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An interesting read, Emulating Nature: The Reef Habitat Tank

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sfsuphysics

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I don't know what BAR's policy is with copying articles from other sites, or if it even has one, however feel free to modify this as such. I will be splitting this up into multiple posts in this thread, so you can zip to whichever part you want with a little more easy. It'd be interesting to get some feedback on this as well.

http://www.fishchannel.com/saltwater-aquariums/aquarium-frontiers/natural-coral-reef.aspx

Article by Richard Harker

A common assumption is that the typical reef tank is modeled after a natural coral reef — a little slice of reef, if you will. Well, it’s not true. The typical reef tank is not actually aquascaped like a real reef. It’s more like bits from many different parts of a reef put together to fit inside a glass or acrylic tank. I’d like to see reef aquarists begin to create reef tanks modeled after real habitats found on real natural coral reefs; but to do that, we have to understand the natural reef.

If we approach a coral reef from the open ocean, we first come upon the reef wall and fore reef. The reef wall is a solid vertical rock structure scoured on top by the full brunt of storms, ocean surge and tidal currents. Not much grows on top of the fore reef. One finds the occasional sturdy coral living within the depressions of an otherwise barren seascape.

Several feet below the surface is where one finds abundant corals, such as sea whips and sea fans. The majority of corals on the reef wall are filter-feeding animals drawing nourishment from the ocean water flowing past the reef wall. The few photosynthetic stony corals found in this environment are modest in size, growing slowly as they cling to the reef wall. The fish life found in this habitat is abundant. This is where one finds numerous surgeonfish, including clown, blue and convict.

Behind the protection of the fore reef lies the reef flat. This is generally where we find the most abundant and diverse aggregations of corals. The calmer waters, combined with plenty of light, create the ideal environment for a wide range of soft and hard corals.

As we move closer to land, the reef flat gives way to patches of rock surrounded by areas of sand. This is the back or patch reef. Sand accumulates in this area because of a combination of environmental and biological processes. As storms pound the most exposed areas of the reef, forces grind coral rock into sand, and currents carry the sand to the protected back reef. This transitional area varies widely, depending on topography, currents and how the area has evolved. Soft corals dominate some back reefs, whereas delicate branching hard corals dominate others. Back reefs in areas under biological stress can be overrun with fleshy algae.
Sea Grass

A sea grass tank represents a different approach to reefkeeping.

Moving even closer to shore, coral rock gives way to sand, and the sand itself changes, becoming finer and intermixed with detritus. This is a lagoon, the final resting place for all that accumulates on a reef. Lagoons are shallow, by definition. Wind and water currents push sand and detritus from the reefs toward the shore. This builds up over time and gradually becomes a lagoon that is sometimes (not always) attached to a sandy beach. The windward side of an island will be just rock because it gets hit with storms; the leeward side is where one finds lagoons because they are protected from storms (if the area is exposed to strong currents, it isn’t a lagoon).

The sand can often be covered with filamentous algae and cyanobacteria. At first glance, lagoons appear sparsely populated by animals. This is where one finds lone shrimp gobies posted at regular intervals across the sand. Yet a closer look reveals that lagoonal habitats are some of the most biologically diverse habitats of the reef. The great diversity, however, is not found in a lagoon’s waters but rather in the detritus-enriched sand and silt, the sand having high nutrient levels.

There are small transitional areas between each of these habitats, but for the most part, the habitats are visually distinct. One can readily tell the difference between fore reef, reef flat and back reef because of distinct topographies, as well as distinct mixes of animals. Different animals and aggregations of animals have evolved to exploit available niches in each of these habitats.

This is one of the greatest problems of the traditional reef tank: Ignoring the linkage between habitats and residents leads a hobbyist to inadvertently risk the well-being of the tank’s inhabitants. Placing animals from one habitat into another can potentially stress or impair either the transplanted animals or animals forced to deal with animals they rarely encounter on a natural reef. By modeling a reef tank after a single natural habitat, the hobbyist doesn’t just have the satisfaction of creating a reef tank that actually looks like a real coral reef — he or she has also created a potentially healthier environment for the tank’s inhabitants.
 
Building the Habitat Reef Tank
From the descriptions of coral reef habitats, I hope it is obvious that the typical “rocks-in-a-glass-box” reef tank so common in the hobby is not the place to start when designing a habitat reef aquarium. The traditional reef tank unnaturally combines reef wall aquascaping with reef flat inhabitants. A more natural approach is to combine the aquascaping of a specific habitat with the animals that naturally live there.

