Marine Biology: An Overview

By Dr. Supriya Subramanian, Ph.D.Reviewed by Lily Ramsey, LLM

Marine biology is the scientific study of marine organisms, including their behaviors, interactions, and the ecosystems they inhabit. As oceans cover more than 70% of the Earth’s surface and produce over 50% of the world’s oxygen, they play a crucial role in regulating climate and supporting life on Earth.

The vast marine ecosystem also serves as a primary source of protein for billions of people globally. However, climate change, pollution, overfishing, and habitat destruction are significant threats to marine biodiversity, making marine research essential for the development of sustainable resource management strategies and ocean health preservation.¹

Image Credit: Rich Carey/Shutterstock.com

Core Areas of Marine Biology

Marine ecosystems are the foundation of the marine environment, supporting a wide variety of organisms ranging from microscopic plankton to large marine mammals like whales. These ecosystems include coral reefs, kelp forests, and deep-sea environments, each housing unique species adapted to their specific habitats.

• Coral Reef Ecosystem: Coral reefs are among the most diverse ecosystems on the planet. They provide food, shelter, and protection for numerous species, including fish, invertebrates, and marine mammals. Hard corals, which form the structure of the reef, create a complex habitat by building calcium carbonate skeletons. These reefs are home to species such as sea turtles, dolphins, and a vast array of fish.^2-3
• Kelp Forest Ecosystem: Found in cool, nutrient-rich waters, kelp forests provide a habitat for diverse marine life, including mammals like sea otters and seals. Kelp forests also support various fish species, such as sardines and seabass, and are vital in maintaining marine biodiversity.^2-3
• Deep-Sea Ecosystem: The deep sea, located at depths greater than 1,000 meters, is a unique ecosystem characterized by its lack of sunlight. Creatures in the deep sea have adapted to extreme conditions, such as high pressure and cold temperatures. Notable species include deep-sea squids, octopuses, and giant crabs.^2-3

Marine Organisms

Marine organisms are categorized into various groups, each playing a vital role in the ocean’s food chain and ecosystem dynamics.

• Plankton: Plankton are the base of the marine food web. Phytoplankton, which are photosynthetic microorganisms, serve as the primary producers in marine ecosystems. They are crucial for producing oxygen and supporting marine life. Under favorable conditions, phytoplankton can multiply rapidly, resulting in blooms that can cover large ocean areas. However, certain species of phytoplankton can produce toxins, leading to harmful algal blooms, also known as red tides, which can be deadly to marine life and harmful to humans.⁴
• Marine Invertebrates: Invertebrates make up about 97% of marine biodiversity and are essential to the health of marine ecosystems. These organisms are classified into several phyla:
  • Porifera: Sponges, which filter-feed by pumping water through their bodies, are key contributors to nutrient cycling in the ocean.
  • Cnidaria: This group includes jellyfish, corals, and sea anemones. Cnidarians use specialized stinging cells called nematocysts to capture prey and defend themselves.
  • Arthropods: Marine arthropods, such as crustaceans and horseshoe crabs, have a hard exoskeleton that protects them from predators. They periodically shed their exoskeleton to grow.
  • Mollusks: Mollusks include species like oysters, mussels, and octopuses. These organisms are vital for maintaining marine ecosystems and contribute significantly to the biodiversity of coastal habitats.⁵
• Fishes: Marine fish are adapted to survive in diverse environments, from the deep sea to coral reefs. They are categorized into jawless fishes, cartilaginous fishes, and bony fishes. Sharks and rays, which are cartilaginous, have skeletons made of cartilage, while bony fishes like seahorses have skeletons made of bone.⁶
• Marine Mammals: Marine mammals, such as whales, dolphins, and sea otters, are highly adapted to life in the ocean. These animals play critical roles in marine ecosystems. For example, sea otters help maintain kelp forest health by controlling sea urchin populations, which would otherwise devastate kelp forests.⁷

Marine Ecology and Interactions

Marine ecology focuses on the interactions between marine organisms and their environment, which are essential for maintaining the balance of marine ecosystems.

