The profiles and guides on this site use a small number of technical terms, and each is defined here in plain language. Entries are alphabetical, and where a term is covered in more depth, a link points to the guide that explains it. If a word you met on the site is missing, tell the editors through the contact page and it will be considered for the next review.
A
- Ampullae of Lorenzini
- Jelly-filled pores on the snout and head of sharks, rays and their relatives that detect the faint electric fields produced by living animals. They work over a few inches and are used for the last stage of a strike. Read more: How Ocean Predators Find Their Prey
- Anaerobic metabolism
- Energy production that does not use oxygen. Diving animals switch to it when stored oxygen runs out, producing lactic acid that takes time to clear after surfacing. Read more: How Marine Animals Dive Deep on One Breath
- Apex predator
- A predator at the top of its food web that is not regularly hunted by other animals once fully grown. Orcas and white sharks are common examples, though even apex predators are affected by disease, pollution and human activity. Read more: Ocean Food Webs: Plankton to Apex Predators
B
- Bathypelagic zone
- The dark open-water layer roughly 3,300 to 13,000 feet below the surface, sometimes called the midnight zone. No sunlight reaches it and animals there depend on food sinking or swimming down from above. Read more: Marine Ecosystems: Ocean Zones and Habitats
- Bioluminescence
- Light produced by a living organism through a chemical reaction. In the deep ocean it is used to attract prey, camouflage the silhouette of an animal against faint light from above, and communicate. Read more: How Ocean Predators Find Their Prey
- Blubber
- A thick layer of fat beneath the skin of marine mammals that insulates the body, stores energy and adds buoyancy. Read more: Speed, Warmth and Body Design in Ocean Predators
- Bradycardia
- A slowing of the heart rate. Diving mammals use it deliberately to conserve oxygen, in some cases dropping to a small fraction of the surface rate. Read more: How Marine Animals Dive Deep on One Breath
- Bycatch
- Animals caught unintentionally by fishing gear aimed at other species. Sharks, turtles, seals and dolphins are among the animals most often caught this way. Read more: Ocean Predator Conservation: Threats and Recovery
C
- Cathemeral
- Active at irregular intervals throughout the day and night rather than being strictly diurnal or nocturnal.
- Cephalopod
- A member of the group of mollusks that includes squid, octopus, cuttlefish and nautilus. They have a distinct head, arms or tentacles, and in most cases a highly developed nervous system.
- Cetacean
- A whale, dolphin or porpoise. Cetaceans are divided into toothed whales, which echolocate, and baleen whales, which filter small prey from the water.
- Conservation status
- A category that summarizes how likely a species is to go extinct, such as Least Concern or Endangered. Status is a judgment of risk under defined criteria, not a count of individuals. Read more: How to Read a Conservation Status
- Continental shelf
- The gently sloping seabed that extends from a coastline to a depth of roughly 650 feet, where the slope steepens. It is shallow enough for sunlight to reach the bottom in many places and is the most productive and most heavily fished part of the ocean. Read more: Marine Ecosystems: Ocean Zones and Habitats
- Countercurrent exchange
- An arrangement in which two streams of fluid flow in opposite directions side by side so that heat or gas passes from one to the other. Tuna, lamnid sharks and leatherback turtles use it to keep heat in the body. Read more: Speed, Warmth and Body Design in Ocean Predators
- Critically Endangered
- The highest category of threat on the IUCN Red List for wild species, applied when the risk of extinction in the wild is extremely high. Read more: How to Read a Conservation Status
D
- Data Deficient
- A Red List category for species with too little information to assess the risk of extinction. It is not a category of threat and does not mean a species is safe. Read more: How to Read a Conservation Status
- Deep scattering layer
- A band of fish, squid and zooplankton that rises toward the surface at night and sinks to deeper, darker water by day. It was first noticed because it reflected the pulses of early sonar and appeared to be a false seafloor. Read more: Marine Ecosystems: Ocean Zones and Habitats
E
- Echolocation
- Sensing the surroundings by producing sound and interpreting the echoes. Toothed whales do it with clicks produced in the head. Read more: How Ocean Predators Find Their Prey
- Ecotype
- A population that is adapted to a particular environment or way of life and differs from others of the same species in diet, behavior or appearance. Orcas are divided into several ecotypes. Read more: Hunting at the Poles: Predators of Sea Ice and Cold Water
- Ectotherm
- An animal whose body temperature is set mainly by its surroundings. Most fish are ectotherms, with the exception of a few warm-bodied species.
