The Food Of Reefs - Excerpts from Eric Borneman

[SantaMonica]

One of the big benefits of a scrubber is that it keeps food in the water. Here is an update pertaining to this:

Part 1 of 7:

Taken from "Reef Food" by Eric Borneman:
http://www.reefkeeping.com/issues/2002-07/eb/index.php

"Detritus, marine snow, particulate organic material, and suspended particulate matter are all names for the bits of "dirt" [food] that flow around the reef; material that is composed of fecal material, borings, algae, plant material, mucus, associated bacteria, cyanobacteria and other particles. Decomposers (mainly bacteria and associated flora and fauna) break down waste material in the water, on the reef, and primarily, in the soft sediments. The result of their presence and action is not only a food source in and of itself, but provides raw material for channeling back into the food chain, largely through the benthic algae and phytoplankton.

"Phytoplankton [food] are small unicellular algae, or protists, that drift in the water column. They may be very abundant in and around coral reefs, and they are capable of absorbing large amounts of organic and inorganic nutrients. [...] Some of the reef animals can feed directly on phytoplankton; many soft corals, some sponges, almost all clams, feather-duster worms, and other filter feeders utilize phytoplankton directly as a food source. Small animals in the water column, termed zooplankton [food], also utilize phytoplankton as a food source. For the smaller zooplankton, phytoplankton and bacteria are the primary food source.

"Both of the [photos not shown] are from reefs on the Great Barrier Reef, Australia. The left photo shows the clear "nutrient poor" (oligotrophic) waters of the outer reefs. The right photo is of an inshore "nutrient rich" lagoon reef off Townsville. Notice how coral coverage in both systems is high, and even though the green phytoplankton-filled lagoonal reef is nutrient rich, it supports a high density of Acropora.

"Coral reef food sources, then, are largely produced by the ocean. Bacteria, detritus, phytoplankton, zooplankton, small benthic fauna, mucus, and dissolved organic and inorganic material of various types and sizes are what comprise the majority of food on a coral reef.

"In aquaria, we are faced with several realities. Our phytoplankton and zooplankton populations are generally negligible to non-existent in comparison with coral reef communities. Those which do exist are either rapidly consumed without having a chance to reproduce, or they are rapidly removed or killed by pumps and filtering devices or suspension-feeders. Coral mucus, bacteria, detritus, larval benthos and other "psuedo-plankton" might be present in a reasonable amount if the water column were not stripped. On the other hand, dissolved organic and inorganic material [nitrate, phosphate] levels are frequently much higher than they are in the ocean. [...] Even very well maintained aquaria are generally found with much higher levels of nitrogen and phosphorous than wild communities. Even though many desirable organisms are able to utilize these nutrients, levels in most aquaria are very unnatural, and coral reefs under such conditions often wane or die - a process known as eutrophication.

"It is the lack of water column-based food that results in limited success with the maintenance of some desirable animals, such as crinoids, flame scallops, clams, certain corals, sponges, bryozoans, and many other invertebrates. Even the symbiotic (zooxanthellate) corals [like SPS] suffer, despite many obvious long-term successes with these animals.

"In terms of previously mentioned export mechanisms, it really does little good to be cultivating or adding more food material in the water column if it is all being rapidly removed by filtration devices. Live rock and sand provide abundant filtration, and some of the articles in past issues describing the set-up and use of unskimmed tanks are, in my experience, something that should be seriously considered. Algae Turf Scrubbers are also viable systems that provide low ambient water nutrient levels [of nitrate and phosphate] while maintaining higher amounts of food and particulate matter in the water. I also feel that if protein skimmers are used, they should probably be used in an intermittent fashion.

[SantaMonica]

Part 3 of 7:

Taken from "The Food of Reefs, Part 3: Phytoplankton" by Eric Borneman
http://www.reefkeeping.com/issues/2002-10/eb/index.php

"Phytoplankton are the major source of primary [food] production in the ocean, and one of the most important driving forces of global ecology. In fact, phytoplankton production influences all life, by being at the lowest rings of the food chain.

