Fisheries and Aquaculture Management

Lecture 4:

Aquatic Resources

Aquatic Resources

When considering aquatic habitats, many variables come to mind.

Obviously, there is a continuum of salinity ranging from essentially distilled water at glacier faces and high mountain streams, to other freshwaters, to estuaries where fresh and salt waters mix, to oceans, to hypersaline environments such as the Great Salt Lake.

Current is another factor; water may be still and stagnant, or flow in currents of various velocities.

Currents may be unidirectional, such as in streams, or multidirectional, such as when waves wash across a beach.

Aquatic Resources

Aquatic habitats may occur in open water, or they may be associated with the bottom of the body of water, and both will be affected by the mechanical and chemical makeup of the local geology.

All sorts of daily and seasonal temperature regimes can be expected.

Aquatic habitats vary in the amount of light they receive and range in size from tiny pools at the base of a plant to the Pacific Ocean in size.

Characteristics of Aquatic environments:Freshwater vs. Marine Habitats

The obvious difference when comparing these two extremes is the salinity of the water, and the differences associated with that salinity.

One obvious consequence of the difference in salinity is the change in osmoregulatory strategy that must take place.

Many organisms in salt water are osmoconformers, essentially isotonic in relation to the seawater, although they may regulate certain ions at levels different from those of the surrounding ocean.

Characteristics of Aquatic environments:Freshwater vs. Marine Habitats

A fair number of marine organisms are hypotonic in relation to the seawater and must therefore actively take up water to replace that they lose to the seawater.

Of course, in taking on that water, they usually take in too many ions, and they must have some mechanisms for expelling those ions.

Organisms in freshwater have the reverse problem. They tend to take on water from the environment, and, in expelling the excess water, may lose important ions.

Since freshwater is too dilute to make a good cytoplasm, it is no surprise that all freshwater organisms are hypertonic to the environment and that in consequence they must be active osmoregulators. Most have some mechanism to pump ions into the body.

Characteristics of Aquatic environments:Freshwater vs. Marine Habitats

Another difference between freshwater and saltwater, besides the ion concentration, is the depth/ light.

The depth of freshwater systems is usually much shallower than that of marine systems.

Depth is not a critical factor as long as the bottom of the body of water is above the LCP (light compensation point).

Though, that freshwater is highly susceptible to turbidity caused by soil erosion, thus the LCP might be artificially raised above the bottom.

Marine systems, at least those away from the coast, are not usually affected by turbidity.

Characteristics of Aquatic environments:Freshwater vs. Marine Habitats

Temperature relations in marine systems as opposed to freshwater systems are again largely dependent on the relative size of the systems.Generally, the larger marine systems show virtually no diurnal temperature shifts, and very small seasonal ones.On the other hand, small freshwater habitats may experience daily shifts in temperature of over 300C, and pronounced seasonal temperature changes exist even in bodies of water as large as the Lauretian Great Lakes.Oceanic systems are a large part of the global weather system, which in general moves heat from the warm equator to the cooler poles.Oceanic areas exposed to currents involved in this heat transfer may be much warmer or cooler than would be expected due to their latitude alone, for instance, consider the relative warmth of the ocean near Britain due to the Gulf Stream, or the cold water off the southern California coast.

Aquatic PlantsThousands of plant species live in freshwater habitats around the world

Many species of aquatic plants are essentially cosmopolitan, meaning that they are widely distributed around the world.

Some of the widest distributions are attributable to human activities.

Humans have accidentally (sometimes intentionally) transported seeds, fruits, or vegetative clones from one pond or watershed to another, but many of the cosmopolitan distributions are attributable instead to birds, particularly waterfowl, which inadvertently transport the plant propagules when lodged in their features or trapped in mud on the feet.

Q. What roles does aquatic plants play in the aquatic environment?

1.Microscopic plants (algae) form the base of the aquatic food chain.

1. These are Primary producers e.g. “phytoplankton” (or, plant plankton), these plants are eaten by zooplankton (or, microscopic animal plankton).

2. In turn, zooplankton are eaten by small fish, which are eaten by larger fish, and so on up the food chain to humans and other top predators.

Function, Physical Characteristics and Adaptation of Aquatic Plants

Q. What roles does aquatic plants play in the aquatic environment?

•Larger algae and flowering plants (macrophytes) provide habitat and shelter for fish, fish food organisms, waterfowl, and other wildlife.

•Macrophytes provide food for insects, waterfowl, and mammals such as muskrats and beavers. However, bass, bluegill, and catfish do not, as a rule, eat macrophytic vegetation.

•Since all plants, including those that grow underwater, produce oxygen as they photosynthesize, they are the major source of oxygen for aquatic animal life.

Q. What roles does aquatic plants play in the aquatic environment?

5.Rooted plants stabilize shorelines and bottom sediments. They absorb nutrients and filter pollutants from runoff, which improves water quality.

6.A diverse aquatic plant population adds beauty to a water body. Many people recognize and appreciate the aesthetic value of aquatic vegetation, whether in a backyard fishpond, around a retention pond, or along the shoreline of a large lake.

Q. What roles does aquatic plants play in the aquatic environment?

7.Control of algae. Plants are basically highly evolved algae, and have the same essential nutritional requirements. However, healthy aquarium plants can do a better job of obtaining nutrients from the water by stripping phosphate

8.To encourage the breeding of fish. Many fish, such as tetras (minnow like fish), practice "egg scattering." This breeding ‐ ‐strategy is exactly what it sounds like: fish lay non-adhesive eggs all over the tank and provide minimal care. In this case, bushy plants can keep the eggs safe from their hungry parents. Similar strategies work with livebearers. Even sophisticated spawners like Bettas use plants; males use them in their bubble nests and females use them for refuge.

