Nature

Ocean Acidification Turns Marine Animals into Helicopter Parents

October 29, 2015 | Sarah Tse

Alitta succinea (common clam worm) in Epitoky stage
Photo credit: Hans Hillewaert/Wikipedia (CC BY-SA 4.0)

A few hardy sea creatures may be able to ride out the ongoing storm of environmental change by protecting their offspring, but on the whole, the oceans seem to be out of luck.

If global warming was a dangerous convict, ocean acidification would be his little brother: still too young to commit serious crimes, but starting to cause trouble and get in with the wrong crowd. Since the effects of ocean acidification aren’t immediately apparent to humans, we haven’t been paying it much attention. But scientists understand the importance of monitoring atmospheric carbon dioxide as it increases and dissolves in the ocean, acidifying the deep blues and threatening marine life.

In an attempt to preview what will happen to the ocean as it absorbs more carbon dioxide, scientists are studying hydrothermal vents, which are naturally occurring fissures in the ocean floor that spew a volcanically-heated soup of liquid carbon dioxide and dissolved minerals into the surrounding water. CO2 seeps from these vents at concentrations equivalent to projections for the end of the century. So far, it doesn’t look too promising.

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One thing that we can expect in a world with more acidic seas is overprotective parenting. A recent study compared populations of polychaete worms that live directly at hydrothermal vent openings with those living in less acidic waters. Polychaete worms are marine segmented worms covered with bristled, feet-like appendages. While the worms living in cooler, more basic waters release numerous young into the water column to fend for themselves—a typical reproductive strategy for these types of invertebrates — the ones living in the hot, acidic water near the vent exhibit completely different parenting behavior.

Further genetic analysis revealed that this second population recently diverged into a different species from the first population, as it adapted to the more extreme environment. Instead of surrendering their eggs to the whims of fate, this new species lays much larger and fewer eggs in a tubular brooding pouch. In an act of self-sacrifice, the female invests all her energy into producing these eggs and their protective pouch, but dies soon afterward. The father, in a rare display of paternal care, sticks around to ventilate and protect the embryos as they develop.

These results tell us that certain species may be able to adapt to the increasingly acidic ocean by switching to more intensive parenting strategies. However, it’s unclear whether this can happen quickly enough to match the rate at which the ocean’s chemical composition is changing. Even if such dramatic transformations are possible, they may have unforeseen consequences on these species and their roles in the ecosystem.

Hydrothermal vents
Much of the ocean may look like this within a century. Photo credit: NOAA

Other than the adaptations of a few resilient worms, the future of the rest of the oceans’ vibrant biodiversity looks grim. These worms are part of a relatively small selection of animals that can survive the harsh conditions surrounding hydrothermal vents. In another study surveying life near these vents, Professor Sean Connell of the University of Adelaide described the sobering desolation we might expect in oceans of the future: “As you swim from one area to the other you see a dramatic difference. One minute you’re in a kelp forest with one-metre-high kelp and lots of different fish. Then you move into the vent area where everything is barren with short turf algae, just a few centimetres high and devoid of the life and colour of the other areas.”

Based on these studies, it looks like the rich ocean life we’ve gotten used to admiring in nature documentaries is not long for this world. If you’ve always wanted to see the Great Barrier Reef in person, you’d better book that trip as soon as possible.

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