Lectures 11 & 12 - Coral Reefs Flashcards Preview

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Flashcards in Lectures 11 & 12 - Coral Reefs Deck (23):

Give six key points about coral reefs

> high diversity only matched by rainforests
> 60,000 identified species but suspected 423,000
> Occour in oligotophic waters
> 3 times as productive as coastal upwellings
> make up 2? of oceanic area
> over / under exploited


What are Cnidarians

There are what corals essentially are, they are multicelluar simple organisms that have nematocysts for predation and defence. After firing they regenerate after a few hours


Give 6 facts on reef distribution

> Found between the 18oC isotherms
> Tropical and equatorial (between cancer and capricorn)
> Optimum water temp 23 - 25 oC
> not found on western coasts as corilois gyre brings cold water into coastal region
> not found by river outflows
> occour in warm oceanic currents


What is an essential relationship between two species in coral ecology

Endosymbiosis between algea and animal (polyp)


Give some details on the algea in this symbotic relationship

Autotrophic, dinoflagellate zooanthella. Outher meber thin and leaks metabolites which benefit the coral polyp. Algea non-motie and fragile depends on the polyp for structural surport


Could you draw a coral polpy?



Cross section of a polyp membrane shoulding the zooanthellea algea

Probably not


What are the three ways in which a coral can reproduce

> Fragmentation (in storm conditions / stress)
> Colony Fission
> Budding


Explain budding in corals and the three types

Young polyp grows out of an older one, three types:
> Longtiudinal division - divides into two smaller ones
> Transverse division - Divides horizontally to form mouth and base region
>Intratentacular budding - new one forms on oral disc of old one


What are the pros and cons of spawning

Cons - mass spawning means they are vunerable to predation and can even smother corals
Pros - "swamp" predators, there are so many that some will get fertilised eggs and sperm released at the same time


Could you draw a diagram of sexual reproduction of corals with regards to brooders and broadcasters

flow diagram needed here ...............................................................................................................................................................................


What are the 8 factors effecting time of spawning (not really known)

> Sea Temp
> Lunar cycle (tides??)
> Day lenght
> Irradiance
> Wind and currents
> Rainfall
> Chemical stimuli
> Latitude


Explain colony growth 4 types and explanataion

Colony is called a Coenorsarc
Division - gradual laying down of calcium carbonate between corallites
Stolons - root like growth that covers surface and then polyps grow out of it
Monopodal growth - growth of new polyp on older one
Sympodal Growth - young one grows on the edges
Dycotomic growth - symmetric division of polyps


What are the four reef forms



Explain reef zonation from shore to sea

Back reef
reef flat
reef crest
fore reef


Explain reef zonation in terms of depth on the fore reef

Branching coral zone
mixed coral zone
massive coral zone
deep fore reef
platy coral zone


Explain morphology of corals with regards to wave energy (most tollerant at the bottom)



Zonation of coral reefs - Lagoon. Explain

sandy substratum, seagrass beds, e.g. Syringodium spp.- important nursery grounds for reef fish. Also benthic organisms, e.g. echinoderms - holothuroidae - sea cucumbers in high densities. Also get coral growth from fragments broken off by wave and storm damage. These small areas of coral also act as nursery grounds for reef species of fish and invertebrates.


Zonation of coral reefs - reef back

Limited water movement, therefore low diversity massive corals are found here such as:
Fire coral - big time sting
Giant Clam - englufed in corals
Also get soft corals as wave energy decreases


Reef flat explain

At low tide can be exposed, dominated by branching taxa, fauna found is fish, invertbrates, filametous algea. Massive diversity of fish


Reef front explanation

Reef crest quite shallow, high wave action of no corals as frequently exposed, as you move down the reef front there are fast growing corals then slow growing tabular corals to low light levels, turtles and marine mammals


Give three examples of species mutlatlism

> Predatory fish and cleaner fish (e.g. Labroides spp.).
> Trapezia crab spp. and Alpheus pistol shrimp spp. defend their host coral Pocillopora against grazing asteroidae e.g. Acanthaster spp.
> Clown fish (Amphiprion spp.) and anemones (Hetractic spp.)


What are the main threats to coral reefs

Natural - grazing pressure, urchins, crown of thornes starfish
Human - coral bleaching linked to high temp of sea water, light damage, the zooxanthellae are ejected or die