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**mesocosm** · 01-28-2006, 08:18 PM

Greetings All !

Another classic ...

Diversity and ecology of zooxanthellae on coral reefs
Rowan, R
Journal of Phycology [J. Phycol.]. Vol. 34, no. 3, pp. 407-417. Jun 1998.[/b]
Animal-algal endosymbioses are a dominant feature of coral reefs and an enduring theme in coral reef biology. They combine heterotrophic (animal host) and autotrophic (algal symbiont) organisms into single functional units (holobionts) that contribute substantially to coral reef productivity. Indeed, algal symbiosis in scleractinian corals is probably responsible for the existence of coral reefs as we know them. Taxonomically, and therefore ecologically, the hosts are better defined. Evolutionary studies are also animal-biased because many hosts leave fossils. As we learn more about the algal symbionts, we approach a real understanding of these systems. A wide variety of microalgae live as endosymbionts with marine protists or invertebrate animals, either within or among host cells. The plural noun zooxanthellae describes the golden-colored ones, which predominate on coral reefs and are therefore the subject of this minireview. Recent studies of zooxanthella diversity have sought to establish evolutionary and ecological relationships, both among symbionts and between symbionts and their hosts. A progress report is given here, along with comments and speculations.

Descriptors: Symbionts; Hosts; Coral reefs; Coral; Literature reviews; Zooxanthellae; Species diversity; Algae

Abstract Source

Some of you might recall me gibbering about "holobionts" when examining the mechanisms which are enhanced by the ZEOvit methodology. This is one of the sources for my use of the term.

FYI

**mesocosm** · 01-28-2006, 08:24 PM

Greetings All !

The hits keep coming ...

Influence of the population density of zooxanthellae and supply of ammonium on the biomass and metabolic characteristics of the reef corals Seriatopora hystrix and Stylophora pistillata .
Hoegh-Guldberg, O; Smith, GJ
Marine ecology progress series. Oldendorf. Vol. 57, no. 2, pp. 173-186. 1989. [/b]

In May 1987, the population density of zooxanthellae in the reef coral Seriatopora hystrix around Lizard Island (great Barrier Reef) varied within and between colonies. This naturally occurring variability made it possible to examine the effect of the population density of zooxanthellae on the physiological characteristics of S. hystrix and its zooxanthellae. To test the hypothesis that zooxanthellae in S. hystrix and Stylophora pistillata are nitrogen-limited at their highest population densities, colonies of S. hystrix and S. pistillata with high densities of zooxanthellae were incubated in aquaria to which ammonium (ca 10 to 40 mu M) was added at regular intervals. After 3 wk, the population density chlorophyll a content and maximum rate of photosynthesis of the zooxanthellae had significantly increased, indicating that the biomass of zooxanthellae in reef corals can be limited by the availability of inorganic nitrogen to the association.

Descriptors: population density; biomass; corals; zooxanthellae; nutrient availability; photosynthesis; Stylophora pistillata

Abstract Source

Much of the current discussion of zooxanthellae in current reefkeeping cyberspace seems oddly focused on the limiting role of carbon ... as though there weren't other significant factors. Re-read the last sentence ... inorganic nitrogen is also potentially limiting. Makes you wonder just what the functional synergy of ZEOsupplements might actually be, doesn't it?

FYI

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**mesocosm** · 01-28-2006, 08:31 PM

Greetings All !

This one's a little more "advanced", but the topic of "heat stress" in SPS is kind of interesting ... at least to my warped little mind ...

Temperature-induced bleaching of corals begins with impairment of the CO2 fixation mechanism in zooxanthellae

Authors: JONES R.J.; HOEGH-GULDBERG O.; LARKUM A.W.D.; SCHREIBER U.
Source: Plant, Cell & Environment, Volume 21, Number 12, December 1998, pp. 1219-1230(12)

Abstract:

The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 °C for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (Fv/Fm) of photosystem II (PSII). Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 °C as opposed to 28 °C). qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen. Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S. pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants. Damage to PSII and a reduction in Fv/Fm (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco. Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, and (2) light plays a key secondary role in the initiation of the bleaching phenomena.

