Marine Ecosystem and its Abiotic and Biotic Components microbiologystudy

Marine Biology is the branch of biology that studies living beings in marine surroundings such as seas and oceans.

• Marine life supports numerous organisms ranging from microscopic plankton, viruses, and large animals like blue whales.
• It is believed that Life on Earth originated in the hydrothermal vents on the ocean floor around 4 billion years ago.
• Marine organisms have developed various modes of feeding to achieve a complete food web in their ecosystem.
• Marine ecosystems encompass estuaries, coral reefs, open oceans as well as deep-sea oceans, mangrove forests, and salt marshes.
• Each ecosystem consists of distinct communities of organisms and serves certain functions globally.
• The complexities of marine food webs are due to the presence of various trophic levels starting with primary producers like phytoplankton up to apex predators like sharks.  
• Coral reefs are among the most diverse and productive ecosystems on Earth. Many marine species find homes in these areas while protecting coastlines from erosion. However, these ecosystems have high sensitivity to environmental changes including ocean acidification and climate change.
• Marine ecosystems face many challenges such as overfishing, pollution climate change as well as habitat destruction.
• According to several cultures around the world, the Ocean is considered spiritually significant. In several cultures, marine creatures are viewed as gods possessing some mystical powers e.g., whales, dolphins, sharks, etc.
• The use of sea organisms for different fields converging into Science includes medicinal purposes.

What is a Marine Ecosystem?

Marine ecosystems take over about seventy-one percent (71%) of Earth’s surface area and are hence the biggest aquatic system on this planet. The highest concentrations of dissolved salts are observed here, which characterizes it from freshwater ecosystems. Generally, Marine ecosystems have about 3.5% dissolved salts which amounts to approximately thirty-five grams (35 g) per liter of seawater. This is important in terms of life on earth since these ecosystems provide many services as well as support various forms of biodiversity.

Components of Marine Ecosystem

Like other ecosystems, marine ecosystems have many components that resemble a web-like structure held together by movements in ecological balance and functionality. Such systems are characterized by both biotic or living (animals and plants) and abiotic or non-living aspects that cooperate to form an ecosystem. Abiotic Components: Non-living components that regulate the environment and its organisms form crucial parts of marine ecosystems known as abiotic elements.

Abiotic Components of Marine Ecosystem

The factors associated with this element include: 

1) Water Chemistry

2) Ocean Geography

3) Solar Energy

4) Ocean Current

5) Aerial Exposure

6) Nutrient availability

7) Tides and Waves

1. Water Chemistry

Water Chemistry is a broad term for the many chemical attributes of seawater that have an impact on marine life and ecological processes. Seawater comprises 96.5% water, 2.5% salts, and other substances in a complex mixture. In freshwater, seawater contains more dissolved ions; the major cations are sodium (Na+), chloride (Cl−), sulfate (SO42-), magnesium ion (Mg2+) calcium (Ca2+), and potassium (K+). In the same way, major cations such as chloride (Cl−) and sulfate (SO42-) have been observed. Different properties in the Water Chemistry may include:

a) Salinity

b) Density

c) pH

d) Sound in water

e) Thermal properties

f) Gases in Seawater

g) Viscosity

a) Salinity: Salinity is defined as the amount of salts present in seawater that affect processes related to osmoregulation among different organisms living in it. They need to keep their body fluids constant against varying environmental conditions. A salinometer measures salinity through either electrical conductivity measurements or optical properties of seawater. To survive marine organisms need to control their internal salt and water balance. Physiological mechanisms differ for species that are adapted to stable osmotic salinity conditions (e.g., oceanic fish) compared with those inhabiting fluctuating osmotic environments (e.g., estuarine species).

b) Density: Density is the mass of seawater per unit volume, usually given in kilograms per cubic meter (kg/m³). The average density of seawater is approximately 1.025 kg/m³, but it may differ on account of several factors. Colder water densifies more than warmer water as temperature decreases because water molecules move less and thus pack more closely together.  

