[Coral-List] Diademia Coral-List Server
Szmant, Alina
szmanta at uncw.edu
Fri Oct 6 18:28:02 EDT 2006
I'd like to add to this discussion an observation and some prelim experimental data that we collected (with students) in Curacao during the spring of 2005. We noticed very high densities of coral recruits, and not just of the Agaricia/Porites/Favia group but of bradcasters such as Diploria, Siderastrea, some Montastraea, at several locations we worked along the S coast of Curacao. Some of these sites also had high densities of Diadema while others had none. A group of students did their project collecting data to determine whether there was any quantitative correlation between Diadema density and coral recruit density. We went as far as doing all the Diadema censuses at night so as not to miss any that were hiding during daytime hours. The results showed that there are sites with high Diadema and high coral recruit density, and areas with no/none/zip nada Diadema and even higher coral recruit density. Accompanying lab tests showed that when we had higher Diadema densities some of the coral recruits got grazed and scarred too. What these data show is that at least along this Curacao coast, coral recruitment rates are high almost everywhere we looked (and algal cover low) but not because of high Diadema densities. We didn't measure fish grazing but grazing fish abundance was low, especially compared to what I am used to in Fla Keys and even Puerto Rico. We'll make sure to include this measurement when we go back next spring. The sites we used were directly offshore a major desalination plant, one mile from a big cruise ship dock, and several sites that were nice breakwaters made up of boulders immediately offshore of major hotels. These boulders were well liked by both the Diadema and juv corals. We also had sites more to the west where there was less immediate development. Two of the sites are long term Carmabi study sites.
My take on all this is that because this part of the Caribbean has been exempt from major bleaching impacts and thus also, low incidence of coral disease (E. Weil has the data to show this), there is higher live coral cover here than most rest of Caribbean. More live coral, less substrate available to algae, thus even an overfished herbivore community can keep algae grazed (see paper by Williams and Polunin where they experimentally increased 'coral' cover and got higher grazing rates on remaining substrate). Also, more live coral cover, more reproductive coral tissue, higher larval supply and better coral recruitment. Diadema also like the more grazed less macroalgal cover to recruit in (work done by Les Kaufman's lab). Thus the same conditions that favor coral recruitment also favor Diadema recruitment and survivorship. Thus, at least in the system we looked at I do not think there is any support for a cause and effect between higher Diadema abundance and higher coral recuit density, but rather both groups responded to the same favorable environment conditions.
By contrast in Puerto Rico in La Parguera, Diadema has made an excellent recovery on many reefs even offshore, and now even at depths to 30 to 60 ft in some places. But coral recruit density is not as high as it is in Curacao, and in fact mostly is low for the broadcasting spp I list above. Bleaching has had a major effect on La Parguera corals, and coral populations are nothing compared to what they used to be. There is also lots of overfishing and plenty of sedimentation stress because of poor land management and clear cutting up in the hills, which make the situation worse. So a similar and even higher abundance of Diadema on La Parguera reefs is not associated with any increase in coral recruit density.
Yes, its complicated out there and we need to be careful about over-simplifying the situation for whatever reason, even to prevent development! Too may humans, too many local and global impacts; none of this is good for corals, walruses, tigers, sharks, most fish and marine inverts that aren't toxic, and trees everywhere.
*******************************************************************
Dr. Alina M. Szmant
Coral Reef Research Group
UNCW-Center for Marine Science
5600 Marvin K. Moss Ln
Wilmington NC 28409
Tel: (910)962-2362 & Fax: (910)962-2410
Cell: (910)200-3913
email: szmanta at uncw.edu
Web Page: http://people.uncw.edu/szmanta
******************************************************************
________________________________
From: coral-list-bounces at coral.aoml.noaa.gov on behalf of Eric Borneman
Sent: Fri 10/6/2006 3:05 PM
To: Martin Moe
Cc: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] Diademia Coral-List Server
There is such a wealth of information on this topic that it seems
fruitless to even begin any sort of literature "justification" in
posts. Workshops, meetings, special issues of journals, reports, and
more have debated bottom up and top down factors for decades and at
this point if we do not realize that both, and more, play roles in
community structuring then we are indeed in trouble. As Martin said,
the complexity is enormous and, in fact, each reef is different. The
polarization of views regarding factors contributing to coral reef
decline or to the reasons for the existence of alternate stable reef
communities, such as phase shifts, as being due to a single dominant
ecological, biological, or environmental factor serves to hinder
understanding unless, of course, that particular reef is strongly
influenced by one or a few dominant factors.
But what it comes down to in my mind, at least, is the following?
How then do you explain luxuriant coral growth to the near exclusion
of macroalgae in nutrient rich lagoons (many examples in the Pacific,
even with high sedimentation rates from decaying vegetation) but
macroalgal abundance in remote, offshore nutrient poor and population-
free areas (e.g Mona Island, Glover's reef)?
