Scientists
from the Dauphin Island Sea Lab, the U.S. Fish & Wildlife Service,
and the National Park Service are studying this black mangrove bush,
which is growing farther north than any other mangroves along the Gulf
of Mexico. A wasp can be seen in the center of the photo, about to
alight on a mangrove flower. (Press-Register/Ben Raines)
A low shrub sitting at the mouth of the big lagoon on Horn Island
provides another piece of evidence that our climate may be changing.
The
bush, covered in small, butter-yellow flowers and thick green leaves,
looks out of place amidst the surrounding sea of black needlerush marsh
grass. It is a black mangrove, a plant typically associated with the
coastlines of south Florida and the Caribbean. This particular bush is
believed to be growing farther north than any other black mangrove on
the Gulf Coast.
Scientists from the Dauphin Island Sea Lab, the
U.S. Fish & Wildlife Service, and the National Park Service are
studying the bush and three smaller black mangroves growing nearby. The
other bushes are all a few hundred yards farther south, but still many
miles north of the next closest group of mangroves, which grow on the
Chandeleur Islands off Louisiana. The mangroves there are relatively
recent arrivals as well, apparently gaining a foothold after warmer
winters in recent years.
Each month, the scientists visit the
trees to measure their growth and study the plant and animal colonies
surrounding them. Last week, blue crabs, hermit crabs, and stone crabs
all were visible beneath the mangrove's canopy. Sediment cores drilled
out of the swamp muck around the bushes revealed a variety of marine
worms, known collectively as polychaetes, and a host of tiny creatures
seldom seen by humans. A gas generator floated into the marsh on
pontoons was used to power a suction pump that vacuumed up shrimp,
minnows and other creatures swimming in the shallow marsh.
In their native habitats, mangroves support a diverse ecosystem, but one that is different than the typical salt marsh systems of the northern Gulf Coast. By studying the creatures around the plants, the scientists hope to understand what it will mean if warmer winters allow the species to proliferate along Alabama and Mississippi's shores.
A
light dusting of salt can be seen on the tops of these mangrove leaves.
Black mangroves are able to survive with their roots in the salty gulf
waters due to the ability to expel salt through their leaves.
(Press-Register/Ben Raines)
A light dusting of salt can be seen on the tops of the leaves,
evidence of the mangroves' unique ability to expel salt sucked up
through the roots. Scientists say the plants excrete salt at night and
on cloudy days, which allows them to live in places traditional plants
cannot.
"They really change the area. They can change the
sediment composition in the area around them," said Whitney Scheffel,
with the Sea Lab. Scheffel said the lab is studying how the plants
affect nutrient levels in the sand and mud of the marsh, and is
investigating any changes in the creatures using the adjacent marsh.
"They've
just started showing up in this area. We hope it won't have a
negative consequence, but right now we don't have the data to say one
way or the other," Scheffel said. "We want to see if having these black
mangroves here will actually change the growth rates of the spartina and
the juncus, the marsh grasses we have here. That could be important."
Matt
Johnson, a marine ecologist with the Gulf Islands National Seashore,
said mangroves have colonized the area in the past, but ultimately were
wiped out in particularly cold winters.
"This is right at the edge of their range. This population is the northernmost example we have," Johnson said.
The plant at the edge of the lagoon has died back a couple of times, but managed to rebound.
"We
call it 'dead but not dead.' The top dies off, but the roots don't
and the plant comes back," Johnson said. He said he didn't think the
arrival of the plants in the area represented an ecological threat.
"You can't really say (marsh or mangroves) are a better habitat. They both hold the land in place, they both support a lot of life, so as long as you've got one, that's good."
al.com
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