Because of these benefits, some aquatic plant growth is desirable.

Eliminating native aquatic vegetation from a site should never be the goal of a management plan.

However, excessive aquatic plant growth can lead to several common problems:

• Too much vegetation can impair recreational activities such as swimming, fishing, and boating.

• Excessive plant growth can provide too much shelter for small fish and reduce predation. This leads to an overpopulation of prey fish.

3. An overabundance of aquatic plants and algae can reduce oxygen levels in the water, which can contribute to fish kills. Fish kills that are vegetation-related can occur in the summer or winter.

4. Certain algae impart foul tastes and odors to water. This is an extremely important concern for the managers of municipal and private drinking water sources.

5. Excessive plant growth can impede water flow in drainage ditches, irrigation canals, and culverts and cause water to back up.

6. Excessive plant growth lessens aesthetic appeal and lowers property values.

7. Excessive plant growth can trap sediment and debris, gradually filling in bodies of water. When the plants die and fall to the bottom, they accelerate this process.

8. Aquatic weed growth can provide the quiet water environment that is ideal for mosquito larvae development.

9. Invasive plant species such as Eurasian water milfoil and purple loosestrife can completely destroy stands of native vegetation. This can have adverse effects on the animals that depend on the native vegetation for habitat and food.

Characteristics common to aquatic plants:

1.Most aquatic plants do not need cuticles or have thin cuticles as cuticles prevent loss of water.

2.Aquatic plants keep their stomata always open for they do not need to retain water.

3.On each side of their leaves are a number of stomata.

4.Aquatic plants have less rigid structure since water pressure supports them.

Function, Physical Characteristics and Adaptation of Aquatic Plants

Characteristics common to aquatic plants:

5.Since they need to float, leaves on the surface of plants are flat.

6.The presence of air sacs enables them to float.

7.Their roots are smaller so water can spread freely and directly into the leaves.

8.Their roots are light and feathery since they do not need to prop up the plants.

9.Roots are specialized to take in oxygen.

Adaptation of aquatic plants is evident by their structure: deeply dissected and waxy leaves, specialized pollination mechanism and variation in growth pattern.

These are the types of plants based on adaptation:

1. Totally submerged plants – Are considered true water plants or hydrophytes. Example: Water starwort submerged in a marsh pond, eel grass, sago pondweed, water milfoils etc

2. Floating plants – Are rooted in floating water (example: water lily) or not rooted in the sediment just on the surface (example: duckweed, water lilies, American lotus, spatterdock and water shield).

3. Swamp plants – Are emergent plants with their lower part submerged. Example: reed mace, .

Function, Physical Characteristics and Adaptation of Aquatic Plants

Function, Physical Characteristics and Adaptation of Aquatic Animals

The characteristics of aquatic animals are as follows:

1.Most of their Species live in water and some of them live on the land

2.They have paired and unpaired fins which help them to swim.

3.They have either webbed limbs or limbs are modified to paddles for swimming.

4.Their body shape is streamlined and their bones are light and spongy.

5.The skull undergoes modification to form a slender snout.

6.The neck is reduced and external ears are disappeared.

Function, Physical Characteristics and Adaptation of Aquatic Animals

Adaptation of Aquatic Animals

Marine organisms have adapted to the great diversity of habitats and distinctive environmental conditions in the marine environment.

Adaptations are many and varied but they are generally grouped into 3 main categories:

1. structural,2. physiological and3. behavioural.

Function, Physical Characteristics and Adaptation of Aquatic Animals

Adaptation of Aquatic Animals

Structural adaptations

Seawater is much denser than air – as a result, there are vast numbers of microscopic organisms suspended in it. Cockles, as well as many other bivalves, are filter feeders.

They have adapted specialised siphon structures to filter these organisms and any other particles of food from the surrounding water.

Estuaries have quite variable conditions – tides, waves and salinity fluctuations affect the animals and plants that live there on a daily basis.

Many animals, such as cockles, are adapted to live in these conditions. They have strong shells that protect them from wave action, drying out and the prying beaks of predators.

Function, Physical Characteristics and Adaptation of Aquatic Animals

Adaptation of Aquatic Animals

Physiological adaptationsPhysiological adaptations enable the organism to regulate their bodily functions, such as breathing and temperature, and perform special functions like excreting chemicals as a defence mechanism. Some marine mammals, such as whales, migrate over large distances and may spend time in a combination of arctic, tropical and temperate waters. To cope with these temperature changes, they are endothermic or ‘warm blooded’. This means that they are able to maintain a constant body temperature that is not dependent on the surrounding water.Slow-moving species have adaptations that help protect them from predators. For example, many marine organisms can only move slowly or not all. This means they cannot easily get away from mobile predators, and they have other adaptations to protect them from being eaten. These can include chemical defences in their skin, for example, sea stars.

Function, Physical Characteristics and Adaptation of Aquatic Animals

Adaptation of Aquatic Animals

Behavioural adaptations

Behavioural adaptations are learned or inherited behaviours that help organisms to survive, for example, the sounds made by whales allow them to communicate, navigate and hunt prey.

Bryozoan colonies are found in high numbers on the continental shelf in New Zealand. They look like plants but are actually made up of hundreds of tiny individual animals that have banded together in order to more successfully find food and survive predation.