Why are algal blooms transient and reef coral-dominated at the Flower
Garden Banks despite relatively low Diadema densities? Is this a
bottom-up factor community or is it because there are a lot of
grazing fish by comparison with other Caribbean reefs?
Historically, I think, it is pretty well demonstrated that the
Caribbean was out of whack before anyone really started studying it,
and since then I think it is also pretty well established what a
critical role Diadema played throughout most of the Caribbean in more
recent times. There are currently sites with relatively high Diadema
and relatively low coral cover, and conversely low Diadema and high
coral cover. Maybe the the historical grazing factors are forever
lost, and maybe Diadema is rightly credited for allowing for the
conditions Martin alludes to in his words and the studies cited (I
think he is, fwiw), for indeed where there are a lot of Diadema,
there tends not to be much macroalgae.
Moreover, there are areas with no Diadema having lots of macroalgae
and areas with Diadema having no macroalgae separated literally by a
few meters of sand from each other.
As to aquariums, the fact that you can grow corals in closed systems
with highly elevated nutrient levels without macroalgal dominance in
the presence of high and diverse numbers of grazers is a certainty,
as well as the certainty of absolute dominance of algae over corals
in closed systems that lack any grazers. In the latter case, the
algae pulls nitrogen and phosphorus to almost unmeasurable levels in
the water column to the point where other nutrients become limiting
to further growth. Even corals not eventually overgrown with algae
eventually die, likely from starvation. Where does this leave us?
Eric
_______________________________
Eric Borneman
Department of Biology and Biochemistry
University of Houston
Science and Research Bldg. II
4800 Calhoun Rd.
Houston, TX 77204-5001
ph: 713-743-2667
On Oct 6, 2006, at 9:23 AM, Martin Moe wrote:
> Hi James,
>
> You make some very good points in your post. I am, of
> course, not unaware of the great stresses we have
> placed on our reefs from anthropogenic release of
> nitrogen and phosphorus, addition of a great variety
> of organic and inorganic pollutants, global warming,
> microorganisms and nutrients from sewerage discharge,
> outfall, and seepage, environmentally unsound and
> unsustainable fishing practices, and just excessive
> human visitation. And these problems must be, and are
> being, addressed. But the biological world is very
> complex and coral reefs are among the most
> ecologically complex ecosystems that exist.
>
> It has been demonstrated that return of Diadema to
> stressed reefs improves coral ecology. For example
> Carpenter and Edmunds (Ecology Letters, (2006) 0:
> 271-280 stated, "Here, we show that dense populations
> of Diadema now occur over a multi-kilometer wide scale
> at six locations scattered along a 4100 km arc across
> the entire Caribbean. In all cases, these dense
> populations are found in shallow water (<6 m depth) on
> outer reef communities and are associated with reduced
> macroalgal cover and enhanced coral recruitment. We
> conclude that grazing by this echinoid is creating
> conditions favoring the recruitment of coral." And the
> concluding statement in the paper by Precht and
> Aronson, Death and Resurrection of Caribbean Coral
> reefs, a palaeoecological perspective, (November 2005,
> Coral Reef Conservation, Cambridge University Press,
> Zoological Society of London, 2006). ".... recovery of
> the sea urchin D. antillarum is probably the key to
> facilitating coral recovery throughout the region."
> There are a number of other recent papers as well that
> document and explore the phase shift from algae to
> coral that occurs when Diadema return to the reefs,
> significantly in Jamaica, where the reefs have been
> long studied.
>
> But as I mentioned, coral reefs are a very complex
> ecosystem and "one size does not fit all". I'm sure
> that there are situations, especially in areas under
> development and near population centers, where the
> effects of herbivory would be greatly overshadowed by
> human influence and effluence. Also the presence or
> absence of complex reef structure influences the
> success of Diadema establishment. Extensive complex
> habitat greatly aids recovery of Diadema. (Habitat
> complexity and consumer-mediated positive feedbacks on
> a Caribbean coral reef Lee, 2006. and Rapid
> Phase-Shift Reversal on a Jamaican Coral Reef. Idjadi,
> Lee, Bruno, Precht, Allen-Requa, and Edmunds, Coral
> Reefs (manuscript submitted Nov. 2005) Reestablishment
> of Diadema populations in isolated areas where there
> is little cover probably depends on the kind of
> massive recruitment that can only occur when dense
> populations are widespread over a great area. However,
> all in all, recovery of Diadema where and when it can
> occur is a very good thing for a coral reef.
>
> However, as you mention there is the specter that the
> forces of development and the political support that
> developers acquire (buy?) can use loss of herbivory
> and the potential to replace herbivory as tools to
> create support for environmentally unsound
> development. As deplorable as this may be, ignoring
> and repressing research on the potential of returning
> hervibory to Atlantic reefs because it may be used as
> a development tool, is, to put it mildly, counter
> productive. Return of herbivory is an important tool
> in coral reef restoration efforts, but by no means the
> only tool.