Regardless of the habitat the aquarist chooses to emulate, this matching is the most important consideration. One can start with the aquascaping, then choose animals that match, or start by choosing the tank’s inhabitants, then creating aquascaping that is appropriate for them.
 
The Natural Lagoon
Despite the beauty and bio-diversity of a healthy lagoon, few hobbyists actually set out to create a lagoon in their reef tank. They inadvertently end up with one when they combine poor water conditions, minimal water movement and fine sand. The end result is an accumulation of detritus, algae and cyanobacteria — characteristics of an impaired natural lagoon. Combining lagoonal conditions with fore reef aquascaping and reef flat inhabitants is the problem.

A lagoonal tank should be aquascaped with only sand — not live rock. There is a misconception that a reef tank needs live rock, but all of the biological benefits of live rock can be provided by live sand. Having only sand and no rock creates a more natural-looking lagoon and has multiple advantages, from initial expense to ease of maintenance.

Good inhabitants for a lagoonal tank include shrimp gobies and their commensal shrimp (e.g., Alpheus sp. randalli). These animals constantly build and rebuild burrows in the sand. They need plenty of sand and the kinds of tankmates one would normally find in a lagoon (e.g., Pomacentrus, Neoglyphidodon and Amphiprion). Another option is a lagoon tank aquascaped around an anemone and anemonefish. Several anenomes popular in the hobby are only found in sandy lagoonal areas (such as Stichodactyla mertensii, S. haddoni and Heteractis crispa), despite the fact that too many hobbyists insist on filling anemone tanks with live rock.
 
The Patch Reef
The back reef, with large areas of sand surrounding the occasional rock structure, is perhaps the most photogenic portion of the reef. The open areas — with plenty of water circulation and intense light — create ideal conditions for stony corals. Unfortunately, most reef tanks fail to capture this striking portion of the reef. The primary reason is, once again, the typical aquascaping of a reef tank. Most tanks tend to have a low surface area relative to their height. Most reef tanks are too tall; and because of the height, most hobbyists put too much rock in their tank.

Although this approach to aquascaping a reef tank is the traditional method, it falls short if one is trying to emulate nature as much as possible. There is no habitat on the natural reef that resembles this stack of rocks. On the natural reef, most fish spend their time swimming in the open water above the reef. In the typical reef tank filled with rock, fish are essentially pressed against the reef structure and have no open areas in which to swim. A reef tank filled with rock is also more difficult to maintain. Many of the husbandry problems that develop over time as a reef tank ages are compounded by too much rock in the tank.

If one’s goal is to re-create a natural patch reef habitat, the first step is to purchase a tank with a large surface area. The proportions of the so-called “breeder tank” offer the hobbyist a greater opportunity to create a realistic patch reef than the more common “display tank.” An even better solution is a low-profile custom tank. A large surface area enables the construction of isolated rock clusters surrounded by sand, which characterize the back reef. Large open areas allow fish to swim freely and hover over the rocks, as they would on a natural reef. In addition to being more realistic, the isolated rocks and shallow depth make the tank more accessible. From simple chores, such as cleaning the glass, to more labor-intensive tasks, such as vacuuming the sand, every aspect of maintenance is simplified.

A less common type of patch reef is the sea grass patch reef. These areas have an interesting mix of small corals, rubble and sea grass. Environmental requirements for this type of reef tank are similar to the patch reef outlined above. Sea grasses tend to be more challenging to grow, so a sea grass tank should be reserved for advanced hobbyists; but for those who appreciate a challenge, they are a wonderfully unique display.
 
The Reef Flat
On a natural reef, as we move back toward the ocean from the patch reef, we reach the reef flat. The reef flat is where we encounter the highest densities of stony corals. So, for a hobbyist primarily interested in creating a reef tank that focuses on hard corals, this is the habitat to use as a model.

This habitat presents a number of challenges for aquarists. It is a reef zone that experiences strong currents and intense light. It is also an area regularly flushed by pristine water with low levels of nutrients. And it is an area where rock predominates, and what little sand that exists is coarse gravel too heavy to be carried away by strong currents. In short, it is a habitat that is virtually never re-created in the hobby. The irony is that given the popularity of stony corals, such as Acropora, this should be the habitat most frequently emulated.

