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Global warming could lead to more anxious fish, study reports

Dec. 5, 2013
Courtesy of the Scripps In­sti­tu­tion of Ocean­og­ra­phy
and World Science staff

Ris­ing ocean ac­id­ity linked to glob­al warm­ing may be mak­ing fish more anx­ious, hun­ker­ing down in dark wa­ters rath­er than ven­tur­ing in­to the light, a study sug­gests.

As the ocean ab­sorbs hu­man-produced car­bon di­ox­ide—linked to global warm­ing—its ac­id­ity rises. Stu­dies have al­ready found this dis­rupts the growth of shells and skele­tons of some ma­rine an­i­mals, but oth­er ef­fects are un­clear.

In a study pub­lished in the jour­nal Pro­ceed­ings of the Roy­al So­ci­e­ty B, sci­en­tists at the Scripps In­sti­tu­tion of Ocean­og­ra­phy at the Uni­vers­ity of Cal­i­for­nia San Die­go and Mac­Ewan Uni­vers­ity in Ed­mon­ton, Can­a­da, found that ris­ing ac­id­ity in­creases anx­i­e­ty in young rock­fish, an im­por­tant com­mer­cial spe­cies in Cal­i­for­nia. 

The re­search­ers com­pared a group of rock­fish kept in nor­mal seawa­ter to anoth­er group in wa­ters with el­e­vat­ed ac­id­ity lev­els match­ing those pro­jected for the end of the cen­tu­ry. Us­ing camera-based track­ing soft­ware, they meas­ured each group’s pref­er­ence to swim in light or dark ar­eas of a test­ing tank, a known test for anx­i­e­ty in fish. 

They found that nor­mal ju­ve­nile rock­fish con­tin­u­ously moved be­tween the light and dark ar­eas. But those un­der more ac­id con­di­tions for a week pre­ferred the dark ar­ea, a pref­er­ence that con­tin­ued for sev­er­al days even af­ter their wa­ter was nor­malized.

The sci­en­tists said the anx­i­e­ty is trace­a­ble to mo­le­cules in the fish sen­so­ry sys­tems known as GABA A re­cep­tors, al­so tied to hu­man anx­i­e­ty. The ac­idified en­vi­ron­ment leads to changes in the lev­els of ions, or elec­tric­ally charged atoms, in the blood. This re­verses the ions’ flow through these re­cep­tors, which act as ti­ny gate­ways. The end re­sult is a change in nerve cell ac­ti­vity, re­flected in be­hav­ior.

The find­ings “re­veal a po­ten­tial neg­a­tive ef­fect of ocean ac­idifica­t­ion on fish be­hav­ior that can pos­sibly af­fect nor­mal popula­t­ion dy­nam­ics and may­be even af­fect fish­eries,” said Martín Tres­guer­res, a Scripps ma­rine bi­ol­o­gist and study co­au­thor.

For rock­fish, “if the be­hav­ior that we ob­served in the lab ap­plies to the wild… it could mean that ju­ve­nile rock­fish may spend more time in the shad­ed ar­eas in­stead of ex­plor­ing around,” said Tres­guer­res. “This would have neg­a­tive im­plica­t­ions due to re­duced time for­ag­ing for food, or al­tera­t­ions in dis­per­sal be­hav­ior, among oth­ers.”


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Rising water acidity associated with global warming may be making fish more anxious, hunkering down in dark waters rather than venturing into the light, a study suggests. As the ocean absorbs human-produced carbon dioxide the water acidity rises, scientists say. This is known to disrupt the growth of shells and skeletons of some marine animals, but other effects are unclear. In a study published in the journal Proceedings of the Royal Society B, scientists at Scripps Institution of Oceanography at the University of California San Diego and MacEwan University in Edmonton, Canada, found that rising acidity increases anxiety in young rockfish, an important commercial species in California. The researchers compared a group of rockfish kept in normal seawater to another group in waters with elevated acidity levels matching those projected for the end of the century. Using camera-based tracking software, they measured each group’s preference to swim in light or dark areas of a testing tank, a known test for anxiety in fish. The researchers found out that normal juvenile rockfish continuously moved between the light and dark areas. But those under more acid conditions for a week preferred the dark area, a preference that continued for several days even after their water was normalized. The scientists said the anxiety is traceable to molecules in the fish sensory systems known as GABA A receptors, also tied to human anxiety. The acidified environment leads to changes in the levels of ions, or electrically charged atoms, in the blood, reversing their flow through these receptors, which act as tiny gateways. The end result is a change in nerve cell activity, reflected in behavior. The findings “reveal a potential negative effect of ocean acidification on fish behavior that can possibly affect normal population dynamics and maybe even affect fisheries,” said Martín Tresguerres, a Scripps marine biologist and study coauthor. For rockfish, “if the behavior that we observed in the lab applies to the wild… it could mean that juvenile rockfish may spend more time in the shaded areas instead of exploring around,” said Tresguerres. “This would have negative implications due to reduced time foraging for food, or alterations in dispersal behavior, among others.”