- Endothermy
- The production of body heat by the animal's own metabolism. Mammals and birds are fully endothermic, and a few fishes are regionally endothermic. Read more: Speed, Warmth and Body Design in Ocean Predators
- Epipelagic zone
- The sunlit surface layer of the open ocean, from the surface to roughly 650 feet, where there is enough light for photosynthesis. Read more: Marine Ecosystems: Ocean Zones and Habitats
F
- Food web
- The set of feeding relationships in an ecosystem, showing who eats whom. A food web is more realistic than a single food chain because most animals eat a variety of prey. Read more: Ocean Food Webs: Plankton to Apex Predators
G
- Generation length
- The average age of parents of the current population of a species. The Red List measures population decline over the longer of ten years or three generation lengths, so slow-breeding animals are judged over long periods. Read more: How to Read a Conservation Status
- Gigantothermy
- The retention of heat by very large body size, which gives a low surface area relative to volume. Leatherback turtles use it, together with insulation and heat exchange in the flippers, to stay warm in cold water. Read more: Speed, Warmth and Body Design in Ocean Predators
H
- Hemocyanin
- A copper-based protein that carries oxygen in the blood of squid, octopus and many other mollusks and crustaceans. It gives their blood a blue color. Read more: How Marine Animals Dive Deep on One Breath
K
- Krill
- Small shrimp-like crustaceans that feed on algae and form enormous swarms, especially in the Southern Ocean. They are the main food of many baleen whales, seals, penguins and fish. Read more: Hunting at the Poles: Predators of Sea Ice and Cold Water
L
- Lamnid shark
- A member of the family Lamnidae, which includes the great white and the shortfin mako. Lamnids are powerful, warm-bodied sharks with streamlined bodies and crescent-shaped tails. Read more: Speed, Warmth and Body Design in Ocean Predators
- Lateral line
- A row of pressure-sensing organs along the sides of fishes that detects movement and pressure changes in nearby water. Read more: How Ocean Predators Find Their Prey
M
- Matriline
- A group of animals related through the female line, such as a mother, her offspring and their offspring. Resident orcas live in lifelong matrilines.
- Melon
- A fatty organ in the forehead of toothed whales that focuses the clicks used in echolocation into a beam. Read more: How Ocean Predators Find Their Prey
- Mesopelagic zone
- The twilight layer of the ocean between roughly 650 and 3,300 feet, where some light penetrates but not enough for photosynthesis. Read more: Marine Ecosystems: Ocean Zones and Habitats
- Myoglobin
- An oxygen-binding protein in muscle. Deep-diving mammals have very high concentrations, which store oxygen in the muscle and give their flesh a dark color. Read more: How Marine Animals Dive Deep on One Breath
N
- Near Threatened
- A Red List category for species that are close to qualifying for a threatened category or are likely to qualify without conservation action. Read more: How to Read a Conservation Status
O
- Oceanic zone
- The open water beyond the continental shelf, where the seabed is far below. It covers most of the ocean's volume. Read more: Marine Ecosystems: Ocean Zones and Habitats
P
- Pinniped
- A seal, sea lion or walrus. The name means fin-footed and refers to the flippers that all members of the group share.
- Pod
- A group of whales or dolphins that travel and feed together. The size and stability of a pod varies widely between species and populations.
- Primary production
- The creation of organic matter from sunlight or chemical energy by algae, plants and some bacteria. It is the base of every food web. Read more: Ocean Food Webs: Plankton to Apex Predators
R
- Regional endothermy
- The ability of some fishes to keep particular parts of the body, such as the swimming muscle, eyes or brain, above the temperature of the water. Read more: Speed, Warmth and Body Design in Ocean Predators
- Rete mirabile
- A dense network of small blood vessels that works as a heat exchanger. In tuna and lamnid sharks it keeps muscle heat from being lost through the gills. Read more: Speed, Warmth and Body Design in Ocean Predators
S
- Sea ice
- Frozen seawater that floats on the surface of the polar oceans. It forms, drifts and melts with the seasons and provides a platform for hunting, resting and breeding. Read more: Hunting at the Poles: Predators of Sea Ice and Cold Water
- Seamount
- An underwater mountain that rises from the seafloor without reaching the surface. Seamounts disturb currents and attract concentrations of plankton, fish and their predators. Read more: Marine Ecosystems: Ocean Zones and Habitats
- Statocyst
- A small organ of balance and motion sensing found in squid, octopus and many other invertebrates. Read more: How Ocean Predators Find Their Prey
T
- Thermocline
- A layer of water in which temperature drops rapidly with depth. It separates warm surface water from cold deep water and affects where animals live and hunt. Read more: Marine Ecosystems: Ocean Zones and Habitats
- Trophic level
- The position of an organism in a food web, counted in steps from primary producers. Plants and algae are level one, herbivores level two, and so on. Read more: Ocean Food Webs: Plankton to Apex Predators
U
- Upwelling
- The rising of cold, nutrient-rich deep water to the surface, often along coasts where wind pushes surface water away from the shore. Upwelling zones support some of the richest fisheries and predator populations in the world. Read more: Ocean Food Webs: Plankton to Apex Predators
V
- Vibrissae
- Stiff whiskers with a rich nerve supply. Seals and walruses use them to detect the movement of prey in dark or cloudy water. Read more: How Ocean Predators Find Their Prey
- Viviparous
- Giving birth to live young rather than laying eggs. All marine mammals are viviparous, as are many sharks.
- Vulnerable
- A Red List category for species that face a high risk of extinction in the wild. Read more: How to Read a Conservation Status
Z
- Zooplankton
- Small drifting or weakly swimming animals, such as copepods, krill and the larvae of fish. They graze on algae and are food for fish, squid, seabirds and whales. Read more: Ocean Food Webs: Plankton to Apex Predators
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