Another distinctive niche for the animal community is that above (epineuston) and below (hyponeuston) the water surface. Epineustic animals receive food from the surrounding hydrosere vegetation, where small animals fall into the water from vegetation and are preyed upon by these epineustic animals. Below these surface dwelling animals are a collective of animals called the nekton, which live in the pelagic and profundal regions, though rise to the pelagic regions to feed upon these epineustic animals. Fish are included in this nekton community, which play a vital cog in these freshwater communities. Some of these fish are only temporary members of the community, as they move between fresh and salt water. Anadromous fish spawn in freshwater, but live much of their lives in salt water. Catadromous fish are the opposite of this, and spend much of their lives in the freshwater community. Each way, the fish present in the environment at any time form the link between the upper and lower layers of the freshwater community. Freshwater Lentic Communities & Animals Plants that live partially or completely submerged in water are deemed hydrophytes. A form of symbiosis occurs with these hydrophyte plants, which provide means for algae and other organisms to survive in the surrounding environment. This is because the hydrophytes provide the conditions for the likes of algae and bacteria to survive in the environment. In return, herbivore animals tend to feed on this rich blanket of algae as opposed to the plants themselves, therefore protecting them from being consumed.
Animals in this environment feed on these algae, and also upon the detritus matter, the organic material that is rich on the water bed. It is an area of abundant organic material because the plants that survive in this area provide a source of food, and also a source of shelter which can provide protection from predators or a location to hatch offspring in a closed protected area. The ecological niche alongside the still water banks is occupied by plants called hydroseres, which are partially or totally submerged by water along the banks. Some of these hydroseres are rooted in the water, though some of their leaves penetrate the water surface, while others float on the surface, one side in contact with the water, the other side in contact with the open air environment. In essence, hydroseres possess evolutionary adaptations and dithering respiration rates from land plants that have allowed them to adapt in live in such an environment. Such evolutionary adaptation in plants has meant that their physical structure has changed to suit the environment, and therefore making freshwater plants distinctly unique in appearance. An example of these adaptations is the lack of rigid structures in freshwater plants. This is due to the density of the water (much higher than that of an open air environment), which 'pushes' against the plant in its daily life. This allows such plants to be more flexible against oncoming water tides, and prevents damage to the plant. As plants require a minimum concentration of gases in their diet such as carbon dioxide, they require a degree of buoyancy so that contact can be made with the open air environment. Adaptations may include; Air Spaces - Air spaces in the plant will decrease density and increase buoyancy. Broad Leaves - Broader leaves will spread their weight more evenly across the water surface allowing them to float. Waxy Cuticle - On the upper half to allow water to run off the surface to prevent the weight of the water dragging the leaves under the surface In still water plants, the method of transpiration as a whole is altered in freshwater plants, due to the abundance of water in their external environment, or in the case of some, uptake of water from a wet environment, but loss of water via their leaves in the open air environment. An example of transpiration problems for such plants is as follows; The plant lives in a marshy environment, where roots uptake water from soaked ground, allowing plenty of water to be up taken and transported up and across the plant. The difference in water concentration between the plants' leaves and the open air environment is so great that much of the water absorbed is lost to the external environment, meaning the plant loses water rapidly Such a problem is solved by evolutionary adaptations. These adaptations essentially address the issue of re-balancing the critical deviations between the water that is absorbed and lost in a plant.
Freshwater Plants & Nutrients On top of the need for plants to maintain a suitable water concentration in plant cells, they also require various nutrients which are found in the nutrient rich soil and the surrounding waters. In addition to the carbon, hydrogen and oxygen required for photosynthesis, plants require a range of macro-elements, notably magnesium (Mg), nitrogen (N), phosphorous (P) and potassium (K). Some of these elements, notably the gases, are readily available in the atmosphere, while carbon dioxide is produced from decomposing organic matter. Other elements are readily available in the soil, with nutrients becoming available from decomposing matter adding to the fertility of the surrounding soil. Oxygen becomes available from the photosynthetic activities of plants, which provide the link between oxygen and carbon dioxide concentrations in the area. Lotic Communities Running water freshwater communities are also known as lotic communities (lotic meaning running water). Lotic communities are formed by water being introduced to the freshwater body from a variety of sources; Rainfall - A percentage of water in the running water community will be present as a result of rainfall directly entering it. Ground Surface Water - Deriving from previous rainfall, water will enter the running water community. Underground Water - Water absorbed into the soil can also enter. Water Table - Deep underground there is a 'water table' which can also provide water for the running water community. Fig