• Symbiosis: Many marine species live in symbiotic relationships, where two organisms benefit from each other. For example, boxer crabs use anemones’ stinging tentacles for defense, while anemones feed on the crab’s leftovers. This mutualistic relationship is beneficial to both species. Other forms of symbiosis include commensalism, where one organism benefits while the other is unaffected, and parasitism, where one organism harms the other for its benefit.^9-11
• Predation: Predation plays a crucial role in regulating species populations and maintaining ecosystem balance. For example, sea otters control sea urchin populations, which prevents the destruction of kelp forests. This interaction not only supports the kelp forests but also provides a habitat for other marine organisms.¹²
• Adaptations: Marine organisms have evolved a variety of structural, physiological, and behavioral adaptations to survive in their environments. Whales use echolocation to navigate and hunt in deep waters, while crabs use sound to locate suitable habitats.¹³​​​​​​​

Applications of Marine Biology

Marine biology is integral to conservation and the sustainable use of ocean resources. However, overfishing, pollution, and habitat destruction have put many marine species at risk of extinction.

• Conservation: Efforts to conserve marine biodiversity include the establishment of marine protected areas (MPAs), where commercial fishing is restricted to allow species populations to recover. Public participation in conservation initiatives, such as Reef Check, enables citizens to contribute to data collection and support marine biologists in protecting endangered species.^14-16
• Sustainable Fishing: Overfishing is a significant threat to marine ecosystems. Sustainable fishing practices ensure that fish populations are maintained at healthy levels, preserving marine biodiversity and protecting the livelihoods of coastal communities. Fisheries management strategies include limiting fishing during spawning seasons, using selective gear to avoid bycatch, and protecting vulnerable habitats from destructive fishing practices.¹⁵

Challenges Facing Marine Ecosystems

Marine ecosystems face numerous challenges, including overfishing, habitat destruction, pollution, and climate change.

• Overfishing: The growing demand for seafood has led to unsustainable fishing practices that deplete fish populations and disrupt marine ecosystems. Overfishing not only threatens marine biodiversity but also impacts the livelihoods of fishers and coastal communities.²⁰
• Marine Pollution: Pollution, particularly plastic waste, has devastating effects on marine life. Marine organisms can ingest plastic, leading to injury or death, while industrial pollutants and heavy metals accumulate in marine species, causing long-term health effects.²¹
• Climate Change: Rising temperatures, ocean acidification, and deoxygenation—often referred to as the “deadly trio”—are significant threats to marine ecosystems. Warmer waters can disrupt species distribution, while acidification affects organisms like corals and mollusks that rely on calcium carbonate to build their shells and skeletons.^17-19

Future Directions and Technological Advancements

Innovative technologies are helping marine biologists address these challenges and improve our understanding of marine ecosystems.

• Environmental DNA (eDNA): eDNA provides valuable insights into marine biodiversity by analyzing genetic material shed by organisms in the water. This technology allows scientists to detect the presence of species, including invasive species, and monitor population dynamics.²⁴
• Drones and Autonomous Vessels: Technologies like Saildrone and autonomous wave gliders are used to gather real-time data on marine environments. These devices help researchers track fish populations, monitor ocean health, and map the seafloor.^23-26

Conclusion

Marine biology is essential for understanding the complex interactions between marine organisms and their environments. As the ocean faces increasing threats from human activities and climate change, marine biologists are working to develop sustainable practices to protect marine ecosystems.

Technological advancements, such as environmental DNA and drones, provide valuable tools for monitoring ocean health and supporting conservation efforts. By addressing challenges like overfishing, pollution, and habitat destruction, marine biologists can help ensure the long-term health and sustainability of the world’s oceans.

