Abstract
Ocean acidification (OA) refers to the decrease in ocean water pH resulting from the increasing absorption of atmospheric CO2. This will cause changes in the ocean’s carbonate chemistry system with a resulting impact on reproduction of marine organisms. Reproduction is the fundamental process that allows the conservation of the species; in free-spawning marine invertebrates, this process is highly sensitive to changes in seawater quality and chemistry. To date, the majority of the studies concerned OA effects on reproduction has been focused on embryo and larval development. Despite several evidence for the impairment of reproductive success by environmental perturbations through altering gamete quality, sperm physiological responses to OA are poorly investigated. In this study, we evaluated the effects of exposure to acidified seawater (pH 7.8), which approximate the predicted global averages for oceanic surface waters at the end of this century, on sperm quality of the mussel Mytilus galloprovincialis and the ascidian Ciona robusta by evaluating several endpoints, such as motility, vitality, mitochondrial activity, oxidative state, and intracellular pH (pHi). Following sperm exposure to acidified seawater, the percentage of motile spermatozoa, mitochondrial activity and pHi decreased in comparison to the current seawater pH of 8.1, whereas vitality and oxidative state were unaffected by the low external pH in both the species. In broadcast spawners, a relationship between sperm intracellular pH and the initiation of motility are well known. Spermatozoa are immotile in the testes and motility is induced after the spermatozoa are released into seawater; the alkaline pH of seawater, in fact, increases the pHi activating motility and mitochondrial respiration. The results of this study suggest that the lowering of seawater pH as predicted to occur for 2100, through the inhibition of pHi increase, prevent sperm motility activation. Sperm motility is a key determinant of fertilization success; consequently, a corresponding drop in fertilization success would be expected with important implications for the fitness and the survival of marine invertebrates.
Highlights
Ocean acidification (OA) is a claimed issue of global change started over than 250 years ago when the industrial era has taken place (Feely et al, 2008)
Motility In M. galloprovincialis, after 30 min exposure to filtered natural seawater (FNSW), the percentage of motility in control spermatozoa was 66.9 ± 3.9% and it significantly dropped at 50% ± 2.0 after 60 min (P ≤ 0.01)
After 30 min and 60 min of exposure to acidified seawater (AcSW), the motility rate significantly decreased compared to the control spermatozoa (54.4 ± 4.5% vs. 34.4 ± 4.7%; P ≤ 0.05)
Summary
Ocean acidification (OA) is a claimed issue of global change started over than 250 years ago when the industrial era has taken place (Feely et al, 2008) It can be defined as a longterm decrease in oceanic water pH mainly due to the humandriven intensification of the atmospheric carbon dioxide (CO2) (Doney et al, 2009). The atmospheric man-made CO2 dissolves in the seawater increasing the bicarbonate ions and decreasing the carbonate ions These have already caused a drop of the global mean seawater pH levels of 0.1 units compared with pre-industrial levels (pH 8.2) (Orr et al, 2005) and are projected to decrease the oceanic surface waters pH by approximately 0.3–0.5 pH units by the end of the century A metaanalysis combination of different taxonomic groups revealed that survival, growth, and reproduction were all negatively affected by OA (Kroeker et al, 2010)
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