Natural Foundations: What is a Reef?

Has "What is a reef" + "Reef Characteristics" material + "Where are Reefs" + "Parts of a reef"

Structural

The complex ridged structure built from the skeletons of organisms that forms in-place and rises above the seafloor (middle)

Reef Tract (Class definition)

The suit of interconnected ecological zones around and including the structural reef and the associated high diversity biological community (biggest)

Classic Reef

Most diverse part of the reef; popular for tourism. (smallest)

Maritime

Anything that gets in the way

Atolls

Donut shaped, often without high island in the center. Deep ocean, islands on the side (typically)

Fringing Reef

Reef located a short distance offshore

Barrier Reef

Reef follows the coastline, a distance offshore, separated by a deep lagoon

Bank Reef

Don’t fit other definitions. May not be associated with a coastline, islands, or a lagoon/barrier

Patch Reef

Many scales. Some just a few meters across, others 1km across. Usually located within the lagoon of a bigger reef system

Physical Environment: Warm water

Reefs occur in the tropics. Average > 20 deg C, not colder than 18 deg C. Warm water dissolves more: Holds less CO2 (Which is acidic) and dissolves CaCO3

Physical Environment: Carbonate

CaCO3 is the material that corals and clams and other organisms use to make skeletons

Physical Environment: Hardbottom

Rock pieces settle by gravity while organisms grow skeletons that make more sediment (filling in areas) and that can fuse together into big structures

Physical Environment: Low Nutrients

Reefs are good at recycling nutrients; too many nutrients can lead to too much plankton, algae, etc. which can kill the coral. The tropics don’t have winter, so there’s no change in temperature to stir up the nutrients, hence low nutrients year round

Biological: Modular Organisms

____ have parts that can replace each other; doesn’t need to reproduce, can just grow a new part

Why are corals functional plants?

They have zooxanthellae (Symbiodinium microadriaticum). Its a single cell algea and it helps the corals get food.

Constructiors

Coral skeletons, an algae that is plaster-like

Bafflers

Keeps things in place; slowing down the water and forcing sediments together

Binders

Grab stuff and puts them together

Destroyers

Parrot fish, etc. Eating away at parts of the reef

Dwellers

Live on the reef but not making the reef

Aphoric

No light

The Cryptos

Not a true zone. Hidden areas: Holes, underside of boulders, up to 8x the planar surface (if you count the holes).

Aphotic and Dysphonic zone

Poorly known, need submersible to get there

Disphotic zone

Filter feeding organisms

Deep Forereef

Some photosynthesizers can live deeper than others. Reflect red light to absorb more light because green light cannot reach that deep

Spur and groove

Primarily in shallow water. Waves crash into coral, causing an area next to the coral to constantly be rolling around and nothing can grow

Barren Zone

Absorbs full of energy of waves. Zone that waves always break during storms so nothing grows.

Closer to the reef crest

Lower wave energy, fast growing branch coral (because of storms these corals can on occasion be broken by the stornger waves, so they need to be able to regrow quickly)

Very shallow water - near reef crest: Algae Pavement

Gets so many waves that nothing can live there

Reef Crest

Exposed at low tide, debris piled up during storms, cemented together by encrusting coralline algae

Algal Ridge

Form where there are substantial tides. Can accrete close to high tide level, and thus as tides fall it keeps the reef flat submerged. Almost like a bath tub

Reef flat

Landward of the crest. Flat area, surface close to sea level. No accommodation space; can’t grow higher because all the area is one level and the coral can’t grow out of water. Can be a productive reef environment. Best developed in fringing reefs. Easy access for local people

Carbonate Shelf

Lagoon, wide and shallow, protected by barrier reef from waves. Studded with islands (cayes) and patch reefs. Algal carbonate production, flooded swamps

Sea grass beds

Algae are major carbonate producers. Seagrass and associated invertebrates are a major energy source for the reef (fish hide in reef during the day, forage over grass beds at night)

Mangroves

Trees growing directly in seawater. Nursery for fish, interesting invertebrates, protects islands from storms

Forereef outline

• Aphotic (not really a reef zone)
• Disphotic (also known as rariphotic)
• Deep fore-reef- Red Algae Zone
• Mesophotic

• Euphotic Fore-reef
- Platy coral zone
- Massive coral zone
- High diversity zone
- Branching coral zone

• Wall/Drop off
• Cryptos
• Spur and Groove (Butress)
• Barren Zone

Reef Crest outline

• Algal Pavement
• Reef Crest/Algal Rim

Backreef / Lagoon outline

• Reef flat
• Sand and mud bottoms
• Seagrass and algae beds
• Hardgrounds
• Patchreef/Fringing reefs
• Sea grass beds
• Mangroves
• Cays (not a reef zone)
• Salt turns (not a reef zone)