c) pH: The availability of essential nutrients and the health of marine organisms depends on seawater pH levels. Most marine organisms thrive under stable pH ranges of around 8.1 to 8.3. The ocean’s average pH ranges around 8.1, which means that it is basic or alkaline due to weak acids and buffers that resist change in acidity level (additions of H+ ions). This alkaline characteristic is because the oceans also consume dissolved minerals from groundwater, raising their pH levels. Therefore, any substantial fluctuations in the ocean’s pH result in an acidic environment known as ocean acidification.

d) Sound in Water: In the marine ecosystem, sound is a vital abiotic factor that influences the communication, and navigation of marine creatures as well as prey-predator relationships and choice of habitat. In water sound transfers faster – about 1,500 meters per second compared to an average of thirty-three hundred meters per second in air due to increased density. For instance, whales, dolphins, and seals are marine mammals that utilize sound for communication while others such as dolphins use it for echolocation and navigation. Moreover, dolphin species can use echolocation to find food.

e) Thermal Properties: The temperature of water in seawater ranges from the warm tropical waters near the equator down to the polar freezing regions. The polar regions drop as low as -2°C, while the tropics hover at about 25-30°C. Such temperature differences, therefore, form distinct marine habitats that support different kinds of organisms. The surface layer is in direct contact with solar radiation and atmospheric conditions to make it have relatively warm temperatures.

Below the surface layer, there is a thermocline, which is the zone where temperature decreases with depth very rapidly. The thermocline behaves as a barrier to the mixing of surface waters with deeper, colder waters. At the bottom of the thermocline, the deep ocean has a constant low temperature that usually ranges from 0 to 4°C. Global warming causes an increase in ocean temperatures, resulting in the following ecological effects:

Coral Bleaching: When sea temperatures rise, this stresses the coral, causing it to bleach—a process in which the corals release the symbiotic algae living in their tissues, turning them white and further killing the coral.

f) Gases in Seawater

Gases, including oxygen, carbon dioxide, and nitrogen, along with others, all have an important role in supporting marine life, controlling biogeochemical cycles, and, in general, affecting the health of an ocean. 

Gases in solubility are influenced by temperature. For example, when it comes to oxygen, 8.1 ml is dissolved per liter of water at 0°C. However, this dramatically plunges to 5.3 ml per liter at 20°C. Some marine life organisms, like worms, snails, and crabs, are burrowers into the mud or sand and therefore have smaller respiratory needs than other larger swimming organisms, such as fish that are swimming rapidly. Low dissolved oxygen is an average indication of pollution and heightened activity among decomposers. Middle to high oxygen levels mean the system is in good health and there is a balance between rates of oxygen production (photosynthesis) and oxygen consumption (respiration).

Carbon dioxide, on the other hand, is significantly more soluble than oxygen and is not affected by temperature, being 8,700 ml/l at 0°C, and 7,350 ml/l at 20°C, respectively. Approximately 25-30% of CO₂ produced from human activities either from the combustion of fossil fuels or deforestation of the environment is sequested in the oceans. Acidification depletes the number of carbonate ions (CO₃^2- ) required to deposit calcium carbonates in the shells of marine organisms

Methane (CH₄) is another gas that is fairly soluble in seawater, with approximately 558 ml per liter dissolving at 0°C under high pressure (found at depths 500-1000 m) and low temperature (below 4°C), methane forms a solid known as methane clathrate. In other words, it is a crystal structure that traps methane in the water. These methane clathrate deposits are formed over long periods and are not in equilibrium with the dissolved methane; they can easily release a huge amount of flammable methane whenever they melt. The rise of seawater temperatures provokes the melting of methane clathrate, releasing more methane into the environment.

g) Viscosity

Viscosity, or the resistance to movement in water is another very relevant parameter in how different organisms move in the ocean. Movement is measured by something called a Reynolds number, R_e, which is the ratio of inertial forces, that is, the tendency of an object to keep on moving, against viscous forces.

