norse harvesting behavior. Shell length, conicity, and modeled age all declined between Phases 1 and 2, suggesting intensive, size-selective harvesting of limpets and a shift to harvesting lower in the intertidal zone between phases. Length and conicity varied in Phases 2 and 3 and no major changes seem to have occurred over these periods, indicating that harvesting maintained the limpet population at an impacted level throughout the later phases. The conicity decline between Phases 1 and 2 may also have been caused by increased storminess that accompanied the onset of the Little Ice Age. The mean length of modern limpet populations near the Norse site did not differ from the archaeological phases, but did vary among collection years. Limpets were 26% larger in 2015 than in 2012 and 2013, indicating that large interannual variations in population structure can occur over short time periods. Potentially the result of extreme storms removing small limpets, this result raises the possibility that size and conicity changes during the Sandwick South Site occupation, as well as in other early populations, could also be the result of environmental factors rather than human harvesting alone. We feel, however, that the most parsimonious explanation for the patterns we document is human harvesting.