Introduction to Marine Biology (Chapter 1)
1/28/2026
Samuel Clifford
These notes come from the marine biology text book Marine Biology: Function, Biodiversity, Ecology by Jeffrey S. Levinton. The mla citation for the book is below:
Levinton, Jeffrey S. Marine Biology: Function, Biodiversity, Ecology. 6th ed., Oxford University Press,
Chapter 1: Sounding the Deep
“Functional Biology refers to the way organisms solve problems and how physical and chemical factors constrains and select the solutions.” (pg. xvi)
“Ecology examines the interactions of organisms with their environment and tries to understand the distribution and abundance of organisms.” (pg. xvi)
“Functional Biology is the study of how an organism carries out basic functions such as reproduction, locomotion, and feeding as well as the cellular and biochemical processes related to digestion, respiration, and other aspects of metabolism.” (Pg. 1)
“Ecology, on the other hand, is the study of the interaction of organisms with their physical and biological environments and how these interactions determine the distribution and abundance of the organisms.” (Pg. 1)
-Edward Forbes (1815-1854) of the Isle of Man was an English-speaking marine biologist who possibly put forth the first marine biological hypothesis when he suggested the azoic theory which stated that no life existed on sea floors deeper than 1800ft.
-Marine Biology as an academia flourished in many universities and World War II expanded our knowledge of the ocean as countries needed more navigational information. Advances in navigation, deep-sea bottom drilling, remote sensing, and other techniques led to great expansion of our knowledge of the sea.
Equipment Used For Marine Biology:
-Remotely Operated Vehicles (ROVs): unmanned vehicles that can make precise surveys and take samples.
-Autonomous Underwater Vehicles (AUVs): robots not connected to the ship.
-Gilders: a variant of AUVs which use simple balancing devices to allow the vehicle to rise and fall through the water column or be moved by vanes in a constant direction by wave action.
The water column is a concept used in oceanography to describe the chemical and physical characteristics of seawater at different depths for a defined geographical point.
*Gliders made observations of the water column during the major Hurricane Sandy in New York-New Jersey waters in 2012.
Nothing in shallow water has matched the importance of scuba diving. It was developed in the 1940s but wasn’t often used until the late 1950s when biologist Thomas Goreau pioneered the study of coral reefs in Jamaica.
Classifying Marine Organisms By Habitat:
Plankton are organisms that live suspended in the water as though they may have some locomotory power they do not have enough to counteract ocean currents or turbulence.
Neustons are organisms that inhabit the thin surface layer of the ocean, living right at the interface between air and water. They include a wide range of life forms, from tiny microbes to small invertebrates, all adapted to survive in this unique, sunlit boundary zone. Some microorganisms even cling to the sea‑surface slick, a delicate film of organic material that forms on calm waters. A well‑known example is the cyanobacterium Trichodesmium, which often gathers into reddish‑brown patches that float visibly at the ocean’s surface.
Nekton are actively swimming aquatic animals that can move independently of water currents. Unlike plankton, which drift, nekton have strong locomotion and can migrate, hunt, and navigate through the water column on their own. Examples include fish such as tuna, marine mammals like dolphins, and fast‑moving invertebrates such as squid.
Benthos are animals or plants that are associated with the sea floor. Some animals are infaunal meaning they burrow within the sea floor. Others are epifaunal which means they live on the sea floor surface. Organisms that are more mobile and yet are still associated with the sea floor are called demersals.
Below are a photo and video of an Ocellated Flounder (Ancylopsetta quadrocellata) I have taken. Flounders are an example of Benthic Demersal organisms. They are mobile and able to swim as seen in the videos which makes them demersal. Yet, they are still associated with the sea floor as they rest on the substrate, feed on bottom-dwelling prey, and use camouflage to blend in to the seafloor.
Depth Zones:
The ocean depth can be separated into zones. These depth-based marine zones form a vertical structure that reflects how light, temperature, and pressure change as you move downward through the ocean. At the surface is the epipelagic zone, extending from 0 to 200 meters. This is the sunlit region where enough light penetrates to support photosynthesis, making it the most biologically productive part of the ocean. Warm temperatures and abundant nutrients support fish, plankton, marine mammals, and most of the life people commonly associate with the sea.
Below this lies the mesopelagic zone, ranging from 200 to 1,000 meters. Often called the twilight zone, it receives faint, filtered light, which is too little for photosynthesis. Temperatures drop sharply here, and many organisms rely on bioluminescence for communication, camouflage, or hunting. Creatures such as lanternfish and deep-diving squid dominate this region, and many species migrate vertically each day to feed in shallower waters at night.
Descending further leads to the bathypelagic zone, stretching from 1,000 to 4,000 meters. This is the midnight zone, a realm of complete darkness where sunlight never reaches. Temperatures hover near freezing, and the pressure becomes immense. Life persists through extreme adaptations: slow metabolisms, flexible bodies, and specialized sensory systems. Iconic deep-sea species such as anglerfish and giant squid inhabit this layer.
Below that is the abyssopelagic zone, from 4,000 to 6,000 meters. Conditions here are even more severe as it is in perpetual darkness, crushing pressure, and near-zero temperatures. The seafloor in this depth range is known as the abyssobenthic zone, consisting of vast, flat plains where organisms like sea cucumbers, brittle stars, and other extremophiles survive on sinking organic material from above.
The deepest environments in the ocean belong to the hadal zone, which includes trenches that plunge beyond 6,000 meters. These narrow, isolated regions experience the most extreme pressures found on Earth. Despite the harshness, life persists in the form of specialized amphipods, snailfish, and microbial communities. The Marianas Trench, reaching roughly 11,000 meters, is the most famous example of a hadal environment and represents one of the least explored habitats on the planet.