Chapter 9: coral reefs and beaches

difference between dirt and soil:

• dirt: mostly dead; mostly inorganic

• soil: is alive; has microorganisms

structure of a reef

• cross-section of reef

  • like a transect

    • think about gradients and zonation!

  • 3 main parts

    • reef flat

      • the shallow part between the stone & the reef crest

      • the bottom is mostly sand and coral rubble, with any reef framework filled in

      • often see sea grass and sea cucumbers

      • as the water gets deeper begin to see

    • reef crest

      • shallower than the reef flat (the edge of the reef)

        • reef crest as seen at low tide

      • waves break at the edge of the reef, may be exposed at very low tide

        • live coral is essentially intertidal, so often has algae on the actual crest

        • is higher than the reef flat

        • e.g., Tagachang

        • often see channels resulting in “spur & groove” formation

    • reef front or forereef

      • Slopes steeply into deep water

      • often very productive, with lots of fishes

Limestone & sand from Reefs

• coral reefs and all limestone rocks

  • Pacific islands are made of calcium carbonate,

  • the results of millions of years of growth by coral symbioses.

• limestone

  • fossilized coral reef

    • as limestone weather, fossil corals are exposed

• Sand is a product of bodies of hard organisms

  • the sand for beaches and filling in of reef flats and deep reef slopes comes from

    • coral skeletons

    • shells

    • calcified and coralline algae (e.g., Halimeda)

      • dies and the body on the reef crumbles to from sand

    • Star sand (foraminiferans)

• Erosion of Limestone results in sand

  • limestone erodes easily

Corals are colonial

• usually asexual reproduction

• Share common “skin” and skeleton of calcium carbonate

• “individuals” are termed polyps

• growth of the colony occurs in 2 ways

  • extra-tentacular growth (outside tentacles)

    • Polyps from between older polyps

    • new polyps start a new trace in the skeleton

  • Intratentacular growth (inside tentacles)

    • new polyp buds off older polyps

    • new polyp trace branches off older polyp trace in the skeleton

Coral spawning

• corals also reproduce sexually

• Guam’s next coral spawn

  • 7-10 days after a full moon (third quarter)

Reef symbioses

• we are now familiar with the symbiosis between corals and their zooxanthellae

  • some sea anemones, some coralline algae, giant clams, and ciliates also have zooxanthellae

• there are many other symbioses on a coral reef

  • some sea ha

Other symbioses

• star sand

  • foraminiferans with star-shaped shell

  • symbiotic alga inside (dinoflagellate or diatoms)

  • Brownish-red in color

Ciguatera

• food poisoning

• symptoms of ciguatera poisoning generally begin six to eight hours after eating the contaminated fish.

• symptoms include:

  • nausea

  • vomiting

  • diarrhea

  • muscle pain

  • numbness

  • tingling

  • abdominal pain

  • dizziness, and vertigo

    • Gambierdiscus toxicants is the main dinoflagellate (algae) that produces a toxin to discourage herbivores

      • small, 1/10 mm

      • chemical structure of the toxin complex

Biological Magnification

• sometimes also termed bioaccumulation

  • toxins stored in fat, not lost

    • so each time a herbivore eats a toxic dinoflagellate, the toxins accumulate

  • each level of the food chain accumulates toxins

  • toxin concentration increases as we move up the food chain

  • this was the problem with the insecticide DDt

    • Sprayed on mosquitos → “nuked” swifts

    • diversity is important

    • most organisms are food for something else

Values of reef

• fishing/harvest

• protection from wave

• cultural uses and beliefs

• tourism & souvenirs

• building materials

• potential medicines

Fisheries

• reef organisms are a renewable resources

  • but harvest is both valuable and a threat to reefs

• note that archaeological evidence suggests that early Chamorro people didn’t have domestic animals, so they used fisheries extensively

  • fisheries are especially important where crops are few

• What do fisheries include?

  • shellfish (clams, oysters, snails, etc.)

  • shrimp, lobster, crab, etc.

  • octopus

  • sea urchins & sea cucumbers

  • turtles (are now endangered)

    • federally protected through US Fish & Wildlife Act

    • internationally protected through CITES

• Fishing is important for food, for cash, & to maintain families & culture

• traditional fishing methods, combined with small populations were probably sustainable

  • but people now have much larger population

  • fisher now use monofilament instead of natural fiber

  • some fishers use poison & dynamite

The mercury cycle

• Non-food harvest

• shells, corals & shell crafts can be significant exports

  • are they sustainable?

• Fishes may be harvested for sale to aquarists

  • many are not sustainable

Tourism & Coastal Development

• may represent threats to reefs

  • construction for hotels, marinas, etc.

