bio 207 chapter 14: coral reefs

coral reefs

have the greatest biodiversity of any marine ecosystem, biological communities and geologic structures, made of caCO3 or limestone deposited by organisms

corals

cnidarians with cnidocytes and nematocysts, soft polyp is enclosed in a hard shall of CaCO3

hermatypic corals

reef builders (scleractinian corals, AKA stony or true corals), contain zooxanthellae, restricted by water temperature and quality

zooxanthellae

symbiotic photosynthetic dinoflagellates that live within the gastrodermis of each coral polyp, produce glucose through photosynthesis which is passed to coral, helps coral grow faster

ahermatypic corals

do not build reefs, no zooxanthellae, not restricted by water temperature or quality

coral reef polyps

interconnected by thin layers of tissue, share nervous system ad digestive connections, colony developed from one original polyp that asexually reproduced through budding

polyp growth

each polyp lays down new CaCO3 beneath body so colony can grow upward

mushroom coral

a single polyp

brain coral

a colony of polyps

corallite

the cup housing each polyp

taller, branching corals

more common in shallower areas of the reef due to competition for space and light

flatter corals

more common in deeper areas of the reef, assisting with capturing all possible light

sheets of mucous

used to capture zooxanthellae or detritus

mesenterial filaments

extensions of the gut wall that possess additional cnidocytes and digestive enzymes, can be extended allowing coral to feed and digest food outside the body

encrusting coralline algae

grown in rock hard sheets over the reef, deposit CaCO3, keep the reef from washing away, grows over sediment that build up and cements them in place

algal ridge

formed by encrusting coralline algae to protect the reef from waves and erosion

cementing corals in place

allows for upward growth and prevents sediments from damaging polyps

other reef builders

sponges, sea urchins, crustaceans, bryozoans, calcareous green algae, shells of forms, snails and clams

bioerosion

the gradual breakdown and removal of coral material by other organisms, caused by burrowing into the reef or scraping the surface of the reef, sediment does get reincorporated into the reef

burrowing into the reef

sponges, clams and polychaete worms, create spaces where other organisms can hide

scraping the surface to feed

sea urchins, snails, parrotfish

asexual reproduction

budding

sexual reproduction

planula larva, rides on the water currents to a new environment, settles out and begins growing on existing reefs or other hard substrates

light requirements

light must be able to penetrate to the depth of the coral allowing zooxanthellae to photosynthesize, corals mainly found on continental shelves, near islands or on seamounts

temperature requirements

corals can only thrive if water temperatures are over 68 degrees F, above 86 degrees F causes coral stress

coral stress or bleaching

the expulsion of the zooxanthellae from the coral, coral is bleach white, caused by poor water quality, increased sediment in water column, wave stress, disease, low salinity, can die if zooxanthellae are gone for too long

salinity requirements

corals maintain good health around 35 ppt, do not exist near areas where rivers deliver freshwater to marine environment

wave action

corals do not grow in areas of high wave action because it results in suspension of sediments in water column, causing damage to coral and reducing water clarity

pollution

coral is very sensitive, low levels can kill coral

eutrophication

high nutrient levels, allow algae levels to rise which can then shade light-sensitive corals and zooxanthellae

fringing reefs

simplest and most common form, develop near shore in tropical waters as narrow strips along the shore, consists of an inner reef flat and an outer reef slope

reef flat

wide, gently sloping and may be exposed during low tide, slowest growth due to land runoff

reef slope

more steep and is not exposed to air, biodiversity is high, contains living and dead corals, seagrass, soft corals, algae and invertebrates

reef crest

shallow, upper edge of the reef slope, greatest biodiversity and growth

barrier reefs

occurs along shore but separated by a lagoon, consists of a back-reef slope, reef flat, crest, and fore-reef slope, waves wash sediment onto back reef slope or reef flat causing reduced coral growth

fore-reef slope

more pronounced than the back-reef slope, depth of the water drops quickly, growth is highest here or at reef crest

back-reef slope

slope may be steep but not to the degree of the fore-reef slope

keys/cayes

small islands that form from sediment accruing on barrier reefs

Great Barrier Reef

found off the coast of Australia, considered the largest reef structure int he world, length exceeds 1200 miles, width varies from 10-200 miles, consists of many cayes

atolls

circular reef structures surrounding a central lagoon and may contain sand cayes, width varies from 1-20 miles, form when. volcanic island is formed

atoll formation

coral begins as a fringing reef around newly formed island. weathering and geologic activity lowers the level of the island. island dips below water surface leaving the outer band of the coral

inner atoll reef slope

has a more gradual slope than the outer slope

atoll lagoon

normally has a depth of 200 feet or less

the 2 largest atolls

Maldives (Indian Ocean) and Marshall Islands (Pacific Ocean)

coral reef ecology

water column surrounding reef is low in nutrients because reef position away from rivers and other sources of nutrients, water does not support a lot of primary production by phytoplankton

cyanobacteria

fix nitrogen which is then available to other reef inhabitants who feed on the coral

coral reef food chain

producers: seaweeds, coralline algae, photosynthetic bacteria, corals/zooxanthellae
predators: fishes, squids, snails

soft coral and sponge protection

some reef inhabitants deter predators by producing toxic chemicals that are released into the water to kill organisms ro limit growth

spicule protection

sponges produce spicules of CaCO3 or silica and soft corals produce CaCO3 needles for protection

sclerites

CaCO3 needles produced by soft corals for protection

limiting exposure

used to limit competition, some corals grow fast to maximize their ability o reproduce quickly, others grow slow but massive to outcompete others