Population ecology and shell chemistry of a phytal ostracode species (Loxoconcha matagordensis) in the Chesapeake Bay watershed

Abstract

Population ecology and shell chemistry were studied in the phytal ostracode Loxoconcha matagordensis (Swain 1955) collected from Zostera marina seagrass beds in the Chesapeake Bay to provide seasonal constraints on shell secretion time for paleothermometry. Population density and age structure were defined by two main breeding cycles that occurred between 01 to 15 June and 02 to 16 August 2001. The time interval between breeding cycles was~2 months and total juvenile standing crop increased almost three-fold between the first and second breeding cycles. Dark brown over-wintered adults comprised the majority of the population between March and April 2001, while newly secreted translucent adults were predominant between June and September. Seasonal shell Mg/Ca and Sr/Ca ratios were positively correlated with water temperature at both sites, with the strongest correlations occurring between June and September from newly secreted shells at Dameron Marsh. Old, dark brown shells contained 10% to 23% and 1% to 6% less Mg/Ca and Sr/Ca, respectively, than new shells. Because a fossil assemblage of L. matagordensis will contain~30% old shells (dark-brown), these results suggest that fossil Mg/Ca ratios yield an integrated late spring to summer temperature signal. Shell Mg/Ca and Sr/Ca ratios of specimens of L. matagordensis collected from living Zostera were positively correlated, suggesting that temperature may influence both elemental ratios. Mg/ Ca and Sr/Ca ratios of fossil shells of the related species Loxoconcha sp. A obtained from four sediment cores were also studied and exhibited a weaker correlation between the two elemental ratios.

The Medieval Climate Anomaly and Little Ice Age in Chesapeake Bay and the North Atlantic Ocean

“…A total of 258 samples from MD03-2661 yielded L. matagordensis suitable for analysis (see chronology); the RD-2209 record included 450 analyses . Mg/Ca ratios were converted to warm-season temperature using the calibration equation y =0.644x −2.4284 (r 2 =0.805) derived from field, culturing and laboratory analyses of Loxoconcha from Chesapeake Bay and the adjacent continental shelf (Dwyer et al, 2002;Cronin et al, 2003;Vann et al, 2004). These calibration studies demonstrated that temperature is the primary factor influencing Chesapeake Bay Loxoconcha Mg/Ca ratios and, at least over the sampled salinity range (~15-35 psu), salinity does not appear to be important.…”

Multiproxy evidence of Holocene climate variability from estuarine sediments, eastern North America

“…It is also important to consider the seasonal ecology and time of shell secretion in both Loxoconcha and Elphidium for interpreting paired δ 18 O foram and Mg/Ca values. Ostracodes grow in 8 or 9 discrete molt stages and studies of the seasonal ecology of Loxoconcha matagordensis [ Vann et al , 2004; Cronin et al , 2005] indicate that most adults secrete their shells during spring and summer seasons and thus the paleotemperature record is mainly a warm season record. Other temperate species of Loxoconcha have similar seasonal ecology and grow adult shells during spring and/or summer.…”

Late Holocene sea level variability and Atlantic Meridional Overturning Circulation

“…To reconstruct the CB SL variability over the past 2000 years, we applied the 1.94 and 1.48 cm sensitivity values to paleo‐SST records generated from magnesium/calcium (Mg/Ca) paleothermometry [ Cronin et al , , ; Vann et al , ]. Mg/Ca in calcite (CaCO 3 ) shells of the ostracode Loxoconcha (crustacea) is controlled by the water temperature at which the adult animal grows its shell during molting.…”