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Lecture Notes
Marine Biology (MARSC 180)
L. Snyder
Ch. 10: The Open Sea
Pelagic Zone – away from coast/continental shelf.
Little upwelling & low primary productivity = most animals stay near photic zone
Pelagic Inhabitants
•Plankton!
•Holoplankton: Permanent
•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)
•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
•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: Examples – Lanternfish, Anglerfish (female with attached male
(see text for more)
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
•Purposes:
Search for prey: photophores under eyes helps them find prey (flashlight)
Avoid Predation: Squirt out a bioluminescent cloud onto predator, escape into darkness
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
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
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) – contains primarily O2 & N2 (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: H2O 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
Fast Swimmers!
•Streamlined
–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.
Amazing Tuna!
•Red muscle fibers = 50%+ of swimming muscles
–Rich in myoglobin (O2): used for aerobic activity
•Countercurrent heat exchange system:
•Cold blood enters system & is warmed by blood leaving red muscle
–Don’t lose any heat
Migration
•Larger & faster nekton have regular long-distance migrations
•To better exploit food resources
•Mating & spawning grounds
–May take months/year
–Difficult to observe
–Scientists rely on tagged individuals
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
Elephant Seal Migration (Feed & Breed)
•Forage at sea: 8-9 months
•2 migrations to breeding rookeries/yr.
•Molt & fast
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
Elephant Seal 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
•Sharks hunt near seal rookeries
•45% of Gr. White attacks on humans in red triangle