Spatial and Temporal Variability during Periods of "Recovery" after Mass Bleaching on Western Atlantic Coral Reefs

Western Atlantic coral reefs were differentially affected bya mass bleaching (discoloration) event in 1987. We periodicallyassessed the "appearance" of zooxanthellate organisms betweenDecember 1987 and June 1988 at nine conspicuously affected sitesin the Bahamas, Florida, St. Croix, and Venezuela, using a standardizedpoint-count technique. Three to four months after the localinitiation of the event, the "bleached" state was still presentin one to three of the most abundant reef coral taxa and ina few of the less common species (n = 5 sites). "Recovery" occurredsomewhat faster at shallower depths, at least in the Bahamasand Florida. Scleractinian corals which were "prolonged bleachers"had foliaceous or massive, rather than branching, morphologies."Bleached" points disappeared from the point counts after $6to $8 months. Long-term field data on spatial and temporal variability inthe dynamics of zooxanthellate organisms would help us to understandthe ecological consequences of bleaching. More generally, weneed to distinguish anthropogenic changes in the structure andfunctioning of reef ecosystems from those which occur naturally.Point-count techniques are well suited for collaborative studiesinvolving rapid quantification of coloration states and healthin reef corals.     

Food limitation in the fungus‐gardening ant,Trachymyrmex septentrionalis

Abstract 1. Most ants are more like plants and marine invertebrates than other insects because the adults are sessile and the immature stages are motile. 2. This paper reported the results from a field experiment that increased food levels on the fungus gardening ant, Trachymyrmex septentrionalis, which has served as a model system for understanding the complexities of these obligate mutualisms. 3. Food supplementation increased the growth of the symbiotic fungus and this led to an increase in the amount of fungal biomass. The amount of fungal biomass was generally more important in determining the amount of ant offspring than colony size. 4. The results indicate that the population is food limited and colonies may compete for relatively rare fungal substrate. However, competition in this species is not obvious.     

SIGNIFICANCE AND TECHNIQUE OF SHORT-TERM EXPERIMENTS ON SOLUTE ABSORPTION BY PLANT TISSUE

The significance of short-term absorption periods in experimentson solute absorption by plant tissues is discussed. A techniqueis described for such short-term experiments. As applied inexperiments on ion absorption by barley roots, the techniquepermits accurate absorption rate determinations to be made inabsorption periods of ten minutes or even less. The heterogeneityof cation uptake by this tissue is demonstrated. A readily exchangeablefraction is often present which must be accounted for if ratesof metabolically active transport are to be determined. ¹ Present address: Department of Botany, Southern Illinois University,Carbondale, Illinois. (Received December 4, 1962; )