Dispatches - Frontiers in Ecology and the Environment
Dispatches - Frontiers in Ecology and the Environment
Dispatches - Frontiers in Ecology and the Environment
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DISPATCHES<br />
DISPATCHES DISPATCHES<br />
Fake seagrass makes <strong>the</strong><br />
case for conservation<br />
Claire Miller<br />
Scientists <strong>in</strong> New Zeal<strong>and</strong> are us<strong>in</strong>g<br />
plastic seagrass beds to study how<br />
juvenile fish respond to changes <strong>in</strong> a<br />
vital but shr<strong>in</strong>k<strong>in</strong>g habitat. While<br />
meadows teem<strong>in</strong>g with fish survive<br />
<strong>in</strong> remote areas, sediment <strong>in</strong> runoff<br />
from adjacent l<strong>and</strong> development has<br />
killed much of New Zeal<strong>and</strong>’s subtidal<br />
seagrass <strong>and</strong> degraded what little<br />
rema<strong>in</strong>s.<br />
Fisheries ecologist Mark Morrison<br />
(National Institute of Water <strong>and</strong><br />
Atmospheric Research, Auckl<strong>and</strong>,<br />
New Zeal<strong>and</strong>) says that creat<strong>in</strong>g fake<br />
mats allows researchers to control<br />
<strong>the</strong> density <strong>and</strong> length of fronds, <strong>and</strong><br />
<strong>the</strong>n measure <strong>the</strong> effect of <strong>in</strong>creas<strong>in</strong>gly<br />
dense seagrass on fish abundance.<br />
The mats (24 <strong>in</strong> all, each<br />
3 m 2 ) used <strong>in</strong> <strong>the</strong> experiment covered<br />
a range of six densities, from<br />
sparse to very thick, <strong>and</strong> were spread<br />
over 2000 m 2 <strong>in</strong> <strong>the</strong> Whangapoua<br />
Plastic seagrass is a haven for juvenile fish.<br />
Estuary, near Auckl<strong>and</strong>, just before<br />
<strong>the</strong> fish recruitment period over <strong>the</strong><br />
sou<strong>the</strong>rn summer. The study found<br />
that <strong>the</strong> denser <strong>the</strong> seagrass, <strong>the</strong><br />
more abundant <strong>and</strong> diverse <strong>the</strong> fish.<br />
Maximum abundance for some<br />
species was reached at <strong>the</strong> highest<br />
grass-blade densities, with food limitation<br />
<strong>the</strong>n probably kick<strong>in</strong>g <strong>in</strong> as<br />
fish consumed all <strong>the</strong> zooplankton<br />
pass<strong>in</strong>g over <strong>the</strong> mats.<br />
“There is only one seagrass species<br />
<strong>in</strong> New Zeal<strong>and</strong>, <strong>and</strong> it grows <strong>in</strong> both<br />
<strong>the</strong> <strong>in</strong>tertidal <strong>and</strong> subtidal zones”,<br />
Morrison expla<strong>in</strong>s. “Subtidal seagrass<br />
NIWA<br />
beds are thought of as be<strong>in</strong>g rare, but<br />
I don’t th<strong>in</strong>k it was always so. I th<strong>in</strong>k<br />
we have just lost a lot of it over <strong>the</strong><br />
past 100 years. When <strong>the</strong> system is<br />
stressed, <strong>the</strong> subtidal beds are <strong>the</strong><br />
first to th<strong>in</strong> out <strong>and</strong> disappear. But if<br />
only <strong>the</strong> <strong>in</strong>tertidal beds are left, <strong>the</strong>n<br />
much of its habitat value disappears,<br />
because <strong>the</strong> fish may have to move<br />
out <strong>in</strong>to bare seafloor areas, where<br />
<strong>the</strong>y are susceptible to predation<br />
when <strong>the</strong> tide goes out.”<br />
While seagrass is mak<strong>in</strong>g a tentative<br />
comeback <strong>in</strong> some areas, threats<br />
cont<strong>in</strong>ue from l<strong>and</strong>-based activities.<br />
One problem is that people view<br />
recover<strong>in</strong>g seagrass as a weed to be<br />
removed, to keep beaches s<strong>and</strong>y.<br />
“Coastal managers need to protect<br />
dense seagrass beds <strong>in</strong> <strong>the</strong> subtidal<br />
zone”, says Morrison. “Restoration of<br />
seagrass is very expensive, so <strong>the</strong><br />
take-home message is to look after<br />
what you’ve got <strong>and</strong> create <strong>the</strong> right<br />
conditions, by controll<strong>in</strong>g degrad<strong>in</strong>g<br />
activities, so seagrass can restore<br />
itself.”<br />
n<br />
203<br />
Re-exam<strong>in</strong><strong>in</strong>g <strong>in</strong>vasive<br />
<strong>in</strong>dicators<br />
Virg<strong>in</strong>ia Gew<strong>in</strong><br />
In a recently published paper, ecologists<br />
Ken Thompson (University of<br />
Sheffield, Sheffield, UK) <strong>and</strong> Mark<br />
