W7 Reefs and Paleoecology Flashcards
Why are reefs important
diversity (hot spots) particularly rich in species - carbonate producers - recorders of past environmental change - concerns over response to climate change - economics • palaeoreefs - reservoirs, limestone, cement • modern reefs - fish, tourism
Ordivician diversification
after the Cambrian explosion
almost exponential increase in diversity
and also increase in the complexity of the ecosystems
ex. vertical expansion of seafloor etc, moves away from floor
Reefs role in carbon fixation
Carbon fixation (primary productivity) on coral reefs is amongst the highest of any ecosystem on the planet
e.g. reef flats produce around 3.5kgC/m2/yr, compared to around 2kgC/m2/yr for seagrass beds and tropical rainforests, and around 1kgC/m2/yr for temperate deciduous forests
some experimental data show that more CO2 is problematic for calcifying organisms, like corals
recent observations have shown coral ‘bleaching’ associated with warming sea surface temperatures
modern corals made up of aragonite (calcite) are more at risks
Co2 seasonal change visible in graphs
borreal forests summer, not tropics (cause no change)
short term carbon cycle
as Co2 in water increases, pH drops → Acidification
Extinction events effect on reefs
each major mass extinction events hs an accompanying reef crash
significant reduction in reef animals and production
Reef as reservoir
source , reservoir, seal
reef systems are good geological reservoirs economic interesting to understand the structure
What are reefs (geological)
mound or rise on the sea floor which is built by the influence of organisms
built shallow for sunlight, then rubbly slope and theen finer graineed material to off reef
reefs form
grow on volcanoes → volcanoes submerge → reefs keep growing → Atoll
oceans used to be more shallow because back then “land” was flooded because now ice age
Reef formers
have changed through time often because of mass extinctions
before cambrian : stromatolites form reefs
post cambrian: sponges, corals, bryozoans, algae
Phylum Porifera (Schwämme)
Phylum Poriferaphylum of sponges
often build verticlly, abr like structure
often called Parazoans : part animal , transition?
vase like structures
have cells on insidee which create curreents , draw in water through porous wall, water sucked into sponge, pick out organic particles “filter feeding”
hatch from zygote → lava → adult
simplest of animals
• intermediate evolutionary grade - parazoans
• vase-like body shape
• no true plane of symmetry
• 4 types of co-operative cells, 2-layered perforate body wall
outer layer - pinacoderm
inner layer - collar cells/choancytes
median gelatinous mesenchyme with amoeboid cells (amoebocytes)
• cells not organised into tissues
• skeleton variable
colloidal jelly, spongin, spicules, calcareous
• no excretory, circulatory, respiratory systems, tissues, organs
most common residue sponge: flint (chalk)
Phylum Cnidaria (Nesseltiere)
radial symmetry very characteristic! diploblastic (true tissues) two-layered body wall with gelatinous mesoglea polyp and medusa body forms nematocysts (stinging cells) nerve net complex life cycles no excretory, circulatory, respiratory systems polyp: mouth points up, attached medusa: floating, mouth points down often medusas settle to polyp lifestyle later Subclass Zoantharia (stony corals) – Order Rugosa – Order Tabulata – Order Scleractinia
Cnideria (Coral) Order Tabulata
colonial, calcite coralites, prominent tabulae, septa absent or small
Ordivician Permian
(Coral) Order Rugosa
solitary and colonial
calcite coralites with prominent septa, tabulae and dissepiments commonly present
Middle Ordovician- Permian
(now extinct)
Coral) Order Scleratinia
new corals, after extinction, Triassic til present day
solitary and colonial, aragonite coralites, prominent septa, light, porpous structures, septa inserted in sets of 6
Reef forming corals
hermatypic (reef building) vs. ahermatypic (not reef builfing)
typically zooxanthellate corals form reefs
i.e., symbotic with dinoflagellate algae
alga gains protection
coral gains food, oxygen, nitrogen
boosts growth rate (x3) allowing rapid construction of skeleton
• constrains habitat
photic zone (sunlit)
warm (>18˚C, 25-29˚C optimum)
clear water
