Generic

Human and natural influences can have different impacts on corals and coral reefs, depending on which part of the system they act upon. Use the table below to describe the relationship of several selected "partner" species to corals. Then you are asked to determine the impacts that selected human or natural alterations to those species will have on corals and the coral reef ecosystem.

Relationships & Impacts	Partner species
Relationships & Impacts	Zooxanthellae	Zooxanthellae	*Diadema* sea urchin	*Bolboneton* Parrotfish
Nature of relationship to coral	Mutualistic symbiosis; provides organic carbon photosynthate for nutrition in return for habitat & nutrients derived from coral waste	Mutualistic symbiosis; provides organic carbon photosynthate for nutrition in return for habitat & nutrients derived from coral waste	Herbivore that grazes on macroalgae that live on reef	Feeds on coral, incidentally removing some CaCO₃ reef material ("Bioerosion:") & macroalgae
Benefit to coral & ecosystem	Supplements heterotrophic diet of zooplankton in low-productivity waters	Supplements zooplankton diet in low-productivity waters	Reduces competition by algae with corals for space	Shapes the reef to make it more resistant to heavy wave action. Some control of coral species composition Reduces competition by algae with corals for space.
Observed alteration to natural conditions	Turbidity from land development	Increased surface water temperature	Pathogenic infection	Overfishing
Impacts on coral & ecosystem	Reduced coral growth & increased mortality	Coral "bleaching" & mortality	Reduced coral growth & increased mortality	Structural instability of reef Alteration of coral species composition Algae overgrowth
Explanation for impacts on coral & ecosystem	Reducing water clarity & photosynthesis, reduced food supply for coral. Clogging of feeding mechanism of coral	Zooxanthellae exit the coral polyp, reducing food supply for coral	Overgrowth of algae so that there is less suitable habitat for coral polyp larvae to settle & asexual expansion of polyp area. Overfished parrotfish could not replace grazing activity of Diadema. (loss of functional redundancy)	Shape of reef is more vulnerable to heavy wave action. Increase of coral species that are not grazer-resistant. Reduced incidental macroalgae consumption
"Top-down" or "Bottom-up" effect?	Bottom-up	Bottom-up	Top-down	Top-down