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