    • results in changes in sedimentation

      • may also need silt fences & ponding basins

      • sediment plumes may eventually kill the reef

        • fishes have nowhere to move to

        • unless new corals are recruited, then the fleshy seaweeds dominate and the community is lost

    • Tourism requires infrastructure, water pollution leads to eutrophication

    • could affect the growth of seagrasses & mangrove

• other threats to reefs include:

  • the reef is sometimes dredged

    • to deepen channels for ships

    • to provide building materials

    • to develop tourist attractions

  • oil appears to affect the reproduction of some corals

• other threats to reefs include:

  • drivers and dive boat anchors may potentially harm reefs

  • global warming, which may lead to ocean acidification (more on this later)

Climate Change and Corals

• CO2 emissions that are part of global climate change have negative consequences for reefs

  • Coral bleaching

  • Ocean acidification

Coral Bleaching

• rate of photosynthesis depends on the amount of light

  • saturation point: the amount of light at which more light does not produce more photosynthesis

  • photoinhibition: more light than saturation point & photosynthesis in inhibited

  • saturation is reached at lower light levels when the temperature increases

• Coral near the surface are close to their tolerance levels for both light and temperature

• When water temperature increases, the algal symbionts are damaged, so the corals eject them

• we call this Coral Bleaching

• Corals will die, if the algae are not replaced

• it is the most extreme days that cause the greatest problem

  • especially if these days have conditions that are outside the boundary conditions of the habitat for the coral.

Ocean Acidification

• there is relationship between CO2 in the atmosphere and acid in seawater

• CO2 + H2O → H2CO3 → HCO3- + H+

• more CO2 results in more H+

• If pH is decreased by 0.11 units

  • there is a 30% increase in [H+]

    • note: that pH of seawater has averaged 8.2 for millions of years until the Industrial revolution

    • pH of seawater now averages 8.1

• why does this matter?

  • animals can still use CO2 and HCO3- to build skeletons (no problem)

  • but increased acidity dissolves the CaCO3 skeletons & affects cellular functions

Modelling Climate Change

• In summary, coral reef scientists are modeling climate change

  • they showed that an increase in temperatures & decrease in carbonate ions taken now

    • corals won’t grown if temp. increase to 2C

Mariana region Back-arc

open ocean

• When we look at the open ocean we use a classification based on

  • 1. the distance from shore

  • 2. the depth

  • 3. the penetration of sunlight

    • it will determine how much food is

oceanic zonation

• the 3 systems of classification are not mutually exclusive

• instead, used together to define a habitat & determine

Deep ocean

• cold & dark

• Close to pacific islands, compared to continental areas

• once considered without life & just a place to dump waste & mine minerals

  • later ocean sampling found some animals, but they were

Hydrothermal vents

• organisms live off energy from chemicals &/or heat coming out of the earth

• 3 types

  1. black smokers

  2. white smokers

  3. serpentinite seeps

Black smokers

• release hot water (360-400 C)

• water saturated with H2, CH4 & minerals

• cold seawater seeps into the crust & is superheated, dissolves minerals (mostly sulfides &irons) & rises out of the main chimney

• typical in areas of sea

whiter smoker

• release hot water (360-400)

• water saturated with H2, CH4 & minerals

• cold seawater seeps into the crust & is superheated, dissolves minerals (mostly barium, calcium, & silicon) & rises out the main chimney

• typical in areas of seafloor spreading

cold seeps

• release color water (40-90c); still warmer than 4C seawater

• water saturated with H2, CH4, but low in minerals

• typical of area with plate subduction

• includes the Shinkai Seep Field (SSF) near Challenger deep

Hydrothermal Vent Ecosystems

• Depend on chemicals in the water for both energy & nutrients

• Primary producers are bacteria

  • both free-living &endosybionts

  • plants: CO2+ H2 → C6H12O6 + O2

  • Bacteria: CO2 + H2S → C6H12O6 +SO2

Vent Organisms

• Giant tube worms (riftia)

• get over 2m in length

• no gut, instead their trophosome is filled with bacteria

• bacteria fix, CO2 from the environment and make sugars (then share these with the tube worms)

• Tube worms supply the bacteria with the CO2 & H2S from the surrounding seawater

• both the worm and the bacteria need O2, which the worm takes from the seawater

• Vent organisms not all are invertebrates

Mariana Trench Marine National Monument

• 2 parts:

  • Trench unit (red)

  • Island unit (yellow)

• Note that the location of the Shinkai Seep Feild (SSF)

• “HMRG Deep “ is now (after a competition by Marianas Students) named Seriana Deep

  • 2nd or 3rd deepest location after challenger deep

Vocabulary:

• calcareous

• coral reefs

• Biogenic rock

  • reef creatures deposited all of the limestones on tropical islands.

  • it has a biological origin, as opposed to rock derived from the earth’s crust, such as volcanic rock.

• Foraminifera

• feeding deterrents

• chemical ecology

  • how plants and animals use chemicals to defend themselves against predators or to compete successfully.