Transcript How realistic can we be?

Coral/algal Reefs IV
Variation and Alternative
States
Variation in Florida Keys corals, 2005
Brandt, M. E. 2009. The effect of species and colony size
on the bleaching response of reef-building corals in the
Florida Keys during the 2005 mass bleaching event. Coral
Reefs 28:911-924.
• Background
– Summer & fall, 2005 – high SST in ne
Caribbean
– Mass bleaching documented
• Methods
– Monitor corals for 191 colonies in permanent
quadrats
Bleaching was correlated with heating
Bleaching prevalence varied among spp
Bleaching incidence varied with colony size
Why and what’s next?
• Symbiont “clades” vary genetically
– Corals can switch
– Symbiodinium communities can vary across
environmental gradients
– Degree of flexibility is debated
• Hosts (corals) also vary
– Different fluorescent proteins for protection
– Different abilities in heterotrophy
– Coral structure affects the light environment
Will coral reefs respond to fast climate
change?
• Climate shifts
– More peak temperature events
– More extreme temperature events
• Physiological response?
• Evolutionary response?
Competitive dynamics
• Exploitation competition (for light)
– Upright, branching corals can shade massive
corals
– Encrusting algae can spread over corals
• Interference competition (for space)
– External digestion by some corals
– “Sweeper” tentacles for some species
• Hierarchy of competitive dominance
– Algae easily overgrow most corals
– Among corals Pocillopora is nastiest
Mix of coral polyp and algae
Algal overgrowth
Shading by Sargassum, chemical effects
Herbivores on algae
Dynamics of predation on coral reef species
• Coral-feeding fish are present but usually
not devastating
– Territorial damselfish create safe zones (up to
60% of surface area)
– Coral-feeders have their own predators
• Starfish, such as “Crown-of-Thorns” can
be problematic
– Population “outbreaks” can damage living
corals
Dynamics of grazing on algal reef species
• Urchins are major
•
•
•
consumers (e.g., Diadema
antillarum)
Grazing by herbivorous fish
can be specialized on algae
(more impact than fish
feeding on corals)
Grazing can suppress
competitively dominant
algae (>90% removal)
Indirect effects can become
important
Evidence for herbivorous fish indirectly
helping corals
R = redband parrotfish
S = ocean surgeonfish
Burkepile & Hay, 2010, PLoS
One, 5 (e8963)
Mangrove /Mangal
A tropical and subtropical
boundary community
Questions:
• Why are trees found in some ocean
boundaries?
– Aquatic/terrestrial
– salt/freshwater
• What are the characteristics of these
ecosystems?
• How is mangal important to marine
ecosystems?
Definitions:
• Mangrove
– A type of tree that tolerates variation in
inundation and salinity
• Mangal
– A community (set of species) on the marine
fringe
– Dominated by a special set of salt-tolerant
trees
– Includes many other, associated species, both
of terrestrial and marine origins
Characteristics: very low wave action,
with silty substrates (sometimes sand)
Extent: 2/3 – 3 /4 of tropical shores
were fringed with mangal