Exam 1

** Only intro to coral reef slide deck added so far

What percent of the world’s reefs are threatened or destroyed?

70%

True or False: Even though they occupy less than 0.1% of the world’s ocean surface, coral reefs contain 25% of marine species.

True, they are the most diverse ecosystems on earth.

What are coral reefs?

Compacted and cemented underwater structures made from calcium carbonate secreted by the corals.

What are the biological/coral aspects of a reef?

• Organic, biogenic

• Coral and algal communities

• Mostly hermatypic corals, al

What are the geological aspects of a reef?

• Carbonate

• Buildup

• Wave resistant

• Cemented, consolidated

How old are coral reefs?

~500 Million years old (late cambrian)

How old is the earth?

4.6 Billion years old

True or False: Corals started as solitary organisms.

True, they eventually evolved to become colonial.

What extinction events have corals gone through?

• Ordovician-Silurian extinction: drop in sea level and temp

• Devonian (410 MYA): coral re-appeared, formed extensive reef systems

• 350 MYA corals disappeared from fossils

• 260 MYA corals reappeared

• Permian-Triassic extinction: wiped 96% of marine spp, hypoxia and hypercapnia (high CO2)

• 65 MYA cretaceous-tertiary mass extinction: meteor

• 55 MYA Paleocene/Eocene thermal maximum: global warming

• 20 MYA Great barrier reef formed

What do tropical reefs need to live?

• High light levels

• High water transparency

• Water temp >20 C (68F)

• Low nutrient waters

• Hard substrate

• Good water circulation

• Shallow water

• Salinity

True or False: Of the 34 animal phyla, 23 are found on reefs.

True, reefs are the most diverse habitat on earth at the phylum level!

Is the Indo-Pacific or Atlantic more diverse? Why?

The Indo-Pacific has higher diversity because of the higher abundance of atolls/rings of islands. It is also older, and has a different dominance of coral species (more fleshy corals)

True or False: Corals are in phylum ctenophora.

False. Corals are in phylum cnidaria (domain eukarya, kingdom animalia)

What is the difference between the polyp and medusa stage of Cnidarians?

• Polyp: sac-like stage with mouth and tentacles oriented upward

• Medusa: jellyfish-like, basically an upside-down polyp adapted for swimming

How do cnidarians capture prey?

They use cnidocytes with specialized stinging cells called nematocysts.

What are examples of anthozoans?

• True corals, anemones, sea pens

• Solitary or colonial polyps without a medusa stage

What are examples of cubozoans?

Box jellies

What are examples of Hydrozoans?

Siphonophores, hydroids, fire corals, medusae

What are examples of sycphozoans?

true jellies

What subclasses are within class anthozoa?

• Zooantharia: true corals, sea anemones

• Octocorallia: soft corals, sea pens, sea fans

• Carantipatharia: burrowing anemones, black corals

What are hermatypic corals?

Reef building corals, where the polyp produces the calcium carbonate skeleton. They have symbiotic zooxanthellae.

What are scleractinian corals?

Stony or “true” corals, have symbiotic zooxanthellae

What are ahermatypic corals?

Non reef-building corals:

• precious corals

• black corals

• Often LACK zoozanthellae

Octocorallia is also called what?

Alcyonaria

Zoantharia is in what group?

Hexacorallia

What groups are within octocorallia/alcyonaria?

• Alcyonacea - soft corals

• Helioporacea - blue corals

• Pennatulacea - sea pens, sea pansies

What groups are within zoantharia/hexacorallia?

• Actinaria - sea anemones

• Corallimorpharia - mushroom anemones

• Scleractinia - hard corals

Describe a coral polyp:

• Cylinder of tissue with a ring of tentacles

• Capture food with nematocyst-armed tentacles

• Connected by coenosarc

• Skeletal calyx - actual CaCO3 cup that forms the connective foundation

What are the coral growth forms?

• Plate-like

• Foliaceous

• Columnar

• Massive

• Branching

• Encrusting

• Free-living

What are the 3 classic reef types? Describe each.

