Geosc040, Lecture 18; March 25

• Coral, • Coral Reefs in

Danger

Every Teardrop is a Waterfall ColdplayThanks to Zach W.

Island In The Sun Shwayze & Cisco Thanks to Rich S.

Rock You Like A Hurricane, ScorpionsThanks to Marissa W.

Required Reading• Clownfish help their

anemones breathe• Algae bloom kills record

number of manatees• Seasat: the beginning of

oceanography from space

• On-Line Assignment 9 due today (25 Mar) at 11pm• Homework 3 Due Apr.

1

• Chesapeake Bay on Thursday, see Review Questions on-line.

Read Chapters 14 & 15

Seasat: the beginning of oceanography from space

Seasat: the beginning of oceanography from space

Seasat: the beginning of oceanography from space

Seasat: the beginning of oceanography from space

http://science.nasa.gov/missions/seasat-1/

Seasat: the beginning of oceanography from space

http://science.nasa.gov/missions/seasat-1/

Which of the following are True:

A. A study in 2009 revealed that waste excreted by clownfish provides vital nutrients to anemones.

B. Clownfish and anemones live on coral reefs where oxygen levels in the water often plunge at night as photosynthesis shuts down

C. Anemone provides a tentacle-guarded home for clownfish and the clownfish drive off predators that would chew its protector.

D. All of the above

E. None of the above

Which of the following are True:

A. Last year at this time, an algae bloom off southwest Florida, called Florida red tide, killed over 174 manatees

B. A red tide is a higher than normal concentration of a microscopic algae that appears in the Gulf of Mexico. At high enough concentrations, the algae can turn the water red or brown, hence the name.

C. Red tides are generally not caused by pollution, they have been documented in the 1700s and along Florida's Gulf coast in the 1840s.

D. All of the above

E. A and B

The World’s Coral Reefs

Coral reefs are confined to a relatively narrow climatic zone, where mean annual temps are greater than 20°C

Structure of Coral Reef Systems

Most Coral live at a narrow range of water depths

Structure of Coral Reef Systems

Most Coral live at a narrow range of water depths

http://en.wikipedia.org

Reef Structure

Reef terrace

grooveAlgal ridge

Buttress zone

• The algal ridge occurs on the windward side of the reef and endures the pounding waves.

• The buttress zone is the reef slope extending down from the algal ridge.

• The reef face extends downward from the buttress zone and usually is devoid of living colonial corals because insufficient light reaches this depth.

• The reef terrace is landward of the algal ridge and lies at mean water level.

Coral Reef

Reef terrace

grooveAlgal ridge

Buttress zone

Reef Structur

e

Reef terrace

grooveAlgal ridge

Buttress zone

Reef Structur

e

Reef Building• By definition, a coral reef is an

organically constructed, wave-resistant, rock-like structure created by carbonate-secreting organisms.

• Modern reefs are usually built around corals, but can include calcareous algae and other organisms that make skeletons and eventually become “lithified”

• Most of the reef is composed of loose to well-cemented organic debris of carbonate shells and skeletons.

• The living part of the reef is just a thin veneer on the surface.

Reef Building• The living part

of the reef is just a thin veneer on the surface.

--how do they grow and accumulate layers? Is sea level rising or the sea floor dropping lower?

Atolls and GuyotsSubmarine volcanism builds a seamount, which, through continuing volcanism builds above sea level.A fringing reef forms initially, growing into a barrier reef as volcanism ceases and the crust upon which the island was built cools and begins to subside.The reef continues to grow upwards at a rate that keeps up with the sinking of the island initially, but eventually “gives up”.

Which of the following are True:

A. The hydrologic cycle involves Evaporation

B. We all affect the ocean. So, turning off the water when you brush your teeth and turning the lights out when you’re not using them is a good idea…

C. Coral turn white when they are dieing.

D. Some coral spawn by releasing all of their eggs on a single night of the year

E. All of the above

Healthy CoralCorals need nutrients and they need to be in the photic zone for their symbionts to photosynthesize

But, if there are too many nutrients, blue-green algae can become too plentiful and smother a coral colony

Healthy Coral Corals do best in nutrient-poor water. They are easily out-competed by benthonic filter feeders in nutrient-rich water where phytoplankton are abundant.

Certain types of reef fish are also important to a healthy reef ecosystem. They graze on algae

Unhealthy signsCoral “black band” disease (possibly a virus or bacterial infection) kills coral tissue, especially if corals are already under stress for some other environmental factor.

The Crown-of-Thorns starfish can wipe out huge tracts of coral reef. These occur in the western Pacific Ocean and proliferate rapidly when predators are somehow affected (human activity?)

