dendro nutrition

[charles matthews]

Eric,

Regarding the study on phytoplankton and carbon uptake in dendros, the conclusion- that additional components of the seston were needed for carbon needs- wasn't supported by the information cited.

I understood from the article that about a third of the 24 hour carbon needs were assimulated within the first hour; thereafter, about 3% or so per hour for the next eight hours. If one assumes that the 3% rate persisted over 23 hours, then the full carbon budget could be met by phytoplankton, or very close to it- a conclusion identical to that of Katrina Fabricius.

I don't understand how this result could indicate that something other than phytopoankton is needed.

Additionally, I don't draw from this the conclusion that the aquarist should "pulse" phytoplankton? It does appear that each additional hour after the first contributes significantly in total over 24 hours.

I am wondering also how this study relates to the observed inflation/deflation behavior of dendros. Is it possible that continuous provision of phyto during the deflation periods are necessary to provide that last 60% of the carbon budget? Were they assimulating 3%/hr when deflated?

If you have anything on these questions I would appreciate it very much.

Charles

[EricHugo]

Hi Charles:

The uptake efficiency depending on numerous factors, but including incubation time, cell density, cell size, respiration, digestion/utilization, species specific and colony specific aspects, etc. At normal cell densities, maximal uptake and utilization occurred, and met maximally 34% of the daily C needs. At higher densities, and at longer incubation periods, assimilation efficiency decreased due to the "digesting blockade." Their results roughly match Katharina's findings of 11-29% daily C needs. Any which way you slice any of the findings, phytoplankton isn't going to meet daily C, much less N requirements.

I am not seeing where you are seeing that a third was assimilated within the first hour and 3% for the next eight hours, assuming persistence for the next 23 hours.

In Katharina's other works, in this work, and in talking to her, these corals aren't very good at capturing motile prey, and so anything other than very very small or non-motile things will not be ingested - hence the utilization of phytoplankton. The question is where does the rest of the nutrition come from, and it appears that DOM is only part of the answer with a relatively low contribution (but something). Perhaps particulates and bacteria?

My comment about pulsing phytoplankton is speculative. If the maximal efficiency occurs at natural densities, and there is a resulting pharygeal block with a time lag to digestion, then pusling might keep the efficiency optimal for the coral. Of course, other aspects are also important (flow speed, etc.). It seems wasteful to continue dosing phytoplankton continuously or at high densities to closed systems if attempting to keep these corals if the material is not well utilized.

In terms of inflation/deflation, have you looked at the numerous studies by Fabricius? If not, I can provide some of those to you as .pdf. I have her dissertation work, as well, but it is pretty large!

[charles matthews]

Eric,

I would dearly love to havae those files! You are very generous.

Charles
Luvstns726@aol.com

[charles matthews]

Hi Eric

I wanted to describe my laboratory to you and ask if you would be interested in advising me on projects of interest.

I have finished construction on a marine system to investigate nutrition in obligate filter feeders. The tanks are all connected to a central sump, with automatic RO/DI topoff at SG 20.05 at 80 degrees. Turnover from the central system can be regulated for each tank, or a tank can be isolated as needed for study. the lab has some indirect window light. Ca/Alk presently via Two Little Fishies supplements- (I like the vanadium in the product for tunicates). There is a large skimmer only used if needed.

The first 120 gallon is an acrylic tank with black sides; the front has a removable panel for light exclusion. Lalo live rock was recently installed on eggcrate, including a shelf overhang which is availabale for suspending organisms. There is no substrate. The tank is connected to an Eco-Wheel (as you probably know, a large rotating algae scrubber); the scrubber has a refugium below it with bioballs; there are observation chambers here. Water movement is by the Eco-Wheel which provides about 20/ turnover/hr with a very gentle surge when the wheel turns;
there is also a Wave 2K providing additional gentle surge in the back of the tank. Turnover may be in the range of 40-60x/hour. There is, of course, circulation available back to the main system.

The second 120 gallon is a glass tank with 4-6 inches of Carib-Sea "macromedia" as a substrate. The tank has a partial divider down the long way made of coarse filter padding sandwiched between two eggcrate layers. Powerheads provide laminar unidirectional current- currently using a Turbelle classic on one side, and an Aquaclear on the other- total about 2000 gallons/hour. I plan to add two Turbelle Streams with a control system to study effect of water flow on feeding. I have been studying detritus formation on different inert substances in this tank, and plan to install a pump to blow water under the substrate on a timer. Both the tanks above are nonphotosynthetic.

A 75 gallon receives partial window light only. It is likely that I will put in a crushed coral sand bed for dedicated sand stirring (probably with lighting to encourage some photosynthetic epiphytic material).

A 25 gallonH is lit by a 175WMH; water comes in through a needle valve and is titratable to droplets. I plan to use a soil substrate (OK, magic mud I admit it but I've experimented with others) to take advantage of iron photoreduction, and use this as a photosynthetic settling filter. The filter will be inoculated with Nannochloropsus and lit continuously. I have some good experience in growing greenwater cultures- I am interested in how this polyculture performs as a model of open ocean planktonic communities.

Another 25 gallonH is set up as a batch fluidized bed fliter. There is Southdown sand to about 10 inches; a pump draws from the surface and pumps to the bottom fo the sand, fluidizing the bed; this will be set on a timer to 30 minutes aerobic/6 hours settling/anaerobic. After fliudizing, the supernatant returns slowly to the main tank via the overflow. It will be interesting to see if batch fluidized beds will work in this context, and whether we can get denitrification and increased aragonite dissolution with this method. I will be looking at this both with light and without it. This technique was suggested to me by wastewater engineering techniques of "luxury phosphorus uptake".

I plan to obtain a videomicroscope to photograph and observe feeding behaviour and responses.

I will be supplementing low dose Lugol's mixed with tyrosine to test my hypothesis that secretion of thyroid hormone-like coupounds through herbivore feces is critical to cryptic communities where mucous capture is a significant feeding strategy. I will be looking at feeding responses to amino acids and other substances as well.

I also would like to investigate the possibility that material released from shifting sand surfaces- which would be expected to include epiphytic material, bacteria, phospholipid cell wall ground up material, peptides, enzymes, nucleotides, intracllular organelles, and mucopolysaccharide "gums" from bacterial films- may be underappreciated sources of nutrition for filter feeders. This material might well be finer grained and more "predigested" than epiphytic material say from surfaces or sea grasses, and total quantity may well be much higher than open water feces/detritus or material from vertical surfaces. The possibility of developing a batch fluidized bed filter device comes to mind. This line of investigation interests me the most.

My background is in clinical neurology.

I was hoping that you might be willing to advise and participate in this project.

Sincerely


Charles Matthews MD