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Aquatic Ecology. Aquatic ecosystems consist of communities of living organisms—ranging from microorganisms to large fish and mammals—and the environment they inhabit.
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Aquatic ecosystems consist of communities of living organisms—ranging from microorganisms to large fish and mammals—and the environment they inhabit. • Relationships between different types of living organisms, and their interactions with their environment, are often complex and interdependent. • Interdependence is depending on one another.
Understanding these relationships and how human actions can affect them allows for better management of aquatic resources. • This section describes aquatic environments, the types of organisms that inhabit them, and the processes affecting life in these habitats:
This lesson will focus on aquatic environments, the types of organisms that inhabit them, and the processes affecting life in these habitats. • The lesson sequence is: • Introduction to Aquatic Ecology • Life in Aquatic Ecosystems • Aquatic Habitats • Aquatic Organisms • Factors Affecting Aquatic Ecosystems
Introduction to Aquatic Ecology • Ecology: The scientific study of how organisms interact with each other and with their environment. • This includes relationships between individuals of the same species, between different species, and between organisms and their physical and chemical environments. • Aquatic ecology includes the study of these relationships in all aquatic environments, including oceans, estuaries, lakes, ponds, wetlands, rivers, and streams.
An ecosystemis a community of living organisms and their physical and chemical environment, linked by flows of energy and nutrients. • Ecosystems function as a discrete ecological unit, and can be defined at a variety of scales. • For example, the Athabasca River basin can be considered an ecosystem, as can a small pond, a log, or the entire planet.
The boundaries of an aquatic ecosystem are somewhat arbitrary, but generally enclose a system in which inflows and outflows can be estimated. • Ecosystem ecologists study how nutrients, energy, and water flow through an ecosystem.
The physical characteristics of aquatic habitats affect the types of organisms found there. • Living organisms in a particular environment are directly affected by environmental characteristics such as nutrient concentrations, temperature, water flow, and shelter. • Only the organisms that are able to survive in the conditions of a particular habitat and use the resources available there will thrive.
Interactions between living organisms also affect the type of organisms found in an aquatic ecosystem, as competition for resources (e.g., food, habitat) and predation affects species abundance and diversity. • In turn, the living organisms in an environment can influence some aspects of their environment (e.g., beaver dams can change water flows).
Understanding the basic components of aquatic ecosystems and the interaction among living organisms and their environment can lead to better management of human impacts on these systems.
Life in Aquatic Ecosystems • Organisms living in aquatic ecosystems are dependent on the resources of their environment. • Biological communities—including the types of animals present and their relative abundance—are also shaped through the interactions with other organisms.
All living organisms need water, energy, carbon, nutrients and oxygen to stay alive, grow and reproduce. • Living organisms differ in their specific requirements and in the processes they use to secure these essentials.
Water: • Living organisms are primarily composed of water and cannot function without it. • In aquatic habitats, water is a source of oxygen (i.e., dissolved oxygen) and food (e.g., suspended particles of organic matter).
Energy: • Almost all energy used by organisms is derived, directly or indirectly, from the sun; the exception includes some bacteria that derive energy from chemical sources (e.g., by oxidizing inorganic compounds such as sulphide). • Plants use energy from sunlight to manufacture a range of sugars by the chemical process of photosynthesis.
When animals eat plants, they make use of the energy 'fixed' by the plant. • Organisms who cannot manufacture their own food using the sun's energy must consume other organisms to obtain carbon, energy and nutrients.
Carbon: • Carbonis a building block in the sugars, proteins, and fats that make up the tissues of all organisms. • In plants, carbon dioxide and water, together with energy derived from sunlight, are incorporated into sugar molecules during photosynthesis.
The sugars are stored in the plant body in the form of starch, but can be combined with other chemicals to form different types of molecules (such as protein). • A diagram of the carbon cycle is shown on the right.
Nutrients: • Nitrogenand phosphorusare the most important nutrients for the growth of algae and aquatic plants, as they are often in short supply relative to the needs of these organisms. • Other nutrients, such as potassium, iron, sulfur, and selenium, are also required, though these are usually abundant relative to the amount that algae and plants require.
