Composition and Dynamics of Phytoplankton in the Coastal Bays of Maryland, USA, Revealed by Microscopic Counts and Diagnostic Pigments Analyses

Ozuem Oseji,Paulinus Chigbu,Chunlei Fan

doi:10.3390/w11020368

Ozuem Oseji, Paulinus Chigbu + Show 1 more

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https://doi.org/10.3390/w11020368

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Abstract

Maryland Coastal Bays (MCBs) have undergone changes in water quality in the past two decades due to nutrient enrichment but the composition and dynamics of the phytoplankton community have not been adequately described. Microscopic counts and photosynthetic pigments of samples collected monthly in 2012 at selected sites in MCBs that differed with regard to the degree of anthropogenic impacts were examined. Sixty-three (63) phytoplankton genera were recorded, of which 40 species are being reported for the first time in the Bays. Among the dominant species were Dactyliosolen fragilissimus (Bacillariophyta), Paulinella ovalis (Cercozoa) and Cryptomonas sp. (Cryptophyta). Bloom densities of Heterocapsa rotundata (Miozoa), which previously had not been reported in the Bays, were observed bay-wide in December, particularly at the mouth of St. Martin River. Diatoms dominated (>40%) the phytoplankton community in winter and decreased in spring (<40%), while Cercozoa and microphytoflagellates (MPF) co-dominated in summer (July). From August to October, diatoms dominated with maximum contributions from an unidentified small (<10 µM) centric species and co-dominated the assemblage with cryptophytes in late fall (November). Canonical correspondence analysis indicated that diatoms were favored by high salinity and total dissolved phosphorus (TDP), cercozoans and chlorophytes by total dissolved nitrogen (TDN) and cryptophytes by dissolved organic carbon. The spatial and seasonal differences in the composition of phytoplankton species, coupled with the occurrence of potentially toxic species and bloom densities of H. rotundata suggest that important changes have occurred in the phytoplankton assemblage that likely have affected the food web of these eutrophic bays.

Highlights

Understanding the variation of species composition and biomass of phytoplankton gives insight into the structure and dynamics of productive aquatic ecosystems such as coastal lagoons, as these organisms regulate the structure and efficiency of food webs and are vulnerable to cultural eutrophication [1,2]
Canonical correspondence analysis indicated that diatoms were favored by high salinity and total dissolved phosphorus (TDP), cercozoans and chlorophytes by total dissolved nitrogen (TDN) and cryptophytes by dissolved organic carbon
The objectives of this study were to: (1) use microscopic counts and pigment markers to investigate the composition and seasonal and spatial variations of phytoplankton assemblage in the Maryland Coastal Bays (MCBs) based on monthly samples collected from February–December 2012 and (2) conduct multivariate analyses to explore the relationships between key environmental factors and phytoplankton community composition and dynamics

Summary

Introduction

Understanding the variation of species composition and biomass of phytoplankton gives insight into the structure and dynamics of productive aquatic ecosystems such as coastal lagoons, as these organisms regulate the structure and efficiency of food webs and are vulnerable to cultural eutrophication [1,2]. Microscopic techniques allow the identification and characterization of phytoplankton to the species level, this process is strenuous and fragile species do not survive the procedural rigors [6,7], necessitating the first use of chlorophyll a as a measure of biomass [8] and more recently the use of pigment signatures from high performance liquid chromatography, HPLC [9,10,11,12,13]. The HPLC technique measures the contributions of chloro- and carotenoid biomarker pigments, which are representatives of different algal classes, to chlorophyll a [14,15,16]. Combining HPLC and microscopy provides a robust method for monitoring phytoplankton assemblages, yielding information which can be used to understand phytoplankton dynamics in aquatic ecosystems since the sole use of photosynthetic pigments could give misleading information [17]

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