Keywords: Zooxanthellae; bleaching; Calvin cycle; coral; fluorescence; Mehler reaction;

Abstract Source

BTW ... 33' C = 91.7' F.

A handy little "conversion" site is:

California Aquaculture
University of California, Davis

FYI

**mesocosm** · 01-28-2006, 08:42 PM

Greetings All !

Another classic regarding nitrogen limitation, but with an interesting twist: Nitrogen was delivered to Stylophora test specimens using brine shrimp nauplii ...

The Effect of External Nutrient Resources on the Population Dynamics of Zooxanthellae in a Reef Coral
L. Muscatine, P. G. Falkowski, Z. Dubinsky, P. A. Cook, L. R. McCloskey
Proceedings of the Royal Society of London. Series B, Biological Sciences, Vol. 236, No. 1284 (Apr. 22, 1989) , pp. 311-324

Abstract

Experiments were done to determine if ammonium, phosphate and feeding on Artemia nauplii affected the population density of symbiotic algae (zooxanthellae) in the Red Sea coral Stylophora pistillata. Corals were incubated for 14 days under natural sunlight at reduced intensity in running seawater aquaria. The seawater was continuously spiked to give final concentrations of either 20 muM ammonium or 2 muM phosphate, or both. A second set of similarly treated corals was also fed Artemia nauplii daily. Population density of zooxanthellae in corals spiked with ammonium, or ammonium plus phosphate, approximately doubled, and the ratio of zooxanthellae carbon-nitrogen decreased. Phosphate supplementation alone had no effect. The increase in zooxanthellae numbers was linearly proportional to the increase in protein in zooxanthellae, suggesting that availability of inorganic nitrogen leads to increased protein synthesis in zooxanthellae. Feeding on Artemia alone or together with phosphate had no effect on the population density of zooxanthellae. Feeding on Artemia and ammonium produced a small increase in population density but it was not statistically significant. The small effect could be due to insufficient influx of ammonium in fed animals, or growth of both animal and algae resulting in little or no net change in the population density of zooxanthellae. The results are consistent with the hypothesis that the growth of zooxanthellae in S pistillata from the Red Sea is nitrogen limited.

Abstract Source

Proteins via Artemia ... hmmm.

FYI

**mesocosm** · 01-28-2006, 08:53 PM

Greetings All !

For anyone pondering feeding strategies for their SPS specimens, this one might be useful ...

Ratio of energy and nutrient fluxes regulates symbiosis between zooxanthellae and corals
Dubinsky, Z; Jokiel, PL
Pacific Science [PAC. SCI.]. Vol. 48, no. 3, pp. 313-324. 1994.

Ambient irradiance levels determine the rate of carbon influx into zooxanthellae at any given time, and thereby the energy available for the whole coral symbiotic association. Long-term photoacclimation of zooxanthellae to the time-averaged light regime at which the host coral grows results in optimization of light harvesting and utilization. Under high irradiance light harvesting is reduced, thereby avoiding photodynamic damage, whereas under low light, photon capture and quantum yield are maximized. Most of the photosynthate produced by the algae is respired. However, the capability of the zooxanthellae and the coral to retain carbon beyond that required to meet their respiratory needs depends on the availability of the commonly limiting nutrients, nitrogen and phosphorus. Therefore, the ratio of the flux of these nutrients into the colony to that of the photosynthetically driven carbon flux will regulate the growth of the zooxanthellae and of the animal. Nutrients acquired by predation of the coral on zooplankton are available first to the animal, whereas those absorbed by the zooxanthellae from seawater as inorganic compounds lead first to growth of the algae.

Descriptors: zooxanthellae; coral reefs; symbiosis; energy balance; nutrient flow; bioenergetics; Algae; marine invertebrates; nutrients (mineral); Anthozoa

Abstract Source

Review the last sentence. Want to feed your Cnidarian first? ... deliver nutrients via prey. Want to feed your zooxanthellae first? ... deliver nutrients dissolved in the water column. Interesting that the ZEOvit methodology utilizes both mechanisms simultaneously, isn't it?