1. Fringing. When corals fringe an island, they develop a fringing reef.

2. Barrier. A line of reefs form a barrier reef: channel develops between reef and shore.

3. Atoll. When island subsidence is complete, the remaining ring of reefs enclosing a central lagoon is an atoll.

Describe fringing reefs:

• Simplest, most common

• Develop near shore in tropics on hard surfaces

• Grow in a band along shore

• Vulnerable to sediment, freshwater runoff, human disturbance

—Longest reef:

—Red Sea

—2,500 mi

—Dry climate/ no streams to bring in sediment/ freshwater

Where is the reef slope, crest, and flat?

Describe barrier reefs

• Similar to fringe reefs

• Occur along coast, but farther from shore (~60mi)

• Separated from the shore by lagoons

• Great Barrier Reef (~1,200 mi)

Describe atoll reefs

• Ring of reef

• Occur in Indo-West Pacific Regions

• Can be far from land

• Form when volcanoes or sea mounts subside

• Reef builds around “island”

What is a patch reef?

The term “patch reef” is applied to any size reef that does not fit the “Classical Three”

Where are ridge reefs?

Along a continental plate, you can see them from afar ringing around the land mass.

Describe deep-water coral communities:

• Known since 18^th century

• Cold-water corals, mounds

• Occur individually or form patch reefs

• Over 800 species of cold-water coral, 1,300 in association

• Shallow up to 6,000 meters

• 4-12° C waters

• Mostly stony corals, black corals, soft corals

• No zooxanthellae or photosynthesis

• Capture zooplankton with tentacles

Where are cold-water reefs distributed?

What are the two scales for the life cycles of corals?

Biogenic and glacial

What are the cyclic stages of mound growth/glacial cycle of growth?

• Initiation

• Development

• Retirement

• Recolonization

What are the stages of coral life on the biogenic scale?

• Hard substrate exists

• Corals come in

• Loose sediment fills in the areas between corals

• Encrusting coraline algae cements loose sediment

• Live rock is formed and corals continue to grow

Describe the back reef/ reef flat:

• Back reef: located on the sheltered side of the reef

• Extends outward from shore

• It can be 20-30 meters to 1000’s of meters

• May be exposed at low tide

• Substrate is coral rock and loose sand

• Beds of sea grass develop in sandy regions

• Relatively shallow

• UV radiation

• Experiences widest variations in temperature & salinity

• Can heat to over 40°C

• 1/3 less dissolved O₂

• Input of fresh rainwater

• Protected from waves

• Reduced water circulation= accumulation of sediment

Describe the biodiversity of the reef flat:

—Two kinds of life:

• Species that live exclusively on the reef flat- high tolerance for environmental extremes

• Low numbers of spp, but some may be abundant 

• Well adapted for heat stress, UV radiation, salinity extremes

• Low competition

• Mollusks, worms, crustaceans, corals  

—

• Species for which the reef flat is at the extreme edge of their normal range

• Usually live deeper on reef flat

• Richer in abundance & diversity

• Staghorn coral (sheltered back reef)

Describe the reef crest

• Wave action is more vigorous, especially at high tide

• Greater water exchange=

  • Less heat

  • More O₂

  • Uniform salinity

Describe the biodiversity of the reef crest

• Calcareous algae is dominate

• Deposit a form of limestone: high-magnesium calcite

• “spur & groove system”

• Small crabs, shrimp, gastropods

What is the reef crest spur and groove system?

• Spurs project into prevailing waters

• Grooves (channels) carry water outwards

What coralline algae is in the Indo-Pacific?

Porolithon spp.

What coralline algae is in the Atlantic?

Lithophyllum spp.

What conditions are needed for coralline algae?

• Require strong water movement & high aeration

• Greater the wave energy= the more widely spaced the algal spurs

Describe the reef slope

• Fore-reef

• Reef plunges steeply at seaward edge of reef flat/crest

• Continuous or irregular

• 2 slopes on atolls

• Maximum corals live here, small fish, large fish, sharks, jacks, barracudas

• Greatest diversity at intermediate depths

• Greatest competition for space

• 30-40 meters down sediment starts to accumulate= corals become patchy 

• Can support corals up to 50-60 meters in Pacific, 100 meters in Atlantic

• Sponges, sea whips, sea fans, ahermatypic corals become abundant

What factors does the reef slope zone depend on?

