Environmental Science · Science

Biological Evolution in the Ocean


The biological evolution in the marine environment plays a crucial role in understanding the origin of life on Earth. To understand how marine life evolved, we need to study the historical geology of marine life and elemental components and processes. Historical geology studies show that fossil records are essential in order to understand the emergence of life in the marine environment. The discovery of hydrothermal vents gave the scientists vital information about the primitive life in marine. Marine biology is also crucial to identify conservation strategies of marine life. The methods of reproduction, taxonomy, and marine food webs are the tools of marine biology needed to be studied. Other important factors that help to establish conservation strategies are adaptation strategies including, for example, locomotion and propulsion, development of organisms’ parts and shape, osmoregulation, thermoregulation, reproduction system and sensory system development.

The Origin of Marine life

Life on Earth evolved 4 million years ago (Weber, 2014). The Earth’s atmosphere was containing volatiles, such as methane, ammonia, hydrogen sulfide, water vapor, and carbon dioxide. That volatiles released from volcanic activities and in the early stage of the earth’s formation. Marine is formed when the earth cooled, and water vapor became liquid. Also, asteroids and icy comets hit the primitive earth holding water to the earth.

Evolution of the Bioshpere

Erickson, J., 2002, Historical Geology, New York, Library of Congress Cataloging-in-Publication Data

Evolution of life in the marine is explained in many hypotheses. At this moment some of these assumptions:

The panspermia theory states that the seeds of life exist in all over the universe and can be transported from place to place through space. This theory explained that solar radiation and the pressure causes a change in the interstellar dust. Extremophile microorganisms may travel through space within meteorites, comet and/ or asteroids.  Another theory is called Special Creation. This theory is widely accepted theory as it explains the origin of life from religion point of view. It states that God created life on Earth. Spontaneous Origin theory explains that life evolved from inanimate matter. The life evolved by continuous chemical changes in molecules. The changes affect the molecules making them more stable and persist. By the time, these molecules create more complex molecules until the cell is formed. These chemical changes are mainly happened in the marine.

From all previous theories, I can accept the theory of Spontaneous Origin, although it cannot, completely, explain the gap in the evolutionary record. The other two approaches cannot provide any realistic evidence on how life emergence on earth.

As the chemical evolution of the life on earth more acceptable for me, I would like to discuss the elemental components and process associated with this theory. Aleksander Ivanovic, 1936 states that the ultraviolet radiation from the sun is the energy source provided to transform the atmosphere volatile in the early stage of the earth into organic molecules. This is the spontaneous synthesis that existed only in the primitive environment. Miller and Urey, 1953 simulated the conditions of the primitive earth atmosphere – volatile gases and electrical charges from storms. They found that under these conditions, organic molecules have been formed when the energy provided. After a week, carbon content components have been established such as formaldehyde and hydrogen cyanide, which are combined forming formic acid and amino acids. Protein is formed by accumulated amino acids. Both Aleksander’s theory and Miller and Urey experiment are magnificent evidence on the theory of spontaneous Origin.

Scientists proposed their evolution theories according to physical evidence. This physical evidence is fossil records. Fossils play a crucial role in understanding biological evolution and historical geology. In 1998, scientists found a fossil as a transition between a sea creature and land creature. This animal called Tetrapod. Tetrapod has a hand-like fin. The transition fossils can be considered the milestone of the importance of fossils in evolution. For example, Eusthenopteron had a skull and spin like those in tetrapod. The braincase and teeth of Panderichthys are similar to the tetrapod.

Hydrothermal Vents

They are underwater volcanos occur at oceanic ridges and convergent plate boundaries that produce hot springs.  They support the theory of evolution as some previously unknown organisms have been found in the hydrothermal vent areas. The conditions of the hydrothermal vent are similar to those of primitive earth and by discovering the presence of some organisms; it can give a very clear proof that life is originated during the formation of earth. I guess that evolution started with the beginning of primitive metabolism. This metabolism created increasingly complex chemical reactions leading to the formation of DNA and RNA. This what Professor Wächtershäuser assumed and I totally agree with him.

