Image: Flickr: Florida Memory

Climate change has had a significant effect on land, and is having an even greater effect on the oceans. Though we can’t see the effects underwater, scientific research is finding that marine ecosystems are more sensitive to even the most subtle temperature changes.

Global warming caused by human activities that emit heat-trapping carbon dioxide has raised the average global temperature by about 1°F (0.6°C) over the last century. In oceans, this increase has been about 0.18°F (0.1°C). Ocean temperatures are changing more slowly than land temperatures, but the impact is just as large.

While this increase has proven to be life-threatening for some underwater species, others are thriving.

Cephalopods — squids, octopuses and cuttlefish — are alive and flourishing in warmer water temperatures.

“Cephalopods have increased in the world’s oceans over the last six decades,” said Zoë Doubleday, a marine ecologist from the University of Adelaide in Australia, and lead author of a new study published Monday, told The New York Times. “Our results suggest that something is going on in the marine environment on a large scale, which is advantageous to cephalopods.”

The study states that cephalopods are highly adaptable predators and increased predation by cephalopods could impact many prey species. Increases in cephalopod populations could even benefit marine predators that rely on them for food, as well as human populations that rely on them as a fisheries resource for food and income.

This unusual adaptability is being amplified by overfishing of certain fish that prey on cephalopods--resulting in expanding populations.

“Cephalopods are often called ‘weeds of the sea’,” Doubleday told the Guardian, because their “rapid growth, short lifespans and flexible development” allow them to adapt to environmental changes more quickly than other marine species.

Perhaps the least adaptable species is coral.

Increased temperatures cause coral to bleach, which makes them unable to re-establish themselves. More than 90 percent of the Great Barrier Reef is already bleached. This is a problem because coral reefs are essential to the life of other marine species and are responsible for biodiversity in the ocean and providing the world’s poor with a source of food.

Ocean acidification, or an increased acidity level in ocean water, is also to blame for coral decay. Acidification is caused by excessive amounts of carbon dioxide dissolving into the ocean. Higher acidity levels have been proven to inhibit shell growth in marine animals and can cause reproductive disorders in fish.

The oceans currently absorb about one third of all man-made carbon emissions, about 22 million tons a day, causing alarmingly high levels of acidity. These high levels of acidity are also a cause of coral bleaching.

If ocean temperatures continue to rise, the water will become too warm for coral reefs by 2050. If coral reefs cannot survive, there will be a decrease in oceanic biodiversity by at least 25 percent, as well as reduced fisheries production and coastal protection.

This is not just the loss of a few fish here and there, though. This decrease in species is the unraveling of an entire ecosystem that sustains not only fish, but human life on Earth.

Additionally, other marine organisms have decreased by nearly half. Even species living at the bottom of the food chain have been affected. This decrease can create a cascading effect by disrupting the food chain, causing food shortages for higher predators--up to humans. Nearly 1,200 species of fish, including commonly eaten fish like grouper, mackerel and tuna, are steadily declining.

The big question is why are cephalopods doing so well while other marine life is decreasing? Climate change and overfishing seem to be the top two answers.

Scientists are continuing research as to why there has been such an increase in cephalopods and decrease in fish. Some even believe that finding an answer may point to ways we can reduce carbon emission to help maintain ocean temperatures.


Defend the Planet

Why are squids thriving in warming oceans?

By Krista Watson