Malacological insights into the marine ecology and changing climate of the late Pleistocene – early Holocene Queen Charlotte Islands archipelago, western Canada, and implications for early peoples

The first intertidal species to colonize the Queen Charlotte Islands archipelago along the northeastern Pacific margin of Canada after the last glacial maximum (LGM) was Macoma nasuta at 13 210 ± 80 14C years BP. Prior to this time, molluscs were likely excluded where grounded ice extended from the 2 km thick Cordilleran ice sheet on mainland British Columbia. Low water temperatures, high sedimentation rates, high turbidity, dilution, and low primary productivity limited invertebrate colonization subsequent to the LGM, a period of rapid sea-level and climate change. As an adult, M. nasuta is a facultative deposit-suspension feeder that tolerates high turbidity and lowered salinity, and its pediveligers and early juveniles must also have been able to survive these conditions. Subsequently, in addition to M. nasuta, Macoma irus (inquinata), Saxidomus giganteus, Protothaca staminea, Protothaca tenerrima, Hiatella pholadis, Clinocardium nuttallii, and Mytilus trossulus constituted a typical intertidal bivalve assemblage. These findings are explained in terms of the physiology, feeding mechanisms, development, and sediment preferences of living molluscs. The disappearance of most bivalve species between ~11 000 and 10 000 14C years BP indicates the onset of a short interval of low sea-surface temperatures coincident with the Younger Dryas cooling event. Some cold-hardy species persisted, including Clinocardium californiense, Mya truncata, and Serripes groenlandicus. Bivalve species not previously reported as Pleistocene fossils were collected in sediments dating older than 10 000 14C years BP. They include Macoma incongrua, Musculus taylori, Mytilimeria nuttallii, and Tellina nuculoides. Fossil assemblages of intertidal molluscs are used to map ancient shorelines and indicate which species were available as a subsistence resource for early peoples from at least 13 210 ± 80 14C years BP. Intertidal food biomass densities may have reached present commercially harvested levels on southern Moresby Island by 8800 ± 70 14C years BP and on northern Graham Island by 8990 ± 50 14C years BP. When early peoples might have been migrating along the littoral zone, the molluscan productivity of the outer coast was much higher than it is at present.

Response of Infaunal Bivalves to the Exxon Valdez Oil Spill and Related Shoreline Treatment

ABSTRACT Infaunal bivalves monitored in Prince William Sound intertidal sediments between 1990 through 1996 appear to have been affected more by shoreline treatment than by exposure to oil. Lower numbers were observed at oiled but treated (Category 3) sites whereas highest numbers were observed at reference (Category 1) sites. Species richness, very similar at reference and oiled but untreated (Category 2) sites after 1990, declined slightly during the study. Abundance, also quite similar at reference and Category 2 sites, peaked in 1992 or 1993 and then gradually declined through the remaining years. In contrast, averages for Category 3 sites exhibited no apparent trends representing recovery. Differences in both variables were highly significant between reference and Category 2 sites, on one hand, and Category 3 sites, on the other hand. Dominance patterns and behavior provide important insights into the effects of the spill, shoreline treatment, and the recovery process. Mysella tumida, Macoma spp., and Protothaca staminea dominated at reference and Category 2 sites but were far less common at Category 3 sites. These dominant species generally are relatively long-lived, slowly reproducing species that bury up to several centimeters below the surface of stable sediments. Mysella is typically commensal with larger burrowing species that are mostly absent or uncommon at Category 3 sites. In contrast, Hiatella arctica, the dominant at Category 3 sites, is an opportunist that nestles on the surface of disturbed sediments.

Effects and Trends in Littleneck Clams (Protothaca Staminea) Impacted by the Exxon Valdez Oil Spill

ABSTRACT Littleneck clams, Protothaca staminea, are a common intertidal clam species in Prince William Sound. With several years of results from National Oceanic and Atmospheric Association/Hazardous Materials Response and Assessment Division (NOAA/HAZMAT) monitoring available, it is possible to infer some trends in clams affected by the Exxon Valdez incident:At oiled and washed sites, Protothaca staminea numbers reflect a different pattern of impact and recovery than other infaunal species, i.e., they do not show a depression in abundance followed by the dramatic population increase observed among many recovering species.Abundance differences between washed sites and unoiled sites may reflect lingering spill impacts. Extrapolation of the current trend suggests population abundance at oiled and washed sites could converge to that at unoiled sites by 2006.Chemistry results showed large declines in tissue aromatic hydrocarbon concentrations between 1990 and 1992. However, statistically significant differences between results for oiled sites and unoiled sited remained until 1997.Littleneck clams bioaccumulate oil to slightly higher concentrations than co-located mussels. Route of exposure has not been identified, but hydrocarbons adsorbed to particulates and food is a likely source.Subtle impacts to Protothaca staminea age structure and other population features may manifest themselves over the longer term. The authors' goal is to identify and characterize such effects. The overall task of impact and recovery assessment is complicated by factors such as sea otter predation, recovery from other major disruptions like the 1964 earthquake, and El Niño-Southern Oscillation shifts.