Abstract
Substantial variations are reported for egg production and hatching rates of copepods exposed to elevated carbon dioxide concentrations (pCO2). One possible explanation, as found in other marine taxa, is that prior parental exposure to elevated pCO2 (and/or decreased pH) affects reproductive performance. Previous studies have adopted two distinct approaches, either (1) expose male and female copepoda to the test pCO2/pH scenarios, or (2) solely expose egg-laying females to the tests. Although the former approach is more realistic, the majority of studies have used the latter approach. Here, we investigated the variation in egg production and hatching success of Acartia tonsa between these two experimental designs, across five different pCO2 concentrations (385–6000 µatm pCO2). In addition, to determine the effect of pCO2 on the hatching success with no prior parental exposure, eggs produced and fertilized under ambient conditions were also exposed to these pCO2 scenarios. Significant variations were found between experimental designs, with approach (1) resulting in higher impacts; here >20% difference was seen in hatching success between experiments at 1000 µatm pCO2 scenarios (2100 year scenario), and >85% at 6000 µatm pCO2. This study highlights the potential to misrepresent the reproductive response of a species to elevated pCO2 dependent on parental exposure.
Highlights
Mesozooplankton play a pivotal role in marine food webs, mediating the transfer of primary production to higher trophic levels
While reduced egg production, hatching rates and naupliar production have been found in some species (e.g. Acartia tonsa, Tisbe battagliai) exposed to pCO2 lower than that projected for 2100 year scenario [i.e. 1000 matm pCO2, (Fitzer et al, 2012b, 2013; Rossoll et al, 2012)], other species (e.g. Centropages typicus, C. finmarchicus and Temora longicornis) have shown no reproductive effects upon exposure to concentrations that are more than twenty times the current level [8–10 000 matm CO2, (Mayor et al, 2007; McConville et al, 2013)]
We have found substantial variations in the reproductive success of the calanoid copepod, Acartia tonsa, dependent on whether the parents were pre-exposed to the egg production rates (EPR) declined significantly with elevated pCO2 under both combined male and female exposure (MFE) and sole female exposure (FE) protocols
Summary
Mesozooplankton play a pivotal role in marine food webs, mediating the transfer of primary production to higher trophic levels. Copepods are the most abundant organisms of the mesozooplankton and in consequence any potential effect on their productivity and population structure, as a result of ocean acidification (OA), will likely impact on available online at www.plankt.oxfordjournals.org # The Author 2014. While reduced egg production, hatching rates and naupliar production have been found in some species (e.g. Acartia tonsa, Tisbe battagliai) exposed to pCO2 lower than that projected for 2100 year scenario [i.e. 1000 matm pCO2, (Fitzer et al, 2012b, 2013; Rossoll et al, 2012)], other species (e.g. Centropages typicus, C. finmarchicus and Temora longicornis) have shown no reproductive effects upon exposure to concentrations that are more than twenty times the current level [8–10 000 matm CO2, (Mayor et al, 2007; McConville et al, 2013)]
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