Marine biology is the study of animals, plants, and microbes that live in oceans and other saltwater environments, including estuaries, mangroves, and wetlands. It covers everything from microscopic plankton to blue whales, and from shallow tidepools to trenches more than 6,000 meters deep. What sets it apart from oceanography, which focuses on the ocean’s physical and chemical properties, is that marine biology centers on living organisms: how they survive, interact, reproduce, and respond to a changing planet.
What Marine Biologists Actually Study
The field is broader than most people expect. A marine biologist might spend years tracking whale migration patterns, studying how temperature shifts change the timing of salmon runs, or cataloging bacteria that thrive near volcanic vents on the seafloor. The University of Washington’s marine biology program organizes its research around specific groups of organisms: marine mammals, sharks, fish, invertebrates, seabirds, marine microbes, and seaweeds. Many researchers specialize in a single group for their entire career.
But the work isn’t limited to studying one species in isolation. Marine biologists also investigate how entire ecosystems function. That means examining food webs, tracking the effects of pollution on coral reefs, measuring how oil spills ripple through plant and animal communities, and figuring out how human activity reshapes coastal habitats. The unifying thread is understanding life in saltwater, whether that means dissecting the life cycle of a single-celled organism or modeling the global importance of ocean ecosystems.
Ocean Zones and Where Research Happens
The ocean is divided into distinct zones based on depth, and each one presents different conditions for life. The surface layer, down to about 200 meters, is where sunlight penetrates and photosynthesis occurs. This is where you find coral reefs, kelp forests, and the vast majority of familiar marine species. Below that, from 200 to 1,000 meters, light fades and temperatures drop sharply. Creatures here have evolved bioluminescence and other adaptations to survive in near-darkness.
Deeper still, from 1,000 to 4,000 meters, is a zone of permanent darkness, crushing pressure, and near-freezing temperatures. The abyssal plain sits between 4,000 and 6,000 meters, covering enormous stretches of flat ocean floor. And at the very bottom, deep-sea trenches plunge past 6,000 meters into what’s called the hadal zone. Life exists at every one of these depths, though it looks radically different at each level.
The intertidal zone, where the ocean meets the shore, is one of the most accessible and intensively studied habitats. It includes rocky shorelines, sandy beaches, mud flats, tidepools, salt marshes, and mangrove roots. These areas are ecologically rich because organisms must cope with constant shifts between being submerged and exposed to air, making them natural laboratories for studying adaptation and resilience.
How Much of the Ocean Remains Unknown
As of mid-2025, only 27.3% of the global seafloor has been mapped using modern high-resolution sonar technology. The rest is essentially uncharted. Scientists estimate that roughly two-thirds of all marine species, possibly more, have yet to be discovered or formally described. Nearly 2,000 new marine species are accepted by the scientific community each year, a pace that underscores just how much remains to be found.
This is part of what makes marine biology distinct from terrestrial biology. On land, most large animals have been cataloged. In the ocean, there are likely thousands of fish, invertebrates, and microorganisms that no human has ever observed.
Tools of Modern Marine Research
Fieldwork in marine biology has changed dramatically in recent decades. Researchers at institutions like Woods Hole Oceanographic Institution now deploy remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) to explore depths that humans can’t safely reach. The crewed submersible Alvin, which has been in service since the 1960s and undergone major upgrades, still carries scientists to the deep ocean floor. Newer vehicles like the Mesobot are designed to quietly shadow deep-sea animals without disturbing them.
Environmental DNA sampling, known as eDNA, is one of the newer tools in the field. Instead of physically catching or observing animals, researchers collect water samples and analyze the genetic material organisms leave behind. This can reveal which species are present in an area without ever seeing them directly. Ocean gliders, which are torpedo-shaped autonomous craft, drift through the water column for weeks or months at a time, collecting data on temperature, salinity, and biological activity. Satellite telemetry allows researchers to track tagged animals across entire ocean basins, mapping migration routes that would have been impossible to follow a generation ago.
Climate Change and the Ocean
Climate research has become one of the most urgent branches of marine biology. Ocean acidification, caused by seawater absorbing excess carbon dioxide from the atmosphere, weakens the shells and skeletons of corals, mollusks, and many plankton species. Warming waters have triggered mass coral bleaching events off the coastlines of Florida, Hawaii, Puerto Rico, the U.S. Virgin Islands, and Pacific Island territories.
Marine species are responding to warming by moving. NOAA Fisheries reports that many species are shifting toward the poles at a rate of about 44 miles per decade, seeking cooler water. Others are moving into deeper zones. These shifts are already changing the location and abundance of important fish stocks, with real consequences for commercial fishing communities and the ecosystems those species support. Marine biologists are working to model how species distributions will continue to change, using data on life history, current ranges, and projected ocean conditions to estimate which populations are most vulnerable.
Medicine From the Sea
Marine biology has direct implications for human health. Around 15 to 20 compounds derived from marine organisms have been approved for clinical use, primarily against cancer but also for pain, viral infections, and heart disease. One pain medication derived from cone snail venom was approved in 2006 as an alternative to morphine, with up to 1,000 times greater pain-relieving potency through a completely different mechanism. Several cancer drugs trace their origins to sea sponges, marine bacteria, or other ocean organisms. These include treatments for metastatic breast cancer, multiple types of lymphoma, bladder cancer, cervical cancer, and soft-tissue sarcoma. The ocean’s biodiversity, much of it still undiscovered, represents a vast library of chemical compounds that evolution has refined over hundreds of millions of years.
Education and Career Path
Most marine biologists start with an undergraduate degree in biology, with strong coursework in chemistry, physics, math, and environmental science. Statistics is essential: analyzing experimental data is a core part of nearly every marine biology role. Geography also proves useful, since the field relies heavily on mapping tools and spatial analysis. Many positions in research require a master’s degree or doctorate, though fieldwork technician roles and some government positions are accessible with a bachelor’s degree.
Practical skills matter as much as academic credentials. Researchers who work in the field often need scuba diving certification, and those conducting scientific dives may need specialized training in areas like open-water rescue or polluted-water diving. Comfort with technology is important too. Modern marine biology involves operating underwater vehicles, programming data loggers, and working with complex software for statistical modeling and geographic information systems.
In the United States, marine biologists earn an average salary of about $71,300 per year. The range is wide: the bottom 10% earn around $33,600 annually, while the top 10% earn roughly $114,800. Salaries vary significantly depending on whether you work in academia, government agencies like NOAA, nonprofit conservation organizations, or private industry. The field is competitive, and people who succeed typically combine genuine passion for ocean life with strong quantitative and technical skills.