Climate velocity speeds marine animals along
Continental shelf ecosystems contain the most productive areas of the ocean, supporting the areas of highest species diversity and producing about 90% of global fisheries catches. Tracing the influences of changing climates from physics to biochemistry, phytoplankton, physiology, fish, and fisheries, however, is a challenge that we are only just beginning to address, despite the substantial impacts that are expected.
For example, oceans have warmed somewhat more slowly than the atmosphere (0.67°C vs. 0.74°C over the past century), but thermal gradients are also less steep in the ocean than on land. The consequence is that climate velocities (the rate that climates shift in space) are as fast, and sometimes faster, in the ocean than they are on land. Climate velocities are calculated as the product of warming (°C/decade) and the slope of thermal gradients (km/°C) to yield the speed in km/decade that species would have to shift in order to maintain constant temperatures (see figure). Median velocities from 1960-2009 in the ocean have been 21.7 km/decade, but reached 200 km/decade near the tropics and in the sub-Arctic.
Figure 1. Map of climate velocities in the ocean from 1960-2009. Graph on the left shows average velocities on land (red) and in the ocean (blue) by latitude. From Burrows et al. 2011 Science 334: 652-655.
Fish appear to respond quickly and often quite predictably to changes in water temperature. There are physiological reasons to expect this effect, including the “thermal envelope” within which fish have sufficient oxygen for growth and survival. These envelopes vary among species, and marine species distributions match closely to their physiological limits (i.e., closer than on land).
Recent work in our lab is working to understand how the distribution and abundance of marine fishes and invertebrates respond to climate velocities, how these changes affect marine communities, and what impacts this will have on marine fisheries and conservation. For example, it has long been confusing why many marine species (up to 60%) do not appear to be shifting northward as global temperatures have warmed over the past few decades. By mapping the thermal envelopes for 325 marine species, however, we showed, that climate velocities in many parts of North America are actually shifting south and have been for the past 3-4 decades. Many of these southward shifts are a result of geographic constraints or climate variability (e.g., Pacific Decadal Oscillation, El Nino Southern Oscillation, etc.). When we compared these climate velocities to observed shifts in species distributions (see figure), we found that species largely follow local climate velocities. Going forward, it appears that climate velocity will be a powerful tool for predicting future species distributions as well.
Figure 2. Figure 2. Vectors show the average shift in latitude and longitude for each taxon (colors) and the mean shifts in each region (black). Insets show the mean (black), maximum (blue), and minimum (red) latitude of detection for Pacific cod (Gadus macrocephalus) in the Gulf of Alaska, big skate (Raja binoculata) on the U.S. West Coast, and American lobster (Homarus americanus) in the Northeast. From Pinsky et al. 2013 Marine taxa track local climate velocities Science 341: 1239-1242.
Ongoing work is now working to understand the mechanisms the allow species to shift north. Are species colonizing new habitat through larval dispersal or adult migration? Or are shifts observed to date primarily the result of differential growth in population size, growing in the north and shrinking in the south? Through a collaborative project funded by a number of Mid-Atlantic Sea Grant programs, we’re digging into these questions for summer flounder, one of the species that has been shifting north most rapidly on the east coast. It is also one of the most important commercial and recreational fishery species. The team is led by our lab at Rutgers University, but includes partners at Stony Brook (NY), George Mason (VA), and the University of North Carolina. Among other activities, we’ll use genetics (SNPs genotyped with RADtag methods) to understand where larvae settling in NJ and NC have come from, and how these patterns have changed through time.
We’re also interested in how fisheries are affected by these shifting species. Do fishers travel further? Intensify effort? Change to new species? Are there important lags, feedbacks, or thresholds in this coupled social-ecological system as climate pushes species along? Are there important cumulative impacts of fishing and climate change on marine species?
Figure 3. Figure 3. Lobster boats sit on their moorings. American lobster in the northeast U.S. is one of the species that has been moving north most dramatically over the past four decades, largely ending the fishery in Long Island Sound but benefiting ports further north. Photo by M. Pinsky.
Existing work has documented that fisheries do shift north when their target species moves (see figure), but we’re still working to document the extent that movements, shifts in species, or changes in effort produced these patterns. Intriguingly, fisheries appear to lag substantially behind the fish, fishing the trailing edge much harder than the leader edge.
Figure 4. Figure 4. Ocean species have shifted northward in the northeast U.S. as ocean temperatures have risen. As a result, over the past 40 years more northern ports have gradually increased their landings of four marine species. While some species move north out of an area, other species move in from the south. From Doney & Rosenberg 2013 Oceans and Marine Resources in NCADAC Draft Climate Assessment Report, U.S. Global Change Research Program.
Much of this research is just beginning, and the lab is actively recruiting interested graduate students and postdoctoral scholars to work on these projects.
Dr. Malin Pinsky, Principal Investigator