Large R_e: An organism is large or the current is high in velocity, so inertial forces dominate, resulting in turbulent flow. For example, large fish, whales, and submarines move through water at high Reynolds numbers of about 100 to 10⁸. Under these circumstances, inertial forces hold sway, making the water flow turbulent and creating eddies and vortices quite easily.

Low R_e: In organisms of small size or with very weak currents viscosity dominates, and flow is smooth and laminar. Drifting plankton are very small, typically experiencing low R_e from 0.001 to 10. Water behaves as a thick viscous liquid—think swimming in honey—at these values, and movement becomes very slow and drag-dominated with reversible flows.

2. Ocean Geography

Ocean geography refers to the physical features and layout of the ocean’s surface and floor. It influences the distribution of marine habitats, the availability of nutrients, the flow of ocean currents, and the overall health and productivity of marine ecosystems. 

Studying the depth and shape of the ocean floor is called bathymetry which is mapping the underwater topography, including features like continental shelves, slopes, abyssal plains, seamounts, and trenches. It influences ocean currents, sediment distribution, and habitat availability. For example, deep trenches create environments with high pressure and low temperatures, while shallower continental shelves are more conducive to life due to increased light and nutrient availability.

The ocean can be divided into three zones based on distance from shore and depth (Zonation). Based on the distance from the shore zones include the following

• Intertidal zone: Area between high and low tide. During the high tide, it is covered with water, and during low tide, it dries and is exposed to air. 
• Neritic zone: Area over the continental shelf up to 200-500 meters deep where many organisms live due to the availability of nutrients.
• Oceanic Zone: Beyond the extent of the continental shelf lies the oceanic zone, which comprises the vast open ocean. Nutrient is sparse in this area and fewer organisms live.

Based on the depth, the Ocean can be divided into the following zones

• Photic Zone: The top layer, with penetration of sunlight to allow photosynthesis.
• Bathyal Zone: Deep areas below the photic zone with less light; this is also called the mesopelagic zone.
• Abyssal Zone: Even deeper, completely dark and cold.
• Hadal Zone: This refers to the deepest parts of the ocean, including ocean trenches.
• Example: Due to tides, the intertidal zone has fluctuating conditions; the deep oceanic zone is permanently dark, with high pressures, and supports specially adapted species.

3. Solar Energy

Solar energy arrives in the form of radiant heat and light to Earth, therefore being the main source of energy. It acts as the principal controller for living organisms and, simultaneously, some physical processes that are independent, like ocean currents and climatic patterns.

It is in this upper layer, called the photic zone and extending into the ocean to depths of only about 200 meters (656 feet), that the vast majority of the solar energy is captured.

Algae and phytoplankton form the base of the marine food web, acting as primary producers in the photic zone. They absorb sunlight and store it, through photosynthesis, as energy in the form of carbohydrates. These stored carbohydrates then become the base food for all life in the ocean.

4. Ocean Current

Ocean currents are the continuous, dominant movements of seawater, driven by forces that include wind, the Coriolis effect, waves, and water temperature and salinity gradients. The Coriolis effect leads to the phenomenon of the deflection of objects moving over the Earth’s surface towards the right in the Northern Hemisphere and towards the left in the Southern Hemisphere, including ocean currents. Probably the most important of these is what is referred to as the Global Conveyor Belt or, more technically, thermohaline circulation (THC). This is brought about by density differences that result from changes in water temperature and salinity. Such circulation carries warm water from around the equator towards the poles, where it cools down, sinks, and moves back, thus mixing ocean basins and influencing global climate. Examples include the Gulf Stream and the Humboldt Current. The Gulf Stream is a warm current, so those regions experiencing this current are warmer. e.g., Northwest Europe, milder than other locations at the same latitude. The Humboldt Current is a cold current that makes coastal areas of Peru cooler than other tropical regions.

