Special Issue Survey of Cetaceans in Captive Care

354 CouquiaudNatural seawater is buffered, meaning it can resistsudden, large changes in pH. Seawater copes withit through the carbon dioxide buffering system (vander Toorn, 1987). It is also referred to as the “hardness”of water. Biological activity, such as nitrification,can alter pH. Alkalinity control is importantwhen chlorination is the primary means of disinfectionas the chlorination removes the alkalinity andmakes the pH more acidic, and also when autotrophicdenitrification mechanisms are installed.Alkalinity is expressed in mg/l of equivalentcalcium carbonate (CaCO3), or meq/l (milliequivalentper litre, 1 meq/l = 50 mg/l CaCO3). The bestlevels are between 100 and 150 mg/l. Alkalinitylevels can be determined by using test tablets orby titration. The presence of salt and chlorine mayaffect the accuracy of these pH-sensitive dyes, andthe latter might “bleach” out the colour and givefalse results (Manton, 1986).Turbidity and VisibilityTurbidity is the amount of small solid particlessuspended in water as measured by the amount ofscattering and absorption of light. Turbidity blockslight and makes the water opaque. It is influencedby the size, shape, colour, and concentration ofsuspended particles in the water. Turbidity is measuredin Nephelometric Turbidity Units (NTU)(Anonymous, 1999). Water preferably will notexceed 0.5 NTU. Levels > 0.1 NTU, combinedwith turbulences in the water circulation system,can enhance air entrapment (Fasik, 1991) (see“Water Flow and Drainage” section). Turbiditymeasurements are usually taken daily. It is measuredby a nephelometer, which is an instrumentmeasuring how changes in light scatter comparedto a sealed calibration vial (Faulk, 1990).Turbidity affects transparency and, therefore,visibility. Although high levels of particles donot usually affect the animals, it is not aestheticallyappealing to the public. It affects the abilityof the trainers to observe the animals, and mightalso reflect some malfunction in the LSS system.Visibility can be measured in vertical or horizontaldistance with a Secchi disk placed in the pool(survey).Dissolved OxygenDissolved oxygen (DO) refers to oxygen gas that isdissolved in the water. Oxygen enters the water byphotosynthesis of aquatic biota and by the transferof oxygen across the air-water interface. Theamount of oxygen that can be held by the waterdepends on the temperature, salinity, and pressure.Colder water holds more oxygen than warm waterdoes, and freshwater holds more oxygen than doessaltwater (Smith, 1990). Even though they are airbreathers and therefore do not depend on DOin the water, cetaceans benefit from good waterquality that is maintained with the help of acceptableDO levels. Mechanical filters operate moreefficiently, and water is less turbid when properlyoxygenated (Faulk, 1990).Ideally, seawater DO levels will be maintainedbetween 5.0 and 8.8 ppm DO (equivalent to mg/l)and testing performed once weekly (Faulk, 1990;survey). Measurements can be made with variousmethods—the most reliable being the iodometricmethod. It is time-consuming and difficult tointerpret. Care must be taken when collecting thesamples for DO measurements; they can neither beleft in contact with air, nor agitated—both problemschange the gaseous contents of the water. Alterationin temperature also affects results. The membraneelectrode method, used in field testing (Anonymous,1992a), is faster and more convenient provided thatthe electrodes are well-maintained.Ammonia, Nitrite, and NitrateAmmonia is a product of urinary waste and has to beremoved for health and aesthetic reasons. Ammonialevels should be kept below 0.05 mg/l of water(Boness, 1996). Chlorination, ozonation, filtration,and water exchange help reduce ammonia levels.Nitrites and nitrates are the other byproducts of urinebreakdown. Nitrite occurs after Nitrosomonas bacteria(among other “nitritifier” bacteria) break downammonia. Nitrite is converted into the less toxicnitrate by Nitrobacter bacteria (again, among other“nitratifier” bacteria) (Faulk, 1990; van der Toorn,1987). Ten mg/l is indicated as a safe drinking waterlimit by the Water Quality Association. A build-up ofnitrate causes a drop in pH level because nitrificationproduces acids. The side effect of nitrate presence isa build-up of algae. Ammonia, nitrite, and nitrate arenot known to be toxic to marine mammals, but theycan lead to an unsightly and unhealthy system due toexcessive algae (Faulk, 1990). Build-up of nitrate ina system can be avoided by the denitrification of aconstant side-stream of the water volume.Readings of nitrites and nitrates will be takenonce daily, and once weekly when the systembecomes stable. Ion analysers, with specific ionprobes, are efficient and reliable. They have to becalibrated for saltwater (Faulk, 1990). Specifictest kits are also available.BacteriaBacterial contaminants, some of which are pathogenic,must be monitored to ensure protectionagainst disease (Faulk, 1990). Bacteria, such asStreptococcus sp., Pseudomonas sp., and Pasteurellasp., among others, have been isolated from fish fedto dolphins. This revealed that food is probablythe prime source of potentially harmful bacteria inthe biological water treatment system (Overath et