Abstract
Elevated partial pressure of carbon dioxide (pCO2) as a concomitant of global climate change may facilitate the establishment of future seagrass meadows and subsequently its benefit could be incorporated into techniques to increase restoration success. In five manipulative experiments, we determined how increased CO2 affects the maturation of flowers, and the development of seeds and seedlings for the foundation species Zostera marina. Experiments tested the development from both seeds collected from non-treated flowering shoots (direct) and seeds harvested from flowering shoots after CO2 exposure (parental carryover). Flowering shoots were collected along the western coast of Sweden near the island of Skafto. The seeds produced were used in experiments conducted at Kristineberg, Sweden and Dauphin Island, AL, United States. Experiments varied in temperature (16, 18°C) and salinity (19, 33 ppt), as well as duration and magnitude of elevated CO2 exposure. Flowering maturation, spathe number, seed production, and indicators of seed quality did not appear to be affected by 39–69 days of exposure to CO2 conditions outside of natural variability (pCO2 = 1547.2 ± 267.60 μatm; pHT = 7.53 ± 0.07). Yet, seeds produced from these flowers showed twofold greater germination success. In another experiment, flowering shoots were exposed to an extreme CO2 condition (pCO2 = 5950.7 ± 1,849.82 μatm; pHT = 6.96 ± 0.15). In this case, flowers generated seeds that demonstrated a fivefold increase in an indicator for seed viability (sinking velocity). In the latter experiment, however, germination appeared unaffected. Direct CO2 effects on germination and seedling production were not observed. Our results provide evidence of a parental CO2 effect that can benefit germination or seed viability, but early benefits may not lead to bed establishment if other environmental conditions are not well suited for seedling development. Outcomes have implications for restoration; CO2 can be supplied to flowering shoot holding tanks to bolster success when the purpose is to redistribute seeds to locations where beds are extant and water quality is adequate.
Highlights
Seagrass meadows serve as important ecosystem engineers hallmarked for their ability to sequester carbon and provide habitat for a diversity of marine organisms (Heck and Orth, 1980; Hemminga and Duarte, 2000; Hernán et al, 2017)
Low and high CO2 conditions were maintained for 69 days and monitored for the first 39 days (Supplementary Table 1)
The number of spathes in stage 1 was greatest on day 1 and declined through time, while the number of spathes in stage 3 was highest on day 9
Summary
Seagrass meadows serve as important ecosystem engineers hallmarked for their ability to sequester carbon and provide habitat for a diversity of marine organisms (Heck and Orth, 1980; Hemminga and Duarte, 2000; Hernán et al, 2017). Seagrasses are in decline due to anthropogenic stressors, like eutrophication and ocean warming, which have accelerated global decline in coverage while simultaneously increasing susceptibility to natural stressors like disease (Orth et al, 2006; Waycott et al, 2009; Zimmerman et al, 2015). Efforts to restore seagrass beds serves as a possible adaptive strategy for protecting coastal systems from disruptions in marine carbonate chemistry (Unsworth et al, 2012). The ocean absorbs carbon dioxide (CO2) from the atmosphere increasing seawater (SW) concentrations of inorganic carbon [DIC] and CO2 while simultaneously decreasing pH in a process referred to as ocean acidification (OA). Carbon in its dissolved form [DIC] can exist as one of three species: aqueous carbon dioxide [CO2(aq)], bicarbonate (HCO3−), and carbonate (CO32−) (Doney et al, 2009). Surface ocean average pH has decreased by 0.1 units since the beginning of the industrial revolution with a further decline (0.06–0.32 units) projected over the century (Ciais et al, 2013)
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