Corals in Decline Many coral reef areas are in

decline. Is this natural (have we been looking carefully for long enough?)? Or is is it anthropogenic in origin?

Beautiful appearing “white” corals are, unfortunately, not healthy

Upper panel shows “black band” disease progressing, while the lower panel is a brain coral that is “bleached”--expelled its zooxanthellae (?) Both in Florida reef tracts.

Images courtesy Gene Shinn, USGS

Unhealthy Signs

Parrot fish eating blue-green algae which is growing over coral

Below, urchins graze over coral heads (dead)

Some Potential Contributors to Coral Reef Demise

Urbanization brings additional problems

Such as: sediment (from

development, agriculture) influx and

excess nutrients (effluents from sewage treatment, septic systems)

Overfishing (note: a general problem with popularity of reef fish for aquaria)

USGS, Hawaii

Parrot fisha) Ingest coral skeletons and polyps in their

quest for algae.b) Are responsible for considerable reef

erosion c) Produce much of the carbonate sand

found in reef systems and tropical islandsd) Are found in small schools over the reefe) All of the above

Corals forming reefs require:a) Clear, warm, shallow waters and sunlightb) High nutrients supplied in upwelling zonesc) Abundant dissolved silicon for their

skeletonsd) Cold water and dark conditionse) a and b

Corals :a) Don’t need nutrients and sunlight because

they are really just rocks and are not alive. b) East mainly Small fish and shrimpc) Obtain 98% of their food from symbiotic,

photosynthetic algaed) Thrive in environments where suspended

sediment is high, such as near river mouthse) None of the above

The Chesapeake Bay watershed includes the Susquehanna River drainage (shown in green!)

Pennsylvania's massive Susquehanna river is Chesapeake bay's biggest tributary

Coastal EcosystemsEutrophication & Hypoxia

Chesapeake Bay: Is there a problem? (yes!)

Susquehanna River flooding, Port Deposit, Md

Pennsylvania's massive Susquehanna river is Chesapeake bay's biggest tributary

…Teeming with raw sewage, animal waste and fertilizer runoff, yet responsible for half the Chesapeake Bay's fresh water, the Susquehanna River is the most endangered river in the United States, according to a recent report by American Rivers, a national conservation group

Recall:Marine Photosynthesis 6CO2 + 6H2O + energy -->

C6H12O6 + 6O2

Requires Nutrients: such asCarbon/Nitrogen/Phosphorous

And the sources of these nutrients?In the Oceans:

Rivers, Upwelling, Mixing.

But too much of a good thing isn’t good! Eutrophication & Hypoxia

The Chesapeake Bay Watershed

• The Chesapeake Bay watershed includes the Susquehanna River system and the Potomac among other smaller rivers and tributaries. In all, parts of 6 states, including some large cities (e.g. Baltimore, Washington DC, Richmond) and industrial regions as well as extensive agricultural tracts, compose the watershed

• Chesapeake Bay is a drowned estuary, incised by rivers during the last glacial sealevel lowstand and flooded during glacial melting and accompanying sea level rise (by about 6 kyrs. ago)

You are in the Chesapeake Bay

watershed

• The Susquehanna River drains into Chesapeake Bay• PennState practices impact the Bay (you can “act locally”)

The viscious cycle:• Excess nutrients supplied in rivers to the Bay support

luxurious growth of phytoplankton (microscopic plants) blooms

• sinking organic matter (sewage sludge has same net effect) is oxidized by bacteria, thereby consuming oxygen

• oxygen deficits occur in bottom waters--these are harmful to benthic organisms, many of which have economic value

• the nutrients released during respiration in deeper waters are cycled back to the surface and produce more blooms and further organic matter loading

• a lack of mixing (stratification) resulting from seasonally strong salinity and temperature gradients (surface to bottom) prohibits oxygenation of bottom waters.

A Major Problem: Eutrophication

Oxygen Concentrations

in Chesapeake

Bay

Plan view and cross sections down the Bay showing seasonal contrasts (top March, bottom July) in dissolved oxygen concentration. Oxygen concentrations drop in July because of thermal stratification (reduced mixing) and increased deep respiration.

Response of Organisms to Low Dissolved Oxygen Concentrations

• Prolonged periods of dissolved oxygen below about 2 mg/L eliminate most “seafood” from the affected region

• Each organism has its own tolerance limits

• Values of dissolved oxygen at or above 5 mg/L are considered “healthy”

• During the summer, between 30 -40 % of the volume of the Bay experiences values <5 mg/L