[34cygni]

Sponges having the ability to consume DOC explains why they're taking over Caribbean reefs now that most of the corals are dead and the fish are gone: the sponges are sucking up DOC released by the algae, and they can also capture bacterioplankton growing on labile algal DOC.

Originally Posted by Natural Diet of Coral-Excavating Sponges Consists Mainly of Dissolved Organic Carbon (DOC)

Traditionally, sponges were considered to be suspension feeders that efficiently remove bacterio-, phyto-, and even zooplankton from water they actively pump through their filtration systems. However, already in 1974, Reiswig hypothesized that sponges may also retain dissolved organic carbon (DOC), which was later confirmed for several sponges, ranging from tropical to temperate sponge species. These tropical coral reef sponges can take up >90% of the total organic carbon (TOC) as DOC, indicating that they foremost rely on DOC to meet their carbon demand. Since DOC also accounts for >90% of the TOC pool on coral reefs, the ability to utilize this food source may aid certain sponges to thrive under oligotrophic conditions, whereas most other heterotrophic reef organisms are unable to capitalize on this resource. ...

Our results further suggest that...sponges can efficiently take up DOC across a wide range of ambient DOC concentrations. This indicates that these sponges are well adapted to utilize DOC as food source. ...

The ability of sponges to take up and assimilate DOC has been proposed to be crucial to maintain biodiversity and high productivity on tropical coral reefs. In the so-called "sponge loop", analogously to the microbial loop, sponges make energy and nutrients stored in the dissolved organic matter (DOM) pool available to the benthic food web via DOM assimilation and subsequent detritus production by the sponges. Our study now shows that excavating sponges most likely also participate in the sponge loop...

[B]eing suspension feeders, coral-excavating sponges were considered to benefit from elevated concentration of particulate resources, such as phytoplankton and bacteria. However, here we could show that coral-excavating sponges mainly rely on DOC to meet their carbon demand. Thus, an increase in DOC production, or quality, on coral reefs is likely to be beneficial for them. Shifts in the benthic reef community have caused major changes in the production and cycling of organic matter on reefs. Due to anthropogenic disturbances benthic algae are increasing at the expense of scleractinian corals on most coral reefs throughout the Caribbean region. Both, scleractinian corals and benthic algae release a substantial amount of their photosynthetically fixed carbon as organic matter in the surrounding water. However, benthic algae are reported to release more DOM than corals and algal-derived DOM appears to be of a higher quality [meaning more labile]. Sponges, including excavating species, could therefore benefit in two ways from an increase in DOM production and quality due to the shift in benthic communities: (1) directly via uptake of DOM and (2) indirectly by feeding on the heterotrophic planktonic microbial community, which is fueled by the DOM release of benthic algae. several Caribbean reefs and is suggested to become more frequent with increasing reef degradation. Here we could show that the coral-excavating sponges Siphonodictyon sp. and C. delitrix are capable of consuming DOC and mainly rely on DOC to meet their organic carbon demand. This suggests that coral-excavating sponges are likely to benefit from an increase in DOC production and quality as a result of the ongoing coral-algal phase shift.

Coral-excavating sponges are a fairly big deal from an ecological standpoint, as massive stony corals building up and sponges drilling down can create enormous topological complexity on and within reefs. A pit excavated by a sponge is a detritus trap (that's probably why sponges evolved this behavior in the first place) and decaying detritus tends to become acidic. Acid eats away calcareous deposits very quickly, and there are internal currents moving through the porous, heterogeneous reef rock driven by pressure differentials from waves and tides that can pull acidic water into the reef matrix and create complex, highly interconnected networks of small caves and crevices beneath reefs.

Originally Posted by Endoscopic exploration of Red Sea coral reefs reveals dense populations of cavity-dwelling sponges

Framework cavities are the largest but least explored coral reef habitat. Previous dive studies of caverns, spaces, below plate corals, rubble, and artificial cavities suggest that cavity-dwelling (coelobite) filter-feeders are important in the trophodynamics of reefs. ...