As the hydrothermal vent emits toxic gases, it was so wired to find some organisms live in these areas. One of those organisms is Riftia Pachyptila, which is a giant tubeworm in the family Siboglinidae. It has a red plume at the head contains a vast quantity of hemoglobin that can bind oxygen and hydrogen sulfide and transport them to the throphosome. Rimicaris exoculata is a species of shrimp that found on hydrothermal vents. It is different than other shrimp species that existed in the deep ocean. I believe that organisms are so beneficial to prove the evolution theory in the ocean.

Marine life has very numerous life forms. Marine organisms are varied where there are unicellular organisms – Prokaryote, and complex-celled organisms – Eukaryote. The self-replication in Eukaryote, for example, consists of 4 phases; G1, S, G2 & M. In G1, the first gap in the cell cycle where the necessary protein for DNA replication is synthesized. The DNA synthesize during S phase. In G2, the second gap phase, the cell undergoes some checks to ensure the cell is ready for the division process. G1, S, and G2 are known as the interphase period. In M phase, is the mitosis phase where the cell divides.

Cell Cycle

Nature Education, The Eukaryotic Cell Cycle, [online], http://www.nature.com/scitable/topicpage/eukaryotes-and-cell-cycle-14046014, [Accessed 19/09/2015]

Self-replication in Prokaryotes is different than that in a eukaryote. The DNA existed in a single circular chromosome. Cell reproduction starts with the replication of this chromosome. The new chromosome migrates to the other side of the cell. The cell starts to split as the plasma membrane in the middle of the cell starts to grow inward until the cell separates into two cells by fission (Boundless Biology, 2015).

From the previous example, I can see that there are two different types of organisms, prokaryote, and eukaryote. This is a part of organisms’ classification which is called taxonomy. The taxonomy helps scientists to recognize easily marine species to conserve marine animals. I guess it is critical in captive breeding strategy, for example, as classification contributes to identifying relative organisms.

Carl Linnaeus classified organisms into categories; Kingdom, Phylum, Class, Order, Family, Genus, and Species. Linnaeus named only two groups, Animals, and Plants. I think this is not sufficient to cover all organisms. Despite his classification was the milestone of the organism’s classification, this classification failed to group bacteria species, for example. Now, scientists’ recognized five kingdoms. They are, Monera, Protista, Fungi, Plantae, and Animalia. An example of animal classification, The Blue Whale classification: its name is Balaenoptera musculus:



















MarineBio Conservation Society, Marine Taxonomy, [Online], http://marinebio.org/oceans/marine-taxonomy/, [Accessed 19/09/2015]

Taxonomy is vital in preserving the biodiversity. It helps to analyze the community and identifies the endangered species in a community. This analysis is very crucial to establish conservation strategies. The study of taxonomy is a milestone for the researchers who are interested in marine life conservation.

Marine Food Webs: It is similar to the conventional food web. They consist of primary producers, e.g., phytoplankton and seaweed, herbivorous consumers, e.g., zooplankton, the first level carnivorous consumers, e.g., jellyfish, the second level carnivorous consumer, e.g., big fish, and the third level carnivorous consumers, e.g., Sharks. Primary Production in the marine food web mainly depends on photosynthesis in marine plants. Marine plants use sunlight as an energy source to convert inorganic materials into carbohydrates, protein, fats, and oxygen. These are the primary production from photosynthesis. Primary production is the most important element in marine life. Any failure in the primary production can affect the entire marine ecosystems.

Organisms in marine food webs can be divided into Trophic Levels. They fall into three levels. Producers lie in level 1, herbivorous lies in level two, and carnivorous lies in level 3.  Producers are autotrophic such as phytoplankton. It converts the energy coming from the sunlight into food by photosynthesis. Phytoplankton classified into cyanobacteria, Chrysophyta, and dinophytes. Cyanobacteria is the source of oxygen in the marine life. It can form mats in shallow environments. It lives in extreme environments such as hot springs, and salt lakes. It can be dangerous to other organisms if they bloom due to rapid cell division. Chrysophyta is a unicellular organism that contains chlorophylls “an” and “c”. They are masked by fucoxanthin and a carotenoid. Some species store food outside of the chloroplast as polysaccharide laminarin.

