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NOTE: QUIZ DATE IS FRIDAY NOV 22 and NOT next Friday. Sorry for the confusion.
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| Lecture 31: GUEST LECTURER: Tegan Churcher-Hoffman – Coral Reef Bleaching Reference: NOAA Website on Coral Reefs: http://www.coralreef.noaa.gov/ Corals are animals with hard Calcium carbonate shells They have specific needs: Warm water – 18 degrees – 23 degrees Live in tropcs Adequate source of positive ions for carbonate shell Shallow water for symbiotic algae to grow Aeration of water to remove waste Food supply – algae or feeding Clean substrate to colonize Geography 65 species in the Atlantic ocean 200+ in the Indian ocean 500+ in Indo-Pacific ocean Anatomy of a coral Coral polyp in limestone cup (coralite) Algae – zooxanthellae The zooxanthellae gets nutrients from coral waste, and provides food for coral Bleaching: zooxanthellae has pigment in cells. When zooxanthellae leaves the coral, the coral becomes white. Coral bleaching discovered in the 1920s by Young, who then experimented to see how it is caused. Zooxanthellae leave as response to imbalance, due to stress occurring either inside the coral cells. Bleaching can be temporary or permanent, partial or complete. Important because: Coral reefs have high biodiversity. Corals are the engineer of coral reef ecosystems. Tourism – provide income for local communities Environmental services – wetlands, nursery, habitat Evolutionary adaptation of Bleaching, possible reasons: 1) zooxanthellae leave when relationship is not beneficial 2) coral expels z zooxanthellae, but why? Some causes of bleaching: Extremely low tides (too much exposure) Increase in sea surface temprature Increase in U.V. radiation Abnormal salinity Sedimentation Increase in chemical toxins (sewage, pesticides, bacteria) Some species of coral have different thresholds to environmental changes and therefore may not bleach as easily. E.g., the species Poriedes can acclimate (adjust) better to changes in environmental conditions. Adaptive Bleaching Hypothesis: different species of zooxanthellae can adapt better to specific environmental factors. Consequences of Bleaching: Increased mortality of corals Decreased reproduction Decreased productivity of reef Change in community structure of reef Increased rates of coral disease, outbreaks of predators – these may be linked to changes in sea surface temperatures Frequency of Bleaching Local scale – common Larger scale (affecting a larger area) less common Intermediate Disturbance hypothesis – in the long term, the changes in environmental factors like changes in sea surface temperatures, hurricanes, etc., result in increased species diversity. Evidence suggests that Coral Reefs are disturbance-adapted ecosystems Human threats: Pollution of reefs is a Chronic threat (i.e., constant), this changes the adaptive capacity of the reef. Climate change and Bleaching Research in the 1980s and 90s. Corals have been around for 240 million years. From 1960 to 1979, only 9 coral bleaching events recorded From 1979 – 2000, more than 65 major coral bleaching events recorded. This may be partially an artifact of record-keeping. But there seems to be a trend towards increased frequency and severity El Ninos: Scientists debating about impacts of Global Warming 1982-83 Event – world wide bleaching and very high mortality 1986-87 Event – even more world-wide and severe 1997 Event – massive bleaching, but not as bad and some coral reefs didn’t bleach at all e.g., Moorea in French Polynesia. Why? -cloudier conditions Sea Surface Temperatures and U.V. Radiation: Corals have a biochemical defense against U.V. radiation, but increased sea surface temperatures reduces that protection. Corals today are being hit by successional bleaching events and by multiple streeses. This year, 2002, while a mild El Nino year, has resulted in a very severe bleaching event in the Great Barrier reef (Australia). Each reef is unique and as they are weakened by pollution, destructive fishing, over exploitation, sedimentation (from deforestation and erosion), increasing temperatures, they become more susceptible to bleaching Strategy for protecting Coral Reefs: 1. Reduce other human stresses 2. protect reefs as Marine protected areas 3. select sites that are both less prone to bleaching and more resilient after a bleaching event |