And to think that there are still people who advocate non-feeding strategies as the way to maximum SPS growth ... go figure.

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FYI

**mesocosm** · 01-28-2006, 09:02 PM

Greetings All !

This one suggests why high nitrates can have a "detrimental" effect on SPS coloration, and reinforces why carbon is a limiting factor in SPS skeletogenesis ...

Nitrate increases zooxanthellae population density and reduces skeletogenesis in corals
F. Marubini and P. S. Davies
Marine Biology;Publisher: Springer-Verlag GmbH; ISSN: 0025-3162 (Paper); 1432-1793 (Online); DOI: 10.1007/BF00942117; Issue: Volume 127, Number 2 ; Date: December 1996

Abstract: Very little information exists on the effects of nitrate on corals, although this is the major form in which nitrogen is prescrit in tropical eutrophie coastal waters. In this study we incubated nubbins of Porites porites and explants of Montastrea annularis in laboratory photostats illuminated by halide lamps, with concentrations of nitrate of 0, 1, 5 and 20 uM, for 40 and 30 d, respectively, At the end of this period it was found that the population density of the zooxanthellae had increased significantly with increased nitrate concentration, suggesting nitrogen limitation of the growth rate of zooxanthellae in the control group. There were also significant increases in the amount of chlorophyll a and e2 per algal cell, in the volume of the algal cells, and in the protein per cell. Overall, the protein per unit surface increased, but this was attributable solely to increased algal protein: there was no significant change in host protein. Maximum gross photosynthesis normalized to surface area was enhanced by nitrate addition, reflecting the increase in algal population density. There was no change when normalized on a per cell basis. Respiration rate normalized to protein content was decreased by nitrate. The most dramatic change was in the rate of skeletogenesis, which decreased by ~= in both species when exposed to nitrate enrichment. A model is presented which suggests that the diffusion-limited supply of CO2 from surrounding seawater is used preferentially by the enlarged zooxanthellae population for Photosynthesis, thereby reducing the availability of inorganic carbon for calcification. It is concluded that enhanced nitrate levels in tropical coastal waters will have a hitherto unrecognized effect on the growth rate of tropical coral reefs.

Abstract Source

FYI

**mesocosm** · 01-28-2006, 09:22 PM

Greetings All !

On a more "obscure and abstract" note ... it turns out that space availability (cellular) and the size of zooxanthellae symbiots might play a role in zooxanthellae density ...

Regulation and control of intracellular algae (= zooxanthellae) in hard corals

R. J. Jones, D. Yellowlees

Philosophical Transactions: Biological Sciences
ISSN: 0962-8436 (Paper) 1471-2970 (Online)
Issue: Volume 352, Number 1352 / April 29, 1997
Pages: 457 - 468
DOI: 10.1098/rstb.1997.0033

Abstract:

To examine algal (= zooxanthellae) regulation and control, and the factors determining algal densities in hard corals, the zooxanthellae mitotic index and release rates were regularly determined in branch tips from a colony of a staghorn coral, Acropora formosa, recovering from a coral 'bleaching' event (the stress-related dissociation of the coral–algal symbiosis). Mathematical models based upon density-dependent decreases in the algal division frequency and increases in algal release rates during the post-bleaching recovery period accurately predict the observed recovery period (ca. 20 weeks). The models suggest that (i) the colony recovered its algal population from the division of the remaining zooxanthellae, and (ii) the continual loss of zooxanthellae significantly slowed the recovery of the coral. Possible reasons for the 'paradoxical' loss of healthy zooxanthellae from the bleached coral are discussed in terms of endodermal processes occurring in the recovering coral and the redistribution of newly formed zooxanthellae to aposymbiotic host cells. At a steady-state algal density of 2.1 x 106 zooxanthellae cm-2 at the end of the recovery period, the zooxanthellae would have to form a double layer of cells in the coral tissues, consistent with microscopic observations. Neighbouring colonies of A. formosa with inherently higher algal densities possess proportionately smaller zooxanthellae. Results suggest that space availability and the size of the algal symbionts determines the algal densities in the coral colonies. The large increases in the algal densities reported in corals exposed to elevated nutrient concentrations (i.e between a two- and five-fold increase in the algal standing stock) are not consistent with this theory. We suggest that increases of this magnitude are a product of the experimental conditions: reasons for this statement are discussed. We propose that the stability of the coral–algal symbiosis under non-stress conditions, and the constancy of zooxanthellae densities in corals reported across growth form, depth and geographic range, are related to space availability limiting algal densities. However, at these densities, zooxanthellae have attributes consistent with nutrient limitation.

