Embargoed until August 18, 2 p.m. EST
URI Scientists' Discovery Sheds New Light on
Species Diversity in the Ocean
Research published in this week's Nature uses satellite observations
to predict count of zooplankton species with 90 percent accuracy
NARRAGANSETT, R.I. -- August 17, 1999 -- Several centuries ago, a simple
mathematical calculation proved the world was round and changed how people
thought about their environment. In a similar fashion, two University of
Rhode Island scientists and their Brown University colleague have made a
simple discovery that may force biologists, ecologists, and evolutionists
to question some long-standing beliefs about diversity in the ocean.
In an article to be published in the August 19 issue of Nature,
URI Graduate School of Oceanography (GSO) paleoceanographers Scott Rutherford
and Steven D'Hondt with Brown University paleoceanographer Warren Prell
show that the diversity of planktonic foraminifera, one-celled animals that
float in the ocean, is greatest in the middle latitudes of the world's oceans.
Comparison of their results to other studies suggests that this is true
of zooplankton in general; all of the microscopic animals that float in
the ocean appear to be most diverse at middle latitudes. This finding runs
counter to the traditional model that biodiversity peaks at the equator
and declines towards the polar regions of the Earth.
Their analysis of Atlantic Ocean data shows that scientists can use
sea-surface temperature to estimate the number of planktonic foraminiferal
species at each spot in the ocean with 90 percent accuracy. The temperatures
are derived from satellite observations that measure the ocean's "skin"
temperature-the top layer of water to adepth of about one centimeter. Their
discovery goes one step farther by showing that oceanic temperature at a
depth of 50, 100, or 200 meters predicts diversity nearly as well, suggesting
that temperatures at the sea surface are highly correlated to the structure
of the water column beneath the surface.
The scientists explain their results by suggesting that the number of
zooplankton species at each site is primarily controlled by the physical
structure of their environment. As D'Hondt explains, "All zooplankton
need food and many zooplankton reproduce sexually. For these reasons, they
need to live in places where they can count on encountering both prey and
other members of their own species. If two different populations of a single
species consistently reproduce in separate places or at different times,
they may eventually evolve into two different species. Conversely, if a
species is composed of a single large population that generally meets and
reproduces at the same time and place, its members have little opportunity
to separate into different species."
At the poles, the water temperature is approximately constant with depth
and zooplankton may be forced to stay near the surface in order to consistently
meet each other and find abundant prey. At the equator, there is a shallow
surface layer of nearly uniform temperature and a deeper region of cooler
uniform temperature with a sharp transition between; this structure may
support more species than the structure at the poles because it provides
a greater diversity of zones where prey may aggregate and reproductive partners
can form separate populations. In middle latitudes, the temperature of the
water changes more gradually with water depth, providing an even greater
diversity of vertically segregated zones where different species can exist
For Information Contact:
Jhodi Redlich, URI, 401-874-2116 Jredlich@advance.uri.edu
Lisa Cugini, URI, 401-874-6642 lcugini@gso.uri.edu
Scott Turner, Brown, 401-863-1862 Scott_Turner@brown.edu
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