Chapman marine biologist looks at climate change’s potential effects on marine life

Photo credit: Chapman University

Photo credit: Chapman University

Some may muse about climate change as a far-off eventuality, but many experts say that for the aquatic critters dwelling in Earth’s oceans, it is a much more immediate problem – of life and death in some cases.

Bill Wright, Chapman’s resident marine biologist, has been studying marine invertebrates for more than four decades, including 15 years at Chapman. Wright’s fascination with the ocean as a surfer eventually pulled him into research on coastal animals like hermit crabs and limpets (a type of mollusk), which can be easily interacted with on nearby beaches.

These creatures are called “intertidal” as they dwell on the rocks of beaches in the low tide, getting wet in the high tide. Such organisms are important to the coastal ecology, but Wright says they are at serious risk should the ocean continue to change.

“Global climate change is really a huge event. They’re going, ‘Oh, is it happening or isn’t it? It’s a big bet,’” Wright said. “It is happening. It really is happening. We, as stewards of the planet need to document what’s going on.”

When it comes to climate change’s impact on coastal ecologies, there are two major considerations: ocean temperature and acidification

Wright explained that most climate change concerns involve gradual, direct effects like changes in standard temperatures. These may be important, but Wright says more attention should be paid to acute effects – rapid changes such as sudden spikes in temperatures that are predicted to come along with increasing temperature norms. Ocean life can adapt to slow changes like the water’s normal temperature increasing, but more sudden heat waves are another story.

The other half of this puzzle is ocean acidification, which Wright compares to cramps caused by increased carbon dioxide when a person is working out. As climate change introduces more CO2 into the ocean, the water steadily becomes more acidic, bringing with it complications for certain sea life. As an example, researchers have found that certain kinds of plankton, dependent on creating hardened shells to protect from predators, are unable to generate their shells in overly acidic water. Without their shells to protect them, these plankton are little more than an all-you-can-eat buffet to nearby predators.

When combined, temperature spikes and ocean acidification pose a threat to many types of sea life. Wright and his team of student researchers work by simulating these predicted temperature spikes and acidity increases according to climate change models, then observing changes in the behaviors of intertidal creatures. Some of the changes they’ve observed leave these coast-dwellers far more vulnerable to their natural predators.

Limpets, a kind of aquatic snail, manipulate their environment to help defend from predators.

While the tide is out, they will slowly scrape away seaweed from the rocks and then firmly attach themselves, making it hard for predators to snatch them up.

Wright’s team has found that, should it become too hot, limpets won’t carry out any of this kind of environmental work, making them easy pickings for predators when the tide comes back in.

Hermit crabs are another big example of how climate change can leave these intertidal organisms vulnerable. Wright’s team performed an experiment where hermit crabs were placed in cups of water at varying degrees and given a pellet of food. As the water got warmer, the hermit crabs’ eating slowed down. Once it reached 29 degrees Celsius – the temperature of some of today’s hotter tides – they stopped eating completely. At 32 degrees Celsius, half of the hermit crabs were dead within half an hour.

Temperature is enough of a threat, but heightened ocean acidity can also leave hermit crabs wide open to predators. When placed into a tank of water where one side has a trace of the hermit crabs’ natural predator, the rock crab, the hermit crabs will most often elect to avoid the water where they smell their foe. When acidity even slightly increases, however, Wright’s team found that hermit crabs lose their ability to tell that the rock crab was there, leaving them exposed to being eaten.

Environmental changes may not directly be killing the creatures in these cases, but Wright says that the environmental link with these destructive behaviors must be observed.

“It’s not that they’re being killed by the CO2, their behavior is changing and they’re more vulnerable to being eaten. Things like that are crazy, and they really matter,” Wright said. “Behavior oftentimes can do things much more rapidly and more extremely than the actual death and destruction of animals because of the environmental perturbation.”

Jonathan Winslow, The Orange County Register, 16 November 2015. Article.

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