Marine ecology

Reconstructive aging techniques were used to construct the age frequency distributions of T. testudinum short shoots in the Salt Ponds of Key West, FL. Median short shoot age was approximately two years. No evidence of sexual reproductive effort was found. A site-specific leaf emergence rate was not used, which may have contributed error in the reconstructive technique. Gradients in salinity, phosphorous availability, community composition, and leaf width were observed along the water flow pathway through the ponds. Populations of short shoots more distal from the tidal source exhibited an older age structure reflecting higher salinity, temperature, and dissolved oxygen stresses. Populations closest to apparent sources of nutrient enrichment were skewed toward young individuals. A significant positive relationship between increasing short shoot mortality and recruitment was identified. A significant correlation between low phosphorous availability and narrow leaf width was observed, and a positive relationship between phosphorous availability and recruitment was suggested.

In natural systems, it has been observed that plankton exist in patches rather than in an even distribution across a body of water. However, the mechanisms behind this patchiness are not fully understood. Several previous modeling studies have examined the effects of abiotic and biotic factors on patch structure. Yet these models ignore a key point: zooplankton often undergo diel vertical migration. I have formulated a model that incorporates vertical movement into the Rosezweig-MacArthur (R-M) predator-prey model. The R-M model is stable only at a carrying capacity below a critical value. I found that adding vertical movement stabilizes the system even at a high carrying capacity. By analyzing temporal stability and spatial structure, my results show that vertical movement interacts with carrying capacity to determine patch structure.