Document Type
Dissertation
Degree
Doctor of Philosophy
Department
Biology
Advisor's Name
James W. Fourqurean
Advisor's Title
Committee Chair
Advisor's Name
Jennifer H. Richards
Advisor's Name
Joel C. Trexler
Advisor's Name
Steven F. Oberbauer
Advisor's Name
Piero R. Gardinale
Keywords
seagrass, nutrient addition, eutrophication, grazing, herbivory
Date of Defense
1-18-2011
Abstract
The importance of resource supply and herbivory in driving competitive interactions among species has been an important but contentious issue within ecology. These variables exhibit different effects on species competition when manipulated in isolation but interact when manipulated together. I tested the direct and interactive effects of nutrient addition and simulated grazing (clipping) on the competitive performance of primary producers and community structure of a seagrass bed in South Florida. One square meter experimental plots were established in a mixed seagrass meadow from August 2007 to July 2009. The experiment was a 3 x 3 factorial experiment: 3 fertility treatments: control, medium (2.4 mg N d-1 and 80 µg P day-1) and high (4.8 mg N d-1 and 160 µg P day-1) x 3 clipping intensities (0, 25% and 50 % biomass removal (G)) x 5 replicates for each treatment = 45 plots). Nutrient additions and simulated grazing were done every two months. Fertilization and simulated grazing decreased sexual reproduction in S. filiforme. Fertilization increased competitive dominance within the primary producers while simulated grazing counteracted this effect by removal of the dominant species. Fertilization ameliorated the negative impacts of simulated grazing while simulated grazing prevented competitive exclusion in the fertilized plots. Nutrient addition and simulated grazing both exerted strong control on plant performance and community structure. Neither bottom up nor top down influences was eliminated in treatments where both factors where present. The effects of fertilization on plant performance were marked under all clipping intensities indicating that the system is regulated by nutrient availability both in the presence or absence of grazers. Clipping effects were strong under both fertilized and unfertilized conditions indicating that the seagrass bed can be simultaneously under top-down control by grazers.
Recommended Citation
Halun, Sitti Zayda B., "The Effects of Fertilization and Simulated Grazing on the Community Structure of a Seagrass Bed in South Florida" (2011). FIU Electronic Theses and Dissertations. Paper 415.
http://digitalcommons.fiu.edu/etd/415