"The reason [phytoplankton] are so important on a regional or global scale is simply by virtue of the fact that the upper 200 [meters] of oceanic waters is filled with phytoplankton and covers over 70% of the earth's surface.

"What eats phytoplankton? In the water column, zooplankton [food] are without question the primary consumers of phytoplankton. Zooplankton grazers vary according the area and the time of year, but include primarily ciliates, copepods, amphipods, and tintinnids.

"Stony corals are generally not well adapted to the sieve or filter type feeding that characterizes the soft corals (Fabricius et al. 1995, 1998). They are, however, well suited to the capture of zooplankton prey.

"It is of paramount importance to recognize that the biomass of potential grazers [which need food] in an aquarium is many times what it would be in the same volume of water or surface area as the bottom of oceans or on reefs, and also, that the availability of water column borne food is many times greater in the ocean than in an aquarium.

"Perhaps most importantly, is the almost ubiquitous interaction between bacteria and phytoplankton. Phytoplankton release dissolved organic substances, and bacteria utilize them as nutrient sources. Most phytoplankton cells, especially large ones, are coupled nearly continuously with coatings of bacteria [which are consuming the dissolved organic substances].

"The amounts of phytoplankton present in reef aquariums are not known but are probably considerable. However, they are also probably rapidly removed by grazing and export devices [skimmers].

[SantaMonica]

Part 4 of 7:

Taken from "The Food of Reefs, Part 4: Zooplankton" by Eric Borneman
http://www.reefkeeping.com/issues/2002-12/eb/index.php

[Note: "Zooplankton" are tiny animals (food) floating in the water]



"Copepods comprise by far the largest fraction of total zooplankton - more than all the other groups combined.

"Zooxanthellate corals (many diverse species) could survive "indefinitely" if provided with adequate zooplankton, even if totally deprived of light. In contrast, corals provided light and deprived of zooplankton did not survive.

"One of the greatest myths among reefkeepers is that "SPS" corals depend mostly on light, and require less food than "LPS" corals. This is entirely untrue. As an example, consider the data from [pic not shown]. This graph shows the capture rate of an equivalent biomass of two corals, the large-polyped Montastraea cavernosa and the very small-polyped Madracis mirabilis. For those unfamiliar with Madracis, it is related to and somewhat resembles Pocillopora and Stylophora. The capture rate of the small polyped coral was 36 times greater than the large-polyped coral! Furthermore, M. cavernosa has been shown in other studies to be a voracious zooplanktivore.

"Many other studies confirm the predatory [feeding] abilities and requirements of "SPS" corals. It should not be surprising, given the fast growth rate and fecundity of many small polyped species. In other words, more growth and reproduction requires more energy, especially nitrogen for tissue growth. The difference, if one exists between "SPS" and "LPS" corals, lies primarily in the size of the food captured. Most of the prey of small polyped corals may just be too small to see. Aquarists have a tendency to be strongly visual, and so if gross observations don't indicate that a coral is consuming food offered to it, they wrongfully assume the coral must not need to be fed.

"Some species rely more on zooplankton than others, and if anything, the "SPS" corals feed on zooplankton a lot. In fact, most corals show linear feeding saturation dynamics under all but extremely high particle concentrations. What this means is that corals have a hard time "getting full." They continue to capture prey, and do not get satiated until prey densities become so great that such levels are almost never possible. To put it another way, even if you were to pour a pound of food per day into an average sized reef aquarium, the corals would still "be hungry."

"In a September 2002 coral reef conference in Cambridge, several papers were presented that should give an idea of not only the very latest information, but also emphasize what is written above.