5. Aerial Exposure

Aerial exposure refers to the state of marine organisms, mainly those of the intertidal zone, being exposed to air. This affects the survival, distribution, and behavior of such organisms in numerous ways, most of which can be harmful. It creates huge changes in temperature fluctuations to survive, and an organism has to bear it. For example, barnacles and mussels develop features that prevent overheating or freezing in case they are exposed to direct sunlight or cold air. Similarly, crabs; on the other hand, aerial exposure refers to the condition where marine organisms are exposed to air, which might prove harmful.

6. Nutrient availability

Nutrients are substances needed by an organism for growth and life. The nutrients are nitrogen, phosphorus, carbon, iron, sulfur, potassium, and magnesium. Nutrients are required in the synthesis of molecules such as DNA, proteins, and carbohydrates. 

Areas having tropical water have low nutrient levels, like in the case of the tropical coral reefs.

Areas with the temperate waters near the continental shelf have high nutrient levels. During upwelling, deep nutrient-rich water is brought up to the surface of the ocean because of the winds blowing across the coast or open ocean. The sunlight allows the plants and algae to grow on replaced surfaces, which are rich with nutrients; hence, high productivity and more nutrient cycling. Also, downwelling specimens allow surface water to plunge into the deeper layers of the ocean. While they sink back to the base again to replenish the bottom sediments, the Nutrient cycle continues.

7. Tides and Waves

Tides are periodic rising and falling of sea level due to the gravitational pull of the moon and the sun. They occur in cycles, usually twice a day, semi-diurnal, or once a day, diurnal. Tides distribute nutrients and clear waste. Since they go in and out, they bring in nutrients from the ocean and take away waste; hence, they contribute to the productivity of the intertidal and coastal ecosystems. Essentially, the ocean areas most affected by tides include all coastal components, particularly salt marshes, mudflats, rocky shores, and sandy shores.

The wind produces tides. It is as a result of this that waves form and start hitting the shore with varying intensity, thus causing the erosion of the shores, moving sediments, and forming habitats.

Waves thus have a physically stressful impact on coastal and intertidal organisms. Species must therefore be highly specialized to withstand strong wave action and the resulting changes in water levels. Some are even specially adapted to counter the force of breaking waves. Many bury themselves in the sand, while others have characteristics that allow them to grip rocks.

8. Substrate

Substrate means the type of surface or material on the ocean floor or shore where marine organisms live. It is one of the habitats of different kinds of marine life. Substrates could be in the form of a natural object like sand, clay, or coral reef, or an artificial object like a shipwreck, or a metal object. All Coelenterates start their life as free-floating plankton and attach to a substrate to survive. The attached sea anemone provides a site for the protection of fish and invertebrates from their predators.

Biotic Components of Marine Ecosystem

Biotic components include all the living components of marine ecosystems. These constitute organisms that interact with each other and their environment in a very complex manner to create nature’s balance. Concerning habitat and mobility, marine organisms may be divided into: Plankton, Nekton, and Benthic organisms.

1. Planktons

Planktons refer to those organisms that possess limited or no mobility due to their floating characteristic and are transported by the currents of oceans. The term is derived from the Greek word “planktos” meaning drifter. They are situated in the pelagic zone of the ocean which is the largest habitat on the Earth. Planktons can be as tiny as less than 1 micrometre to several metres as witnessed in the case of Jellyfish.

Based on the photosynthetic ability, plankton can be classified into Phytoplankton and Zooplankton.

a. Phytoplankton

Phytoplanktons are microscopic and capable of photosynthesis in the marine ecosystem, being the major producer of Earth’s Oxygen. They can convert carbon dioxide and water into energy-rich organic compounds and oxygen; they are autotrophic. The key examples of Phytoplankton are Diatoms, Dinoflagellates, and Cyanobacteria.

