Otter (Lutrinae) Care Manual - Association of Zoos and Aquariums

Association of Zoos and Aquariums 151
Otter (Lutrinae) Care Manual
Part 5: ALGAE CONTROL
The presence of algae in an otter exhibit pool has some benefits. A manageable amount can help
control nitrate levels. However, if the level of algae exceeds manageable limits, it makes the water
unsightly, reduces oxygen levels, and potentially reduces water circulation.
Algae need light, appropriate temperature, and nutrients. Control is a concern, particularly in outdoor
otter pools exposed to significant amounts of sunlight. By providing for a suitable amount of shade and
controlling the amount of available nutrients, it is possible to keep algae manageable. Therefore
controlling algae is best addressed in the design phase of the exhibit when solutions to these concerns
can be built into the exhibit design. Some of them can be added after the fact but it is usually more
expensive and troublesome to do so.
Light: If the exhibit is located where the amount of direct sunlight is a problem, a suitable shade structure
should be found or fabricated. Coloring agents added to the water can limit the penetration of light to the
algae growing below the water's surface by coloring the water. It seems most of them turn the water
various shades of blue. Without light, the algae cannot grow. If you have Ultra Violet (UV) disinfection
devices on your filtration system, coloring agents will render them useless and the colored water may be
an aesthetic issue. They claim to have no effects on animals, but blue tinted otters would be very
unsettling.
Trees provide shade but they may also provide falling leaves and branches which foul the water.
They also may be toxic in some instances. In such cases, it would be worthwhile to mount some sort of
structure, such as a net, to deflect the material from the water.
Nutrients: Algae need nutrients to grow. Nitrates and phosphates are the main concerns. Nitrates come
mostly from decaying organic material, found in a variety of sources such as animal waste,
uneaten/leftover food, or decaying leaves and branches. Good hygiene and a properly designed filtration
system will help. In an outdoor exhibit, a raised lip around the pool will divert rain runoff around the pond
and help keep dirt out.
Phosphates usually come in the source water or in food for the animal. At this writing, they can be
dealt with by filtering the source water to remove phosphates (expensive) or by treating the system with
lanthanum chloride in its various commercial forms. To the best of my knowledge, lanthanum chloride is
not harmful to otters but you should check with your vet regardless.
If possible, additional floating plants in the exhibit can compete with the algae for nutrients and also
reduce the amount of available light.
Mechanical Filtration and UV Sterilizers: Mechanical filtration moves undesirable organic matter from
the water column to the filters. This means the algae have a reduced amount of nutrients available to
them. The organic material is typically retained in the filtering material, so keeping the filter regularly
backwashed and working efficiently is vital.
UV sterilizers are installed in line after the mechanical filter. The cleaner and clearer water helps UV
sterilizers function properly. The clearer the water, the more effective the UV. When water is pumped
through the UV sterilizer, the ultraviolet light that is emitted will break down the cell wall of the algae and
the algae will then die. UV’s also have disinfectant capabilities.
UV dose = UV intensity X exposure time.
Make sure to get the appropriate sized UV sterilizer for your pond, and also make sure that the water
flow through the UV allows for sufficient exposure time. Note that the effectiveness of UV drops
dramatically as the temperature goes down. Of course, in terms of algae control in outdoor exhibits, algae
populations are likely to drop down with the temperature.
Water Additives: Most water additives developed for algae control come from the swimming pool and
ornamental pond industry. Many of these products are toxic, not only to algae, but to other forms of life. It
is important to take this into account when considering them for use in an otter exhibit. Always check the
label and the MSDS sheet to make sure that it is safe for the life in your pool.
Additives can either be algiscidal or algistatic. Algiscidal products kill the algae outright. Most metal
ion complexes (copper, silver) fit into this category. Other products, such as barley straw, suppress the
growth of algae in some fashion and are usually used in a preventative manner. It is important to
understand at what stage the algae problem is so that the correct product is used. For example, barley
straw, an algistatic substance, is not as effective after the algae in your exhibit have bloomed. At that