Research Highlight: Climate Change Disrupting Fish Habitats

Scripps research depicts warming’s vast influence across marine life spectrum

While he was a graduate student at Scripps Institution ofOceanography at UC San Diego, Chih-Hao Hsieh and Scripps professorGeorge Sugihara began asking questions about how climate change andwarming ocean waters might be influencing marine life.

They began answering some of those questions based on data from theCalifornia Cooperative Oceanic Fisheries Investigations (CalCOFI), aprogram based at Scripps that has monitored the marine environmentof the California Current for nearly 60 years. They started to seepatterns emerge as they evaluated the sensitivity of fish habitatsin response to climate-driven ocean warming.

The study progressed steadily, but it was taking time away fromHsieh’s core thesis work. The project needed to be delayed.

Flash forward a year. Hsieh, with a Scripps Oceanography doctoraldegree under his belt, was hired as a professor at the Institute ofOceanography at National Taiwan University. Shortly thereafter,Hsieh dug back into the data and with several colleagues completedthe analysis, which was recently published in the journal GlobalChange Biology.

The resulting work, the first broad study of its kind, describes howthe effects of climate change are being felt across a wide ensembleof sea life. The climate-induced changes span from migration patternalterations to key population shifts.

"This is the first evidence in the ocean that climate change canhave dramatic effects on large-scale fisheries ecosystems," saidSugihara. "These are some very interesting consequences that peoplehaven’t really thought about. These warming events could actuallycause a constellation of species that normally don’t interact tobegin to interact and that could have potentially large effects onwhat we think ought to be the natural ecosystem. This is akin to theaction of invasive species but on a very large scale."

Sugihara said large-scale studies on ecosystem responses to climatechange have been done in terrestrial systems, such as for birds andplants. In addition, anecdotal studies have been suggested for a fewisolated marine species, such as Bearing sea pollock, for whichchanges in distribution could be due to fishing pressure. Hsieh’sstudy, however, is the first to show the effect in the marineenvironment using non-fishery-based data on a large scale and for alarge ensemble of species.

To arrive at their results, the scientists studied quantities oflarvae for 34 fish groups. Numbers and geographic locations of fishlarvae—a quantity known as "biomass"—are indicative of theabundance of fish species. They compared that information withphysical measurements, including water temperature.

Among their findings, the researchers describe a boost in thepopulation of 25 fish groups as the water temperature shifted fromcold to warm temperatures over recent decades.

They also found that fish species that typically migrate verticallyin the marine water column shifted geographically northward tocolder waters, a change that wasn’t seen in fish that don’t migrateas such in the water column. The authors speculate this is becausethe upper layers of the water column warmed considerably more thandeeper levels, leaving the bottom dwellers less impacted. Migratingspecies would have sensed the warming more readily and moved inresponse.

The researchers also discovered that groups that typically reside inthe far open ocean shifted closer to shore as the temperatureincreased and species that normally reside in coastal areas movedeven closer to shore.

"These sensitivities to climate can cause different fish species tostart interacting," said Sugihara. "It’s almost like seeing oceaninvaders come into the coast and these ad hoc mixed ecosystems couldpotentially have large ecological and commercial consequences downthe road. They could further destabilize fish stocks, making themmore variable and less predictable, adding risk to the alreadyrisk-prone fishing industry."

A related study led by Hsieh that recently appeared in the CanadianJournal of Fisheriesnd Aquatic Sciences showed that fished orexploited species are more sensitive to environmental changes.

"Open-ocean fishes that were rarely studied due to their loweconomic values may in fact provide important clues signifying howmarine organisms are responding to climate variations," said Hsieh."The interactions found between oceanic and shallow water coastalspecies also imply that anthropogenic disturbances, for examplefishing, could have profound indirect effects on other components ofthe marine ecosystem."

In addition to Hsieh and Sugihara, coauthors of the Global ChangeBiology paper include Hey Jin Kim (Scripps Oceanography and MontereyBay Aquarium Research Institute), William Watson (SouthwestFisheries Science Center), and Emanuele Di Lorenzo, aScrippsgraduate now at Georgia Institute of Technology.

The study was funded by The National Science Foundation CAMEO(Comparative Analysis of Marine Ecosystem Organization) program, theNational Marine Fisheries Service, National Science Council’s(Taiwan) Long-term Observation and Research of the East China Sea,and National Taiwan Ocean University’s Center for Marine Bioscienceand Biotechnology.

—Mario C. Aguilera

May 2009