Dinophyta is a unicellular organism. Some species are photosynthetic, and other is heterotrophic. Dinoflagellate provides the coral with essential organic food. It is crucial as it can be considered as toxin producers in a coastal marine environment. These poison species have been responsible for the death of some marine species such as sea bird, and sea mammal. It may affect the health of human as well. Zooplankton plays an imperative role in the tropic level. They provide foods to higher trophic levels. They dissolve organic matters through sloppy feeding and excretions. It forms the base of most marine food webs as they considered a source for consumers of high trophic levels. Zooplankton may act as a source of disease. Crustacean zooplankton is a house of bacterium Vibrio cholera which causes cholera. Zooplankton can be divided into holoplankton and meroplankton. Holoplankton is permanent plankton that is paramount in the marine food web. Diatoms, as an example of holoplankton, can be considered an oxygen producer and are the first step in the food chain.

Protection of the marine food web is essential to conserve marine environment. I believe that each organism in the trophic levels is important, and any failure in food producing may affect the whole food chain. Any declines in the food chain due to acidification, for example, may jeopardize the food web and marine conservation efforts. I believe that we need to conserve all trophic levels of marine food webs. Any removal of one or more of the trophic levels may impact the marine ecosystem. For example, Sharks has a crucial role in balancing food webs. They are considered a keystone species. I guess that the removal or depletion of Sharks results in the loss of important fish and shellfish species down the food chain such as Tuna, which is responsible for maintaining coral reefs’ health.  However, keeping apex predators such as Orcas Killer Whale can impact the food web. Orcas Killer Whale is known to prey on Sharks and all organisms. The population growth of such apex predator may affect the marine ecosystem.

Adaptation Strategies

Adaptation is a critical process in order to maintain the viability of an organism. Many factors are affecting the sustainability of an organism:

  • Population: as the population of an organism decreases, the likelihood of extinction increases.
  • Genetic factor: in a small population community, the probability that all or most offspring of all remaining females will not survive or will be one sex is greater than the large population community. The chance to find one another to mate is less than the large popular
  • Environmental factors, the variation in demography, natural catastrophes and human factors all can affect the viability of an organism.

There are several adaptation strategies, such as structural adaptation, physiological adaptation, and behavior adaptation.

Structural or morphological adaptation is the change of the physical feature of the organism. It can be found in shape or body covering and internal organization. For example, the filter feeders animals like Bivalves, have specialized siphon structures to filter their food from the surrounding water. Coastal plants are another example; as they attached firmly to rocks to protect themselves from sweeping away by waves. Physiological adaptation, the organism can regulate its temperature (thermoregulation), breathing, its osmoses (osmoregulation) and perform some special functions such as excreting chemical substances as a defense strategy. Behavioral adaptation as the organism can learn or inherit some behaviors. Whales make sounds communicate, navigate and hunt.

Some examples of adaptation strategies have evolved such as locomotion, propulsion, shape, speed, fin development, swim bladder development diet and foraging.

Locomotion and propulsion in marine organisms are varied from species to another. Locomotion depends on the size of an animal, and the movement medium. An example of organism locomotion development is amoeboid motion. It is performed by extending a portion of the cell to form a pseudopodium. In larger animals such as flatworms, cilia are responsible for locomotion. They secrete film mucus. This is called mucociliary locomotion. Jet propulsion is a type of propulsion that is used by few aquatic animals to escape, such as octopus and squid. It is working by pushing water from inside to outside in a narrow jet. This strategy is found in hydrostatic skeleton animals, animals with internal skeletons such as squids, external skeleton, such as dragonfly larva, and scallops and no skeleton such as Jellyfish.

The shape of an animal plays a major role in locomotion and propulsion. Many of marine organisms have modified their external shape. For example, fish has pointed shape body – long and thin body. This is called streamlined shape. The speed of an animal differs from an organism to another. Some pelagic fish has muscles to help it to swim faster and longer than other organisms. Albacore Tuna (Thunnus alalunga), for example, they swim for long distance at rapid speed up to 80 km/h (Bularz, 2011). Fins have been developed to help marine species to maintain their speed and motion. Caudal Fin helps the fish to move fast and quickly while dorsal fin keeps the fish in a straight line. Caudal fins have different shapes. Rounded (butterfly), truncated (salmon), forked (herring and perch), lunated (tuna) and heterocercal. The lunated shape is said to be high-speed cruisers as they have high aspect ratio while the rounded shape is said to be slowest as they have a low aspect ratio.

