• live suspended in the seawater
• comprise the vast majority of the oceans biomass
• split into floaters and swimmers

• some animals increase their buoyancy
• with containers of gas
• have soft bodies with no hard high density parts

• neutral buoyancy is achieved by the presence of a gas bladder
• not normally present in very active swimmers such as tuna or bottom dwellers
• some fish have a duct that is connected to the esophagus and can add air through this
• in other fish gases must be exchanged with the blood (slower)
• changes in depth cause the gas in the bladder to expand or contract so the fish adds or removes gas to maintain a constant volume

• range in size from microscopic to relatively large such as the jellyfish
• second largest biomass in the oceans after phytoplankton
• microscopic forms have a hard shell
• larger forms have large gelatinous bodies with no hard tissue

• primary consumers- eat phytoplankton-herbivores and omnivores
• three most important groups are
• radiolarians
• foraminifers
• copepods

• single celled
• shell made of silica
• spikes and spines a defense against predators
• also increase surface area so they can float

• single celled
• can be planktonic or benthic
• shell of calcium carbonate
• segmented or chambered

• shrimp like animals in te subphylum Crustacea
• hard exoskeleton
• segmented body jointed legs
• majority of zooplankton biomass
• filter floating food from seawater

• includes
• krill
• coelenterates
• including jellyfish and siphonophores

• means young fry of fish in norwegian
• crustaceans
• 1500 species
• abundant near Antarctica
• eaten by sea birds and whales-important food source

• Portuguese man-of-war
• gas chambers serve as floats and sails that allows the wind to push them across the ocean
• can be washed ashore
• tentacles may be meters long
• possess nematocysts that sting

• bell shaped body
• fringe of tentacles
• mouth hanging below the bellshaped float
• range in size up to 6.6 feet
• tentacles can be 200 feet long
• move by muscular contraction

• includes squids
• fish
• marine mammals

• common squid, flying squid and giant squid
• active predators
• trap water in their body cavity and pass it out through a siphon to move
• use arms with suction pads to catch prey
• mouth resembles a beak

• locomotion occurs when a wave of lateral body curvature passes from the front of the fish to the back
• achieved by the alternate contraction and relaxation of muscle segments called myomeres

• most active swimming fish use two sets of paired fins- pelvic and pectoral to turn brake and balance
• can be folded against the body when not in use
• vertical fins- dorsal and anal- serve as stabilizers
• tail fin (caudal fin) most important for propulsion

• 5 basic types of caudal fin
• rounded fin
• truncate fin
• forked fin
• lunate fin
• heterocercal

• mostly species of fish that are specifically adapted to the deep water environment
• food source is either detritus or each other
• lack of food limits the number and size of these organisms
• specially adapted to efficiently find and collect food
• have long antennae, or sensitive lateral lines
• large sensitive eyes
• some species are blind and rely on smell

• over half of deep sea fish can bioluminesce which means they can produce light organically
• use specially designed cells called photophores which contain symbiotic luminenscent bacteria

• attracts prey
• staking out territory by patrolling
• communicating or seeking a mate
• escaping predators by using a flash of light to blind them

• lungers
• some fish wait for prey and exert themselves in short bursts when they lunge at the prey
• such as the grouper
• truncate caudal fins for speed and maneuverability

Cruisers

• actively seek prey eg. tuna

• fish are mostly cold blooded and are not fast swimmers
• tuna have body temps much higher than their environment- warm blooded this allows them to swim faster

• large numbers of fish that form well-defined social groupings
• in the school individuals move at the same speed and are evenly spaced
• provides protection from predators