[Coral-List] Algae and nutrients and herbivory in oligotrophic waters
klaas.pauly at ugent.be
Thu Jun 19 13:25:13 EDT 2008
Dear Imam, Alina and others,
Based on my field experience, I tend to agree with Thomas:
Together with Tom Schils (University of Guam), I've made seasonal
observations during 4 consecutive years in Dhofar, Oman. One could see the
very intense seasonal upwelling in Dhofar as a huge natural enrichment
experiment: during summer monsoon, nutrient concentrations are very high
because of the seasonal upwelling, and macroalgae occur in huge quantities
(up to several kg per m²), growing in between, over and sometimes literally
on coral colonies (sea Tom's front picture on Journal of Phycology 42(4) ).
During winter monsoon, with very oligotrophic conditions (no upwelling, no
runoff, no nearby cities), the region is almost devoid of algae. This
difference is definitely not due to herbivores: on the contrary, the wealth
of nutrient-rich algae attracts more herbivores during summer, and yet the
algae persist. It is only at the end of the monsoon (when upwelling stops)
that algae die. The difference is also not explained by temperature
differences (alone): further north, in Al-Wusta and Ash-Sharqiyah regions of
the Arabian Sea, there are sheltered areas where seasonal temperature
differences are far less pronounced, but the same pattern of seasonal algal
dominance over coral colonies persists.
It seems that grazing does influence algal species composition (as Thomas
pointed out: herbivores eat certain species and leave the rest): I've
carried out several caging experiments along the Arabian Sea coast and Gulf
of Oman, although unfortunately, many plots were destroyed during an
unusually stormy season, so I could not publish statistically sound results
yet. It was very remarkable to see that at one particular site in the
Arabian Sea (Barr al Hikman), one gelatinous red algal species, Botryocladia
sp., attained biomasses exceeding 1.5kg/m² in the closed cages (i.e.,
filling the entire cage), while it was virtually absent from open plots and
the entire surroundings. Other species were found in similar quantities in
open and closed cages.
Klaas Pauly - Teaching Assistant, PhD Student
Phycology Research Group, Biology Dept., Ghent University
Krijgslaan 281/S8, B-9000 Gent, Belgium
Tel. + 32 9 264 8507
Fax. + 32 9 264 8599
From: Thomas Goreau [mailto:goreau at bestweb.net]
Sent: 18 June 2008 19:06
To: Imam Bachtiar
Cc: coral-list coral-list
Subject: [Coral-List] Algae and nutrients and herbivory in oligotrophic
Very few of the studies on herbivory and algae are any good, because
only a tiny handful have made accurate nutrient measurements. When
this is done properly it is clear that nutrients drive algae
productivity and herbivory is only a secondary factor, because
grazers prefer to eat some species and avoid others. I've looked at
the zonation of algae species in reefs all around the world and these
are sharply zoned by nutrients in ways that clearly reveal the
sources. Every place I've looked with nutrient sources are dominated
by algae whether or not herbivores are present (and herbivore always
dominate the fish where there are nutrient sources, whether these are
from human land-based sources or from upwelling), and algae are
absent or rare where there are no nutrient sources, again whether or
not there are herbivores (which there rarely are). This is the exact
opposite of what top-downers predict.
As far as coralivores go, I also think the popular conceptions are
often erroneous. Most alleged coral eating is much less than is
claimed. Butterflyfish mostly just suck off surface mucus and there
is little or no physical damage to polyps. Parrotfish that are
allegedly biting coral are almost inevitably biting algae growing on
dead coral, and avoiding the coral tissue, as you can see if you look
closely where they bite. The popular claims that parrotfish eat coral
is probably largely untrue, and much of their biting of corals is
really territorial marking the boundaries of breeding territories
rather than for food. Almost every time you look where a bumphead
parrotfish or Napoleon wrasse has bitten into large bubble coral
colonies, you will see the tubes of the burrowing clams and worms
inside the coral that they were really eating rather than coral tissue.
I'll talk a bit about this at the next Gili Trawangan workshop in
early December. Look forward to continuing to work with you there and
other sites around Lombok. My best to all my friends in Bogor.
Thomas J. Goreau, PhD
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net
Date: Wed, 18 Jun 2008 11:28:37 -0700
From: "Imam Bachtiar" <ibachtiar at telkom.net>
Subject: [Coral-List] Herbivory on oligotrophic waters
To: <coral-list at coral.aoml.noaa.gov>
Cc: coremap2 at yahoogroups.com
Content-Type: text/plain; charset="us-ascii"
Herbivory is thought to be a key process in coral reef resilience.
studies have shown its importance in controlling macroalgae and provide
space for larval settlement. Most papers discussing about herbivory
exclusion experiments, however, do not clearly explain whether the
of study is oligotrophic or mesotrophic. Some other papers also indicate
that nutrients is not limiting factor of macroalgae growth. I would like
therefore to have your opinion or comments about this.
1) Is there any paper studying herbivory in oligotrophic waters?
2) Which one is more important in reconstruction of reef communities in
oligotrophic waters: herbivory vs corallivory?
Looking forward to have your reply.
Institut Pertanian Bogor, Indonesia
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