"Many years ago, one of the only [food studies] for a coral was done for what might be considered the ultimate shallow-water "SPS" coral, Acropora palmata (Bythell 1988, 1990). The study showed, basically, that 70% of this coral's nitrogen needs were met by feeding, and that 91% of its carbon needs were met by light. [In 2002] three more corals, the larger polyped Montastraea cavernosa, M. annularis and Menadrina meandrites [were studied, and the researchers found] zooplankton to provide 20-80 times the carbon and 112-460 times the nitrogen previously shown for Acropora palmata. Finally [in 2002, researchers studied] the role of zooplankton consumption on the metabolism of the small-polyped coral, Stylophora pistillata under 3 different conditions of light (80, 200, 300 µmoles m-2 s-1) and 2 feeding regimes (Artemia and natural plankton). They found that regardless of light, fed corals had higher chlorophyll-A concentrations, higher protein levels, and had photosynthesis rates 2-10 times higher than those deprived of food. This group also measured calcification rates, both in the dark and in light, and found that calcification, as is well known to be the case, is enhanced by light. However, for the first time it was shown that feeding results in calcification rates 50-75% higher than in control corals (not fed). It was also found that feeding does not affect the light-enhancement process of photosynthesis on calcification. To make these results completely understandable, if corals can feed on zooplankton, they will calcify 50-75% faster irrespective of light levels provided.

"Of all the many things that can potentially increase respiration, photosynthesis, and calcification -- and have been shown again and again to do so absolutely -- feeding and water flow are the major players. Light, of course, is critically important as well, but aquarists by and large can and do provide enough quantity and quality of light for corals. Period. Phytoplankton, while a very beneficial addition to aquaria, does not feed most corals (Borneman 2002). Something as significant as zooplankton to both coral and coral reefs would seem worthy of the highest efforts in trying to produce, add, grow, substitute or in some way provide to tanks. I cannot think of a single greater accomplishment and advance for aquarists than to provide by whatever means (higher export and higher input, larger refugia, purchase, plankton tow, culture, etc.) significantly greater levels of zooplankton or zooplankton substitutes to their corals. I hope I am being dramatic enough by writing this, for this is among the most important steps that must be made to realize the majority of those lofty goals and ideals that are so often stated and desired by those keeping corals in aquariums.

[Skimmers remove zooplankton; Scrubbers add zooplankton]
.

[SantaMonica]

Part 5 of 7:

"The Food of Reefs, Part 5: Bacteria" by Eric Borneman
http://www.reefkeeping.com/issues/2003-01/eb/index.php

"Given the enormous bacterial biomass in all ecosystems, it should be of little surprise that [bacteria] are food for something, if not many things. Bacteria, being composed of living material, contain a relatively large amount of nitrogen, an element in very short supply in coral reef waters.

"The biomass and productivity of bacteria on [natural] coral reefs are as great as those in nutrient-enriched (or eutrophic) lakes, and up to a hundred times greater than in the open ocean. Planktonic bacteria in coral reefs [..] have filamentous processes to allow them to absorb and consume dissolved organic molecules [DOC].

"In virtually all studied marine environments, bacteria are water purifiers, decomposers of organic material, and a primary source of protein for both those animals that directly graze on them and those that acquire them indirectly through secondary consumption.

"Given the importance of bacteria as a food source in marine ecosystems, it might not be surprising to learn that they are also a primary food source for corals. It has been found that bacteria alone can supply up to 100% of both the daily carbon and nitrogen requirements of corals. All corals studied consume dissolved organic material [DOC], bacteria, and detrital material [waste].

"Bacteria not only provide carbon and nitrogen for the [coral] polyp, but also provide an important source of phosphorous for the zooxanthellae, in addition to other elements such as vitamins and iron.

"Bacteria exist in very high diversity and biomass in the marine environment, and especially on coral reefs and on coral surfaces. They play critical roles in virtually all ecological processes that control reefs, and are a major component of food webs. Corals feed on bacteria at levels and efficiencies that rival all other bacterial consumers.

