Subsea
7500 Club Member
As I reread some of this thread, I decided to resurrect the thread and see where it goes.
Total Organic Carbon (TOC) and the Reef Aquarium: an Initial Survey, Part II
Department of Chemistry, The Pennsylvania State University, University Park, PA 16802. Ken and Kelly continue to report on their work on Total Organic Carbon and how it relates to the reef aquarium.reefs.com
To further understand the biochemistry of the Coral Holibiont requires an understanding of physics, chemistry, micro biology.
When Felderman said that photosynthesis was the combining of the inorganic & the organic world, he got my attention.
Conclusions
Coral reefs have been characterized as oases of biological productivity in a marine desert (Capone, 1992). The surrounding oligotrophic (= nutrient depleted) waters provide little sustenance to the reef biota. As a consequence, complex nutrient recycling webs have evolved on reefs to retain and reutilize essential elements like nitrogen and carbon. The carbon cycle on reefs is multifaceted and is beginning to be unraveled. Reliable measurements of dissolved organic carbon (DOC) levels are critical for this goal, and the introduction of the Shimadzu TOC Analyzer represents an unequivocal leap forward in research capability. On thriving reefs, most carbon input originates with atmospheric CO2, which is “fixed” via photosynthesis first into carbohydrates, and then into a multitude of other organic molecules. Much of this carbon, which is generated by the zooxanthellae in corals, is reemitted as coral mucus. This coral contribution significantly enriches the pool of DOC.
This DOC is prime food for a large variety of reef microbiota, including bacteria, both in the water column and in the corals themselves, and microplankton, etc. Finally, these microflora and microfauna serve as food for a variety of filter feeders, including, again, the corals. Thus, the interdependency of reef organisms, both large and small, is revealed as the carbon-based nutrients are recycled. The surrounding oligotrophic ocean serves as a buffer which can absorb excess nutrients that might otherwise prove harmful to reef inhabitants and modulate the levels of dissolved species by import and export, depending on relative (reef vs. open ocean) concentrations. Our captive reefs fall far short of this nutrient commerce model; we have, of course, no open ocean buffer to dilute away waste and so we rely on water changes to perform this vital function, and it remains unclear whether our aquaria contain all of the components, in appropriate proportions, of authentic reefs necessary to promote efficient nutrient recycling. Nevertheless, what we do seems to work, at least most of the time. But, what happens when things go wrong? Circumstantial evidence from Rohwer’s studies implicates DOC imbalances in coral mortality, with runaway bacterial growth as a likely mediating culprit. Can these observations inform aquarists, and is there a response that might ameliorate the problem? Certainly the first step is to establish a baseline of TOC ( DOC) levels in healthy reef aquaria under different husbandry protocols. In this article, data has been presented that accomplishes this goal, and further, validates these TOC numbers by comparison to TOC/DOC levels on healthy reefs around the world. In addition, the surprisingly minimal impact of protein skimming on TOC levels was revealed. On this point, it is apparent that if TOC levels can be monitored to assay the effects of one skimmer (the H&S A200 in this case), then they can be monitored to measure the impact of different types of skimmers operating on an experimental tank. In addition, these types of experiments also can be used to probe more directly and quantitatively the TOC removal capabilities of Granular Activated Carbon (GAC) that was hinted at in the tank #2 vs. tank #3 comparison. These types of experiments might allow, for the first time, a quantitative evaluation of skimmer and, independently, GAC performance which is divorced from the hype and misinformation that seems to surround these areas of marine aquarium maintenance/equipment. These experiments are ongoing and results will be reported in due course.
Finally, the goal of identifying approaches to halt incidents of coral mortality in reef tanks may benefit from data collection from “sick” tanks rather than the healthy aquaria examined in this study. If tanks undergoing coral crashes have an unusually high (or low) amount of TOC in the water but otherwise have acceptable water parameters, then a new and otherwise unappreciated villain will be in hand. Under these circumstances, what can the aquarist do? One experiment described by Ferrier-Pagès on Galaxea provides food for thought. Specimens of this coral were treated with the combined antibiotics penicillin, streptomycin, and amphotericin; subsequent bacterial uptake of DOC, which Rohwer identified as a mechanism for coral mortality when occurring in excess, ceased.
Let the good times roll.
