Characteristics of aquatic ecosystems are; water-based physicochemical properties, dominance of microscopic producers, inverted biomass pyramid, highly-adapted biodiversity, and relatively-low solar penetration.
This article discusses some key characteristics of aquatic ecosystems, as follows;
1). Water-Based Physicochemical Properties (as one of the Characteristics of Aquatic Ecosystems)
Physicochemical properties are a combination of physical and chemical properties that influence the internal and external conditions of a given environmental system.
Altogether, the physical, chemical and biological properties of aquatic ecosystems determine their overall conditions .
Because they are dominated by water, most of the physicochemical parameters used to evaluate the health of aquatic ecosystems, as the same which can be used to assess the general quality of water.
Physicochemical characteristics of water are; dissolved oxygen (DO) concentration, temperature, turbidity, pH, biochemical oxygen demand (BOD), acidity, alkalinity, salinity, chemical oxygen demand (COD), total dissolved solids (TDS), electrical conductivity (EC), and relative concentration of elements like chlorine .
Other parameters that may be useful in the analysis of aquatic ecosystems are; solar penetration and sediment composition. In terms of biological evaluation, parameters like the presence and growth-rate of phytoplankton can be used.
The physicochemical properties of aquatic ecosystems listed above, distinguish them from terrestrial ecosystems, which can be assessed using non-aquatic physicochemical parameters like humidity and air pressure.
Physical and chemical properties of aquatic ecosystems are significant because they play a key role in controlling the aquatic organisms capable of surviving in a given water body, as well as the environmental impact of aquatic ecosystems on a global scale, such as their function as carbon sinks that sequester atmospheric carbon and reduce climate change rates.
2). Dominance of Microscopic Producers
Microscopic aquatic organisms are a wide range of genetically and physiologically diverse organisms like protozoans and some non-vascular plants that can only be studied in detail with the help of a microscope.
In both freshwater and saltwater biomes, these micro-scale plants and animals usually constitute the largest and/or most dominant group of autotrophs, or primary producers which introduce bioenergy into the aquatic ecosystem using solar energy and inorganic elements, by the process of photosynthesis.
Microscopic producers of the ocean are mainly phytoplankton , such as microalgae and cyanobacteria; which are classified based on their possession of photosynthetic pigmentation, proximity to the water surface, and tendency to drift along with prevailing currents.
While the various species of microalgae are examples of microscopic aquatic plants, prokaryotes like bacteria are non-plant aquatic microbes. (It must be noted that aquatic bacteria are neither plants nor animals, due to their prokaryotic cell structure that lacks a membrane-bound nucleus . These organisms may instead be referred to as ‘Monerans’, because they fall within the biological Kingdom Monera).
3). Inverted Biomass Pyramid (as one of the Characteristics of Aquatic Ecosystems)
An inverted biomass pyramid is an ecological pyramid showing relative distribution of dry biomass across the various trophic levels of an ecosystem; in which the higher consumer levels have more biomass than lower levels.
For terrestrial biomes like forests, deserts and grasslands; the biomass pyramid is usually upright; meaning that lower trophic levels hold more biomass than higher ones. However, aquatic ecosystems like rivers, lakes and oceans usually have inverted biomass pyramids ; whose geometric trend can be described as widening-upward.
The shape of the pyramid of biomass in the sea is inverted because consumers tend to be several times larger in size or mass than their prey. This leads to a scenario where, even when prey populations are larger; their total organic mass tends to be smaller than that of their predators.
An example of the inverted biomass pyramid in aquatic ecosystems can be seen in the comparison between killer whale and tuna, or tuna and shrimp, in terms of size. While killer whale populations might be smaller than tuna populations, there is a high chance of their total organic mass being much larger.
The drastic size differences between aquatic organisms at various trophic levels is a unique attribute of aquatic ecosystems, and contrasts sharply with terrestrial ecosystems where the size range of interacting organisms is less-broad.
Below is a diagrammatic illustration of the inverted biomass pyramid in a marine ecosystem;
4). Highly-Adapted Biodiversity
All aquatic organisms have adaptations and highly-specialized features that enable them breathe, navigate, feed, and elude potential competitors and predators in water.
There are various types of aquatic adaptations, and various types of aquatic organisms that can be distinguished or defined based on adaptive features.
Types of adaptations that might be found in aquatic organisms are behavioral and physiological. Behavioral adaptations refer to learned patterns of behavior like seasonal migration, parasitism, scavenging and burrowing, which aquatic organisms adopt in order to survive and multiply.
Physiological adaptations are the more obvious ones; including the possession of streamlined bodies, fins, scales, dorsal vision, webbed digits, branchial (gill-based) and cutaneous (skin based) respiratory mechanisms; among others.
Types of aquatic organisms based on adaptive features include; amphibious, pelagic, benthic, parasitic, and predatory organisms.
Biodiversity in aquatic environments is relatively high, so that several thousands of species of microbial, macrobial, reptilian, ornithological (related to bird/aves), mammalian, and amphibious groups can be found in rivers and oceans. This biodiversity goes along with (and is caused by) biological differences developed over multiple generations, as organisms strive for survival in freshwater and saltwater zones.
5). Relatively-Low Solar Penetration (as one of the Characteristics of Aquatic Ecosystems)
When solar radiation falls on water bodies, the electromagnetic waves interact with water molecules, suspended materials and submerged objects through reflection, refraction and diffraction.
Examples of electromagnetic waves in solar radiation, which interact with water bodies are; infrared, visible light, and ultraviolet (UV radiation). These various waves have different effects on aquatic systems and organisms.
Light penetration affects an aquatic ecosystem by determining how bioenergy is produced through photosynthesis.
Unlike terrestrial ecosystems that are generally exposed to solar radiation; aquatic ecosystems have varying degrees of exposure at various depths.
The level of exposure to solar radiation tends to decrease with depth, because of the attenuation of rays as they interact with water molecules and underwater objects that decrease their velocity, while causing loss of radiation through reflective, diffractive and refractive scattering.
In oceans, there is little to no light at great depth, so that this zone is biologically inactive. On the other hand, shallow water bodies can have high productivity at all depths, because there is less obstruction to solar rays at shallow depth .
The limitations of light penetration through water can be summarized as; depth-based attenuation, ray deflection, absorption and scattering.
Infrared rays entering into the aquatic ecosystem are absorbed and stored as thermal energy, which plays a role in physicochemical conditions and survival of organisms..
The absorption of radiation like UV rays can be excessive in some cases, such as in tropical regions with intense and prolonged sunlight. This can have major effects on both saltwater and freshwater ecosystems .
Aquatic life is affected by excessive UV radiation through photochemical reactions that affect biomass distribution and water chemistry, as well as physical changes from the absorption of heat; such as ice-melting, which can further expose the ecosystem to solar radiation .
Penetration of solar rays into aquatic ecosystems is considered to be relatively-low because it reduces with depth. This explains why most photosynthetic organisms in water bodies occur at or close-to the surface.
The depth-based light variation can be used to divide large aquatic ecosystems like oceans into photic (lighted) and aphotic (non-lighted) zones.
Characteristics of aquatic ecosystems are;
1. Water-Based Physicochemical Properties
2. Dominance of Microscopic Producers
3. Inverted Biomass Pyramid
4. Highly-Adapted Biodiversity
5. Relatively-low Solar Penetration
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