Davis (Macalester College, St Paul,<br />
MN) assert that global changes <strong>in</strong><br />
nutrient deposition, climate, <strong>and</strong><br />
l<strong>and</strong>scape disturbance are mak<strong>in</strong>g <strong>the</strong><br />
dist<strong>in</strong>ction between native <strong>and</strong> nonnative<br />
species less ecologically mean<strong>in</strong>gful<br />
(Trends Ecol Evol 2011; doi:<br />
10.1016/j.tree.2011.01.007).<br />
“Species are simply w<strong>in</strong>ners –<br />
plants able to thrive <strong>in</strong> <strong>the</strong>se conditions<br />
– or losers, those that can’t”,<br />
says Thompson. “There’s noth<strong>in</strong>g<br />
special about be<strong>in</strong>g alien or nonnative.”<br />
A number of <strong>in</strong>vasive species<br />
experts agree with <strong>the</strong> essence of<br />
Davis <strong>and</strong> Thompson’s claims. “There<br />
is noth<strong>in</strong>g really fundamental about a<br />
species status as ‘native’ or ‘alien’ that<br />
expla<strong>in</strong>s how <strong>the</strong>y ‘work’”, agrees<br />
Dave Richardson, Deputy Director of<br />
Science Strategy at <strong>the</strong> University of<br />
Stellenbosch’s Center of Excellence<br />
for Invasion Biology (Stellenbosch,<br />
South Africa). At issue is whe<strong>the</strong>r or<br />
not country of orig<strong>in</strong> matters.<br />
Many ecologists believe that dist<strong>in</strong>guish<strong>in</strong>g<br />
plants <strong>in</strong>to native or nonnative<br />
does still has value. “Plant<br />
traits are only one aspect of <strong>in</strong>vasions”,<br />
po<strong>in</strong>ts out Thomas Stohlgren,<br />
a research ecologist at <strong>the</strong> US<br />
Geological Survey’s Fort Coll<strong>in</strong>s<br />
Science Center (Fort Coll<strong>in</strong>s, CO);<br />
o<strong>the</strong>r factors – eg <strong>the</strong> pathways<br />
responsible for mov<strong>in</strong>g species, as well<br />
as <strong>the</strong>ir current <strong>and</strong> potential distribution<br />
– also play a role <strong>in</strong> determ<strong>in</strong><strong>in</strong>g<br />
whe<strong>the</strong>r a plant has <strong>the</strong> potential to<br />
become <strong>in</strong>vasive when <strong>in</strong>troduced.<br />
“The best, most consistent predictor<br />
of species <strong>in</strong>vasion is whe<strong>the</strong>r <strong>the</strong>y<br />
have successfully <strong>in</strong>vaded ano<strong>the</strong>r<br />
habitat”, says Doria Gordon, Director<br />
of Conservation Science for The<br />
Nature Conservancy (Ga<strong>in</strong>esville,<br />
FL). While Thompson says this is<br />
consistent with <strong>the</strong> view that w<strong>in</strong>ners<br />
will be w<strong>in</strong>ners anywhere, Gordon<br />
suggests that predictive tools based on<br />
traits, history of <strong>in</strong>vasiveness, <strong>and</strong><br />
biogeography avoid <strong>the</strong> import of<br />
“w<strong>in</strong>ners” with high economic <strong>and</strong><br />
environmental costs.<br />
While Thompson <strong>and</strong> Davis split<br />
species <strong>in</strong>to w<strong>in</strong>ners <strong>and</strong> losers, alternative<br />
ways to classify species are<br />
appear<strong>in</strong>g <strong>in</strong> <strong>the</strong> literature. For example,<br />
Richardson characterizes <strong>in</strong>vasiveness<br />
as <strong>in</strong>herent or <strong>in</strong>duced. He<br />
hypo<strong>the</strong>sizes that <strong>in</strong> some plant groups<br />
<strong>in</strong>vasiveness has a strong <strong>in</strong>herent<br />
component (species are ei<strong>the</strong>r likely or<br />
unlikely to become <strong>in</strong>vasive), whereas<br />
<strong>in</strong> o<strong>the</strong>rs, <strong>in</strong>vasiveness is <strong>in</strong>duced,<br />
<strong>in</strong>fluenced more by humans mov<strong>in</strong>g<br />
species or modify<strong>in</strong>g <strong>the</strong> environment.<br />
Philip Hulme, a plant ecologist at <strong>the</strong><br />
Bio-Protection Research Centre <strong>in</strong><br />
Christchurch, New Zeal<strong>and</strong>, suggests<br />
splitt<strong>in</strong>g species <strong>in</strong>to “passengers” or<br />
“drivers” of environmental change.<br />
“Unfortunately, we can’t yet predict<br />
impact-based traits”, he says. As researchers<br />
explore <strong>the</strong>se new paradigms,<br />
it seems unlikely that rely<strong>in</strong>g on native<br />
or non-native status alone will prove<br />
sufficient to identify<strong>in</strong>g <strong>in</strong>vaders. n<br />
© The Ecological Society of America www.frontiers<strong>in</strong>ecology.org