(CN) — The impact of human-caused climate change on marine creatures has a new twist: acidifying oceans are wreaking havoc on the abilities of species to ejaculate and fertilize eggs.
According to a study published this week in the journal Scientific Reports, increasing ocean acidification — brought about by man-made carbon emissions — reduces sperm performance in a species of sea urchin. Specifically, the acidic oceans are diminishing sperm competitiveness and slowing their swim to the eggs.
The oceans absorb about one-third of the carbon dioxide produced by human activities, which is changing seawater chemistry. As a result, the acidity of seawater has increased by about 25 percent since the industrial revolution, with further change projected over the coming century — unless emissions are drastically reduced.
“The majority of marine species, including sea urchins, reproduce by releasing their sperm and eggs directly into the seawater,” said study co-author Ceri Lewis. “Reproduction is often the most sensitive life stage to environmental stress, so it is really important to understand how these changes in ocean chemistry will affect this essential process.”
The team measured sperm performance in existing and simulated future conditions using the same techniques employed by fertility clinics to look at the health of human sperm. The researchers also ran competitive fertilization trials where males attempted to fertilize a batch of eggs in each seawater condition, with the paternity of the offspring analyzed to identify the “winning” males.
The researchers, led by University of Exeter doctoral student Anna Campbell, found that ejaculates containing a greater volume of swimming sperm and ejaculates containing faster swimming sperm were more successful in current ocean conditions. However, in conditions of increased ocean acidification, the number of actively swimming sperm in ejaculate became much less important in securing fertilization under competition.
In many cases, the male urchins that won the sperm competition battle under existing ocean conditions were not the winners under future acidification levels.
“We know that males rarely gain sole access to a batch of eggs in the sea, and most fertilization takes place under competition from rival male ejaculates so it’s important for a male to produce a highly competitive ejaculate,” Campbell said.
“We set out to establish how the projected changes in seawater chemistry will affect the competitive quality of a male’s ejaculate to assess how the share of paternity might change in future oceans.”
David Hosken, a co-author of the study and evolutionary biology expert said of the findings: “The results of the study indicate the fundamental impact climate change could have on reproduction in the sea.”
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