A reef tank designed to mimic the reef flat and create a realistic environment for reef flat stony corals should be built around the unique environmental conditions of this habitat. The tank should have intense, turbulent water motion and strong lighting. Like the patch reef tank, a tank with a substantial surface area is preferable, but the more turbulent water motion requires higher walls and a greater concern for water containment. In fact, all other aspects of the tank’s design should be secondary to creating intensely turbulent water motion.

Outlining water motion regimens that mimic reef flat intensities are beyond the scope of this article, but a search of hobby literature will produce a wide range of options. There is the traditional method of employing powerhead pumps, which tend to produce only shallow surface turbulence. Other options, such as the so-called Carlson surge device (named after Bruce Carlson, the professional aquarist who first popularized it), can create much stronger turbulent water flow. Closed loops using powerful pumps can also create strong currents, though these tend to be more laminar than turbulent.

Strong water motion will preclude the use of fine sand. While many in the hobby continue to defend the notion that fine sand helps maintain a healthy reef tank, studies show growing evidence suggesting that the opposite is true (e.g., Toonen, R. and C. Wee. 2005. “An Experimental Comparison of Sandbed and Plenum Based Systems” [Parts 1 and 2]. Advanced Aquarists Online). Furthermore, fine sand is only found in lagoonal and near-lagoonal habitats. Fine sands are washed away from reef flats by strong water motion. The inability to keep fine sand on the bottom of the tank is actually a good sign when creating a realistic reef flat habitat. The best substrate for a reef flat is a solid rock base with no sand to trap detritus. Ideally, this would be a slab of rock that virtually covers the bottom of the tank and that is placed right on the bottom; one could also simply put down a layer of rock, as if creating a rock sidewalk.

The other requirement for a successful reef flat tank is high-quality water. Acropora and other stony corals growing on the reef flat are bathed in clean nutrient-free ocean water. Stony corals produce a great deal of mucus that keeps the coral free of fouling particulate matter. On the natural reef, this nutrient-rich mucus is carried away, ending up as part of the lagoonal detritus. Lacking this export mechanism, the hobbyist is faced with finding some other means to remove these nutrients. Reverse osmosis replacement water, high-capacity foam fractionation (protein skimming) with modest ozone, activated carbon and mechanical filtration are all required to keep the tank’s water as pristine as possible.
 
Very interesting! Reading this seems like a lot of us have a wrong setup if our goal is to recreate a "patch of reef"
 
While I agree with most of the sentiments expressed by the author, he is mistaken in one important aspect. This may be due to a limited exposure to wild reefs or perhaps just a reflection of the few reefs he's seen. I have also only seen a few wild reefs but his description of the fore reef (reef wall) doesn't reflect what I've seen. The reef wall is exposed to some of the highest levels of plankton and nutrient availability and is often densely covered in vibrant live corals. In this respect, many of our reef tanks are very accurate (acros and montis crowded tightly together and growing on the edges and flats of the reef wall). Granted, many of the species we grow don't fit into that picture and so our tanks aren't completely accurate but they're close...
 
What hooked me is I noticed some of what he mentioned in my VERY limited wild-reef experience (a week of snorkling in Maui :D) is that at beach areas there were little "damsel like" fish but not much else. As you got closer to the rock walls (5 feet depth to sand) corals started popping up here and there, still a little too close to the shore to get away from the irritating sand, but as I got further out (15-20 feet to sand, I saw pillars/walls of corals, which I'm guessing is still the patch-reef, with many of the cave dwelling fish and swimmers (tangs, butterfly fish, triggers)

Due to me having a very inexperienced swimmer who's mother would kill me if I let her drown I didn't attempt to go further out, I didn't see many branching coral there mostly encrusting and bushy corals but that might be a locational thing, but what he did say did mimic what I saw. Also the reef geek side in me just let myself get tossed about by the current just to feel exactly how it was flowing around, granted I was on the surface, and I'm sure lower down was vastly different but I only dove under to 8-10 feet max with snorkel gear and very limited as even at those depths I could feel the pressure on my ears, and I'm not scuba certified.

But it really was something to think about, how when I started, throw the deep sand bed, and try to crowd corals in etc. Lots to digest, and I recall the earlier days of Dave vs Rich "I've seen sand on a reef" "Maybe really deep" arguments that were a staple of almost every BAR meeting :D Btw where did Dave go?
 
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