Line transects showed that 26-42% of the projected reef area is riddled by crevices of various sizes. The median opening diameter of only 0.2m renders these crevices inaccessible to visual inspection by divers using conventional technology. We carried out detailed measurements of crevice dimensions with a diver-operated endoscopic video camera... Combining these results with the line transect data yielded a cumulative coelobite living area of 2.5 - 7.4 square meters of crevice wall per square meter of reef. This is a conservative estimate considering the fact that many of the crevices extended beyond the range of the quantitative survey [meaning deeper than the 4 meter limit of the camera's reach], and that the interconnections between anastomosing crevices escaped detection...

Quantitative analysis of 2301 high-resolution images revealed a rich coelobite community covering 2.8 plus-or-minus 0.9 square meters per projected m^2 reef... Coralline algae predominated near the sunlit entrances. Sponges abounded in posterior sections of the crevices, constituting 51-73% of the coelobite cover. The high densities, as well as the dominance of delicate sheet-like growth forms, support the assumption that the distribution and abundance patterns of coral reef sponges are controlled by predators. ...

Current speeds...averaged between 0.9 and 5.5 cm/s. Wash-out experiments with fluorescent dyes featured half-life periods of only 75 plus-or-minus 15 seconds, suggesting complete flushing of cavity waters within a few minutes.

Dye experiments showed that the water flow throught framework crevices was driven by flow speed differences across the bumpy reef surface, much like pressure-induced air flow through termite mounds, where the intake openings are located in troughs near the base and the exhause openings in exposed positions near the crest. As a result, water flow was almost always directed into the crevices, leaving the framework through countless cracks and holes near the elevated parts of the reef.

The largely unidirectional flow pattern allowed us to determine the bulk filtering rate of the coelobite community...

Phytoplankton uptake by the coelobite community [was] equivalent to 22% of the gross community metabolism of the entire reef. Total picoplankton removal, as suggested by the available biomass of bacteria in tropical waters, is probably more than twice this value...

Owing to the long doubling times of phytoplankton and bacteria (6-24 h) relative to the residence time of water over the narrow shelf (1-5 h), most of the picoplankton consumed in the reef originates from offshore, thus constituting a source of new material for the reef ecosystem.

Nutrient enrichments in the cavities suggest intense mineralization of the organic matter by the crevice biota. Nutrient ratios near the Redfield ratio (N:P = 15.5) reflect the planktonic source of the mineralized material, contrasting the higher values reported for intrinsic reef material, for example in lagoonal patch reefs (N:P = 20), pore waters (N:P = 21), or benthic producers (N:P = 30). Stoichiometric conversion of picoplanktonic organic matter to inorganic nutrients (assuming 100% of the ingested food is respired) shows that allochthonous N and P may contribute one-third of the total nutrient flux emanating from the cavities in readily assimilable form (such as ammonia, 42% of N) for corals and algae.

I've known for a while, now, that a coral reef is basically a vast algae scrubber sitting on top of an even bigger bacterial biofilter, and I've seen divers exploring reef caves on TV, but I had no idea there was a full-on cryptic zone underlying the entire reef structure! How cool is that?!? This suggests that the ideal setup for a hobby system would be a reef tank draining into a countercyclically lit display fuge with a Shimek-compliant DSB (...not necessarily in overall volume, but in terms of depth and the absence of counterindicated fauna so as to maintain benthic biodiversity -- at last, an excuse for the marine hobbyist to buy a hex tank!), which drains in turn into a large (ie, spanning the width of the stand for the two tanks above) cryptic sump with LR and a shallow sand bed where sponges consume labile DOC from the nutrient-limited macro and release POC for the corals. Probably wouldn't be hard to accommodate a pelagic (FO or FOWLR) DT downstream of the reef tank by upsizing the display fuge and sump accordingly.

This seems like a good time to mention that carbonate and silicate sands host different bacterial communities -- here's a paper about that, if anyone's interested -- which suggests that a mix of the two will increase bacterial biodiversity, and a cryptic sump would be a good spot to try that as darkness would make life difficult for diatoms. Given that there are other organisms that like silica (radiolarians leap to mind, and about 75% of extant sponge species have siliceous skeletons) that pretty much got kicked in the teeth by the evolution of a primary producer with silicon armor, putting some silica sand in a cryptic zone may benefit benthic biodiversity beyond just bacteria.

