Climate and Life on Earth: Marine ecology 2 Flashcards
List the three major types of coastal tropical ecosystems
- mangroves
- seagrass meadows
- coral reefs
Describe mangroves and seagrass beds
- high biomass of primary producers
- actively sequester huge amounts of carbon
Describe seagrass meadows - the basics
- support high biodiversity
- bottom-up and top-down controls in their productivity
Describe coral reefs - the basics
- extraordinary biodiversity
- threatened by overfishing, rising sea temperatures and coastal pollution
Many parts of the tropical oceans are virtual deserts, because
the permanent thermocline prevents vertical mixing and the return of nutrients from deep waters.
Describe the hot-spots of productivity throughout the tropics
- sometimes due to upwellings
- specialised communities of primary producers (e.g. coral reefs)
Describe mangroves
- trees that grow in coastal brackish or saline habitats
- flowering plants
- trap sediments around their roots (salt mostly excluded)
- need special adaptations, such as lenticels or pneumatophores
- some spp have the ability to excrete salt through the leaves
Describe true mangroves
belong to a single genus: Rhizophora
Describe mangrove roots
often anoxic
Give an example of a mangrove species
Rhizophora mangle at Aldabra Atoll by Seychelles Islands
Describe seagrass meadows - the specifics
- span both temperate and tropical locations
- flowering plants
- 72 spp globally
- 4 families
Describe temperature seagrass beds
- species-poor
- often dominated by eelgrass: Zostera marina
Describe tropical seagrass beds - the basics
more species-rich
Describe seagrass
- no stomata
- thin cuticle
- true roots and a vascular system (take up nutrients from the sediment, unlike algae)
- spread rapidly via rhizomes
- flower (produce pollen and seeds)
- can grow at depths of up to around 55 m, mostly < 30m
- directly grazed by green sea turtles and sirenians
- world’s oldest plant: 200,000 year-old clones in Med
sirenians
manatees and dugongs
Describe seagrass morphology
- roots
- rhizome
- flower
- leaves
Describe small-bodied seagrass
- small, thin leaves
- small rhizome
- “Guerrilla strategy”
- short-lived
- fas turnover
- low biomass
- exploits new space
- abundant flowering
- many small seeds
- seed bank
Describe large-bodied seagrass
- large, thick leaves
- large rhizome
- “Phalanx strategy”
- long-lived
- slow turnover
- high biomass
- holds space
- patchy flowering
- few larger seeds
- seeds germinate rapidly
List some Floridian small seagrasses
- paddle grass (Halophila decipiens)
- star grass (Halophila engelmannii)
List some intermediate Floridian seagrasses
- widgeon grass (Ruppia martima)
- shoal grass (Halodule wrightii)
List some large-bodied Floridian seagrasses
- manatee grass (Syringodium filiforme)
- turtle grass (Thalassia testudinum)
Describe tropical seagrass meadows - the specifics
- high biomass systems
- high productivity
- grow in coastal areas (incl. intertidal zone)
- cope with some water turbidity and brackish water
- grow alongside other tropical habitats like reefs
- important nursery grounds for commercially important fish spp.
Describe tropical seagrass meadows and barrier reefs
- protect by trapping sediment, absorbing excess nutrients and reducing turbidity in coastal waters
- gain protection from wave action
- synergism
List some estuary seagrass species in the tropical indo-pacific
- Halodule spp.
- Halophila ovalis
- Halophila spp.
- Enhalus acoroides
- Ruppia maritima
List some shallow coastal/back reef seagrass species in the tropical indo-pacific
- Thalassia hemprichii
- Syringodium isoetifolium
- Thalassodendron ciliatum
- Cymodocea spp.
- Halodule spp.
- Halophila spp.
List some deep (70m) coastal seagrass species in the tropical Indo-Pacific
- Halophila stipulacea
- Halophila decipiens
- Halophila spinulosa
Where are mangroves associated with seagrasses?
at tropical indo-pacific estuaries
Where are marshes associated with seagrasses
coastal tropical Indo-Pacific
Where is kelp associated with seagrasses?
tropical Indo-Pacific
Where is the sea turtle associated with seagrasses?
deep coastal tropical Indo-Pacific
Where is the dugong associated with seagrasses?
