Abiotic Environment

  • what is the optimum salinity for coral reefs

    • full ocean salinity (34-36 ppt)

  • coral reefs thrive in a narrow range of abiotic conditions

  • abiotic factors that limit coral reefs

    • salinity

    • temperature

    • light

    • nutrients

    • wave action

    • sediment

    • carbonate chemistry

  • salinity

    • corals can’t tolerate wide ranges

      • abundant where salinity is stable around normal seawater

      • some marginal reefs survive in areas where salinity can drop to 23 ppt or as high as 50 ppt

      • salinity may show high variation with tropical storm activity

    • freshwater discharge limits coral reef development

    • pulse events of low salinity can trigger high mortality

    • reefs in marginal conditions have lower cover and diversity

    • high salinity also limits coral reef development

    • an organism that maintains a constant osmolarity across a wide range of salinity is

      • a euryhaline osmoregulator

    • corals are stenohaline with little ability to osmoregulate

      • tolerance of osmotic stress varies between species

      • Porites furcata and Siderastrea siderea have higher tolerance than average

    • multiple stressors can enhance osmotic stress and lead to bleaching

  • Temperature

    • where do you expect upwelling

      • east side of ocean basins

    • healthy coral reef development is typically limited to waters above 21 degrees C

      • roughly between 30 degrees N and S

      • upwelling and cold currents limit reef development

      • warm currents allow development outside this range

    • which would you least expect in marginally low temperatures

      • extensive reef development

    • coral reefs in marginal temperatures typically have lower diversity

    • coral reefs in marginal temperatures may suffer sub-lethal stress

      • partial mortality or bleaching

      • less extensive reef development

    • sustained warm waters lead to coral bleaching

      • worst bleaching event ever in 1998, 16% of the worlds coral died

    • bleaching events are leading to large mortality and decreased cover

    • thermal tolerance varies by clade of zooxanthellae

      • typically bleaching above ~29 degrees C

      • red sea

        • many species routinely survive 36 degrees C

    • some corals can switch to thermal-resistant zooxanthellae after bleaching

      • but the long-term ecosystem effect of this is unknown

  • light

    • benthic photosynthesis represents more than 90% of carbon fixation on reefs

      • photosynthesis not only provides food for coral and higher trophic levels, it also enhances calcification

    • What is not a way in which photosynthesis increases calcification rate

      • it increases CO2 concentration thereby enhancing calcification reaction

    • what are ways that photosynthesis increases calcification rate

      • provides energy for calcification

      • removes PO4 3- thereby facilitating aragonite precipitation

      • increases pH thereby enhancing calcification

    • corals calcify 3x faster in light

    • light is attenuated as it is absorbed, reflected and scattered

    • maximum depth for coral reef formation is 30-50 m deep

    • depth and pattern of reef development varies with light levels

    • growth rate varies by species

    • growth rate varies within species with light levels

    • colony morphology can be modified with varying light levels

    • light may be an added limitation to the development of high latitude reefs

  • Nutrients

    • what are the 2 most important nutrients for primary production

      • nitrate and phosphate

    • nutrients are essential for primary production

      • nitrogen

        • nitrate

        • nitrite

        • ammonium

      • phosphorous

        • phosphate

      • trace elements

        • iron

    • generally, coral reefs thrive in

      • oligotrophic waters

    • coral reefs have high productivity, why?

      • symbiosis allow for tight recycling of nutrients

      • some new sources of nutrients

    • which of these organisms are most likely to be able to use N2

      • cyanobacteria

    • nitrogen fixation is the process of

      • the conversion of N2 to ammonium

    • new sources of nutrients on reefs

      • nitrogen fixation

      • oceanic upwelling

      • geothermal endo-upwelling

      • terrestrial runoff

      • transient visitors

    • eutrophic waters should least favor

      • coral

    • high nutrients may favor phytoplankton and macroalgae

  • Wave action

    • wave action varies with reef zone and depth

    • coral dominance changes with sheer forces and water depth

    • windward side of islands

      • reefs and algal ridges

    • strong and constant wave action is required for algal ridge development

    • coral reefs require a moderate amount of wave action

      • windward or leeward shores

    • spur and groove formation helps dissipate wave energy on windward shores

    • coral reefs attenuate a high proportion of incoming wave energy

      • back reefs/lagoons have low wave energy

      • coastal zones with intact reefs are better protected from large waves

    • corals develop in areas prone to tropical storms

    • why are there no tropical cyclones at the equator

      • the Coriolis effect is negligible at very low latitudes

    • Hurricanes can greatly reduce live coral cover

    • Hurricanes can affect coral species composition

    • at what frequency of hurricanes would you expect the highest diversity of coral

      • medium frequency

    • intermediate disturbance hypothesis

  • sediment

    • effect of sediment on coral

      • decreased light

      • energy to clear

      • reduced recruitment

    • sediment costs energy to clear

    • high sediment levels may cause a shift in coral assemblages, rather than mortality

  • carbonate chemistry

    • what kind of carbonate do scleractinian corals secrete

      • aragonite

    • coral reefs thrive in aragonite super-saturation state

      • Ω > 1

        • seawater is supersaturated

        • aragonite will precipitate

      • Ω = 1

        • seawater is exactly in aragonite equilibrium

        • aragonite does not dissolve or precipitate

      • Ω < 1

        • seawater is undersaturated

        • which results in aragonite dissolving

      • Ω > 4 is optimal for reef growth

    • aragonite saturation decreases with increasing latitude

    • increased CO2 concentration decreases ocean pH

    • aragonite saturation level has decreased worldwide