Coral reefs and coastal wetlands.

Question 1

What term describes the organisms that build reefs?

Answer 1

Biogenic

Question 2

What are the temperature constraints on coral reefs?

Answer 2

warm seas where the temperature doesnt fall below 18 and does not exceed 34.

Question 3

How do coral reefs form?

Answer 3

built by polyps that extract CaCO3 from the water an accrete it onto their surface to provide a skeleton. algae species inhabit the coral and increase the rate of accretion and reproduction of polyps.

Question 4

What type of sea floor do corals require?

Answer 4

a firm seafloor bed where there aren’t mobile sediments.

Question 5

What factors do corals need to survive?

Answer 5

• firm seafloor
• temp: 18 - 34
• sunlight
• salinity 27 - 38, optimal 34 - 36
• nutrient supply
• O2 supply
• no clogging by sediment

Question 6

what is the average growth rate of corals?

Answer 6

0.4 - 0.7 mm/year.

Question 7

What controls the height that corals can grow?

Answer 7

the mean spring low tide. above this the corals are exposed to UV from sunlight, high heat stressors and dessication, resulting in mortality of expose for too long.

Question 8

What is the importance of waves on a coral reef?

Answer 8

waves provide energy to mix the water, in doing so they:

• regulate the water temperature
• keep a good O2 supply
• prevent clogging of corals by sediments.
• provide nutrients.

Question 9

What is coralline sand?

Answer 9

sand produced from the breakdown of corals by waves during storms. much of which is banked on the lower slopes of reefs.

Question 10

What may affect coral reef growth?

Answer 10

• predation
• marine pollution
• quarrying
• excessive nutrient supplies, resulting in eutrophication
• climate change (temp, acidification)

Question 11

What are the three types of reef?

Answer 11

Fringing, Barrier and atoll

Question 12

What is a fringing reef?

Answer 12

a reef that runs parallel to the coastline intersected by inlets. consist of a reef platform and a sloping reef front. Some fringing reefs are separated from the land by boat channels, 200 m wide and 3 m deep, which becomes a lagoon at low tide.

Question 13

What is a barrier reef?

Answer 13

this is a reef that lies offshore but again parallel to the coastline. Developed from a fringing reef during the later holocene from sea level rise. Again reefs are separated by channels, where fringing reefs did not develop becasue of river outflows, but remain open because of the tidal currents that rush through.

Question 14

What are atolls, what are the three types?

Answer 14

atolls are circular or ovoid reef systems surrounding a lagoon. This system is the result of a fringing reef surrounding an island, which has been lost to subsidence.
3 types - oceans, shelf and compound.

Question 15

Where are mudflats formed.

Answer 15

mudflats are formed where the silt and clays settle on intertidal zones where the waters energy is low. e.g along the fringes of estuaries, behind longitudinal bars, within embayments or coves.

Question 16

How do benthic organisms affect the mudflats stability?

Answer 16

benthic diatoms excrete a polymer which forms a biofilm over the surface of the mud, stabilising it.

Question 17

How does a mud flat become a salt marsh?

Answer 17

if the rate of aggradation is greater than the rate of erosion then the mudflat will continue to grow vertically. at the point when the mudflat is only submerged during high tides, rooted vegetation may take hold, salt marshes may then form in the upper part of the intertidal zone.

Question 18

How do salt marshes stabilise mudflats?

Answer 18

roots help to stabilise the sediment, binding it together. Grass then helps to increase the critical shear stress and reduce the boundary shear stress. Grasses help to alter the hydrodynamics of the water flowing through and act as a filter. Grasses also provide organic material to the marsh.
Form tidal creeks over time which are related to the volume of tides.

Question 19

Why are salt marshes important?

Answer 19

important ecological habitats, provide an area rich in foods and are environments for juvenile fish.
they also act to filter pollutants from the water and

Question 20

What type of conditions do mangroves grow in?

Answer 20

tropical intertidal environments, muddy substrate, low wave energy.

Question 21

How are mangrove species zoned?

Answer 21

zonation takes place parallel to the shore, with different species growing best at different intertidal levels, with competition constricting them to their zone of optimal growth.

Question 22

How are mangroves adapted to their habitats?

Answer 22

they have long branching root systems, trap sediment, high dispersal abilities, pneumatophores to absorb O2, deal with salinity and waxy leaves.

Question 23

What is coral bleaching?

Answer 23

this occurs when corals expel the algae within them. This happens due to increased water temperatures, acidification of the water or exposure to UV. It results in reduced growth rates and reduced reproduction.

Question 24

How do corals reproduce?

Answer 24

asexual budding and sexual reproduction

Question 25

What happens to coral larvae?

Answer 25

coral larvae are moved by oceanic currents till they find a suitable substrate, where they metamorphose into a juvenile polyp.

Question 26

What is the name of the algae in corals?

Answer 26

Zooanthellae - gives corals distinctive colour, symbioitic relationship.

Question 27

How does eutrophication affect corals?

Answer 27

results in the invasion of macro-algae communities, out competing the corals.

Question 28

what are the sections to a reef?

Answer 28

Fore reef - on the steep seaward slope, high wave energy.
algal ridge - forms at the edge of fore reef
reef flat - sub-horizontal morphology
back reef - lagoon/land.

Question 29

What happens if the rate of subsidence/sea level rise is greater than the rate of coral growth?

Answer 29

coral will eventually die ~ 50 m