- shallow coastal/back reef tropical Indo-Pacific
Where is freshwater input in tropical Indo-Pacific
deep coastal region
Describe one of the threats to coastal systems
- eutrophication caused by runoff from agricultural systems
- can lead to coastal dead zones
Seagrass growth inhibits
Benthic microalgae
Describe eutrophication
increased nutrient loading in water leads to blooms of phytoplankton
Describe seagrass ecosystem engineering
- Zostera noltii
- trap silts
Describe blue carbon
Describe coastal wetlands in terms of carbon sequestration
- substantial amounts (50-90% in soils)
- long‐term carbon sinks
- potential carbon sources upon conversion
- managed for their carbon sequestration value
Describe some taxa not involved in carbon sequestration
coral reefs, kelp, and marine fauna
Describe long-term phytoplankton carbon sequestration
- fix CO2
- sink when dead to the bottom of the ocean
- deep sediments lock up carbon
Describe coastal wetlands
- tidal inundation keeps the soils wet or submerged
- inhibits microbial action
- slows decomposition
- carbon accumulates in soils and remains relatively stable
Describe healthy coastal ecosystems
- continuously accrete carbon in the soil
- allows them to keep pace with sea‐level rise
- potentially limitless capacity to sequester carbon for long periods of time
Describe mangrove forest drainage
- microbial action in the soil (previously inhibited by tidal inundation) oxidises carbon
- emits it to the atmosphere as CO2
Coastal wetland loss and drainage is estimated to be
between 0.7–3% per year (depending on vegetation type and location), resulting in 0.23–2.25 billion Mg of CO2 released
Describe coral reefs - the specifics
- temperatures between roughly 18 and 30 degrees
- no sudden changes in salinity
- high light intensity
- low turbidity
- oligotrophic waters
Describe the two distinct biogeographic coral regions
- Indo-Pacific (roughly 10x biodiversity)
- tropical W Atlantic
Describe coral spatially
- missing from areas with major river outflows
- sensitive to freshwater and silt
Describe the types of coral reefs
- fringing reefs (Israel)
- barrier reefs (Australia)
Describe fringing reefs
found just beyond shorelines
Describe barrier reefs
- found just beyond lagoons
- start as fringing reefs
- get hollowed out as a lagoon forms and becomes occupied by other life-forms, e.g. seagrass beds
- reef survives further offshore
- grows upwards towards the sunlight
Describe coral growth
build massive structures through the accumulation of their limestone skeletons cemented together with sand
Describe atolls
- start growing on the shore of a high volcanic island as a fringing reef
- island begins to erode and sink
- weight of the volcano can cause subsidence
- reef grows upwards, forming a barrier reef further offshore
- lagoon between barrier reef and high volcanic island becomes wider and deeper
- peak sinks beneath the water, leaving only the reef in place
- island becomes an encircling barrier reef: an atoll
- tens of millions of years to form
- only kept at the surface through the action of the coral
- e.g. Aldabra in the Indian Ocean
What would happen if the coral of an atoll died?
- continue to erode
- end up under the sea
Describe phylogeny of reef-building corals
- scleractinian (stony) corals
- within the class Anthozoa
- within the basal phylum Cnidaria
- arose during the mid-Triassic The ceonosarc creates a common gastrovascular system so that food can be shared among the polyps – they are all clones.
Describe the morphology of reef-building corals
- simple body plan
- two germ layers: ectoderm and endoderm
- mesoglea inbetween
- muscles formed from the epithelial cells (retract and extend the tentacles)
- secrete calcium carbonate skeletons and a corallite
Describe coral ectoderm
contains cnidocytes
Describe coral endoderm
contains photosynthetic algae
corallite
protective cup
Describe the ecology of reef-building corals
- exist as single polyps or as a colony connected by coeonsarc tissue
- colony can grow for years or decades, forming massive structures
Describe Palaeozoic reef-building corals
went extinct during the Great Dying.
Acropora
a branching coral
Porites lutea
a boulder coral that is resisting coral bleaching quite well
Describe coral reef symbiosis
- photosynthetic algae called zooxanthellae in endoderm
- coral provides protection for the algae and CO2 from respiration
- also contributes other essential nutrients (e.g. nitrogen) from feeding
- regulates growth and multiplication of symbionts
Zooxanthellae
- dinoflagellates
- genus Symbiodinium
- essential for coral growth (carbon provision, aiding calcification)
Symbiodinium
- free-living at low density in tropical waters
- 30% of the biomass of a polyp
- symbiont cells separated from host cytoplasm by symbiosomes
symbiosome
specialised membranous structure
Describe coral polyp dependence
- on algae for nitrogen as well as carbon
- symbiont produces amino acids using DIN from water column, and from nitrogenous waste produced by the coral
- polyp acquires more than 80% of N from the algae when feeding rates are low
DIN
dissolved inorganic nitrogen
Describe carbon and nitrogen dynamics within the coral symbiosis
tight recycling
Describe coral reef productivity
- very high productivity (similar to the best agricultural systems)
- corals keep most of the photosynthetic products; channel around 90% of the C fixed by their symbionts into their own growth (much of it is respired away)
Describe algae on reefs
- many kinds
- coralline red algae
- fleshy green and brown algae
- provide a ‘turf’ for grazing fish (e.g. herbivorous surgeonfish)
- herbivorous fish support predatory fish
Describe coral reef biodiversity
- probably the most biodiverse ecosystem on the planet
- take up 1% of the ocean floor
- support 25% of marine life
- over ¼ of the world’s fishermen in 99 countries fish on reefs
List some marine life that corals support
Sponges, echinoderms, nudibranchs, anemones, and lots of fish.
Describe fishing on coral reefs
- begin by targeting top predators (groupers, jacks and sharks); easily overfished
- ‘fishing down the food chain’; targeting smaller herbivorous fish (e.g. parrotfish)
Describe Jamaican coral reefs
- chronic overfishing: began by targeting predatory fish, but then herbivores (e.g. parrotfish)
- sea urchin boom: massive numbers of long-spined urchin Diadema antillarum kept fleshy algae in check, despite loss of herbivorous fish.
- hurricane damage (1980) destroyed much of the Acropora species (short-lived coral recovery)
- sea-urchin die-off (’82-’84): pathogen caused the death of 99% of urchins
- loss of urchins and absence of fish caused dramatic bloom of benthic algae; prevents coral recruitment
- phase-shift
Describe phase-shift
reefs can exist in one of two states and that either is stable
Describe El Niño/La Niña events
large-scale climate phenomenon that occurs every 3-8 years
… of the Great Barrier Reef has bleached to death since 1995
Half
average interval between bleaching events has … between 1980 and 2016
halved
Coral bleaching occurs when
- corals expel their symbiotic algae
- exposed to prolonged high temperatures
- high UV exposure also contributes
What are the two main causes of coral bleaching?
t is thought to have two main causes:
Oxidative stress – the algae produce reactive oxygen and nitrogen species.
High temperatures cause the algae to become ‘selfish’ and stop exchanging nutrients with the host.
