[Coral-List] Let's not forget the bigger ecosystem
katie.cramer at gmail.com
Fri Feb 17 16:03:39 EST 2017
Hello again listers,
I have been attentively following the discussion about the role of
parrotfish and other possible drivers (land based pollution, loss of
predators, hurricanes) in reef growth. It is important to point out that
many studies of modern reefs may give conflicting or counter-intuitive
results because they are focused on highly altered systems with
significantly depleted predator and herbivore populations, reduced water
quality, and more recently, increased thermal stress.
While our Nature Communications paper (
http://www.nature.com/articles/ncomms14160) focused in on the role of
herbivores (parrotfish and urchins) in reef growth, we realize the need for
assessing multiple human stressors to determine their relative importance.
Thus, we have follow-up papers in progress that also assess the impacts of
historical water quality declines (using benthic foraminifera and mollusk
fossils). We did also attempt to track long-term change in predatory
fishes through time. But these teeth are very rare in reef sediments,
likely due to the slow fossil tooth accumulation rate of these longer-lived
species and the greater amount of time these fishes spend in non-reef
habitats. Finally, because we cored in lagoonal settings, our reef cores
were composed of a dense matrix of coral skeleton and mollusk shell
fragments within a sandy-muddy matrix of carbonate grains that were easily
retained by our catcher at the end of the core tube. Thus, we lost very
little sediment and found plenty of teeth (on average 75 teeth per 5 cm
slice of the working half of a core).
We will be sure to post our follow-up papers to Coral List in the upcoming
months, and look forward to continued discussion.
>> On Wed, Feb 15, 2017 at 1:29 PM, Tim McClanahan <tmcclanahan at wcs.org>
>>> I often find the sea urchin - parrotfish - nutrient focus of many coral
>>> reefs studies to lack the bigger ecosystem-environment picture. We each
>>> measure and bring in our own interests and interpretations based on our
>>> disciplinary foci. One of my main foci has been top-down controls and
>>> larger food web interactions within environmental contexts. Sea urchins
>>> and parrotfish exist in a larger food web and so it is always
>>> to conclude about their ability to control the ecosystem without looking
>>> their position in the larger food web-environment.
>>> I think the work in the Caribbean suffers from this limited foci problem
>>> too often. I rarely hear Caribbean coral reef scientists on this list
>>> study and quote any work on the predators who control parrotfish and sea
>>> urchins apart from humans. Certainly these functional groups are part of
>>> the larger food web, so they must have their own influences and not be
>>> isolated or controlling independently of impacts on their own
>>> Is this ecosystem-view just too complicated and difficult to study and
>>> understand? Regardless, I hope reef scientists might make a better
>>> to study the larger system when possible.
>>> In case readers are interested, the paper published open access in the
>>> below looked at many possible controls on calcifiers in the Indian Ocean
>>> and concluded the extreme temperatures and the red-lined triggerfish
>>> probably having strong and equal effects on the calcifying community.
>>> There were no effects of Diadema or parrotfish but a role of Echinometra
>>> via it's interactions with it's main predator - Balistapus undulatus.
>>> Can these regional difference be explained away as another region or
>>> system? Or could work in other systems lack this larger ecosystem
>>> perspective and therefore coming to parochial conclusions? We won't know
>>> until the larger ecosystems are studied in all regions and compared. I
>>> think much critical work needs to be done..
Scripps Institution of Oceanography, UCSD
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