Abstract Source

Full Text Article (.pdf)

Buried in the results and discussion section of the article is an interesting graph showing recovery rates for zooxanthellae after a bleaching event. Might be worth a look if you're "into" that sort of thing ...

FYI

**mesocosm** · 01-28-2006, 10:53 PM

Greetings All !

For anyone interested in how zooxanthellae photosynthetic behavior effects the growth of SPS "growth tips" ...

Why does the white tip of stony coral grow so fast without zooxanthellae?
L. Fang, Y. J. Chen and C. Chen

Marine Biology;Publisher: Springer-Verlag GmbH; ISSN: 0025-3162 (Paper); 1432-1793 (Online); DOI: 10.1007/BF00397270; Issue: Volume 103, Number 3; Date: November 1989; Pages: 359 - 363.

Abstract: The photosynthesis of zooxanthellae in a coral polyp greatly enchances the calcification rate of a coral. However, the white tip of a coral branch is free of zooxanthellae yet still has a very high calcification rate. Furthermore, the reason for the difference is not clear. In this study, the amount of photopigment, total protein (TP), total organic carbon (TOC), ATP, and lipid in polyps from the white tip and brown stalk of a branch of stony coral were measured. Samples of Acropora hyacinthus and A. formosa were collected from southern Taiwan between 1985 and 1987. The results showed that the ATP concentration in polyps of the white tip was much higher than that in polyps of the brown stalk. Conversely, the amount of TP, TOC and measured lipids in polyps of the brown stalk were all higher than those of the white tip. It was the high concentration of ATP in cells that gave these polyp tips the vitality to sustain the energy requirements of such a rapid calification rate. Facilitated diffusion, due to the high metabolite gradient created by cell activity, could be the major driving force for the transport of photosynthetic product from stalk to tip.

Abstract Source

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FYI

**Aged Salt** · 01-29-2006, 07:12 AM

Hi all, these deserve your reading attention--just good tasty bits of information:yesway: Thnx. again Gary

Bob

**mesocosm** · 01-29-2006, 09:24 PM

Greetings All !

Originally posted by Aged Salt

Hi all, these deserve your reading attention--just good tasty bits of information:yesway: Thnx. again Gary

Bob

Thanks Bob! ...

BTW ... Where's Jake? ...

... seems to me he should have some good links ...

It occurs to me that although zooxanthellae are interesting beasties in their own right, what really interests us what they're doing with our corals. Here's one that addresses this tangent ... although it is a little "dry" ...

Metabolite comparisons and the identity of nutrients translocated from symbiotic algae to an animal host
L. F. Whitehead* and A. E. Douglas
The Journal of Experimental Biology 206, 3149-3157 (2003).

