The dynamics of coral reef algae in an upwelling system

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Peter W. Glynn, Committee Chair


This dissertation describes the effects of upwelling on primary producers, primary consumers and possible interaction with corals on coral reefs in the Panamanian Pacific. Similar to higher latitude systems, high inputs of allochthonous material and nutrients were hypothesized to have strong bottom-up influences on the population structure and individual characteristics of algae and herbivores through a stimulation of algal primary productivity. It was found the upwelling conditions created a maximum 400% increase in the growth of algae compared with the same area during nonupwelling conditions. However, this stimulation of algal growth did not influence regional patterns of algal community biomass and only showed moderate and site-specific effects on algal community composition between the contrasting seasons. Location-specific and regional differences in algal community biomass were more attributable to changes in herbivore pressure due to changes in the availability of graze-able substrate, as demonstrated by a significant relationship between the percent cover of algae and the biomass of algae at each site (p<0.016, r2 = 0.80). Regionally, differences in algal growth influence the population characteristics of herbivores in an upwelling gulf as opposed to an adjacent nonupwelling gulf. Sea urchins were more than 8x as abundant (p<0.0001) and 37% larger (p<0.0001) in the upwelling gulf. Damselfish were 41% larger (p<0.0001) and had a biomass 5.3x greater (p<0.0001) in an upwelling gulf. Damselfish abundance was also 1.9x greater in the upwelling gulf, though this difference was not significant. Unlike temperate systems, it appears that strong bottom up forcing effects the demographics of herbivores, while the population dynamics of algae are constrained by the strong influence of herbivory. This suggests that coral algal competition may not have a large role in upwelling systems with unharvested herbivore populations.There was a highly significant positive relationship between water temperature and feeding rates of a dominant parrotfish across the region (p<0.0001) and a marked four-fold change in grazing rates over the range of temperatures encountered in the study (21--29°C). The effect of temperature on grazing rates likely explains seasonal and latitudinal trends in herbivore pressure and may be a factor contributing to algal biomass increases in low-temperature coral reef environments.


Biology, Ecology; Biology, Oceanography

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