A new research published this month shows that cobia, a large tropical fish, have amazing opposition to acidification projections. However, even mild acidification changes their bodily processes. Though a study in 2011 found acidification affects the hearing of clownfish, yet cobia’s inner ear changes considerably when they are raised in higher CO2 concentrations. Ocean acidification, which occurs as CO2 is absorbed by the world’s oceans, is a major concern for marine scientists globally. Studies on coral, mollusks, and other ocean denizens are helping to paint a picture of what the future might demand for specific species, should carbon emissions continue to enhance.
“Increased hearing sensitivity could improve a fish’s ability to use sound for navigation, predator avoidance, and communication. However, it could also increase their sensitivity to common background noises, which may disrupt the detection of more useful auditory information,” said Bignami, who recently completed his PhD in Marine Biology and Fisheries at UM.
The study, a collaboration between UM and NOAA’s Ocean Acidification Program at the Atlantic Oceanographic and Meteorological Laboratory in Miami, is the first to use micro-CT technology to examine otoliths while still inside the heads of the larval fish.
“This effect of ocean acidification represents a significant change to a key sensory system in fish. Although the ultimate ecological consequences still need to be determined, there is the potential for serious impact on important processes such as larval fish recruitment and fisheries replenishment in this species and perhaps other critical fisheries,” Bignami added.
In a new study published in Global Change Biology, University of Miami (UM) Rosenstiel School of Marine & Atmospheric Science researchers Sean Bignami, Su Sponaugle, and Robert Cowen are the first to study the effects of acidification on the larvae of cobia (Rachycentron canandum). Cobia is large tropical fish that spawn in pelagic waters, highly mobile as they mature, and a popular species among recreational anglers.
The team reared cobia in tanks with different levels of CO2 saturation looking for effects on growth, development, otolith (ear stone) formation, swimming ability, and activity level during the vulnerable larval stage of these fish. They found that cobia showed remarkable resistance to end-of-century acidification scenarios in terms of growth, development, and activity. However, more extreme acidification scenarios caused reduced larval size and a 2-3 day delay in their development. The study also reports a significant increase in otolith size (ear stone) at the most mild acidification conditions reported to date.
“The larval period is a critical stage in the marine fish lifecycle and the ability of cobia larvae to withstand ‘business-as-usual’ scenarios of ocean acidification provides an optimistic outlook for this species. However, research on this topic is still limited and if our findings on otolith formation are any indicator, then these fish are not entirely resistant to acidification,” said Bignami, a Marine Biology and Fisheries PhD candidate at UM.
The study is the first to report impacts of ocean acidification on a large, pelagic tropical fish species. “We need additional studies on study how fish, especially those that are ecologically and economically important, react to these environmental changes if we want to find ways to potentially mitigate the effects,” Bignami added. Cobia larvae used in this study were produced from broodstock raised at the UM Experimental Hatchery.
