Marine Biology Cheat Sheet

The core ideas of Marine Biology distilled into a single, scannable reference — perfect for review or quick lookup.

PiqCue — piqcue.com/marine-biology/cheatsheet

Quick Reference

Marine Ecosystems

Complex biological communities and the physical environments they inhabit in the ocean, including coral reefs, deep-sea vents, open ocean pelagic zones, and coastal wetlands. These ecosystems are defined by abiotic factors such as light, temperature, salinity, and pressure, which shape the organisms that can survive there.

Ocean Zonation

The division of the ocean into distinct vertical and horizontal zones based on depth, light penetration, and distance from shore. The major depth zones are the epipelagic (sunlight), mesopelagic (twilight), bathypelagic (midnight), abyssopelagic (abyssal), and hadopelagic (trench) zones.

Coral Bleaching

The process by which corals expel the symbiotic zooxanthellae algae living in their tissues when subjected to environmental stress, particularly elevated water temperatures. Without these algae, corals lose their color and their primary source of nutrition, often leading to death if conditions persist.

Marine Food Webs

The interconnected networks of feeding relationships in ocean ecosystems, beginning with primary producers like phytoplankton and seagrasses, passing through herbivorous zooplankton and small fish, and extending to apex predators such as sharks, orcas, and tuna.

Bioluminescence

The production and emission of light by living organisms through chemical reactions, most commonly involving the molecule luciferin and the enzyme luciferase. In the deep sea where sunlight cannot penetrate, bioluminescence is used for communication, predation, camouflage, and mate attraction.

Ocean Acidification

The ongoing decrease in the pH of ocean water caused by the absorption of excess atmospheric carbon dioxide. When CO2 dissolves in seawater it forms carbonic acid, which reduces the availability of carbonate ions that marine organisms need to build calcium carbonate shells and skeletons.

Marine Protected Areas (MPAs)

Designated regions of the ocean where human activities such as fishing, mining, and drilling are restricted or prohibited to conserve biodiversity, protect critical habitats, and allow depleted populations to recover. MPAs vary from fully no-take reserves to multiple-use zones.

Symbiosis in Marine Environments

Close, long-term biological interactions between two or more different species in the ocean, which can be mutualistic (both benefit), commensal (one benefits, the other is unaffected), or parasitic (one benefits at the other's expense). Marine symbioses are among the most ecologically important relationships on Earth.

Thermohaline Circulation

A global system of ocean currents driven by differences in water density caused by variations in temperature and salinity. Often called the global ocean conveyor belt, this circulation redistributes heat around the planet and plays a crucial role in regulating global climate and transporting nutrients.

Marine Biodiversity Hotspots

Regions of the ocean that support exceptionally high species diversity and endemism, often coinciding with complex habitats like coral reefs, seamounts, and upwelling zones. These hotspots are critical for global biodiversity but are often disproportionately threatened by human activities.

Key Terms at a Glance

Abyssal Plain:Vast, flat areas of the deep ocean floor, typically between 3,000 and 6,000 meters depth, covered in fine sediment.

Algal Bloom:A rapid increase in the population of algae in an aquatic system, often caused by nutrient pollution, which can deplete oxygen and produce toxins.

Benthic:Relating to the bottom of a body of water or the organisms that live on or in the seafloor sediment.

Biodiversity:The variety and variability of life forms within a given ecosystem, biome, or the entire planet, including genetic, species, and ecosystem diversity.

Biomagnification:The increasing concentration of a substance, such as a toxin or pollutant, in the tissues of organisms at successively higher levels in a food chain.

Bycatch:The incidental capture of non-target species during commercial fishing operations, including marine mammals, sea turtles, and seabirds.

Chemosynthesis:The biological production of organic molecules using energy from chemical reactions with inorganic compounds rather than sunlight.

Continental Shelf:The extended perimeter of a continent submerged under relatively shallow ocean water, typically less than 200 meters deep, supporting rich marine life.

Dead Zone:A hypoxic area in a body of water where dissolved oxygen is too low to support most marine life, often caused by eutrophication.

Demersal:Relating to organisms that live near or on the bottom of the sea, such as flatfish, crabs, and lobsters.

Estuary:A partially enclosed coastal body of water where freshwater from rivers meets and mixes with saltwater from the ocean, creating a unique brackish environment.

Eutrophication:The excessive enrichment of a water body with nutrients, especially nitrogen and phosphorus, leading to dense plant and algal growth and oxygen depletion.

Gyre:A large system of circular ocean currents formed by global wind patterns and the Coriolis effect, which can accumulate floating debris like plastic.

Hydrothermal Vent:A fissure on the seafloor from which geothermally heated water discharges, supporting unique chemosynthetic ecosystems in the deep ocean.

Intertidal Zone:The area of the shore between the high-tide and low-tide marks, subject to alternating periods of submersion and exposure to air.

Get study tips in your inbox

We'll send you evidence-based study strategies and new cheat sheets as they're published.

We'll notify you about updates. No spam, unsubscribe anytime.