Fish Fins.png

L. Sumich, J., and F. Morrissey J., (2004), Introduction to the Biology of Marine Life: 8th Edition, Massachusetts, Jones & Bartlett Publishers.

The swim bladder is a gas-filled bag above fish guts. Most fish species have long swim bladders. It helps to control fish buoyance. The mechanism of moving up and down in the water column is controlled by swim bladder. They move up by pumping gas into the bladder and inflating it. They move down by reabsorbing gas into their blood. In depth, the gas inside the swim bladder is at the same pressure as the water outside. That is why the swim bladder does not collapse.

Diet and Foraging strategies in marine life differ from species to another. Some species can prey on the same species, for example, Mollusks prey on other Mollusks. Some organisms are deposit or filter feeders such as flatworm. They ingest a relatively low-quality food. Most of the marine animals are forage in large groups while others feed alone. An example of adaptation for foraging in Pinnipeds is that Pinnipeds has heterodont dentition and different types of teeth. The dentition of walruses has a pair of tusks; it is present in both male and females, but more slender in females.

Another adaptation strategy can be found in osmoregulation, thermoregulation, reproductive processes and sensory system development. Osmoregulation is controlling in the osmoses of the organism. Osmoregulation occurs due to the difference in concentration between marine water and the concentration of bodies of the organism. The main idea of osmoregulation is the water moves from hypertonic to hypotonic. The skin of hypotonic fish absorbs water to regulate their osmoses. The osmoregulation of Salmon is important as they tolerant of a wide range of salinity. They travel to different salinity concentrations. Osmoregulation helps them to survive in a variety of aquatic environments. Thermoregulation is maintaining a constant body temperature. Animals regulate their body temperature by their metabolism. There are two types of animals, endotherms – animal who controls its internal heat and ectotherms – an animal who allow its temperature to follow ambient temperature at about 37° C (The-Crankshaft Publishing’s, N/A). Bladders can be used as a thermoregulatory as it is the source of primary metabolic fuel for marine mammals.

Reproduction processes in marine animals can be done by two types or reproduction, sexually and asexually. Prokaryotic microorganisms, and in some Eukaryote reproduce asexually by fission – by binary fission as an organism splits into two separate organisms. Also by budding – by outgrowth of a part of a cell or body parts leading to separate from the original organism into two individuals such as Hydra, and fragmentation – as body breaks into two parts with subsequent regeneration, such as sea stars, or parthenogenesis egg is developed into complete offspring without fertilization, such as water fleas. Sexual Reproduction is a mating between two individuals to form third unique offspring. Some invertebrates are hermaphroditic as they have both male and female reproduction organs (Boundless Biology, 2015).

Marine species has unique Sensory systems. They have different sensory systems such as hearing, chemoreception, electroreception, Ultraviolet (UV) vision and Magnetic field navigation. Hearing in aquatic species such as fish, have hearing apparatus which is effective underwater. Fish use their lateral line and their otoliths to sense sound. Chemoreception is well developed in sharks. They can determine the direction of scent based on the timing of scent detection in each nostril. Electroreception in marine vertebrates such as sharks is evolved, as they have the ability to detect electrical stimuli generated by muscles and nerve activity. Many fish have developed visual range into UV portion of the spectrum. UV vision in male Ambon is a magnificent example of marine UV vision. It can recognize individuals from their own species and those of other species. Magnetic field navigation is a crucial sense Loggerhead sea turtles. They can distinguish between intensities and angle of inclination at which geomagnetic field line intersect the Earth’s surface.


From the history of primitive Earth, scientists got much information about marine life forms, such as the marine food webs and the way that marine animals evolve and adapt to survive. Adaptation strategies are the key of how most of the marine animals survived. The study of marine animals’ morphology and taxonomy is a vital as it helped scientists and researchers to identify endangered marine species and outline suitable conservation strategies.


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