As CO 2 levels increase in the atmosphere, so too do they in the sea. Although direct effects of moderately elevated CO 2 in sea water may be of little consequence, indirect effects may be profound. For example, lowered pH and calcium carbonate saturation states may influence both deposition and dissolution rates of mineralized skeletons in many marine organisms. The relative impact of elevated CO 2 on deposition and dissolution rates are not known for many large-bodied organisms. We therefore tested the effects of increased CO 2 levels-those forecast to occur in roughly 100 and 200 years-on both shell deposition rate and shell dissolution rate in a rocky intertidal snail, Nucella lamellosa. Shell weight gain per day in live snails decreased linearly with increasing CO 2 levels. However, this trend was paralleled by shell weight loss per day in empty shells, suggesting that these declines in shell weight gain observed in live snails were due to increased dissolution of existing shell material, rather than reduced production of new shell material. Ocean acidification may therefore have a greater effect on shell dissolution than on shell deposition, at least in temperate marine molluscs.

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SummaryFragmentation of formerly continuous habitats can have significant consequences on subpopulations in isolated fragments. This study examined the temporal genetic consequences of historical river fragmentation by hydroelectric dams on lake sturgeon (Acipenser fulvescens Rafinesque, 1817), using temporal samples from two Ontario river systems. Temporal genetic analyses of samples from the Ottawa (dammed) and Kenogami (unregulated) river systems were used to (1) compare changes in genetic structure and diversity within and between free-flowing and regulated systems; (2) assess how impoundments have influenced the spatial and temporal genetic structure and diversity within these contrasting systems; and (3) estimate effective population sizes (N e ) in both rivers using temporal genetic estimators. Levels of genetic diversity did not differ between impounded and free-flowing rivers, nor did genetic diversity differ through time within a river system. Levels of genetic divergence over time were similarly minimal. We did, however, detect a 65% decline in effective population size in the impounded Ottawa River over two generations. Moreover, over the same time period the Ottawa River had substantially lower N e estimates for Lake Sturgeon than the free-flowing Kenogami River system. This study represents one of the first to observe genetic consequences of fragmentation on Lake Sturgeon. As such, this work reinforces the importance of maintaining or restoring habitat connectivity and availability for this migratory species, and mitigating other demographic threats that could compound, or be compounded by the effect of reduced genetic variation.