• Diatoms: This phytoplankton group is distinctly different due to their cell wall being made up of silica, which forms an intricate structure resembling glass, commonly called frustules. They are the most photosynthetically active phytoplankton. It has various shapes, such as a cylinder, triangle, and circle, and most of them with symmetrical patterns. The diversity in their form adds up to their wide distribution in both marine and freshwater environments. Examples: Skeletonema, Nitzschia
• Dinoflagellates: They are protists with two flagella. One encircles the cell, the transverse flagellum and the other extends along the long axis, the longitudinal flagellum. Only a few species of Dinoflagellates are bioluminescent, like Alexandrium. They can form harmful algal blooms. Example: Alexandrium, Symbiodinium.
• Cyanobacteria: These are gram-negative, photosynthetic, and autotrophic organisms capable of fixing atmospheric nitrogen into usable forms by other organisms; hence, they are very important in nutrient cycling in aquatic environments. Examples include Synechococcus, Prochlorococcus, and Trichodesmium.

b. Zooplankton

Zooplankton are heterotrophic organisms that mostly feed on other plankton or organic matter. They act as the primary consumer chain of the food web in a marine ecosystem. Zooplankton varies much in size ranging from the microscopic form, copepods to large forms like jellyfish. They either possess swimming or drifting motility to move from one place to another. Copepods swim with their antennae, while jellyfish are passively carried by ocean currents. 

Other ways to divide zooplankton are by their size or stage in life

By Size:

• Picoplankton: Less than 2 micrometers (tiny, often bacteria).
• Nanoplankton: 2-20 micrometers (small, like tiny algae).
• Microplankton: 20-200 micrometers (small, like some small crustaceans).
• Mesoplankton: 0.2-20 millimeters. This includes most of the small jellyfish and many of the larvae of fish.
• Megaplankton: More than 200 millimeters. That’s enormous. Examples might include some large jellyfish.

By Developmental Stage:

• Meroplankton: This is the larval stage of animals that will grow into different kinds of creatures like fish, crabs, or insects. They are only plankton for part of their life.
• Holoplankton: These remain plankton their entire life. This includes small creatures like copepods, jellyfish, and certain types of shrimp-like animals.

The following are the types of Zooplankton living in the marine ecosystem:

• Protists: They are small organisms, like algae, which photosynthesize their food and form the base of the web of life. The other kind of protist is animal-like; this includes protozoa like amoebas and ciliates that consume bacteria and other small living organisms. Some, like Foraminifera, have hard shells and help to form sediments in the ocean.
• Nanoplanktonic Flagellates: These minute planktons have long tails or hair-like structures called flagella or cilia, respectively, to swim. They maintain the population of bacteria under check and may exert harmful effects like red tides.
• Cnidarians: These include jellyfish-like Velella and Physalia, Siphonophores, often floating near the surface of the ocean with stinging nematocyst capability.
• Rotifers: Small, mostly freshwater with a few in the ocean, living off bacteria and algae; under good conditions, they reproduce fast. They are capable of adapting to stress using sexual reproduction.
• Chaetognatha (Arrow Worms): Transparent worms of about 3 cm in length with fins on their sides, worldwide in distribution, which form important predators in the plankton.
• Marine Gastropods: The larval forms of snails and other mollusks, which are major coastal water dwellers.
• Polychaetes: Marine worms with a bristle on most of their segments, which are major ocean dwellers. They play a lot of roles in marine ecosystems.
• Copepods: Small crustaceans that swim using means of antennae, major freshwater and marine dwellers. They consume phytoplankton and small zooplankton.
• Cladocerans: They are planktonic crustaceans living in coastal waters. The body is two-sectioned in appearance. They also consume phytoplankton and small zooplankton and migrate to the surface at night.
• Krill: They are small shrimp-like creatures and are quite essential in the diets of many whales. They feed on phytoplankton in cold waters and other animals in warmer waters.
• Insect larvae: Some insect larvae, as those of the Chaoborus midge are limnetic, and at night eat other zooplankton.
• Tunicates: Some are planktonic, for example, classes Appendicularia and Thaliacea which filter feed on small particles. Others are only in their larval stage.

2. Nekton

Nekton refers to the organisms, which can swim actively in the marine environment. Unlike Planktons, they can move independently by their well-growing swimming organs. 

