Echinometra sea urchins acclimatized to elevated pCO₂ at volcanic vents outperform those under present‐day pCO₂ conditions

Abstract

Rising atmospheric CO2 concentrations will significantly reduce ocean pH during the 21st century (ocean acidification, OA). This may hamper calcification in marine organisms such as corals and echinoderms, as shown in many laboratory-based experiments. Sea urchins are considered highly vulnerable to OA. We studied an Echinometra species on natural volcanic CO2 vents in Papua New Guinea, where they are CO2 -acclimatized and also subjected to secondary ecological changes from elevated CO2 . Near the vent site, the urchins experienced large daily variations in pH (>1 unit) and pCO2 (>2000 ppm) and average pH values (pHT 7.73) much below those expected under the most pessimistic future emission scenarios. Growth was measured over a 17-month period using tetracycline tagging of the calcareous feeding lanterns. Average-sized urchins grew more than twice as fast at the vent compared with those at an adjacent control site and assumed larger sizes at the vent compared to the control site and two other sites at another reef near-by. A small reduction in gonad weight was detected at the vents, but no differences in mortality, respiration, or degree of test calcification were detected between urchins from vent and control populations. Thus, urchins did not only persist but actually 'thrived' under extreme CO2 conditions. We suggest an ecological basis for this response: Increased algal productivity under increased pCO2 provided more food at the vent, resulting in higher growth rates. The wider implication of our observation is that laboratory studies on non-acclimatized specimens, which typically do not consider ecological changes, can lead to erroneous conclusions on responses to global change.

In situ developmental responses of tropical sea urchin larvae to ocean acidification conditions at naturally elevated p CO 2 vent sites

“…R. Soc. B 283: 20161506 appear to show no apparent deleterious responses (in terms of metabolism, calcification, population size, distributions and growth [26]), their larval stages are negatively affected in terms of development. If these observed effects equate to reduced numbers of larvae reaching settlement (i.e.…”

“…Natural vent systems provide a more realistic opportunity to assess these adaptive processes as vent Echinometra populations complete settlement, metamorphosis and their juvenile and adult lifespan under elevated pCO 2 conditions. Hence their fundamental physiological processes, such as metabolic rate, acid-base regulation, growth and gamete production will be acclimated to OA conditions [26].…”

Risk and resilience: variations in magnesium in echinoid skeletal calcite

“…Vent site studies consistently show that some echinoid species are relatively resistant to high-CO 2 environments (e.g. Fabricius et al 2014, Uthicke et al 2016, while others are not (Calosi et al 2013). In addition, the mineralogy of the test of Tripneustes gratilla reared in ocean acidification conditions from the very early juvenile (5 mm) to the mature adult stage (~60 mm) did not differ from that of urchins reared in control present-day conditions (Byrne et al 2014).…”

A 120‐year record of resilience to environmental change in brachiopods

“…Although information from long‐term laboratory experiments is vital to reveal sensitivities of marine organisms, even they can still only predict responses from exposures of relatively short durations, of months or even a few years, to environmentally unrealistic conditions (Andersson et al., ; Riebesell & Gattuso, ). Field experiments, including in situ mesocosms (Nagelkerken & Munday, ) and CO 2 vent sites (Fabricius et al., ; Hall‐Spencer et al., ; Uthicke et al., ), are another common approach which allows for the investigation of impacts on more long‐term scales and also often include responses at the community level and the physical, chemical and biological variability in their natural environments that cannot be recreated in laboratory experiments. This method, however, has a lack of control of treatment conditions where organisms, for instance near vent sites, are locally exposed to significant short‐term variation in pH levels as well as vents releasing other harmful substances (Gattuso et al., ).…”

“…In recognition of the fundamental role played by seasonal phenotypic plasticity and genetic change across generations, long-term experiments which allow for acclimation (Cross, Peck, & Harper, 2015;Cross, Peck, Lamare, & Harper, 2016;Hazan, Wangensteen, & Fine, 2014;Suckling et al, 2014) and/or adaptation potential in organisms with short generation times (Andersson et al, 2015;Collins, Rost, & Rynearson, 2014) are now being made. Although information from long-term laboratory experiments is vital to reveal sensitivities of marine organisms, even they can still only predict responses from exposures of relatively short durations, of months or even a few years, to environmentally unrealistic conditions experiments, including in situ mesocosms (Nagelkerken & Munday, 2015) and CO 2 vent sites (Fabricius et al, 2011;Hall-Spencer et al, 2008;Uthicke et al, 2016), are another common approach which allows for the investigation of impacts on more long-term scales and also often include responses at the community level and the physical, chemical and biological variability in their natural environments that cannot be recreated in laboratory experiments. This method, however, has a lack of control of treatment conditions where organisms, for instance near vent sites, are locally exposed to significant short-term variation in pH levels as well as vents releasing other harmful substances (Gattuso et al, 2014).…”