Blue Crabs Can Live In Lower Oxygen Levels, But Global Warming Is Still A Threat

Study shows that low oxygen or 'hypoxic' conditions can keep adult blue crabs tolerant and alive.

Scientists at the William & Mary's Virginia Institute of Marine Science used high-tech computer-controlled respirometers to explain the "ecological mystery," according to hngn.

"The notion that blue crabs are relatively intolerant of oxygen-poor waters was counterintuitive, because this species often occupies estuarine environments that can become hypoxic even in the absence of human activities," said lead author Rich Brill, a fishery biologist with NOAA's National Marine Fisheries Service and adjunct faculty at VIMS.

Scientists have been worried about the lowered levels of oxygen in oceans throughout the world and how it might affect vulnerable marine wildlife, including blue crabs. With extensive nitrogen from fertilizers and related human activities, the nitrogen can influence algal blooms to become a source of food for bacteria, in turn leading to decomposition, affecting the marine life.

"Because coastal hypoxia can significantly impact the movements, distribution, growth, and reproduction of inshore fish and invertebrate species, understanding their ability to tolerate hypoxia is becoming crucial; especially in species of ecological and commercial importance," Brill said.

The scientists were able to automate the entire data-recording system and observe crabs all the time with minimal human intervention. Contrary to earlier studies, crabs could maintain a constant rate of aerobic metabolism till they reached a critical oxygen level.

Earlier findings had shown that blue crabs are "oxygen conformers," with their metabolic rate falling with lower environmental oxygen levels. And now scientists find that they can survive in oxygen levels as low as 1.3 milligrams per liter at moderate temperatures, or just 15 percent of the oxygen levels in regular saturated water.

However, the low-oxygen waters may prove to be harmful if the temperatures continue to go up. Water temperatures in the Chesapeake Bay have risen by between 1.5 and 2.5 degrees Fahrenheit since 1960, and are thought to rise by as much as 9 degrees by 2070.

"Our data show that the metabolic rates of blue crabs increase with increasing temperature, and this in turn increases the lowest oxygen levels they can survive. So warming of the Bay will exacerbate the effects of hypoxia on blue crabs, as it will with almost all other organisms," Brill warned.

The findings were published in a recent edition of the Journal of Experimental Marine Biology and Ecology.