Thesis Defense: Angela Zepp- October 6th, 2017


Angela Zepp, originally from the landlocked state of Missouri, developed her love for the ocean at a young age but rarely had the opportunity to visit. To pursue her dreams, she moved to California to attended Humboldt State University and developed a love for diving. Fast forward to 2017, where she is completing her Masters Degree at Moss Landing Marine Lab!  


Thesis Abstract

Tripping on Acid for 2 years: Factors driving demographic and temporal variability in pH of the acid weed, Desmarestia herbacea


Angela Zepp

Demographic studies allow for a better understanding of how populations change over time and establish a baseline to examine how biotic and abiotic factors influence populations.  The annual seaweed, Desmarestia herbacea, or the acid weed, accumulates sulfuric acid (H2SO4) within cell vacuoles, likely as a chemical defense mechanism. Whether pH varies ontogenetically is poorly understood. A D. herbacea population in the Stillwater Cove, central California kelp bed was assessed for two years to measure how internal pH varied relative to demographics, season, grazing pressure, and environmental variability. The timing of spring recruitment and fall senescence varied interannually. Sporophyte recruitment occurred during upwelling season in mid-March and thalli reached maximum length during the Oceanic season (July-October) then senesced during the Davidson Current season (November-February). Mean thallus length was inversely related to density with smaller plants present in 2015 when densities were higher.  In contrast in 2016, individuals were significantly larger and density was lower and the senescence period extended into January 2017. The ontogenetic shift in intracellular pH of D. herbacea was seasonal in both years and may be driven by ocean temperature. In 2016, the pH was highest during the recruitment period (1.38 ± 0.14), followed by a decline in pH during the growth period (0.60 ± 0.01), followed by an elevation during the senescence period (0.65 ± 0.02). Benthic invertebrate grazers had a strong, significant and negative effect on the early recruitment of D. herbacea both in permanent plots and an herbivore exclusion experiment. Plots with higher herbivore abundance had significantly lower recruitment. Higher densities of Desmarestia, and smaller plants in 2015 may have been correlated with higher temperatures in 2015 associated with El Niño.  These findings suggest that despite inter-annual variability in demographic patterns, strong, seasonal shifts in intracellular pH may reflect ontogenetic shifts in chemical defense to protect vulnerable growth phases of life history.

Thesis Defense by Mo Wise- September 25th, 2017

Thesis Abstract


Nutrient Dynamics In Tidally Restricted Regions Of The Elkhorn Slough National Estuarine Research Reserve


Maureen M. Wise

Masters of Science in Marine Science

California State University Monterey Bay, 2017

            The Elkhorn Slough, in the heart of the Monterey Bay, includes water bodies that have been isolated from natural tidal flushing cycles by dikes, levees, roads and train tracks.  This partitioning has changed the functionality of these systems primarily through reduced circulation and increased eutrophication. The Elkhorn Slough is surrounded by a patchwork of lands under varied land-uses, including open space, developed properties, and extensive agriculture, which results in high and variable nutrient loading into the surrounding aquatic habitat. Water bodies of restricted flow disproportionately exhibit impacts due to this loading. In this study, nutrient concentrations were measured using both discrete water column sampling methods and in situ osmotic sampling techniques.  Fluxes were measured using flow measurements, ground water flux correlations, benthic chambers, modeled pore water gradients and estimates of Ulva uptake. These measurements were used to quantify the cycling of nitrate, ammonium and phosphate in these pocket regions and has identified systemic nutrient drivers to be surface water flow, Ulva uptake and groundwater inputs. A box model approach was used to determine the degree to which these drivers contributed to overall nutrient concentrations on a seasonal timescale. The systems of study were all in dynamic disequilibrium, rather than steady-state. Nitrate varied from xx to yy on timescales as short as bb. Ammonium varied from ee to ff, and Phosphate varied from  cc to dd on similar timescales.  These variations were large compared to the same nutrients in the adjacent Elkhorn Slough.  Such variability is significant when characterizing these systems, as it is indicative of the nature of nutrient flux in tidally restricted ecosystems and the rapid extremes in chemical composition experienced by the resident biota. The dominant sources of nutrients in these restricted areas also varied in time with surface runoff dominating in the wet season, and ground water inputs (possibly due to agricultural irrigation) dominating in the fall. Ulva uptake and advective flow were the largest loss terms and these too varied significantly in time.  Understanding the key nutrient drivers, as well as the degree to which these drivers influence biogeochemical cycling of nutrients in these systems, informs mitigation projects as to how best manage estuarine regions with structural barriers inhibiting natural flow, a increasingly common feature of the coastal landscape.