Chapter 9 Key Concepts

Nekton can swim to the degree that they can overcome many ocean currents. Nekton usually live in a world dominated by high Reynolds number conditions.
Cephalopods belong to the phylum Mollusca, are nearly always carnivorous, and are characterized by complex behaviors, a well-organized nervous system, a circle of grasping arms, and a powerful beak.
Some cephalopods can regulate buoyancy by altering the gas content within a rigid structure.
The marine fishes, which occupy nearly all marine habitats, include two major groups: the cartilaginous fish (sharks, skates, and rays) and the bony fish.
While bony fishes have a rigid skeleton for muscular attachment and contraction in swimming, larger sharks strengthen their cartilaginous skeletons with mineral matter within cartilage and with external mineral plates.
Swimming is often accomplished by means of undulatory body movements, with the aid of paired and single median fins.
There are three main functional components to swimming: accelerating, cruising, and maneuvering.
The body form of fishes is often a good indicator of feeding and habitat requirements.
Fish gain oxygen by passing water over gills, within which blood flows counter to the external water current.
Fishes differ in buoyancy owing to bulk composition, but most bony fishes use a swim bladder to alter buoyancy by changing the gas content.
Most fishes feed by means of suction and ram feeding.
Fishes use teeth to scrape algae from surfaces, tear prey, and crush shells. Many fishes use gill rakers to suspension feed.
Fishes perceive other fishes, prey, predators, and the environment using many structures—the eyes, a lateral-line system, olfactory organs, otoliths for hearing, and in some groups, electroreceptors.
Sound travels efficiently through water and therefore is important for detection and for communication.
Sounds can be produced by muscle vibration against the swim bladder, external body part stridulation, and other techniques.
Sounds are produced by some species during the reproductive season.
Tunas, some billfishes, and the butterfly mackerel are warm-blooded, which aids in sustained activity and in maintaining temperature while moving into environments at which temperatures vary.
The mammalian order Cetacea includes the toothed whales and dolphins, Odontoceti, and the baleen whales, the Mysticeti. All are streamlined and highly adapted to a fully marine existence.
Odontocetes generally prey on large animals and have sophisticated oral communication and complex social behavior.
Mysticetes have keratinous baleen plates that replace the function of the more typical mammalian teeth found in odontocetes. They feed on smaller animal prey such as larger crustacean zooplankton and small fishes.
Pinnipeds include seals, sea lions, and walruses and have hair but lack the fat layers of cetaceans. Sea otters are marine mammals belonging to the family Mustelidae that are coastal carnivores.
Sirenians include manatees, dugongs, and sea cows. They are hairless and usually herbivorous.
Diving causes problems of oxygen shortage, which require a number of conservation responses.
Seabirds include the penguins, the petrels and their allies, the pelicans, and the gulls and their allies.
Seabirds are nearly always monogamous and nearly always breed communally in large colonies.
Territoriality and combat are common in seabirds because high-quality nesting sites are in short supply.
Mating pairs may be formed before or after a nesting site is chosen. Courtship often includes elaborate displays, which may involve groups of males.
Nesting sites vary in substratum type, degree of slope, and degree of isolation. Many species may share a given area.
The breeding cycle includes periods of nest site establishment, egg laying and incubation, and fledging.
Seabirds migrate to maximize use of feeding and nesting areas.
Food gathering depends on the alternative strategies of efficient long-distance flying and shallow diving.
Shorebirds migrate great distances between nesting and feeding grounds.
Shorebird feeding is diverse and is related to strong differences in beak morphology.
Female sea turtles lay eggs on specific beaches and migrate between the beach and seasonal feeding grounds great distances away.