Contrasting Patterns of Phytoplankton Community Pigment Composition in Two Salt Marsh Estuaries in Southeastern United States

Abstract

Phytoplankton community pigment composition and water quality were measured seasonally along salinity gradients in two minimally urbanized salt marsh estuaries in South Carolina in order to examine their spatial and temporal distributions. The North Inlet estuary has a relatively small watershed with minimal fresh water input, while the Ashepoo, Combahee, and Edisto (ACE) Basin is characterized by a relatively greater influence of riverine drainage. Sampling stations were located in regions of the estuaries experiencing frequent diurnal tidal mixing and had similar salinity and temperature regimens. Phytoplankton community pigment composition was assessed by using high-performance liquid chromatography (HPLC) and multivariate statistical analyses. Shannon diversity index, principal-component, and cluster analyses revealed that phytoplankton community pigments in both estuaries were seasonally variable, with similar diversities but different compositions. The temporal pigment patterns indicated that there was a relatively weak correlation between the pigments in ACE Basin and the relative persistence of photopigment groups in North Inlet. The differences were presumably a consequence of the unpredictability and relatively greater influence of river discharge in the ACE Basin, in contrast to the greater environmental predictability of the more tidally influenced North Inlet. Furthermore, the timing, magnitude, and pigment composition of the annual phytoplankton bloom were different in the two estuaries. The bloom properties in North Inlet reflected the predominance of autochthonous ecological control (e.g., regenerated nutrients, grazing), and those in ACE Basin suggested that there was greater influence of allochthonous environmental factors (e.g., nutrient loading, changes in turbidity). These interestuarine differences in phytoplankton community structure and control provide insight into the organization of phytoplankton in estuaries.Processes and mechanisms that determine the spatial and temporal patterns of phytoplankton have been a central focus of marine research for decades. This research has led to the identification of biotic and abiotic factors that regulate primary productivity and the development of models that describe phytoplankton growth dynamics under specific environmental conditions (4). Phytoplankton communities are multispecies communities which are highly complex in terms of their diversity and dynamics. Successional shifts in phytoplankton community structure are primarily due to changes in environmental variables (e.g., degree or type of nutrient limitation) and/or shifts in higher trophic levels (e.g., micro-versus mesozooplankton) (23,35,40,54,56). How phytoplankton community composition changes with environmental variables and/or preferential grazing by herbivores is not well understood, particularly in estuarine ecosystems. Identifying the ecological variables that regulate phytoplankton community structure is essential for facilitating the development of broad hypotheses underlying our...

Linking bacterioplankton community structures to environmental state variables and phytoplankton assemblages in two South Carolina salt marsh estuaries

“…These trends were more apparent in ACE than in NI, and are similar to trends in nutrient chemistry found in other estuaries on the eastern seaboard of North America that are characterized by large river inputs and relatively little oceanic influence (Christian et al 1991. In contrast, NI nutrient patterns showed decreasing concentrations of NN and PO 4 , similar to results obtained by Verity (2002) in a study of hydrology and nutrient dynamics within a tidally dominated salt marsh estuary on the Georgia coast.Results of phytoplankton community analysis largely agree with those of Noble et al (2003), with greater phototrophic biomass in the ACE Basin, consistent with the influence of riverine input on increasing nutrient availability and consequent stimulation of phytoplankton production. The findings of Noble et al (2003) further indicated spatial and temporal changes, with higher concentrations of pigments indicative of diatoms, dinoflagellates, haptophytes, and cryptophytes in ACE samples and higher levels of pigments associated with chlorophytes, prasinophytes and/or cyanobacteria in NI samples.…”

“…The influence of freshwater, riverine inflow on overall nutrient chemistry may have been further indicated by the increase in TDP in the seaward direction as observed for ACE samples. Total suspended solids in ACE were shown to be significantly higher than in NI (Noble et al 2003), and, as reported by Gardolinski et al (2004), bound phosphorus tends to be released into the water column from river-borne particles as salinity increases. Additional evidence for the influence of freshwater input on total water chemistry was apparent in NI Stn 1 samples from August, which were collected only a few hours after a rain event.…”

“…In the present study, we used both HPLC of photopigments collected in the summer of 2000 by Noble et al (2003) and DGGE of bacterial 16S rRNA genes to compare communities within and between 2 estuaries on the South Carolina coast, USA. The primary objectives of this study were to (1) assess in situ patterns of bacterial community distribution within and between 2 pristine salt marsh estuaries, (2) determine the ecological factors that control phytoplankton and bacterial community structures, and (3) identify potential associations between phytoplankton and bacterial community structures in these ecosystems.…”

“…The importance of such bottom-up controls on community composition is often assumed for ecosystems; however, owing to the inherent complexity of bacterial communities and the practical difficulty of making comparisons of small-scale phenomena across large spatial scales, such controls are difficult to determine. Additionally, the abiotic factors that influence community dynamics appear to vary among different ecosystems, and among different zones within an ecosystem (Noble et al 2003, Pinhassi et al 2003, Bordalo & Vieira 2005.The composition of bacterioplankton populations is also influenced by the composition of phytoplankton communities. In lakes, estuaries, and the marine environment, bacterial production, function, and community composition change as phytoplankton blooms form, develop, and then collapse (Kirchman et al 1991, Fandino et al 2001, Riemann & Winding 2001.…”

“…High performance liquid chromatography (HPLC) of photopigments has been recently used in numerous studies to generate a composite profile of the phytoplankton community (Higgins & Mackey 2000, Pinckney et al 2001, Rodriguez et al 2002. Group-specific pigments in particular offer information on the relative abundance of phytoplankton taxa within the community, while the relative amounts of all pigments measured give a broad picture of the whole community.In the present study, we used both HPLC of photopigments collected in the summer of 2000 by Noble et al (2003) and DGGE of bacterial 16S rRNA genes to compare communities within and between 2 estuaries on the South Carolina coast, USA. The primary objectives of this study were to (1) assess in situ patterns of bacterial community distribution within and between 2 pristine salt marsh estuaries, (2) determine the ecological factors that control phytoplankton and bacterial community structures, and (3) identify potential associations between phytoplankton and bacterial community structures in these ecosystems.…”