Speaking of diatoms -- fun science fact: the earliest fossil evidence of diatoms follows closely upon the evolution of new, faster-growing grasses on land. Scientists think that the increased production of phytoliths (silica crystals plants make in their tissues to discourage herbivores) sped up the terrestrial silicon cycle, resulting in an increased flux of silica into rivers, lakes, and oceans via erosion which led to rising dissolved Si levels and, eventually, diatoms.

Turns out that this sort of feedback between nutrient availability and evolution illuminates the ecological niches of primary producers on a broad level...

Originally Posted by The role of functional traits and trade-offs in structuring phytoplankton communities: scaling from cellular to ecosystem level

Green algae [meaning green phyto in this context] appear to have intermediate values for nitrate uptake parameters and exhibit the velocity-adapted strategy as they have high maximum growth rates and second highest nitrate uptake rates. They have an extremely high affinity for ammonium...

Coccolithophores are well adapted not only to oligotrophic (low nutrient) conditions, but also to high irradiance levels often associated with such conditions [...low nutrient NSW is usually clear because not much grows in it, and what does grow is usually very, very small because small cells can compete more effectively for nutrients -- hence the previously mentioned vast and diverse population of picoplankton eking out a living in the "nutrient desert" of the oligotrophic open ocean]. In contrast, diatoms have low half-saturation constants for irradiance-dependent growth and are generally more adapted to low light characteristic of high nutrient, intense mixing conditions. Thus, phytoplankton nutrient utilization strategies, in conjunction with their responses to physical environment, such as turbulence and light, to a large extent define ecological niches of the two groups. The idea of phytoplankton functional groups associated with different nutrient and turbulence regimes was pioneered by Margalef and elegantly expressed in his nutrient-turbulence mandala [...diatoms like high turbulence and high nutrients; cocos like low turbulence and low nutrients; dinos like low turbulence and either high or low nutrients].

These ecological niches correspond remarkably well to the distributions of the two groups in the ocean. Diatom relative abundance is positively correlated with nitrogen (and phosphorus) concentrations and negatively correlated with the stability of the water column. In contrast, coccolithophorid abundance is greater at low nitrate and phosphate and high water column stability and irradiance. Consequently, the abundances of the two groups are significantly negatively correlated. ...

All algal groups appear to preferentially take up ammonium over nitrate, likely because nitrate but not ammonium has to be reduced before assimilation and thus may require more energy to be assimilated. However, as our analysis indicates, the relative preference for ammonium over nitrate is greater in green algae, compared to diatoms and other taxonomic groups of marine eukaryotic phytoplankton. This may reflect the effect of the oceanic redox conditions at the time of origin of respective groups: green algae appeared around 1.5 billion years ago in mid-Proterozoic, when suboxic conditions could have caused the reduced form of N (i.e. ammonium) to be prevalent. In agreement with this reasoning, cyanobacteria, the earliest [oxygenic] photoautotrophs, evolved under anoxic conditions, also have a strong preference for ammonium over nitrate. Diatoms appeared much later, c. 150 million years ago, when the oceans were highly oxidized and consequently are better adapted at utilizing nitrate. Therefore, modern strategies of nutrient utilization by major taxonomic groups appear to be consistent with the conditions at the time of their origin and⁄or diversification and suggest conservatism in trait values over groups' evolutionary histories.

Closed captioned for the Science impaired, that means the nutrient requirements of different kinds of algae were shaped by the availability of nutrients in the environments in which they first evolved and have largely been preserved since that time.

Originally Posted by Toward a stoichiometric framework for evolutionary biology

Changes in the relative abundances of elements appear to have been one of the major determinants of macroevolutionary patterns. For example, Quigg et al. (2003) show that micronutrient stoichiometry of extant marine phytoplankton taxa reflects the composition of their symbiotic plastids.