Dinoflagellate algae of the genus Symbiodinium in symbiosis with marine animals release much of their photosynthetic carbon to the animal host. The compounds translocated to the host (`mobile compounds') were investigated by metabolite comparison as follows: a substrate was identified as a candidate mobile compound when comparable profiles of metabolites were generated from host metabolism of this substrate (supplied exogenously) and the endogenous mobile compounds. When the sea anemone Anemonia viridis was incubated with NaH14CO2 under photosynthesizing conditions, most of the radioactivity in the animal tissue was recovered from the low-molecular-mass fraction and distributed in the ratio 1:2:1 between the neutral, acidic and basic sub-fractions. Prominent 14C-labelled compounds included glucose, malate and glucose-6-phosphate. When the symbiosis was incubated with 14C-labelled glucose plus succinate or fumarate (but none of eight other substrate combinations tested), the 14C-labelled metabolites closely matched those obtained with NaH14CO2. These data suggest that glucose and succinate/fumarate (or metabolically allied compounds) may be important photosynthetic compounds transferred from the Symbiodinium cells to the tissues of A. viridis. Metabolite comparisons can be applied to study nutritional interactions in symbioses involving photosynthetic algae and, with appropriate modification, other associations between microorganisms and plants or animals.

Key words: Anemonia viridis, Cnidaria, dinoflagellate alga, nutrition, photosynthetic metabolism, Symbiodinium, symbiosis, zooxanthella

Abstract Source

Full Text Article (.htm)

It gets more interesting," ... A fundamental feature of many symbiotic microorganisms is that they provide the host with nutrients that would otherwise enhance their own growth and proliferation rates. Our understanding of the processes mediating this co-operative trait of nutrient release is limited by uncertainty about the chemical identity of the mobile compounds. The metabolite comparison method outlined in Figure 1 contributes to the resolution of this limitation by identifying candidate mobile compounds on the basis of their pattern of metabolism by the host. The method assumes that animal metabolism of exogenous compounds taken up into ectodermal cells is equivalent to animal metabolism of photosynthetic compounds translocated across the symbiosomal membrane into endodermal cells. Consistent with this assumption, Trench (1971b) has shown that the pattern of metabolism of photosynthetic compounds is similar in the ectodermal and endodermal cell layers of the sea anemone Anthopleura elegantissima. The present study has identified glucose and succinate/fumarate as candidate mobile compounds in Anemonia viridis using short duration experiments. This probably does not represent the total complement of mobile photosynthetic compounds because other compounds, possibly including lipid and amino acids, may be translocated many minutes to hours after fixation (e.g. Battey and Patton, 1984; Wang and Douglas, 1999)."

While "coral feeding" is a worthy and fascinating topic in its own right, I'm also interested in what it is ... exactly ... that the corals are eating.

Hmmm ... Think about it ...

JMO ... FYI

**mesocosm** · 02-07-2006, 09:43 AM

Greetings All !

Host-Zooxanthella Interactions in Four Temperate Marine Invertebrate Symbioses: Assessment of Effect of Host Extracts on Symbionts

D. C. Sutton and O. Hoegh-Guldberg

Sir George Fisher Centre for Tropical Marine Studies, James Cook University, Townsville, Queensland 4811, Australia

Photosynthesis and translocation of photosynthetic products from symbiotic zooxanthellae in four species of temperate-latitude invertebrates were investigated in vivo and in vitro. In vivo, zooxanthellae fixed 14C and translocated a substantial proportion of fixed products to host tissues. In vitro, the effect of host tissue extracts on isolated zooxanthellae varied. Extracts of the soft coral Capnella gaboensis, lysed zooxanthellae after a relatively short exposure. Those of the zoanthid Zoanthus robustus and the nudibranch Pteraeolidia ianthina had little effect on translocation of organic carbon from zooxanthellae. In contrast, host extract of the scleractinian coral Plesiastrea versipora stimulated the release of up to 42% of the total 14C fixed, and the magnitude of release was positively correlated with the protein concentration of the extract. Host extracts had no effect on photosynthetic rates in algal symbionts. The effect of P. versipora extract on isolated zooxanthellae was studied. This extract caused zooxanthellae to divert photosynthetic products from lipid synthesis to the production of neutral compounds, principally glycerol, and these compounds were the predominant form of carbon detected extracellularly after incubating zooxanthellae in this extract. Only organic compounds made during the period of exposure of zooxanthellae to host extract, and not pre-formed photosynthetic products, were translocated. The translocation-inducing activity of host extract was almost completely destroyed by heating (100{deg}C), and a preliminary attempt to fractionate the tissue extract revealed that the active constituent did not pass through dialysis tubing of nominal pore size 10,000 D. These results are discussed in relation to host control of symbiotic partners, and to previous reports of "host-release factors" in other invertebrate symbioses.

