Date of Award

Spring 1980

Document Type


Degree Name

Master of Science (MS)


Ocean & Earth Sciences



Committee Director

Anthony J. Provenzano

Committee Member

Phillip R. Mundy

Committee Member

George Ofelt

Committee Member

Harold G. Marshall

Call Number for Print

Special Collections LD4331.O35 W46


Spatial zonation of symbiotic and aposymbiotic forms of the temperate coral Astrangia danae provides evidence that light attenuation is an important factor in the distribution of this animal. At four locations in the lower Chesapeake Bay and adjacent offshore waters, symbiotic colonies were observed only in well illuminated surface waters, while aposymbiotic colonies were observed in less illuminated deeper waters. A transition zone exists in which both colony types are found. Colonies on substrates forming a plane parallel to the sea-surface receive a greater radiant flux than colonies on vertical substrates. This extends the depth range of symbiotic colonies located on horizontal substrates. Near the Chesapeake Bay mouth, the transition between the symbiotic and aposymbiotic zones does not occur in the same depth range at all locations, rather, it occurs between the depths that correspond to 89 and 95 percent attenuation of surface incident light. These patterns suggest that both genetic and environmental factors influence the symbiosis.

The range of zooxanthellae densities encountered in Astrangia danae is considerably wider than those reported for most other corals (and previously, Astrangia). On the basis of zooxanthellae content, most colonies can be regarded as either symbiotic or aposymbiotic. Very few intermediate forms exist.


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