For phyto in general, the expanded Redfield ratio according to a 2008 review is...

C 124
N 16
P 1
S 1.3
K 1.7
Mg 0.56
Ca 0.5
Fe 0.0075
Zn 0.0008
Cu 0.00038
Cd 0.00021
Co 0.00019


A paper from 2010 gives an average of 29 species of phyto and includes manganese...

C 132
N 18
P 1
S 0.99
Fe 0.018
Mn 0.0028
Zn 0.00134
Cu 0.0005
Cd 0.00011
Co 0.00011

Other researchers compared the requirements for the trace elements Fe, Mn, Zn, Cu, Co, and Cd in what I'm guessing were eight common laboratory strains of coccolithophores, diatoms, and dinos -- the three dominant primary producers in the modern oceans -- and found that the dinos had relatively high quotas for all six metals. The diatoms, interestingly, had very low requirements for all six of these micronutrients (though some planktonic diatoms are known to have high requirements for Fe, possibly because they host cyanobacterial endosymbionts) while the cocos had high quotas for Mn, Co, and Cd, but low requirements for iron, zinc, and copper.

Dinos' high requirements for trace elements would explain and confirm these and a number of similar observations over the life of this thread...

06/24/2013, 01:55 PM #1
DNA
Water changes
Dinoflagellates love water changes and not doing them will for sure make the dinos suffer.

08/29/2013, 04:24 PM #19
Squidmotron
5) I agree that water changes -- if anything -- make it worse. They seem to die off more the longer between the water changes. I read a few articles that they like and depend on selenium and iron. Maybe that affects it.
6) Obvious, but do not dose trace elements.

11/19/2013, 10:08 AM #99
bazeball05
stop doing water changes (Dino's are fueled by trace elements)

10/11/2014, 03:26 PM #342
cal_stir
I to am in the midst of a battle with ostreopsis, about six weeks now, I to am convinced that water changes feed it

As for other primary producers, diazotrophic cyano hearts iron because those species need Fe to make nitrogenase, the enzyme they need to fix nitrogen. Green algaes need iron, zinc, and copper; red algaes have higher requirements for Mn, Co, and Cd and lower quotas than greens for Fe, Zn, and Cu.

Coralline is a red algae, incidentally, and when I looked into its nutrient requirements, I found that the reason hobbyists haven't had any luck pinning down what nutrient levels coralline grows best at is that it grows pretty well at any nutrient level from oligotrophic conditions on a healthy reef to eutrophic conditions on a dying reef. In all likelihood, the reason coralline's epiphytic bacterial community is coral-friendly is that the algae adapted to derive nutrients from the decomposition of coral mucus and its payload of detritus, which explains how it can grow when there's no measurable N or P in the water, but at the same time coralline didn't lose the ability to take in mineralized nutrients from the water -- whatever it can get, it'll use (...there are actually many different species of coralline adapted to different microenvironments, but funny science fact: even scientists who study coralline can't tell them apart without genetic analyses, so I'm sticking with the hobbyist convention of speaking about coralline in the singular).

The bad news for coralline is that it's pretty much flat, which means it can easily be outcompeted for light, if nothing else, by any algae capable of vertical growth. Coralline frequently sheds its surface layer to prevent biofouling and death by overgrowth, but basically coralline's secret weapon is that nothing wants to eat it.

Reef grazers have a clear order of preference in their diets: they like to eat young, nontoxic macroalgae most of all, and then they'll go for the turfs, and nothing really likes to eat coralline. It's chalky and not very nutritious. Basically, coralline is dominant on healthy reefs because in the wild, coralline is nuisance algae.

It's a funny ol' world, innit?

Grazers selecting for a variety of algae that they don't like to eat, or can't eat because it's toxic or too large to fit in their mouths, is a common phenomenon both in the wild and in aquariums. So the good news is that exactly this sort of selection pressure explains the success of coralline, but the bad news is that we lack several keystone grazers in our systems, so this effect may yet prove to be the Achilles' heel of the dirty method.