Extracted from:
The Biological Bulletin, Vol 178, Issue 2 175-186, Copyright © 1990 by Marine Biological Laboratory

Abstract Source

Full Text Article (pdf)

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FYI

**mesocosm** · 03-03-2006, 06:08 PM

Greetings All !

I was a little surprised that zooxanthellae are involved in the production of chemicals that end up in coral mucus. I was even more surprised that at least one of those chemicals acts as a receptor for a pathogenic bacteria ...

Role of endosymbiotic zooxanthellae and coral mucus in the adhesion of the coral-bleaching pathogen Vibrio shiloi to its host.
Banin E, Israely T, Fine M, Loya Y, Rosenberg E.

Abstract

Vibrio shiloi, the causative agent of bleaching the coral Oculina patagonica in the Mediterranean Sea, adheres to its coral host by a beta-D-galactopyranoside-containing receptor on the coral surface. The receptor is present in the coral mucus, since V. shiloi adhered avidly to mucus-coated ELISA plates. Adhesion was inhibited by methyl-beta-D-galactopyranoside. Removal of the mucus from O. patagonica resulted in a delay in adhesion of V. shiloi to the coral, corresponding to regeneration of the mucus. DCMU inhibited the recovery of adhesion of the bacteria to the mucus-depleted corals, indicating that active photosynthesis by the endosymbiotic zooxanthellae was necessary for the synthesis or secretion of the receptor. Further evidence of the role of the zooxanthellae in producing the receptor came from a study of adhesion of V. shiloi to different species of corals. The bacteria failed to adhere to bleached corals and white (azooxanthellate) O. patagonica cave corals, both of which lacked the algae. In addition, V. shiloi adhered to two Mediterranean corals (Madracis and Cladocora) that contained zooxanthellae and did not adhere to two azooxanthellate Mediterranean corals (Phyllangia and Polycyathus). V. shiloi demonstrated positive chemotaxis towards the mucus of O. patagonica. The data demonstrate that endosymbiotic zooxanthellae contribute to the production of coral mucus and that V. shiloi infects only mucus containing, zooxanthellate corals.

MeSH Terms:
Algae/physiology*
Animals
Bacterial Adhesion*
Chemotaxis
Cnidaria/metabolism
Cnidaria/microbiology*
Research Support, Non-U.S. Gov't
Symbiosis*
Vibrio/physiology*

PMID: 11356564 [PubMed - indexed for MEDLINE]

Extracted from:
FEMS Microbiol Lett. 2001 May 15;199(1):33-7.

Abstract

FYI

**mesocosm** · 03-03-2006, 06:16 PM

Greetings All !

Zooxanthellae density in SPS corals is correlated to temperature, dissolved oxygen, nitrate present in the water column, and phosphate present in the water column ... among other things. Since these variables fluctuate, it should be no surprise that zooxanthellae density also fluctuates.

As folks observe the zooxanthellae density fluctuations in their captive SPS specimens, perhaps an awareness of how zooxanthellae density fluctuations occur in "wild" SPS corals could prove useful ...

The Dynamics of Zooxanthellae Populations: A Long-Term Study in the Field.
I. ***oonee, H. B. Wilson, M. P. Hassell, J. R. Turner.

Abstract

Coral bleaching characterized by the expulsion of symbiotic algae (zooxanthellae) is an increasing problem worldwide. Global warming has been implicated as one cause, but the phenomenon cannot be fully comprehended without an understanding of the variability of zooxanthellae populations in field conditions. Results from a 6-year field study are presented, providing evidence of density regulation but also of large variability in the zooxanthellae population with regular episodes of very low densities. These bleaching events are likely to be part of a constant variability in zooxanthellae density caused by environmental fluctuations superimposed on a strong seasonal cycle in abundance.