Types of Nekton

Fish

Most nekton are fish. About 16 thousand species and be found in all ocean depths and regions.

• Pelagic Fish: The most common examples are tuna, marlin, and mackerel, and they inhabit the open ocean. They are usually adapted with streamlined bodies that help them swim fast and other sensitive sensory systems that are designed for effective prey detection.
• Demersal Fish: The best examples are halibut, cod, shark, and stingray, and they are almost entirely bottom dwellers. They have numerous adaptations such as the flattened bodies that help them stay camouflaged.

Marine Mammals

Whales, dolphins, and seals are all adapted for life in the ocean.

• Cetaceans—whales, dolphins, and porpoises are completely aquatic and have radiated into a huge variety of marine realms, from the open ocean to coasts and fresh waters. Examples include the blue whale, bottlenose dolphin, and killer whale.
• Pinnipeds—This includes seals, sea lions, and walruses; they are semi-aquatic — earthly and marine. They have flippers to swim smoothly and are visible globally in temperate and polar regions.
• Sirenians: Including manatees and dugongs, they are herbivores, their diet is mainly made up of aquatic vegetation, in both coastal and riverine habitats.

Cephalopods

Mollusks with a very developed nervous system and eyes. They have a soft body and can swim by jet propulsion.

Types:

• Squids: Elongated bodies, fast swimmers by expel water through a siphon. The giant squid and the Humboldt squid are examples.
• Octopuses: They are round in body shape and able to crawl on the floor or swim using their arms. They are known for their intelligence and disguise ability. Examples are the common octopus and the giant Pacific octopus.
• Cuttlefish: They have a unique internal shell and a color-changing ability that makes them blend into their environment. They move by jet propulsion and have complex eyes. Examples include the common cuttlefish.

Crustaceans: The large crustaceans, like krill, may be planktonic or nektonic, depending on the life stage.

3. Benthic Organisms

Benthic organisms live on or on the ocean floor and differ in size and habitat. Photic zones may have sediments with the only photosynthetic organism being the Benthic Diatoms.

Classification of Benthic organisms regarding size included the following categories:

Macrobenthos: They are large benthic organisms with a size of 1 millimeter.

• Deposit Feeders: Those that consume organic matter in sediments, for instance, sea cucumbers and sea urchins.
• Suspension Feeders: Those that obtain food by filtering plankton above them, for example, clams and brittle stars
• Predators: They are benthic animals that predate on other benthic animals; starfish and predatory snails are good examples.

Meiobenthos: These range from between 0.1 to 1 millimeter.

• Foraminifera, small flatworms, and tiny worms make up the methods, which, in turn, take part in such ecological tasks as nutrient recycling, decomposition of organic matter, and contribution to the food chain.

Microbenthos: these are very small organisms smaller than 1 millimeter

• Diatoms, bacteria, and ciliates form Microbenthos whose ecological tasks include photosynthetic primary production and decomposing.

Benthic plants: also referred to as Phytobenthos, are plants that live on the bottom of aquatic environments. These include various types of algae and angiosperms, particularly flowering plants, and mainly seagrasses.

Algae:

• Cyanophyta (Blue-Green Algae): These are microscopic and often form filamentous clusters or mats.
• Chlorophyta (Green Algae): This is a varied group including several species, some of which are calcareous and help in forming sediments, especially in the shallow waters of tropical regions.
• Phaeophyta (Brown Algae): This is the group of largest seaweeds, including kelps, that inhabit shallow cold waters. Most brown algae have commercial value because algin is a gelatinous substance extracted for use in ice cream, paints, drugs, and cosmetics.
• Rhodophyta (Red Algae): It is the most diverse group, and the red algae are known to inhabit deeper waters of subtidal regions. Some are calcareous, building up reefs in tropical regions.

Angiosperms:

These are seagrasses, flowering plants that grow in marine environments, generally contributing to the ecosystem by stabilizing the sediments and providing habitat for marine life.

References

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