• Wave energy- declines with depth

• Light- declines with depth

• Sedimentation- increases with increased depth

• Temperature- gradually decrease, or abruptly decrease across a thermocline

Describe the differences between a shallow and deep reef slope.

—Shallow:

• Light is abundant

• Wave energy prevents sedimentation

• Wave energy smashes

• Only toughest forms survive the shallows: branching/ table 

—Deep:

• Light is limited

• Lots of sedimentation

• Leafy corals grow outward to trap light

• Also trap sediment so they angle at 45°

Where are all the reef zones?

What are threats to coral reef zonation?

• Increased nutrients

• Sedimentation

• Land use

• Disease

• Sea level rise

• Thermal stress

• Increase in tropical storms

The dominant coral reef biota are corals, soft corals, sponges, algae, seagrasses, and mangroves. What do the ratios of each depend on?

-Ocean

-Water quality

-Exposure

-Depth

How thin is the organic living matter layer within reefs compared to the limestone structures they are on?

Comparatively, it is as thin as if you were to spread a jar of peanut butter over a square meter.

What is an aquatic biosedimentary structure?

A reef comprised principally of CaCO3

Hexacoralia is also called ______.

Zooantharia, since zooantharia is in Hexacoralia. They are both in Anthozoa.

Describe Zooantharia/Hexacoralia.

• 6 or multiple of 6 tentacles

• Stony corals (eg. staghorn)

• Abundant on reefs

• Produce calcium carbonate skeleton

How do coral colonies grow? Why are they advantageous?

• Colonies often result from asexual reproduction, particularly from some forms of budding

• Common cnidarians, ascidians, ectoprocts

• Colony: associations in which the constituent individuals are not completely separated from each other, but are organically connected

• Living extensions or secreted material

• Produce greater functional units: size

• Increased feeding efficiency; facilitate the handling of larger food items

• Reduce chances of predation

• Allow groups of individuals to specialize for different functions (eg. gastrozoids specialized for food, reproductive polyps)

What is a colony?

Associations in which the constituent individuals are not completely separated

What is aragonite?

It is limestone, specifically limestone that was formed from corals

Describe coral skeletons. What are they called?

Coral skeletons are secreted at the lowest part of the body, forming a cup. The skeletons are called corallite.

How can polyps separate without breaking apart?

• Deposit limestone as they grow upward and outward

• Divides into two or more daughter polyps

What is a coenosarc? Describe it.

• A coenosarc is the connective tissue between polyps

• Coenosarc capable of depositing limestone beneath it

• Spaces between polyps fill in

• Grow upwards

What is intratentacular budding?

• Intratentacular budding: polyp constricts in middle to pinch into two polyps

• Budding results from division of ring of tentacles

What is extreme intratentacular budding?

• Dividing with very little or no pinching off

• Results in long ribbons of polyps

• Example: Brain corals

• Each valley has a ring of tentacles

• Each valley has dozens- 100’s of mouths with gastric cavities

What is extratentacular budding?

• Parent corallite produces a daughter corallite external to the wall

What is the difference between intra-tentacular budding and extra tentacular budding?

Intratentacular budding occurs within the polyp wall, whereas the extratentacular budding occurs outside the polyp wall

All limestone deposition causes a colony to expand radially. What happens when division and growth is regular?

Smooth, dome-shaped colonies result. Ex: Porites spp.

In what ways can accidental fragmentation occur?

• Wave damage

• Organisms like sea turtles breaking off pieces of coral

What is an example of radial division nonaccidental fragmentation?

• Radial division in Cycloseris fragilis

• The coral breaks into pieces on purpose and each piece forms a new coral

What is an example of transverse division nonaccidental fragmentation?

• Transverse division in Fungia scutaria

• The stalk regenerates a new disk, which breaks off and then another disk is generated

What is a way to visually identify intertentacular between extreme intertentacular budding?

Extreme intertentacular budding typically has polyps inside of the ridges, whereas with regular intertentacular budding, the polyps are on top of the ridges.