Ocean Reserves Protect The
Invaders As Well As The Natives
Contact: Sharon Keeler
UNH Media Relations
Feb. 22, 2005
Editors/News Directors: UNH Professor Jeb Byers is available
by phone at (603) 862-0006 or by email at email@example.com.
DURHAM, N.H. -- While ocean reserves are increasingly being used
to safeguard exploited native species, there can be one harmful
side effect – non-native species may be flourishing under
such protection, as well.
Jeb Byers, assistant professor of zoology at the University of New
Hampshire, reports in the February issue of the journal “Ecology”
that this is the case regarding a native and non-native little neck
clam species found in Puget Sound, Washington. His work was funded
by Washington Sea Grant and a private, nonprofit called Marine Ecosystem
Health Program (now SeaDoc Society).
Byers studied three reserves and eight nonreserves in the San Juan
Islands to quantify the abundance of these intertidal clams.
“My research focuses on nonindigenous -- or non-native species
and I wanted to know if and how conservation strategies alter the
abundance and impact of this non-native clam,” Byers says.
“I also wanted to know if the relationship between the native
and non-native species varies in a protected environment.”
What his study revealed was that a heavily harvested non-native
species, Venerupis phlippinarum, was significantly greater on reserves.
In contrast, the abundance of a similar, harvested native species,
Protothaca staminea, did not differ between reserves and nonreserves.
The non-native species was also larger on reserves than in non-protected
environments, while size of the native clam did not differ.
To better understand how the relationship between the two species
may be altered by the increased densities of the non-native clams
in a protected environment, Byers followed these surveys with a
yearlong field experiment replicated at three reserve and three
nonreserve sites. The experiment examined the effect of the high
non-native species densities on the native species, as well as what
the impact of natural predators might be. These predators include
crabs, seagulls, starfish and fish.
“Even at experimental densities 50 percent higher than their
natural levels measured in the field, Venerupis had no direct competitive
impact on Protothaca,” Byers says. “But the non-native
clam flourishes in its protected environment. This is due to the
fact that it has a shallower 3-centimeter burial depth, making it
easy prey for natural predators and humans. Remove the predators
and there is little to stop it from thriving. The native clam, on
the other hand, buries deeper, 6 centimeters, potentially providing
itself a better buffer from excavating predators like crabs and
Why they bury at different depths is connected to dissimilar survival
strategies. The native clam buries deeper to protect itself, but
this means it cannot feed as efficiently from the water column.
Less food means it grows and reproduces at a slower rate. The non-native
clam, being closer to the surface, has better access to food. It
grows and reproduces faster.
Byers explains that the more vulnerable non-native clam seemingly
eases pressure on the native clam, because humans and intertidal
foraging crabs more readily harvest it. In a sense, it plays a “sacrificial
role” that partially protects the native clam from predator
mortality in the natural world.
“That the only species consistently benefiting from protection
was nonindigenous highlights a potential, unintended consequence
of marine reserves, “ Byers says. “Land managers routinely
apply control measures for nonindigenous species; our findings suggest
a similar proactive approach for marine reserves, as well. Because,
even though the native clam in our study does not appear to be negatively
impacted by the non-native clam in a protected environment, this
may not be the case for other marine species.”