Within aquatic environments, nutrients are derived from the erosion of minerals and soils within the basin, organic matter, or from human inputs. • The addition of nutrients to aquatic systems—for example, from industrial outputs, sewage or agricultural runoff—can have major impacts on aquatic systems, sometimes leading to eutrophication (excess nutrients leading to excessive plant growth).
Oxygen: • Oxygen is a basic requirement for most organisms, although there are some microorganisms that can grow in (or even require) environments without oxygen, while others can tolerate very low levels. • Organisms that spend their entire life in water ‘breathe’ oxygen dissolved in the water.
Energy and Food: • Every organism must acquire energy to live, grow and reproduce. • In aquatic ecology, biologists often classify organisms according to how they obtain energy. • Because sunlight is the ultimate source of energy used by organisms on the earth's surface, a basic distinction lies between those who use its energy directly—autotrophs—and those who receive it indirectly by consuming other organisms—heterotrophs.
Autotrophs: • Autotrophs, or producers, are organisms that can manufacture their own organic material from inorganic sources. • Most autotrophs carry out this process using photosynthesis, the process by which plants and algae use solar energy to combine carbon dioxide with water to produce starch, sugars and oxygen.
Photosynthesis is the most important biological process on the planet, and its products drive the biological activity of nearly all ecosystems, including aquatic environments. • The oxygen produced is available to be used by other organisms, making photosynthesis an important controller of carbon dioxide and oxygen in the environment.
Photosynthesis in aquatic systems is carried out by a wide variety of autotrophs, which range in size from microscopic single-celled organisms to large aquatic plants called macrophytes. • Autotrophs are primary producers, because they produce the first level of organic carbon from inorganic compounds. • Ultimately, all other types of organisms (heterotrophs) are dependent on the organic carbon produced by autotrophs. Water-lily - Macrophyte Aquatic Bed
Because photosynthesis depends on sunlight, the distribution of autotrophs is reliant in part on the amount of light available in an aquatic ecosystem. • In shallow, stony rivers, periphyton (or biofilm) – especially diatoms and cyanobacteria – are the main source of primary production, but shade from riparian vegetation can limit photosynthesis; nutrients may also be in short supply in these habitats.
In wider rivers, reduced shading from riparian vegetation allows the river surface to receive more light. • However, in deep or turbid sections, light penetration may be insufficient to sustain growth of autotrophs.
Heterotrophs: • Heterotrophs, or consumers, are organisms that must obtain energy by consuming other organisms (autotrophs or other heterotrophs) as food. • From the perspective of energy flow in ecological systems, heterotrophs can be classified according to what they eat:
Herbivores are called primary consumers because they eat only plants. • Carnivores are called secondary consumers because they feed on other animals. • Omnivores feed both on autotrophs and on other heterotrophs; that is, they eat both plants and animals. Many aquatic organisms, including fish, are omnivorous.
Detritivores consume dead organic matter (detritus). Detritivores include many bacteria and fungi, invertebrates such as worms and insects, and some scavenging vertebrates. Aquatic insects, for instance, shred dead leaves, but also consume bacteria and fungi growing on the leaves.
New Discovered Species Feed Only on Dead Whales. Bristleworm
Heterotrophs can also be classified according to how they obtain food energy (i.e., functional feeding groups), and by their specific roles in the aquatic ecosystem (Cummins and Klug 1979): • The grazer-scraper category includes herbivores that feed on periphyton and biofilm. • Shredders are detritivores feeding on coarse organic particles, especially leaf litter derived from the riparian zone.
Collectors eat fine organic particles and can be subdivided according to whether the food particles they collect are suspended in the water (e.g., filtering-collectors or filter-feeders), or have been deposited on the substratum (collector-gatherers). • Deposit-feeders ingest fine bottom sediments and the organic material that they contain. • Predators are species that eat other animals.
Food Chains: • The energy and matter produced by plants and other autotrophs are distributed to other organisms in an ecosystem through pathways known as food chains and food webs. • A food chain is a simple linkage of producers to consumers through feeding relationships. • For example, when a small fish eats an aquatic insect, and a larger fish eats the small fish, the two fish and the insect are linked in a food chain.
