Aquatic Ecology

Exam 1

Alkalinity

is a measure of carbonate and bicarbonate ions, which buffer changes in pH. Optimal alkalinity is 100-400 ppm. Levels below 50 ppm result in rapid pH fluctuations, which are detrimental to most aquatic life.

Ammonia

results from protein metabolism. Ammonia toxicity is greater at higher temperatures and pH. Total ammonia starts to become limiting around 1 ppm.

Carbon Dioxide

is optimal at levels of 5-10 ppm, but becomes limiting at levels above 10 ppm.

Conductivity

is a measure of how well electricity is conducted through water, which is dependent upon the level of dissolved ions in the water. Thus conductivity is a crude measure of dissolved solids, or nutrient level. Optimal conductivity ranges from 100-300 umhos.

Current Velocity

is often a limiting factor for stream living fish. Flattened head, large pectoral fins, and a streamlined body form indicate a fish is adapted for high current velocities. Current velocity limits the distribution of some closely related species such as margined madtoms (prefer moderately swift waters) and tadpole madtoms (prefer stagnant waters).

Depth

can be a limiting factor in a number of ways. Many aquatic organisms are only found a specific depths. For example, sunfish and pickerel are only found in shallow water. In general, as depth increases biomass and productivity decreases. However, in our area, ponds should be at least 10 feet deep to reduce the frequency of winter kill, which in itself reduces biomass and productivity.

Elevation

can be correlated with a number of limiting factors. In our area, trout usually don't occur below 1500 feet (correlated with temperature). High elevation lakes have a shorter growing season and are fed by rain water which is low in nutrients. Thus high elevation lakes have low productivity because of shorter growing season, colder water, low pH and low nutrients.

Embeddedness

is a measure of how deeply rocks are buried in the stream substrate. Salmon parr require space under rocks for refuge particularly in the winter. Many stream living fish such as sculpins, darters and fat head minnows need space under rocks to spawn. As embeddedness increases, spawning areas, thus production and biomass decreases for these species.

Habitat

is made up of a number of components that may be limiting. Riffles habitat has a high biomass of invertebrates and a relatively low biomass of fish. Blacknose dace are most numerous in riffles. If the area of riffles is limited than blacknose dace population will be low.

Hardness

is a measure of magnesium and calcium ions. Optimal levels of hardness are 100-400 ppm, 50-100 ppm is marginal, and levels below 50 ppm are limiting.

Heavy Metals

such as cadmium, copper, lead, mercury, zinc become toxic at levels as low as .002 ppm. Acid waters leach heavy metals from the substrate.

Hydrogen Sulfide

is very toxic to aquatic organisms. Continuous exposure to levels as low as .002 ppm is lethal to most fish. Hydrogen sulfide is more toxic at low temperatures and pH.

Instream Cover

provides feeding stations and protection for trout. Thus, increases in instream cover results in increases in biomass and density.

Light

is required for primary production. Generally trout streams are most productive when half the stream is shaded and half receives sunlight. Too much or too little light reduces productivity. In areas of prolonged cloud cover (e.g. the eastern side of the Great Lakes) production is significantly reduced.

Oxygen

is required for metabolism by most aquatic organisms. It becomes limiting for most fish at 5 ppm.

pH

is a measure of hydrogen ion concentration. Optimal pH for most aquatic organisms is 6.5 to 8.5. Brief exposure to higher and lower pH is often not limiting.

Phosphorus

is the most limiting nutrient in standing waters. Optimal range is .01-3.0 ppm.

Salinity

is seldom limiting for euryhaline organisms. Stenohaline organisms have a relatively narrow range of salinity tolerance. For example, starfish can not tolerate salinities below 25 0/00, while oysters and soft shelled clams can live in salinities of 5 0/00 to 40 0/00.

Shoreline Curves

increase the edge (or ecotone) effect and therefore increase productivity. Round standing bodies of water are less productive than bodies of water with multiple embayments and shoreline curves.

Sinuosity

is a measure of how many curves a stream has in a given length (i.e. the length of the stream divided by the straight line length to travel the same distance). As sinuosity increases the diversity and biomass of fish increases.

Space

is required by all living things. Stream living brown trout require a cube 3 times their length, while brook trout require a cube the size of their length.

Stream Gradient

is usually correlated with other factors that are limiting. High gradient streams have lower productivity and limited species diversity because of their high velocity and low sinuosity.

Stream Order

is a classification system based on the number of tributaries converging on a stream. As stream order increases biomass and productivity increases. Thus first order streams are the least productive, and have the lowest diversity and biomass of invertebrates and fish.

Structure

can include shoals, submerged trees and artificial reefs. Productivity in all areas of the ecosystem is often highest around structure. The presence and density of freshwater fish such as rock bass and smallmouth bass and marine fish such as cunner, tautog, sea bass are highly dependent upon structure.

Substrate

has multiple impacts on the distribution and production of aquatic organisms. Salmonid production is often limited by the amount of spawning gravel. Rooted plants only occur in the presence of fine sediments (sand and silt), while marine algae only occurs in the presence of coarse sediments (cobbles and boulders).

Temperature

optimum differs among species and life functions within the same species. For example, bay scallops, quahogs and oysters require temperature above 20C for reproduction, but have good growth at temperatures below 20C. Most salmonids stop feeding at 2.5C, have optimum production (growth and survival) at 15C, and are stressed at temperatures above 20C. Generally, optimum temperature is 15C for
cold-water fish, 20C for cool-water fish, 25C for warm water fish and 30C for tropical fish.

Turbidity

is a measure of suspended solids. High turbidity reduces photosynthesis, and makes it difficult for aquatic animals to find food and breath. Optimal turbidity of standing waters is 0-2 JTU (NTU or FTU) and 0-10 JTU for flowing waters