Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 124

In natural systems, bacteria break down organics rapidly to supply algae and plants with nutrients to grow. As a result, nutrients typically do not accrue in natural systems (without outside inputs like nitrogenous fertilizer). In artificial systems, when algae and plants are discouraged to grow, organic and inorganic end products build up. Biological filtration is the process in which unnaturally large populations of relatively few bacteria species convert organic waste products. Ecological filtration is the natural process centered on using balanced, diverse populations of vascular plants, algae, microorganisms (bacteria, archaea, protozoa), and/or macroinvertebrates to form an environment that cycles and/or removes waste products in the aquarium while balancing water chemistry. These organisms can also provide a rich source of nutrition for herbivores and omnivores. This type of living refugium filtration is simple to design and operate, and is usually inexpensive compared with traditional methods. This holistic approach may improve animal health, habitat operations, and aesthetics.

Figure A3.12 A sulfur denitrification system.

Refugium filtration based on the previously described deep sand bed filters and the use of live rock have become common in tropical reef aquariums where living corals are the predominant animals. Live rock consists of rock and aragonite originally formed by corals or other calcareous organisms and is heavily colonized by a host of micro‐ and macro‐organisms that live in and on it. These organisms perform anaerobic and aerobic types of biological filtration in an ecologically balanced way. There are many artificially established varieties of live rock available on the market today; these reduce the need to harvest from the ocean environment.

Algae‐based refugium filters are often called algal turf scrubbers or algal scrubbers. They consist of a shallow trough or raceway or rotating wheels connected in‐line with the main system (Figure A3.13). They often have screens to increase the surface area. They need to be well‐lit by light emitting diodes (LEDs), high‐intensity metal halide, or very high‐output (VHO) fluorescent lamps with ample levels of photosynthetically active radiation (PAR) in a cycle opposite to that of the main habitat (Adey and Loveland 2011). Natural sunlight to augment treatment during the day can also be used, if access to unfiltered sunlight is possible. The balanced nature of these filters should provide a robust and diverse microbiome to naturally compete with potential pathogens, rather than serving as a “pathogen reservoir”.

Figure A3.13 Algal scrubber wheels.

Source: Image courtesy of Chris Limcaco, Algaewheel Technologies, LLC.

In tropical seawater, red and blue‐green algae and diatoms usually dominate. With high‐intensity lighting, diatoms will colonize the turf first, followed by the blue‐green algae. Green and brown algae are always present, but in smaller numbers. Once the algal turf matures, it must be continually grazed (e.g. by amphipods or chironomid insects living in these systems) or it goes through succession and produces a less productive macroalgal forest (Adey and Loveland 2011). Periodic human intervention to manually harvest the algae with a tool like a plastic putty knife is occasionally needed.

In the past, aquarists have tried to force the ecological scrubbers to grow edible algae such as Caulerpa spp. While this appears to be a good idea, it has resulted in collapse and the sudden release of nutrients and metals as the plants decay. Ecological scrubbers should by managed with what naturally grows and evolves as this will lead to a much more stable system.