>
> I hope I have not given the impression that I am
> arguing that there is no validity in the points you
> have raised, this was not my intent for this is not
> true. I know that repair of coral reef ecology is more
> than just restoration of herbivory. My position is
> that there are many stresses on coral reefs,
> especially on our Florida reefs, that can not be
> ignored, and loss of herbivory is one of the greatest
> of them. We should do all that is possible to return
> effective herbivory since that will improve the
> ecology and resilience of the reefs and enhance coral
> growth, settlement, and survival. And this should be
> done in addition to efforts to reduce anthropomorphic
> stress, and not at the expense of these efforts. I
> think concentrating solely on either the "top down" or
> "bottom up" concept of reef restoration would be a
> mistake, because successful coral reef restoration
> will require efforts from both directions. There must
> be cooperation and collaboration in the science to
> save what can be saved of our coral reefs.
>
> Martin
>
>
> --- "Dr. James M Cervino" <cnidaria at earthlink.net>
> wrote:
>
>> Hi Martin,
>>
>> I know you are one of the best coral aquarium
>> specialists on the planet as you truly understand
>> the chemical interactions and mechanisms within a
>> closed system. However, I disagree with a few of
>> the comments that were posted below. I am not
>> saying that Diademia grazing has no impact of the
>> abundance of macro-algae on a reef flat, however,
>> we must never ignore the more important impacts
>> of Nitrogen and Phosphorous above the thresholds
>> needed in a oligotrophic system such as a coral
>> reef (P. Bell,1992, Eutrophication and coral
>> reefs: some examples in the Great Barrier Reef
>> lagoon, Water Research, 26: 553-568; B. Lapointe,
>> & M. Clark, 1992, Nutrient inputs from the
>> watershed and coastal eutrophication in the
>> Florida Keys, Estuaries, 15: 465-476; B.
>> Lapointe, in press, Eutrophication thresholds for
>> macroalgal overgrowth of coral reefs, in K.
>> Thacker (Ed.) Protecting Jamaica's Coral Reefs:
>> Water quality issues; Goreau. T., 1992c, Coral
>> reef protection and coastal development in
>> Western Jamaica, p. 39-65 in K. Thacker (ed.),
>> Protecting Jamaica's coral reefs: water quality
>> issues, Negril Coral Reef Preservation Society,
>> Negril, Jamaica; Goreau, T., & K. Thacker, 1994,
>> Coral reefs, sewage, and water quality standards,
>> Proceedings of the Caribbean Water & Wastewater
>> Conference, Kingston, Jamaica) and to think that
>> grazing will control the will control the
>> abhorrent concentrations of nutrients that are
>> being released into coastal reef zones is
>> erroneous .
>>
>> When we fail to address "bottom-up" measures to
>> protect the habitat first and foremost, all the
>> Diademia antiullarun in the Ocean Realm will not
>> be able to control the increasing macro-algae
>> forests that the worlds reefs of the new
>> millennium have evolved into. Myself and a
>> research assistant went to an MPA meeting 8
>> months ago on ManO War Cay (10km from Guana Cay
>> ) where a few "experts"presented a "Top-Down"
>> action plan that will restore the fish
>> populations within designated locations in the
>> Abacos. MPA plans, such as the one being
>> proposed in the Bahamas 8 months ago, tend to
>> favor the actions of the developers in Jamaica,
>> Bimini and Guana Cay instead of the protection of
>> the coral reefs from the bottom up in the decades
>> to come.
>>
>> PS: Developers that want to build golf courses
>> will use this the nutrient debate in court as
>> they watch the coral list server and sort of turn
>> to it as a reference point. Lets not allow
>> developers to think that the nutrient thresholds
>> published by the scientists quoted above can be
>> ignored, as this will give them reason to say
>> that the only reason reefs have shifted from
>> productive Cnidarian reef systems to macro algae
>> dominated habitats is due to the grazer
>> disappearing.
>>
>> James
>>
>>
>>> I am of course, referring to the restoration of
>>> the keystone herbivore of the southwestern north
>>> Atlantic, the sea urchin Diadema antillarum. It is
>>> well documented that when Diadema return to the
>> reefs
>>> in large numbers, the phase shift from coral to
>> algae
>>> is reversed. There is much we don't yet understand
>>> about this fundamental ecological balance, but
>>> aggressive research projects aimed at furthering
>> this
>>> understanding and developing the technology and
>>> techniques for restoration of this keystone
>> herbivore
>>> should be pursued. If we do this now, we can
>> reduce
>>> the rate of coral reef decline and hopefully buy
>> the
>>> time we need to fix the huge problems. OK, so I'm
>> an
>>> optimist.
>>>
>>
>> --
>> **************************************************
>> Dr. James M. Cervino, MS, Ph.D.
>> Marine Pathology
>> Department of Biological & Health Sciences
>> Pace University New York NYC
>> Phone: (917) 620-5287
>> Web site: http://www.globalcoral.org <http://www.globalcoral.org/>
>> ***************************************************
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