Food Webs: • Food webs are more complex, and consist of a network of linked food chains. • Organisms commonly consume, and are consumed by, more than one other type of organism. • Each organism has characteristic feeding preferences and patterns, and can itself be prey to other consumers.
Food webs connect autotrophs, at the lowest feeding level, to the herbivores (primary consumers) and then to various carnivores (secondary consumers). • A simplified view of a food web in a wooded stream is presented on the right.
The trophic level is an organism's position in the food chain as determined by the number of energy-transfer steps required to reach that level (Begonet al.1990). • A fish that has consumed an insect, which itself has just consumed algae, is at a higher trophic level than the insect.
In rivers, as in the majority of other aquatic and terrestrial systems, the energyat the base of a food web comes from the solar energy fixed by plants (through photosynthesis) growing in the water or on land. • Energy derived from terrestrial plants enters the water in the form of plant parts, such as leaves or twigs, or in the form of dissolved organic matter.
This material is used as a source of energy by microorganisms such as fungi and bacteria, and by invertebrates. • Plants in the river are also important in food webs—microscopic algae are often eaten while alive, while larger aquatic plants mainly enter food chains after they have died.
Cascade Interaction: • Cascade interactions: Occur in food webs when one group of organisms indirectly affects another group, by feeding on animals that eat the other group. • For example, when predators consume herbivores, the plants that the herbivores would otherwise have consumed will multiply. • Because of the complex interactions, change to the structure of a food web by introducing or removing species, can have unpredictable results. • Looking at ecosystems in terms of food chains and webs can help us understand how species introduction or removal impacts the environment.
Biomass and Production: • Organisms use energy to maintain biological functions and to enable growth and reproduction. • The organic matter produced by autotrophs and heterotrophs, in excess of what they need to sustain life, adds to the ecosystem's total biomass.
The biomass in an ecosystem includes the mass of all living and dead organic matter. • Production is the incremental increase in biomass produced by organisms over a period of time. • Estimates of biomass and production are one measure that can be used to assess the health of aquatic ecosystems.
Primary Production: • Primary production refers to the production of organic matter, such as body tissue, produced mainly by photosynthetic plants. • It is expressed as a rate of biomass production—for example, the amount of wood produced each year.
Secondary Production: • Secondary production is the assimilation of organic material and building of tissue by heterotrophs, and may involve animals eating plants, animals eating other animals, or microorganisms decomposing dead organisms to obtain the resources (material, energy, nutrients) needed for producing biomass. • Secondary production is also expressed as a rate of biomass production, such as the amount of meat produced by grazing cattle each year.
In a productive environment, living plant or animal tissue will accumulate over time. • Biomass is the amount of this accumulated material at a given moment, while production is the rate of increase in the total biomass. • In a river system, biomass may be lost by export (such as downstream transport of biomass), or gained by import from other systems (such as leaves falling into a stream).
Estimates of biomass and production can be applied at various spatial scales and to broad or narrow groups of organisms, such as all organisms in a lake, all fish in a lake, or all catfish in a lake. • Production is often difficult to estimate, since it requires, among other things, accurate measures of biomass repeated at consistent intervals over a long period.
High biomass does not necessarily imply high production, and vice versa. • For example, the biomass of plankton in a waterbody may be low, but because plankton grow and reproduce quickly, the plankton population may replace itself relatively quickly—it has a high rate of production.
Populations of large, long-lived fish represent a much greater biomass than the plankton; however, the production rate of large fish may be much lower. • The rapidity with which living material can replace itself is measured by the production/biomass ratio. • This ratio is high for plankton (high production, low biomass) and relatively low for fishes (low production, high biomass), and provides a better indication of energy transfer between trophic levels than instantaneous measures of biomass.
Aquatic Habitats Lakes: • A lake is a body of water found inland and is not part of an ocean or sea. • Lakes are fed by rivers and are larger and deeper than a pond. • Lake water consist of fresh water, not salt water.
Lakes vary in morphological features, such as depth, extent of shoreline, basin shape, and basin geology. • Morphological feature: Deals with form and structure, in this case, of a lake. • They also vary in their surrounding vegetation, climate, and river inflows and outflows.
