Pteropods make thinner shells in the upwelling region of the California Current Ecosystem

Abstract

Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. While short-term incubations have demonstrated that pteropod calcification is negatively impacted by ocean acidification, we know little about net calcification in response to varying ocean conditions in natural populations. Here, we examine in situ calcification of Limacina helicina pteropods collected from the California Current Ecosystem, a coastal upwelling system with strong spatial gradients in ocean carbonate chemistry, dissolved oxygen and temperature. Depth-averaged pH ranged from 8.03 in warmer offshore waters to 7.77 in cold CO2-rich waters nearshore. Based on high-resolution micro-CT technology, we showed that shell thickness declined by ~ 37% along the upwelling gradient from offshore to nearshore water. Dissolution marks covered only ~ 2% of the shell surface area and were not associated with the observed variation in shell thickness. We thus infer that pteropods make thinner shells where upwelling brings more acidified and colder waters to the surface. Probably the thinner shells do not result from enhanced dissolution, but are due to a decline in calcification. Reduced calcification of pteropods is likely to have major ecological and biogeochemical implications for the cycling of calcium carbonate in the oceans.

Comparative Sensitivities of Zooplankton to Ocean Acidification Conditions in Experimental and Natural Settings

“…Measuring calcification is a clear choice because of its known sensitivity to low values of ar and the relative wealth of relevant laboratory studies concerning the ability of organisms to create calcium carbonate structures under OA conditions. Recent research studying in situ impacts on calcification found reduced calcification in pteropods collected in the California Current Ecosystem (Mekkes et al, 2021) and severe dissolution in pteropods in our study area (Bednaršek et al, 2020b). Importantly, some measures of calcification can be made on preserved samples, potentially alleviating constraints of some monitoring programs.…”

Using Onboard-Produced Drinking Water to Achieve Ballast-Free Management

“…Indeed, because the ocean is absorbing an increasing amount of human-released CO 2 , seawater is acidifying [22,23]. Previous studies have found that a decrease of pH in the ocean reduces the calcification rate of marine organisms which use CaCO 3 to build their skeleton or shells [24,25]. Meanwhile, freshening of the surface seawater, and the consequence of the capping effect, may cause anoxic bottom water inside the harbor [26].…”

The impacts of past, present and future ocean chemistry on predatory planktonic snails

“…An increase in atlantid shell extension from ambient to 2050 conditions may indicate a stress response to grow to a larger size as quickly as possible under increasing OA. It has been shown that some calcifying organisms are able to increase the rates of BP, such as metabolism and calcification, in response to low pH in order to compensate for the negative effects that increased acidity can cause, such as impaired calcification [85,86]. However, this often comes at a cost to overall fitness [85] and such increased rates cannot be sustained in the long term.…”