[SantaMonica]

Part 6 of 7:

"The Food of Reefs, Part 6: Particulate Organic Matter" by Eric Borneman
http://www.reefkeeping.com/issues/2003-03/eb/index.php

"This article will address a very important food to corals and many other animals, particulate organic material (POM). This food source has many names, including detritus [waste], floculant organic matter, reef snow, marine snow, and suspended organic material.

"Not so long ago, marine aquarists made every attempt to be assured that their water column was "polished." I never fully understood the term, but the premise was that a clean water column was a good water column. Various means were employed to accomplish this, including the use of various power filters, mechanical flosses and screens, sterilizers, ozonizers, canister filters, diatom filters, foam fractionators [skimmers] and many other devices. [However] "polished" water might not be in the best interest of reef tanks or corals.

"Particulate organic material has its origins in life, being composed by and large of the remains, secretions and excretions of living organisms. On coral reefs, it is composed mostly of dead algae, bacteria, mucus, and feces.

"When food, waste, or other particulate organic matter (POM) is trapped, especially in an aerobic environment, it is acted upon by several types of bacteria that break down the substances into more basic dissolved organic and inorganic components. Some of these breakdown components are organic acids and refractory compounds that can impart a yellow tint to the water column. This yellowing has been called "gelbstoff." However, both the substances remaining after [various types of] filtration, as well as the substances removed by the filtration, can be utilized by the life in the aquaria, and are taken up by corals, sponges, some other invertebrates, phytoplankton, bacteria, and algae.

"On reef slopes and crests, the [waste] material is mostly coral mucus, while over the reef flats and lagoons, the material is mostly algae and fecal matter. This material, by itself, has a high carbon content. However, it acts as a substrate for bacteria, ciliates, cyanobacteria, and other microorganisms that coat the particles. Bacteria can even convert dissolved organic material (DOM) into particulate organic material (POM) by aggregating it in the presence of carbon. This provides a substantially enriched particle replete with amino acids and valuably higher nitrogen content. As such, detritus [waste] becomes a very nutritious food source for many organisms. It is such a complex "dirt", that detritus has been described as a completely self-contained microhabitat of its own, with plant, animal and microbial components, and its own "built-in" nutrient source.

"Another major consumer group of detritus is the zooplankton. These small animals, themselves a very important food sources to reef consumers, have been found to have 90% of their gut contents composed of detritus. Mucus-producing animals, like corals, tend to trap detritus, and the material is either removed or consumed by ciliary action across the tissue surface. Many fish also consume coral mucus, and any attached particulate organic material"

"Detritus [waste] forms the basis of several food webs that are part of a balanced autotrophic/heterotrophic community. It also plays a role in establishing various levels of nutrient production and decomposition. It is this material that is the principal food source for the many bacterial species that work in various nitrification and denitrification activities. Before reaching the microbial community, however, it acts as a food source for the smaller consumers such as amphipods, copepods, errant polychaetes, protozoans, flagellates, ciliates and other animals whose activities contribute to the stability and productivity of a coral reef and a coral reef aquarium.

"It is the microbial community, though, that is most important in the detrital processes. On the reef, the productivity of bacteria (both aerobic and anaerobic oxidation and reduction, including important sulfate reduction) depends heavily on detritus. Without this microbial community, coral reefs would cease to exist.

"Corals, in particular, are notable for their consumption of detritus. All corals studied feed to some degree on POM, and coral communities have been found to remove half of the POM present on some reefs. So prevalent is this material, that it is termed "reef snow" in the wild. [...] Given the ability of so many corals to consume and utilize this material, along with its relatively high abundance and ability to provide up to 100% of corals' carbon and nitrogen requirements, it may now (hopefully) seem rather foolish to attempt to remove this material from aquaria.

