Some Other Useful Applications of Turf Scrubbers

We have already mentioned the value of algal turf scrubbers as filters for estuarine and mangrove ecosystems, and their value as refugia and seed for mariculture of plant rocks. There are additional benefits to their use that wre want to mention as well. The incorporation of a flip-flop day/night cycle, which has the scrubbers illuminated at night while the display tank is dark, achieves some nice stabilizing benefits (Adey, 1983). The oxygen produced by the photosynthesizing algae boosts the level of dissolved oxygen in the system at a time when it would otherwise drop. Photosynthesis also removes CO? produced by the organisms in the dark tank, thereby stabilizing the pH. Finally, turf scrubbers do remove heavy metals and other toxins from the water (Adey and Loveland, 1991).

These applications are useful and effective, but turf scrubbing is not the only means of achieving these ends, in the 'Berlin method", the addition of calcareous water by a water level sensing system stabilizes the pH at night. Jaubert's system actually encourages the pH drop at night to help dissolve calcium in the substrate, thereby maintaining the dissolved calcium level and alkalinity. Protein skimming helps maintain the level of dissolved oxygen by removing oxygen-scavenging compounds, and removes he aw metals and other toxins. Activated carbon also removes heavy metals and other toxins.

Of course algal filtration can be employed within the aquarium. With strong illumination and enough herbivores such as tangs and the small herbivorous snails (Turbo and Astraea spp.), the algae growing on the rocks and glass can be maintained at the highly productive state where it is almost not perceptible because it is being consumed as quickly as it grows. If the system employs strong water motion, then the herbivores' lightweight fecal pellets can easily be trapped in a mechanical or settling filter, and removed from the system. With protein skimming and activated carbon the leachate from such algae is easily managed.

Outside of the aquarium realm turf scrubbers have advantages too. The ability to concentrate heavy metals and other toxins from the

water is a key feature in what we believe is a brigl it future for algal turf scrubbing in wrater purification and sewage treatment applications. Scientists, including Dr. Adey, are studying the amazing abilities of plants and microorganisms to purify both air and water. We believe the future standard in "filtration" devices for water purification and treatment of sewage or industrial waste will include a form of turf scrubbing and duplication of wetland or marsh ecosystems with rich populations of microorganisms that consume toxic compounds and convert them into harmless ones. Such wastewater treatment technology combines low cost, low maintenance, and results better than any artificial filtration. The use

■ j of huge protein skimmers would enhance this simple system of water treatment. The use of algae, higher plants, and protein skimmers (foam separation columns) is already in practice in wastewater treatment, but the state of the ait has yet to reach its full potential.

WTe wish to dispel two myths about nitrate that Dr. Adey s philosophy proposes. The first is that even a low concentration of nitrate is toxic to corals (Adey, 1983). As a general statement this claim is certainly false. It is possible that certain species may be affected by nitrate more severely than others, but we have j J

observed many delicate species of Indo-Pacific and Caribbean corals growing extremely well at nitrate concentrations as high as 40 mg/L as nitrate ion. We have not witnessed a direct relationship between nitrate level and coral health, but acknowledge that low nitrate levels in the aquarium are better for the stability of alkalinity and the whole ecosystem. We are not promoting the intentional maintenance of high nitrate. We only wish to point out that it can be demonstrated that nitrate itself does not harm corals. The other myth is that one can only achieve super low nitrate levels by using algal turf scrubbing (Adey, 1993). When protein skimming is combined with sufficient photosynthetic invertebrates, live rock, and anaerobic zones (sand bottom, live rock anaerobic cores), nitrate does not accumulate. The nitrogen can be removed by the photosynthetic organisms and protein skimming before it is converted to nitrate, and any nitrate produced in the system is easily denitrified in the anaerobic zones. It is true, however, that the natural ability to reduce the nitrate can be exceeded by excess food inputs. Turf scrubbing could be employed to solve such a problem, but so could additional protein skimming, or denitrification. The denitrification that takes place within the rocks and deep sand beds is a most efficient means of removing nitrate from the system, and it works fine even in the absence of protein skimming, as we showed in the example of Jaubert s system. Denitrification alone in this system works to keep the nitrate level low, consistently below 0.015 mg/L (Jaubert, 1991).

The use of dump buckets to return the water to the main aquarium, and on algal turf scrubbers is also problematical. Some dump bucket designs require frequent maintenance to ensure that they continue to operate properly. The salt from splash gets into the pivoting parts, and wears the surfaces until they don't turn as easily. Furthermore, the fine salt spray generated by these devices promotes corrosion problems in the immediate vicinity of the aquarium. The surge provided by the dump bucket, however, is very beneficial, and a significant improvement over mere circulation. Some mesocosm exhibits employ a different surge device, using air displacement in a chamber attached to the aquarium (see topic: water motion, next section).