References

1. Renault A. (2022). Fishing, pollution and rising temperatures: how marine science can help us save the oceans. [Online] The Conversation. Available at: http://theconversation.com/fishing-pollution-and-rising-temperatures-how-marine-science-can-help-us-save-the-oceans-176521 (Accessed 1 September 2024).
2. Different types of ecosystems & characteristics. (2020). [Online] Earth Reminder. Available at: https://www.earthreminder.com/types-of-ecosystems/ (Accessed 1 September 2024).
3. Kennedy J. (2019). 9 types of marine ecosystems. [Online] Thought.Co. Available at: https://www.thoughtco.com/types-of-marine-ecosystems-2291779 (Accessed 1 September 2024).
4. Lindsey R and Scott M. (2010). What are Phytoplankton? [Online] Earth Observatory. Available at: https://earthobservatory.nasa.gov/features/Phytoplankton (Accessed 1 September 2024).
5. Spencer E. (2019). Exploring types of invertebrates. [Online] Ocean Conservancy. Available at: https://oceanconservancy.org/blog/2019/03/11/exploring-types-invertebrates/ (Accessed 1 September 2024).
6. Marine fishes. [Online] MarineBio. Available at: https://www.marinebio.org/creatures/marine-vertebrates/marine-fishes/ (Accessed 1 September 2024).
7. Pinnipeds. [Online] The Marine Mammal Center. Available at: https://www.marinemammalcenter.org/animal-care/learn-about-marine-mammals/pinnipeds (Accessed 1 September 2024).
8. Introduction to the Sirenia. [Online] UCMP. Available at: https://ucmp.berkeley.edu/mammal/mesaxonia/sirenia.html (Accessed 1 September 2024).
9. Symbionts, parasites, hosts & cooperation. [Online] MarineBio. Available at: https://www.marinebio.org/conservation/marine-ecology/symbionts-parasites/ (Accessed 1 September 2024).
10. Duong T. (2021). Marine mimics: 5 animals that are always in costume. [Online] PADI. Available at: https://blog.padi.com/marine-mimics-5-animals-that-are-always-in-costume/ (Accessed 1 September 2024).
11. Symbiosis: the art of living together. [Online] National Geographic. Available at: https://education.nationalgeographic.org/resource/symbiosis-art-living-together (Accessed 1 September 2024).
12. Sea otters are ecosystem superheroes. [Online] Sea Otter Savvy. Available at: https://www.seaottersavvy.org/ecosystem-superheroes (Accessed 1 September 2024).
13. Marine organisms and adaptations. [Online] Science Learning Hub. Available at: https://www.sciencelearn.org.nz/resources/142-marine-organisms-and-adaptationsApplic (Accessed 1 September 2024).
14. Darrah P. (2023). Endangered marine species: protecting our oceans’ biodiversity. [Online] GVI. Available at: https://www.gvi.co.uk/blog/smb-endangered-marine-species-protecting-our-oceans-biodiversity/ (Accessed 1 September 2024).
15. What is sustainable fishing. [Online] MSC International. Available at: https://www.msc.org/what-we-are-doing/our-approach/what-is-sustainable-fishing (Accessed 1 September 2024).
16. Sustainable fishing. [Online] Rare. Available at: https://rare.org/pillar/sustainable-fishing/ (Accessed 1 September 2024).
17. How climate change impacts marine life. (2024). [Online] European Environment Agency. Available at: https://www.eea.europa.eu/publications/how-climate-change-impacts#:~:text=Warmer%20water%20alters%20organisms’%20metabolisms,species%20(EEA%2C%202022b) (Accessed 1 September 2024).
18.  Climate change. [Online] Coastal and Marine Sciences Institute. Available at: https://marinescience.ucdavis.edu/research-programs/climate-change (Accessed 1 September 2024).
19. Oceans and climate change. (2016). [Online] International Atomic Energy Agency. Available at: https://www.iaea.org/topics/oceans-and-climate-change (Accessed 1 September 2024).
20. Wright, L. (2023). The impact of overfishing on marine ecosystems. Poultry, Fisheries & Wildlife Sciences. 11(1):1–1. Available at: https://www.longdom.org/.
21. Challenges and preservation of marine ecosystems. (2024). [Online] EUVG. Available at: https://www.euvg.pt/2024/04/03/challenges-and-preservation-of-marine-ecosystems/ (Accessed 1 September 2024).
22. Causes of marine habitat loss and solutions. [Online] Decoding Biosphere. Available at: https://decodingbiosphere.com/2371-2/causes-of-marine-habitat-loss-and-solutions/ (Accessed 1 September 2024).
23. These 5 technologies are helping save our ocean. [Online] National Oceanic and Atmospheric Administration. Available at: https://www.noaa.gov/stories/these-5-technologies-are-helping-save-our-ocean (Accessed 1 September 2024).
24. Exploration tools: environmental DNA. [Online] NOAA Office of Ocean Exploration and Research. Available at: https://oceanexplorer.noaa.gov/technology/edna/edna.html (Accessed 1 September 2024).
25. Pagniello CM, Cimino MA, Terrill E. (2019). Mapping fish chorus distributions in southern California using an autonomous wave glider. Frontiers in Marine Science. 6:526.
26. Dheior M. (2023). Innovations in marine biotechnology: advancing sustainable seafood production. Journal of Oceanography and Marine Research 11(2):1–2.