Hard Anemone An exoskeleton Even though it lies Beneath the animal Some scleractinian coral growth forms massive II. The Coral Host branching plate like foliaceous encrusting columnar Free-living Algae in coral tissue Already present in planula Zooxanthallae participate In a mutualistic Association with Corals. Both members of the association benefit as indicated by the cycling of carbon (one important nutrient is Nitrogen) 1
III. Coral Reef Community Structure Hard Substrate Coral Reef Structure: 3 main types of reef What is the process by which reefs are formed? Hard Substrate Coral rubble Consolidation Fringing Reef Barrier Reef Atoll Hard Substrate Darwin first explained how reefs form. Island Fringing Reef IV. Biogeography of Coral Reefs Where do Coral Reefs Occur? Atoll Barrier Reef Lagoon And that Each type Is a stage In the same process Calcium Carbonate Original Island Where do Coral Reefs Occur? Solar radiation Number of Genera Temperature Indo-Pacific Maximum diversity Atlantic Maximum diversity In areas where mean avg. temp. >20 C Especially where fluctuations are small But not too far above 27 C. 2
V. Physical Factors and Zonation in Coral Reef Communities High temperature, high light (UV), desiccation runoff, etc. keep many corals from the reef flat Wave action, major storms control the reef front Vertical Zonation Of a Fringing Reef A. Competition for space between Corals Competition video B. Herbivory by Sea Urchins and Fish Extensive fisheries starting in the 1950 s had little additional effect on coral reefs However major predators of sea urchin Diadema and herbivorous fish competitors were lost From 1982-84 a mass die-off of sea urchins due to a disease reduced populations by 99% This was followed by extensive take over of reefs by algae Hughes, 1994 Hughes, 1994 3
Hughes, 1994 Hughes, 1994 Impact of fisheries Fisheries vs. hurricanes Resilience Role of herbivory Phase shifts Roberts C.M. 1995. Conservation Biology Vol 9: 988-995 http://www.jamaicachm.org.jm/article/december2005.asp VII. Climate Change and Coral Reefs What Cellular Events Lead to Bleaching? Bleaching Event in the Maldives Two Alternative Mechanisms Before During After 4
Temperature fluctuations in the GBR related to the onset of bleaching (arrows) The displaced symbiont is inferior to invading symbionts Replacement of the resident population in an animal requires depletion of the population (e.g. Hydra with nutritionally inferior and superior strains) An alternative strain is available to populate the bleached animal hosts (may be residual or external in origin) McField (1999) also identifies temperature as the cause of bleaching in Belize during 1995 Hughes et al 2003, Science Vol. 301 p 929 Invariant bleaching threshold leads to massive losses bleaching is an ecological gamble in that it sacrifices short-term benefits for long term advantage. This counters conventional wisdom that bleaching is detrimental from all perspectives, and supports the role of symbionts as adaptive agents. Andrew C. Baker In rebuttal: there is no guarantee that temperature was the stressor that caused bleaching. Also, as light energy is critical to coral survival, stressed corals might survive better when transplanted to the more sunlit site and less well after transfer to deep water. Baker is unable to distinguish newly invading genotypes from other rare genotypes that are present in the host and which simply increase in proportion. The latter is a phenotypic change known as acclimatization and as such is restricted in its provision of new genetic combinations for evolution. Hoegh Guldberg et al. Bleaching threshold as a broad spectrum of responses leads initially to differential bleaching Adaptive bleaching response may lead to evolution in some species Acclimatization vs. Adaptation 5
Acidification of the Oceans Baker et al 2004 Conducted molecular studies of Symbiodinium in corals from reefs differentially affected by 1997-98 ENSO: in Panama before and after bleaching events from heat adapted & bleached Persian Gulf to milder Red Sea severely bleached Kenyan corals to unbleached Mauritius corals Under this model, Coral reefs would reach a point where maintenance of a coral dominated phase rather than an algal dominated phase would be nearly impossible U.S. Coral Reefs Annual revenues from reef tourism in Keys is $1.6 billion Only 6% of the Florida Keys Marine Sanctuary is no take Purple Pandolfi et al. 2005. Are U.S. coral reefs on the slippery slope to slime? Science #307: 724-1726 Pandolfi et al. 2005. Are U.S. coral reefs on the slippery slope to slime? Science #307: 724-1726 6