Originally Posted by Adrnalnrsh

I added an urchin when I added my new fish a few weeks ago and it's almost destroyed everything any algae I've had on my rocks and back wall.

Originally Posted by karimwassef

I'll share a personal ally - urchins. The cheapest ones you can find. Get a bunch.

Urchins are one of those keystone grazers, though not all species are herbivores. The other big ones I'm aware of are surgeonfish, which we call tangs, and parrotfish. Interestingly, though, the biggest algae eater among reef fish is the humble damsel. The others are grazers, but damselfish are farmers -- they're highly territorial and scrupulous about clearing away algae they don't like so as to leave only their preferred food, filamentous turf algae, which they fertilize with their feces. Turns out damsels nom through way more algal biomass than the wandering grazers by growing their own food.

This is the basic, no-frills model of how top-down (grazing) and bottom-up (nutrient) pressures influence the algae population on reefs. If you go looking for exceptions in the scientific literature, you'll find them, but they're the results of real-world complexities, not failures of the underlying model.

               decreasing ecological resilience  ---->
    d
    e              HIGH GRAZING    |   LOW GRAZING
    c                ACTIVITY      |     ACTIVITY
    r          |-------------------|------------------|
    e          |                   |                  |
    a          |  massive corals   |   low-growing    |  
 |  s  LOW     |                   |                  |
 |  i  NUTRIENT|  and corallines   |    algae and     |
 |  n  LEVELS  |                   |                  |
 |  g          |  (healthy reef)   |      turfs       |
 |             |                   |                  |
\|/ r  --------|-------------------|------------------|
 V  e          |                   |                  |
    s          |                   |      large       |
    i  ELEVATED|     coralline     |                  |
    l  NUTRIENT|                   |     frondose     |
    i  LEVELS  |       algae       |                  |
    e          |                   |    macroalgae    |
    n          |                   |                  |
    c          |-------------------|------------------|
    e

Shifts in either nutrient or grazing levels can buy you a little slack in the other. That is, lowering nutrient levels can compensate for a decrease in herbivory -- which is basically how we run our little artificial reefs. Conversely, an increase in grazing pressure can compensate for additional algae growth triggered by a rise in nutrients -- indeed, many natural reefs have nutrient levels above the tipping point that should trigger overgrowth by algae, but grazers are holding the algae in check and maintaining the health of these reefs. This tipping point, where a reef ecosystem dominated by mixotrophic corals begins to transition to one dominated by autotrophic primary producers, occurs at vanishingly low nutrient levels.

Originally Posted by Health of Coral Reefs: Measuring Benthic Indicator Groups and Calculating Tipping Points

Low-nutrient tipping points, where increasing nutrients reach hypothetically critical levels that begin to reduce recoverability from phase shifts (i.e., 0.040 ppm NO3 and 0.007 ppm PO4), have been broadly corroborated for sustaining macroalgal overgrowth of both coral reefs and seagrass beds. As examples, low-nutrient tipping points also have been correlated for macroalgal overgrowth of coral-reef communities at Kaneohe Bay in Hawaii, fringing reefs of Barbados, inshore reefs within the Great Barrier Reef lagoon, and the reefs of the Houtman Abrolhos Islands, Western Australia. ... In our experience, if modern analytical instruments can detect measurable nutrient levels, so can growth-limited macroalgae.

Since cal_stir mentioned he's dosing nannochloris, which is in a sense artificially creating a phase shift from mixotrophic primary production to autotrophy before rising nutrient levels do it for you, and since he said this...

Originally Posted by cal_stir

The diverse micro fauna/plankton was the key but the phytoplankton was the nail in the coffin IMO.

...I went poking around and found that nannochloris in NSW has a very diverse population of bacteria associated with it, but surprisingly, no gamma-proteobacteria were found. The microbiome of nannochloris is probably hostile to the bacteria associated with dinos, which routinely consort with gamma-pros. And as I noted earlier, the decomposition of green algae seems to be associated with flavobacteria and thus may help tip the benthic bacterial community away from dino-friendly Bacteroidetes.

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