Death by dissolution: Sediment saturation state as a mortality factor for juvenile bivalves

Abstract

We show that death by dissolution is an important size-dependent mortality factor for juvenile bivalves. Utilizing a new experimental design, we were able to replicate saturation states in sediments after values frequently encountered by Mercenaria mercenaria in coastal deposits (V aragonite 5 0.4 and 0.6). When 0.2-mm M. mercenaria were reared in sediments at V aragonite 5 0.4 and 0.6, significant daily losses of living individuals occurred (14.0% and 14.4% d 21 , respectively), relative to supersaturated-control sediments (3.9% d 21 ). For 0.4-mm M. mercenaria, significant mortality occurred under the most undersaturated conditions (V aragonite 5 0.4, mortality 5 9.6% d 21 ), although mortality at V aragonite 5 0.6 was not significant (mortality 5 2.7% d 21 ; controlsaturated mortality 5 0.2% d 21 ). For the largest size-class investigated, 0.6 mm, we show significant mortality for clams under the most undersaturated sediments (V aragonite 5 0.4, 2.8% d 21 ). To test if buffered sediments would increase survivorship of juvenile bivalves during periods of recruitment, we manually manipulated sediment saturation state by adding crushed Mya arenaria shell to a mud flat in West Bath, Maine, U.S.A. Although we increased the average sediment saturation state within retrieved cores from V 5 0.25 6 0.01 to only 0.53 6 0.06, numbers of live M. arenaria in buffered sediment increased almost three-fold in 2 weeks. Buffering muds against the metabolic acids that cause lowered saturation states may represent a potentially important management strategy to decrease dissolution mortality.

Limacina helicinashell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem

“…Therefore, the recent observed decline in L. helicina populations on the continental shelf of Vancouver Island [29], where we demonstrated high occurrence of severe shell dissolution, calls for more in-depth characterization of possible dissolution-related mortality [46]. Given the multitude of biological processes at important pteropod life stages that are potentially affected by increased shell dissolution, we suggest that dissolution provides an insight as a potential causal pathway for the observed pteropod decline.…”

“…Although pteropods have been exposed to high CO 2 from seasonally persistent upwelling through evolution, we have not found any evidence of resilience to counteract the scale of dissolution observed currently. While dissolution in juvenile bivalves has been a significant factor for increased mortality [46], the link between undersaturation and dissolution-driven mortality in pteropods has not been directly confirmed. However, with the occurrence of high CO 2 , increased dissolution combined with increased frailty [30][31][32]47] might compromise shell integrity to the extent where indirect effects of bacterial infection and acid-base balance would induce increased acute mortality [46].…”

“…While dissolution in juvenile bivalves has been a significant factor for increased mortality [46], the link between undersaturation and dissolution-driven mortality in pteropods has not been directly confirmed. However, with the occurrence of high CO 2 , increased dissolution combined with increased frailty [30][31][32]47] might compromise shell integrity to the extent where indirect effects of bacterial infection and acid-base balance would induce increased acute mortality [46]. The first bottleneck would primarily affect veligers and larvae, life stages where complete shell dissolution in the larvae can occur within two weeks upon exposure to undersaturation [48].…”

Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish

“…The relative SD of larval survival among replicated vessels per treatment for all times points and experiments was 4% (n = 4 per treatment). (10,14), suggesting CaCO 3 shells were malforming and/or dissolving under more acidic conditions. Altered shell morphology was also obvious in juvenile scallops that had distinct ridges, characteristic of later stages of development, under preindustrial CO 2 , whereas individuals reared under higher CO 2 conditions lacked ridges, a sign of slower development (Fig.…”

“…The experimental enrichment of CO 2 to levels expected in the coming century has been shown to dramatically alter the growth, survival, and morphology of numerous calcifying organisms including coccolithophores, coral reefs, crustose coralline algae, echinoderms, foraminifera, and pteropods (5-7). Many shellfish also produce calcareous shells, and juvenile and adult clams, mussels, and oysters have been shown to be adversely affected by elevated CO 2 (8)(9)(10)(11)(12). The earliest life history stages of shellfish, larvae, have been shown to be especially vulnerable to high CO 2 , displaying large declines in survival and delays in metamorphosis at levels predicted to occur later this century, suggesting recruitment of these populations may be adversely impacted by ocean acidification (12)(13)(14).…”