A Study of the Abundance, Distribution, and Grazing Effects of Zooplankton in the Chlorophyll Maximum (CMAX) of the Neuse River Estuary, North Carolina

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Benjamin D. McGlaughon (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Phytoplankton tend to accumulate in distinct zones referred to as chlorophyll maxima, or CMAX. A pronounced CMAX occurs in the Neuse River Estuary (NRE), North Carolina, where as much as over 60% of the estuary's phytoplankton biomass is located. A sampling study was initiated to determine the seasonal variability in mesozooplankton abundance and species composition in relation to the CMAX in the NRE. Sampling was conducted at four stations along a 40-km transect of the Neuse River from March to October, 2011. The stations were chosen to include areas both inside and outside of the CMAX and the timing of the study included sampling in spring, summer, and fall. Large zooplankton (collected in a 200µm net) were not found to be spatially coincident with the CMAX during our study. Smaller zooplankton (collected in a 60µm net) were present throughout the estuary and showed no spatial differences with respect to the CMAX. Abundances of larger mesozooplankton peaked in spring along with the peak in Chl a, however these peaks were spatially separated. This suggests a diminished grazing role for larger-sized mesozooplankton within the CMAX. Grazing experiments were conducted in June, 2011 in order to quantify the effect of mesozooplankton grazing on phytoplankton abundance both within the CMAX and outside the CMAX. Whole zooplankton community grazing on phytoplankton was highest upon large phytoplankton (>20 µm) upstream of the CMAX. Grazing upon the >20 um fraction of chlorophyll within the CMAX was negative, suggesting no grazing occurred. Grazing by mesozooplankton was minimal in both locations and lowest on >20 um chlorophyll within the CMAX. Microzooplankton grazing rates were positive in all locations and were highest within the CMAX. Data from this study showed significant differences in grazing between the CMAX and upstream locations depending on both the size of zooplankton grazers and the size of the phytoplankton being grazed. When phytoplankton are larger, mesozooplankton will graze them directly. However, mesozooplankton appear unable to directly graze smaller-sized phytoplankton (< 20 um). As the majority of phytoplankton biomass is comprised of small cells (< 20 um) and mesozooplankton are spatially separated from the area of highest phytoplankton biomass (CMAX), grazing by large mesozooplankton on phytoplankton was found to be minimal. This result suggestions that the majority of mesozooplankton grazing occurs on microzooplankton, leading to increased importance of the microbial loop and less efficient energy transfer to higher trophic levels. This finding is consistent with other eutrophic systems that are typified by a decrease in phytoplankton size and increased importance of the microbial food web.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

Biology;Ecology;CMAX;Grazing;Mesozooplankton;Biology, Ecology

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