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Chapter 18 Life in the Ocean’s Depths © 2006 Thomson-Brooks Cole Key Concepts • Several thousand species have adaptations that allow them to survive in the deep-sea environment. • The lack of light has had the most impact in shaping the organisms of the deep sea. • Many deep-sea animals exhibit bioluminescence, which helps them find mates and prey in their dark environment. © 2006 Thomson-Brooks Cole Key Concepts • Deep-sea fishes display a variety of adaptations such as sharp teeth, large mouths, and huge stomachs that help them survive in a habitat with limited food. • The environmental conditions of the deep sea have been relatively stable for more than 100 million years, and as a result, several organisms have changed very little from when they first evolved. © 2006 Thomson-Brooks Cole Key Concepts • Benthic communities consist of sparse populations that survive on the minimal food available in their environment. • Thriving marine communities that depend on chemosynthetic bacteria for primary production exist on the ocean floor around hydrothermal vents. © 2006 Thomson-Brooks Cole Survival in the Deep Sea • The deep sea is an inhospitable place – frigid temperatures throughout the year – tremendous pressure – total darkness • Conditions have remained stable over many years • Some creatures have evolved to survive in this harsh environment © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Survival in the Deep Sea • Adaptations to pressure – fluid pressure within the animal’s tissues matches the pressure of the seawater • Adaptations to cold – nearly all have body temperatures close to that of the surrounding water – slow metabolism – slow movement, growth; less reproduction, longer life – high density of cold water matches that of animal’s bodies – they don’t sink © 2006 Thomson-Brooks Cole Life in the Dark • Color in deep-sea organisms – countershading employed in the disphotic zone—region of dim light (twilight) • photophores (light-producing organs) may be used to make the ventral surface lighter – many species are bright red or orange • appear black or gray in dim light – many are bioluminescent © 2006 Thomson-Brooks Cole Life in the Dark • Roles of bioluminescence – how bioluminescence works • a protein called luciferin is combined with oxygen in the presence of an enzyme called luciferase and adenosine triphosphate (ATP) • chemical energy of ATP converted to light – camouflage • bioluminescence matches the intensity of sunlight, and thus contributes to countershading, in the twilight zone © 2006 Thomson-Brooks Cole Life in the Dark • Roles of bioluminescence (continued) – mating and species recognition • identifies the sex of an individual • allows for identification of species – attracting prey • anglerfish and stomiatoids attract prey with bioluminescent lures • light may be used to locate prey in the dark – defense • deepwater squid and shrimp release clouds of bioluminescent materials to confuse predators © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Life in the Dark • Seeing in the dark – many deep-sea fishes have tubular eyes containing 2 retinas instead of 1 • 1 retina views distant objects, while the other views closer objects © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Life in the Dark • Seeing in the dark – deep-sea squid have barrel-shaped, stalked or unequally-sized eyes – some animals have slightly-functional eyes or are totally blind, relying on chemical stimuli instead © 2006 Thomson-Brooks Cole Life in the Dark • Finding mates in the dark – male becomes a parasite on the female in some species of anglerfish • Finding food in the dark – benthic organisms and scavengers eat detritus which drifts down from above – many small fishes and invertebrates migrate upward at night to feed – adaptations include large mouths and expandable stomachs © 2006 Thomson-Brooks Cole Life in the Dark • Finding food in the dark (continued) – some can eat prey larger than themselves – stomiatoids have barbels (fleshy projections) that may be used as lures, probes or for species recognition – anglerfishes have a spine used as a fishing pole, tipped with a luminous lure © 2006 Thomson-Brooks Cole Giants of the Deep • Giant squids • New species of deepwater squid – large, unnamed species discovered 1988 – have longer arms than other squid, bent downward at sharp angles – exhibit different behaviors • hide in their ink clouds instead of fleeing • pairs have been observed attached, towing each other through the water © 2006 Thomson-Brooks Cole Relicts from the Deep • Spirula – small molluscs resembling squid and octopuses with spiral-shaped internal shells – similar to belemnites common in the sea 100-50 million years ago • Vampire squid – dark-colored, webbing between its arms – thought to be descendents of an intermediate organism between squids and octopuses © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Relicts from the Deep • Coelacanth – fish with large, thick scales and fleshy bundles between its body and fins – thought to be extinct for 70 million years until 1 was caught alive in 1938 • Neopilina – limpet-like mollusc – thought to be extinct for 350 million years until 1 was found in 1952 © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Benthic communities – sources of food for benthic organisms • organic matter rains down from surface waters and accumulates on the ocean floor • a large carcass will occasionally drift down – food chains • bacteria are consumed by meiofauna (e.g. foraminiferans and nematodes) • infauna (e.g. worms, bivalves) eat meiofauna • deposit feeders and suspension feeders • predators include fishes, squids, sea stars © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Benthic communities (communities) – diversity of benthic organisms of the deep • low numbers, but high diversity • ineffective dispersion of young may lead to isolation, which contributes to speciation • stable conditions may prevent extinction of species, so species proliferate © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Vent communities – self-contained communities that are some of the most productive in the sea – formation of vents • vents form at spreading centers • seawater seeps down to where it contacts magma • water is superheated, and loses some minerals while it picks up others, such as sulfur, iron, copper and zinc © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Vent communities (continued) – types of vents • white smokers—produce a stream of milky fluid rich in zinc sulfide; water temperature is normally less than 300o C • black smokers—narrow chimneys that emit a clear water with temperatures of 300o to 450o C that is rich in copper sulfides (which precipitate with contact with cold seawater, to produce the black color) © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Vent communities (continued) – vent communities • residents include large clams, mussels, anemones, barnacles, limpets, crabs, worms and fishes • primary producers are chemosynthetic bacteria • primary consumers filter-feed or graze bacteria from the water • clams (Calyptogena), mussels (Bathymodiolus) and vestimentiferan worms (Riftia) host symbiotic chemosynthetic bacteria © 2006 Thomson-Brooks Cole Life on the Sea Bottom • Vent communities (continued) – rise and fall of vent communities • vents are colonized by organisms shortly after they are formed • when geological changes inactivate the vent (an estimated 20 years later), these organisms all die • vent inhabitants are thought to produce large numbers of larvae which drift to other vent sites © 2006 Thomson-Brooks Cole