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AQUATIC GLOSSARY
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N

Nanoplankton: Plankton that are 2-20 microns in size, and which pass through an ordinary plankton net but can be removed from the water by centrifuging samples.

Nanometer (nm): A unit of measurement of the wavelengths in the light spectrum.

Neap Tides: Tides occurring when the vertical range is minimal.

Nekton: Pelagic organisms that are active swimmers; for example, adult squid, fish, and marine mammals.

Nematocysts: The cells at the tip of an anemones' (corals) tentacles which "sting" when touched.

Nematoda: An animal phylum that includes all roundworms.

Neritic: Seawater environments landward of the shelf-slope break.

Net Primary Productivity: Total primary production, minus the amount consumed in respiration.

Neuston: Planktonic organisms associated with the air-water interface.

New Tank Syndrome: A term that describes the period in which ammonia and then nitrite levels rise to dangerous quantities before being converted into relatively harmless nitrate. This is due to the fact that in a newly set up aquarium, denitrifying bacteria are not present in any sufficient quantity. It takes about a month under normal circumstances for these bacteria to multiply to the point of being able to keep up with the waste output of the fish.

Niche: A general term referring to the range of environmental space occupied by a species and in which it lives and reproduces. The realized niche is largely determined by interactions with other species.

Niche Overlap: An overlap in resource requirements by two species.

Nickel (Ni): MCL has not been established, but for freshwater the concentration should be less than 0.1 mg/L. Element detected using flame atomic absorption, no specific standard for nickel. Nickel may cause dermatitis and nasal irritation.

Nitrate: Mildly toxic end product of biological filtration or the aquarium nitrogen cycle. At high levels nitrate can be stressful to fish and other aquatic organisms. In aquariums, it should be kept as low as possible. In reef tanks it should always be below 10ppm, while fish only tanks can withstand 30-40ppm. Nitrate levels can be used as a gauge to tell when a partial water change is needed.

Nitrification: The process by which ammonia is changed to nitrite, then nitrate, and finally nitrogen gas. See Nitrogen Cycle.

Nitrite: It is the middle element of the aquarium nitrogen cycle, being converted from ammonia. It is harmful to most aquatic creatures at any level.

Nitrogen Cycle: The nitrogen cycle describes how organic wastes are broken down to less toxic compounds in the aquarium. Fish wastes (i.e., urea) and other organic matter naturally decomposes into ammonia, which is highly toxic. Nitrosomonas bacteria process the ammonia into nitrite, which is also toxic. Nitrobacter bacteria then break down the nitrite into nitrate, which is only mildly toxic. This is as far as the cycle goes in most tanks, though under the right conditions, the nitrate is further broken down to free nitrogen gas or utilized by plants and algae.

Nitrogen Fixation: The conversion of gaseous nitrogen to nitrate by specialized bacteria.

Noctural: Plants or animals that are most active during the night.

Node: The part of the stem from which one or more leaves arise. Also refers to bumps on the lower part of the columella.

Non-Point Source (NPS) Pollution: The source of surface or groundwater pollution originating from diffuse areas without well-defined sources. The most common examples of NPS are chemicals that enter surface water during runoff events from cropland and turf grass, and soil erosion from cultivated cropland and construction sites.

No-Take Reserves: Geographic areas where by law no one is allowed to fish or collect biological specimens. Rules could apply to one or all species.

Notum: The dorsal surface of a body segment; usually of thoracic segments.

Nuchal Hump: An enlarged forehead on male Cichlids.

Nudibranchs: Soft-bodies, gastropod mollusks; sea slugs.

Nuisance Bloom: A rapid increase of one or only a few species of phytoplankton, resulting in densities high enough to cause discoloration of the surface water, possible increase of toxins, and degradation of water quality aspects such as dissolved oxygen.

Nutrients: Any one of a number of inorganic or organic compounds or ions required by organisms for maintenance and growth. Examples include nitrogen and phosphorus.

Nutrient Cycling: The pattern of transfer of nutrients between the components of a food web.

Nutrient Pollution: Pollution containing nitrogen and/or phosphorus which stimulates aquatic algal growth, thus robbing waters of oxygen and killing fish and other aquatic organisms. Nutrient pollution comes from runoff of excess fertilizers, animal waste, and other diffuse sources, as well as from wastewater treatment plants and some industries.

Nutrient-Rich Water: Water containing nutrients, typically high in nitrogen, phosphorus, and organic chemicals that cause the abundant production of plankton.

Nymph: The immature stage in insects which do not undergo complete metamorphosis; the life stage between the egg and the adult in hemimetabolous insects.
 
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