Extracted from:
Science 5 February 1999:
Vol. 283. no. 5403, pp. 843 - 845

Full Article (html)

It turns out that zooxanthellae density fluctuation can be significant ...

... there is considerable variation in density, with fluctuations over three orders of magnitude. Although densities from 500,000 to 5,000,000 per square centimeter have been reported in different studies (13-15), here such variability is reported from a single coral colony over time. In particular, there was a bleaching event in the spring and summer of 1993 (density < 100,000 per square centimeter from 28 October to 17 December 1993; ...) and there were other episodes of very low density throughout the study period (on 11 December 1992, 2 October 1995, and 19 February 1997).

(Time series of zooxanthellae density from August 1991 to March 1997. The coral samples were collected on approximately a weekly basis, and density was determined by a standard methodology (13). At three points in the time series, there are gaps because no data were collected during these periods (for logistical reasons). The total number of data points is 159.)

(Seasonal abundance of density of zooxanthellae. For each month the mean density of zooxanthellae was calculated, and the error bars show the standard errors of the means (the number in each month varies between 7 and 19). The curve fitted is a fourth-order polynomial, the highest order polynomial that is significant.)

It turns out the too much dissolved oxygen in the water column of our captive reef ecosystems may not be such a good thing ...

Because dissolved oxygen in the water column is continuous with water in the coelenteron, it may lead to increased oxygen concentration within the coral. High concentrations of oxygen within the coral can precipitate bleaching [M. P. Lesser, Coral Reefs 16, 187 (1997)].

Determining zooxanthellae density isn't as simple as it might appear. There are a lot of factors to be considered when doing data collection ...

Some of this variability is undoubtedly because different parts of the same colony were sampled and the orientation of the coral branch to incident light is known to affect zooxanthellae density [L. R. McCloskey and L. Muscatine, Proc. R. Soc. London Ser. B 222, 215 (1984); Z. Dubinsky, P. G. Falkowski, J. W. Porter, L. Muscatine, ibid., p. 203]. In addition, it is possible that different strains of zooxanthellae exist in different parts of the colony [R. Rowan, N. Knowlton, A. Baker, J. Jara, Nature 388, 265 (1997)]. Thus, the data collected reflect the normal degree of zooxanthellae variability expected over an entire colony. However, this cannot be the only cause of variation, as the test for density dependence specifically examined and rejected the hypothesis that the sole cause of the variability through time is just random sampling from some distribution of zooxanthellae abundance.

Even so, it seems clear that zooxanthellae density fluctuation occurs naturally over time. Oddly enough, it may turn out that the "water chemistry stability" which many of us strive for in our reef systems, is NOT what zooxanthellae experience in natural ecosystems ...

Clearly, shallow coastal lagoons such as this one experience large environmental fluctuations. Because the regression model using environmental variables accounted for 40% of the observed variability, it is clear that the environment was very variable and that this variability had an important influence on zooxanthellae density. The conditions in this lagoon (high degree of anthropogenic activity, large environmental fluctuations) are probably prevalent in lagoons in many areas of the world. Under such conditions, it seems we should expect great variability in zooxanthellae density. Hence, bleaching events in corals within such lagoons may be frequent and part of the expected cycle of variability.

JMO

**Aged Salt** · 03-03-2006, 07:25 PM

Hi Gary, superbly excellent as usual.

Zeo-members that are keeping SPS, this is required reading. [My theory], Natural zoox. density varianation = seasonal pararameter unstability in nature; nature's way to rid "old, inefficient, slower metabolic zoox. & replaced with new, more energetic "youngers," in effect enabling the coral to be have more vitality.

In our closed aquariums, we do not have the luxury of unstable parms that nature uses to "recharge" their animals, therefore, for those who have used ZeoSpur2 with it's ability to expel zooxanthellae[I'm guessing nursing home types], you will notice the lightened color but watch the forecoming growth spurt over the next 7-10 days, as zoox. density refurbishes itself. "Out with the old, in with the new." There's an increased metabolic rate now within the coral with resultant enhanced color, growth & vitality. I'll ask Gary & Jake to prove this

Bob

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