Ch. 10: The Open Sea Ch. 10 The Open Sea: Pelagic Zone Pelagic Zone away Away from coast, over continental shelf from coast/continental shelf. Little upwelling & low primary productivity = most animals stay Little upwelling & low primary productivity = Most animals stay near photic zone near photic zone
Pelagic Inhabitants Plankton! Holoplankton: Permanent Copepod Crustaceans most numerous Jellies (95% H 2 O) Euphausiids (krill) Meroplankton: Temporary Larval stages of broadcast spawning fish & inverts. Benthic & nektonic spp.
Pelagic Nektonic Inhabitants Most are vertebrates Teleosts (Rayfins): Dominant marine vertebrate (90% of all fish) Bluefin Tuna Black seabass Few Invertebrates: Squid, few shrimp
Vertical Distribution Most live in Epipelagic: upper 200m (photic zone) Complex food chain Most animals exhibit countershading Many predatory carnivores
Vertical Distribution Mesopelagic: below photic zone (200-1000m) Many feed directly or indirectly on detritus from above (marine snow) Most fish are small (5-20 cm), large eyes, big mouths & teeth Many have photophores: light producing organs
Unusual Fish of the Mesopelagic Unusual Fish of the Mesopelagic Lanternfish Female Attached male Anglerfish
Bioluminescense Light produced by an organism via a chemical reaction Chemical energy converted to light energy May be generated by symbiotic organisms w/in a larger organism Usually blue color Blue wavelength penetrates deepest through water Used to find food, mates, & defend to against predators
Advertise for mates: unique flash code, or specially-shaped photophores (species specific) attracts opposite sex Lure prey: attract prey with a glowing lure that dangles from end of its fishing pole Search for prey: photophores under eyes helps them find prey (flashlight) Anglerfish Black Dragonfish Avoid Predation: Squirt out a bioluminescent cloud onto predator, escape into darkness
Vertical Migrations Mesopelagic species make daily vertical migrations in water column Exploit both zones: Epipelagic: > Temp., light intensity, food Mesopelagic: Safer from predators (low light) Cold, viscous water = lower metabolic rate & food sinks slowly Copepod migration
Bouyancy Bone, muscle more dense than seawater To avoid sinking & save energy, store less dense substances in body: Fat & oil: Blubber (marine mammals & penguins) Oil in muscles & liver (sharks, teleosts) Air: Pneumatophore (air-filled float in surface jellies) Lungs (mammals, birds, reptiles) Swim bladder! (Teleosts)
Swim Bladder: O 2 & N 2 (nitrogen) Absent in some bottom fish & continuous swimmers (Tuna) Some gulp air at sea surface Gas glands regulate secretion of gas from the blood into the bladder Descending: H 2 O pressure squeezes gas out = fish must air in bladder Ascending: gases expand = fish must get rid of excess gas
Slow Ascension: ensures gases are reabsorbed into bloodstream Rapid ascension: swim bladder expands too quickly Damages internal organs Bladder out mouth or anus
Streamlined Fast Swimmers! Cetaceans (Dolphin, Orca), Sharks (Mako, Great white), billfish, Tuna TUNA: among fastest animals in sea Small, smooth scales Non-bulging eyes Retractable fins Finlets turbulence Swimming muscles = 75% of body wt. finlets
Amazing Tuna! Red muscle fibers = 50%+ of swimming muscles Rich in myoglobin (O 2 ): used for aerobic activity Countercurrent heat exchange system: Cold blood enters system & is warmed by blood leaving red muscle Don t lose any heat Bluefin tuna (Thunnus thynnus) Yellowfin Tuna
Migration Larger & faster nekton have regular long-distance migrations To better exploit food resources Mating & spawning grounds May take months/year Difficult to observe Radio tag Electronic Tag Scientists rely on tagged individuals Visual Tags
Salmon Migration & Mating Anadromous: spend most of life at sea, born & spawn in river (freshwater - FW) Remain in FW for ~ 2 years Migrate to ocean, stay until sexually mature (few yrs.) Swim upstream to spawn & die Make several circuits of gyre Sockeye Salmon
Elephant Seal Migration (Feed & Breed) Forage at sea: 8-9 months 2 migrations to breeding rookeries/yr. Molt & fast Molt & fast Mate 2 wks. after pupping
Elephant Seal Migration (Feeding) Foraging site differences: males prefer oil rich squid near subartctic Females have lower energy requirements: take shorter migrations Dive up to 90% of time Dive up to 90% of time
Mating Habits Polygynous: Adult alpha males defend a harem of ~ 50 females Fight (spar) for dominance Subdominant males sneak copulation when alpha male is distracted Males fast during 3 month breeding season
White Sharks & Red Triangle 120 mile long coastal zone Sharks hunt near seal rookeries 45% of Gr. White attacks on humans in red triangle