[SantaMonica]

Part 2 of 7:

Taken from "From the Food of Reefs to the Food of Corals" by Eric Borneman
http://www.reefkeeping.com/issues/2002-08/eb/index.php

"Nitrogen levels in [natural] coral reef waters are typically extraordinarily low, with most being found as ammonia. This is in contrast to aquaria, where the dominant nitrogen species is usually nitrate. Nitrogen is the be-all end-all for zooxanthellae growth and reproduction [zooxanthellae is what photosynthesizes light into food for corals]. By limiting nitrogen in the form of excretion products, the [coral] polyps keep the zooxanthellae in the numbers and density that maximize photosynthetic efficiency for its own use. Using several released compounds, most of which are still unidentified, the [coral] polyp stimulates the zooxanthellae to release virtually all of the products of its photosynthesis, and these are then used by the polyp for its own needs. If nitrogen was made readily available to the zooxanthellae (for example, if high levels were present in the water and this dissolved nitrogen diffused into the coral tissue), it could then be accessed by the algae without limitation by the polyp, and zooxanthellae could begin to grow and reproduce like a phytoplankton culture. In this case, the symbiosis becomes less advantageous to the coral, and it will expel some of the symbionts to try and re-establish maximal benefit from its algal partners. As a practical note, when very high densities of zooxanthellae exist in coral tissue [because of to much nitrogen], the resultant coloration of the coral is usually a rich or dark brown color.

"Coral mucus, in turn, and as was shown in the previous article, is itself a food source to the reef.

[Skimmer remove mucus, but do not remove nitrogen]

[SantaMonica]

Part 7 of 7:

"The Food of Reefs, Part 7: Dissolved Nutrients" by Eric Borneman
http://reefkeeping.com/issues/2003-04/eb/index.php

"Mucus consists of mainly sugars and glycoproteins - soluble materials in and of themselves. However, the formation of mucus, and its release in a matrix of chains of these materials, may result in a particulate material. This material is both utilized directly by many organisms, and also forms the basis for a predominant fraction of the particulate "marine snow" on reefs.

"In fact, reef waters are 30-40% higher in DOM [disolved organic matter] than oceanic waters.

"In terms of determining the degree to which organisms may use dissolved material as significant source of nutrition, one may examine the surface area of the outer cell membranes exposed to such materials. In general, the larger the absorptive area, the more likely organisms are to depend on absorption. Some cell surfaces are covered with many finger-like processes called microvilli that greatly increase the surface area of the membrane. Furthermore, the presence of cilia is often a good indicator of absorptive surfaces. Perhaps not surprisingly, corals have extensive microvilli and cilia.

"Corals are able to take up various forms of both organic and inorganic dissolved nitrogen.

"Even slightly elevated nitrogen levels can quickly result in rapid increases in the density of zooxanthellae, as they use it to fuel their own reproduction" [and thus turn the coral brown]

"It is also somewhat equivocal that corals are able to utilize nitrate (which exists nearly totally in its ionic state at physiological pH) at all, and an inability to find nitrate reductase in many studies, makes the ultimate importance of this dissolved nitrogen source to corals (and anemones) rather tenuous. However, it is unambiguously true that ammonium is a sought-after nitrogen source by both coral host and algal partner.

"Humic (refractory) compounds: These yellowing compounds are typically found at relatively high levels in aquaria, and they are removed with protein skimming and activated carbon. Humic materials have been thought to be relatively inert and unavailable for use as a nutrient source. However, studies have shown that organisms from bacteria to brine shrimp (Artemia salina) can utilize humic substances as a source of nutrients.

"In terms of corals reefs, the amounts of most dissolved nutrients, except carbon in most cases, are very low.

"The higher nutrient levels may cause corals and other symbiotic partnerships to decline as the partner algae preferentially utilize the increased nutrient sources to the expense of the host. [and thus browning of the coral occurs]

"Without question, corals and many reef organisms are able to utilize dissolved nutrients to help meet their energy requirements and to use in tissue growth.