Lotic Water Communities Animals and Plankton Distribution

Plankton are microscopic organisms that live suspended in the water environment, and form a very important part of the freshwater community.

The running water environment offers numerous microhabitats that simulate favourable conditions for many types of animals to successfully succeed the freshwater lotic community.

As with plants, animals in this ecosystem have also undergone evolutionary adaptations to better suit this running water environment. As with plants and their rooting structure, animals have also adapted to cope with the current of the stream.

Some of these animals are sessile, meaning they are immobile and fixed to the one place. These animals are usually small, and include the protozoans and some freshwater sponges.

These animals either remain attached to the mass of a plant or the water bank surface or rock. They usually obtain their food via tentacles which branch out into the flowing water and form a catchment area that can trap microscopic organisms (such as plankton) that is floating downstream.

As much as these sessile animals have developed adaptations to prevent being washed downstream, they are not thought to be one of the important pillars of the freshwater community.

Over time when biotic and abiotic factors affect the landscape of the ecosystem over time, the location of these animals may not be as favourable as it once was, and they are unable to correct this due to their immobile nature. With this in light some animals have developed adaptations that allow them to travel through the water without being inhibited in same spot.

These animals have developed some of the following adaptations over time that helps them cope with prevailing conditions:

Suckers – These suckers attach themselves to a surface that leeches them into position and can also assist movement in any given direction.

Hooks / Claws – The animals have developed very sharp claw – like objects that can dig into any given object and allow the animal to cling to a position or claw their way around the surface.

Body flattening – This adaptation can allow the animal in the water bear less of the brunt of the force of water moving downstream, therefore reducing it as an inhibitor of their movement. This also allows these animals to enter confined areas (such as under stones) that may present a useful environment for them to live in.

Streamlining – Just like man-made transport, animals that have underwent streamlining adaptations on their external appearance means that less resistance is presented by the running water when the animal attempts to move.

Flight – Some animals have adaptations allowing them to fly, removing themselves from the force of the current at ground level and enabling them to move upstream more easily if need be.

Freshwater Communities and Plankton

Plankton are microscopic organisms that live suspended in the water environment, and form a very important part of the freshwater community.

Their movement is aided by convection or wind induced currents. In almost every habitat of a freshwater ecosystem, thousands of these organisms can be found, and due to their small size and simplicity, they are capable of occupying large expanses of water and multiplying at an exponential rate.

Plankton can be subdivided into two categories;

Phytoplankton – Phytoplankton are microscopic plants which obtain their energy through the process of photosynthesis. However, some species of bacteria are also capable of photosynthesis and also fall under this taxonomic category.

They are important to the ecosystem because they are part of the primary producing community and assist in recycling elements such as carbon and sulphur which are required elsewhere in the community.

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Zooplankton – Zooplankton consist mainly of crustaceans and rotifers, and on the whole are relatively larger than their phytoplankton counterparts.

Plankton are relatively unspecialised as their environment does not resist the large populations that can exist within the ecosystem.

Physiologically, there are many evolutionary adaptations that can be found that assist in the buoyancy of plankton which prevent their deaths by allowing them to be suspended in the water away from harm.

They can be found in large amounts in small areas, and as they are consumed in large numbers by herbivores and carnivores, they reproduce asexually to maintain their population.

This is opposed to sexual reproduction with other organisms, which would take longer although it would increase genetic variation within the species.

Factors Affecting Plankton Distribution

Many factors can affect the distribution of plankton in an ecosystem, which has a detrimental effect on the rest of the ecosystem, because as mentioned, they form an essential part of the ecosystem.

Phytoplankton harness new energy from sunlight and provide many other organisms as a means of food due to this while zooplankton are also an important source of food for many species. In light of this, a knock on effect of starvation would occur if there is a lack of plankton in a particular environment.

Phytoplankton are more abundant in areas with a high intensity of light, as they can convert this light energy into chemical energy while higher temperatures increase growth and multiplication of both phytoplankton and zooplankton.

Elementary, the amount of available nutrients in the environment plays a significant role in the distribution and density of phytoplankton.

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