A scene from the Great Barrier Reef Aquarium in Townsville, Australia. A.J. Nilsen.

Coral ReefsBig Algae Turf Scrubber

Viewing window at the Great Barrier Reef Aquarium in Townsville, Australia. A.J. Nilsen.

A portion of the enormous array of algal turf scrubbers located on the roof of the aquarium. A.J. Nilsen.

Mid 3/4 of Walter Adey's 130 gallon reef. Invertebrates, R to L: Palythoa caribaeorum, Eunicea sp., Diploria clivosa with Pontes asteroides behind, Diploria strigosa, Montastrea cavernosa, Sinularia sp., Tridacna maxima, Sarcophyton sp. Algae: Halimeda discoidea, Caulerpa racemosa, C. sertularioides, Amphiroa fragillissima. S.Gill.

Reef Aquarium Turf Scrubbers Pictures Stony Corals

Close up of Diploria clivosa (brain coral) and Eunicea sp. (gorgonian) with Amphiprion ocellaris in Walter

Adey's 130 gallon reel microcosm. S.Gill.

Cave entrance in the same tank with plate-forming crustose coralline Mesophyllum mesomorphum on wall. Dark red patches are Peyssonnelia sp. and Schizothrix. Ricordea florida (corallimorpharian) is upper right; Pseudochromissp. (fish) below. S. Gill.

South Ricordea ReefOntario Science Centre Tank

Reef microcosm at the Ontario Science Centre, Toronto, Canada. Note the construction of the reef, the colour of the lighting, and the colour of the water. J.C. Delbeek.

A scene from the reef microcosm at the Pittsburgh Aquazoo. See text. J.C. Delbeek.

A young colony of the Caribbean coral Pontes asteroides that settled on an I ndo-Pacific Tridacna maxima clam in Walter Adey's 130 gallon reef microcosm. Pontes asteroides may form planulae asexually like Pocillopora damicornis. S. Gill.

Dr. Adey claims his systems are like wild meadows, while most aquariums are maintained like gardens. This cannot be a completely accurate analogy. It is our understanding from speaking with him that the less than ideal condition that we have seen in reef exhibits using turf scrubbing has been the result of poor husbandly technique or neglect by the keepers, or modifications and additions that he does not recommend, or physical stresses to the system beyond anyone's control (i.e. temperature control difficulties at the Smithsonian). Once a reef is enclosed by glass it can no longer be wild. On the ecosystem level, it depends on the aquarist to provide the proper physical parameters, and on a smaller scale, some specimens may require occasional pruning or re-positioning to avoid being totally lost. This requirement diminishes with increasing size of the system, and higher species diversity and abundance, which is part of the message that Dr. Adey is offering.

We do not want to diminish his message, which is that we should strive to cultivate whole ecosystems with our reef aquaria, not merely individual species in a garden or zoo-like setting. We agree with this, and believe that the book Dynamic Aquaria offers a valuable perspective for all aquarists, not just the reef keepers. Our criticisms are only to remind people that a reef ecosystem with few corals is like a forest with few trees.

Reef aquaria can be maintained by a variety of methods, as long as the critical physical parameters of temperature, light, and water movement are within certain limits, and the accumulation of plant nutrients is kept in check. Not only are there many ways to maintain a reef aquarium, there are also many types of "reef aquaria." Some aquaria emphasize mostly soft corals, Octocorallia, some mostly stony corals, Scleractinia. Some are full of upright algae such as Caulerpa and Halimeda, or smaller turf forming species, while others are dominated by pink and purple coralline algae. Different methods of filtration and water motion affect the ability to create these different types of closed ecosystems, and therein lies a crucial point that must be understood. Choosing the "best" system or the simplest one really depends on the type of environment you wish to create. Even differences in the type of make-up water used can have a dramatic impact on the resulting environment. In this regard, Dr. Adey's philosophical distinction between creating a whole living ecosystem versus a display for numerous chosen species applies. Most aquarists attempt the latter, while Adey is a proponent of the former. In our opinion, the best

philosophy combines the two, recognizing that the constraint of size (i.e. the captive environment) limits the ability to support all types of plants and animals found on the reef, and that it is the aquarist who places the creatures within the tank, so it is his/her responsibility to plan for the proper long term maintenance of each specimen.

We present all of these systems here because each one teaches something valuable about the creation of a captive ecosystem. As an aquarist, you will develop your own successful technique that may incorporate elements of several systems.

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Responses

  • Malva Brandagamba
    How big is a scrubber?
    7 years ago

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