Thursday, December 28, 2006

Ocean temperature predicts spread of marine species

December 26, 2006 - CHAPEL HILL — Scientists can predict how the
distance marine larvae travel varies with ocean temperature – a key
component in conservation and management of fish, shellfish and
other marine species – according to a new study from the University
of North Carolina at Chapel Hill.

Most marine life, including commercially important species,
reproduces via larvae that drift far along ocean currents before
returning to join adult populations.
The distance larvae travel before maturing, called dispersal, is
directly linked to ocean temperature, the researchers found. For
example, larvae from the same species travel far less in warmer
waters than in colder waters, said lead author Mary O'Connor, a
graduate student in marine ecology in UNC's curriculum in ecology
and the department of marine sciences in the College of Arts and

"Temperature can alter the number and diversity of adult species in
a certain area by changing where larvae end up," O'Connor said. "It
is important to understand how a fish population is replenished if
we want to attempt to manage or conserve it."

Using data from 72 marine species, including cod, herring, American
lobster, horseshoe crabs and clams, O'Connor and her colleagues
developed a model that predicts how far larvae travel at a certain
temperature. The predictions appear to hold for virtually all marine
animals with a larval life cycle.

"We can apply this rule to animals without having to go out and
measure every species," O'Connor said. "Our general model gives us a
powerful new way to study larval movement with knowledge about ocean
temperature, which is much easier to come by. With models such as
this, we can see what large-scale changes in ocean temperature may
mean for adult populations."

The study appeared online the week of Dec. 25 in the Proceedings of
the National Academy of Sciences Early Edition.

Knowing dispersal distance is a critical component for managing
commercially important or invasive species, O'Connor said. "For many
animals, the larval phase is the only chance for babies to get away
from parents. Dispersal prevents inbreeding; for some species, this
is a time to move from breeding ground to habitat where they'll
mature," she said.

But less than 1 percent of larvae survive dispersal. They are
consumed by predators, encounter harsh environments or never reach
their destination and starve. For endangered species, survival of
some animals may depend on whether offspring from parents in one
protected area can get to another area where they are safe from
harvest. "In warmer waters, marine protected areas may need to be
closer together than in colder water, since in warmer water
dispersal distances tend to be shorter," O'Connor said.

While a one degree increase in temperature at the ocean surface
means larvae will travel a shorter distance in warm seas, the effect
is more severe when temperatures are below about 59 degrees
Fahrenheit (15 degrees Celsius), O'Connor said. Along California's
coast, sea surface temperature may warm from 53 degrees to 59
degrees Fahrenheit during an El Nino year, when a warm ocean current
appears in the equatorial Pacific Ocean. Larvae that travel 62 miles
at 53 degrees Fahrenheit would disperse only 46 miles at 59 degrees.

"On the up side, shorter dispersal can mean greater survival because
the larvae spend less time in the water, where they are at a high
risk of death. On the down side, it could mean they won't travel as
far and may not make it to their juvenile habitat," O'Connor said.

The researchers suspect temperature plays an important role in
larval dispersal because metabolic processes in larvae are sensitive
to temperature and similar among species. Consequently, larvae in
cold waters develop more slowly and drift further before beginning
their next development stage because colder temperatures cause
sluggish metabolisms.

University of North Carolina at Chapel Hill

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