Distribution and chromatic adaptation of phytoplankton within a shelf sea thermocline

Abstract

Observations of vertical gradients in phytoplankton community structure were made through the water column of the seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton community composition were routinely observed within the thermocline. The cell abundance maxima for Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima. Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales for mixing between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The observed vertical gradients in community structure could therefore result from selection and niche partitioning of phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process.The Celtic Sea, part of the temperate Northwest European shelf, is a tidally dynamic environment where water column structure is strongly influenced by the balance of solar heating and tidally generated mixing (Simpson and Hunter 1974). Much of the region becomes thermally stratified in April, initiating the spring phytoplankton bloom (Pingree et al. 1976). The water column remains stratified throughout the summer, with the thermocline forming a boundary between nutrient-depleted surface mixed layer (SML) above and the nutrient-rich bottom mixed layer (BML) below (Pingree et al. 1977). During this seasonal stratification, a deep chlorophyll maximum (DCM) is present within the thermocline (Pingree et al. 1977). The DCM is typically located toward the base of the density gradient, lies within the euphotic zone, and is strongly coupled to the nitracline (Holligan et al. 1984a,b;Sharples et al. 2001).Energy from tidally induced turbulence is dissipated at the base of the thermocline, causing upward mixing of nitrate into the thermocline from the BML and downward mixing of phytoplankton from the base of the DCM (Sharples et al. 2001). Previous observations in the Celtic Sea have revealed a vertical flux of nitrate into the thermocline of around 2 mmol N m 22 d 21 with the DCM maintained at a depth corresponding to ,5% of surface irradiance (Sharples et al. 2001). The DCM is often observed to be a biomass and photosynthesis maximum as well as a pigment maximum (Holligan et al. 1984a,b;Pemberton et al. 2004;Moore et al. 2006). Monospecific blooms with chlorophyll a (Chl a) concentrations .10 mg Chl a m 23...

A deep chlorophyll maximum nourishes benthic filter feeders in the coastal zone of a large clear lake

“…These dense aggregations of phytoplankton can be manifest as deep chlorophyll maxima (DCMs), a phenomenon that is observed widely, reported from all the world's oceans (Cullen 1982;Huisman et al 2006), from coastal shelves (Hickman et al 2009), as well as from transparent stratified lakes of a wide range of sizes and geographic distribution (Camacho et al 2003;Burnett et al 2006;Pannard et al 2011). DCMs have been reported in the pelagic waters of all the Laurentian Great Lakes (Moll and Stoermer 1982;Barbiero and Tuchman 2001).…”

“…Dense subsurface aggregations of viable phytoplankton are predicted to arise in waters with a pycnocline, a gradient of nutrient concentration supplied from depth, and sufficient water-column transparency to support photosynthesis at depth (Klausmeier and Litchman 2001;Hickman et al 2009). These dense aggregations of phytoplankton can be manifest as deep chlorophyll maxima (DCMs), a phenomenon that is observed widely, reported from all the world's oceans (Cullen 1982;Huisman et al 2006), from coastal shelves (Hickman et al 2009), as well as from transparent stratified lakes of a wide range of sizes and geographic distribution (Camacho et al 2003;Burnett et al 2006;Pannard et al 2011).…”

Variasi Komunitas Plankton Dan Parameter Oseanografi Di Daerah Penangkapan Ikan Pelagis Di Perairan Malang Selatan, Jawa Timur

“…Daerah penangkapan ikan merupakan suatu perairan dimana faktor lingkungan sesuai dengan yang disukai ikan yang menjadi sasaran penangkapan, karena ketersediaan banyak makanan yang cukup bagi ikan [2]. Sehingga, kelimpahan berbagai jenis ikan pelagis kecil, terutama ikan pemakan plankton (planktivor) secara langsung dipengaruhi oleh ketersediaan plankton di suatu perairan [3].…”

An approach for the identification of exemplar sites for scaling up targeted field observations of benthic biogeochemistry in heterogeneous environments

“…full year using *1.8 km resolution for the entire northwest European shelf (Brown et al 2015) where maximum tidal stresses that year occurred in October During the summer months, surface waters become nutrient poor and therefore lacking in phytoplankton. However, the development of a summer deep chlorophyll maximum positioned at the base of the thermocline in the vicinity of the nutricline (Pingree et al 1977;Hickman et al 2009) is a well-known phenomenon. Smaller-celled phytoplankton tend to dominate here due to competition for nutrients and include prymnesiophytes, pelagophytes and the cyanobacteria Synechococcus (Hickman et al 2009).…”

“…However, the development of a summer deep chlorophyll maximum positioned at the base of the thermocline in the vicinity of the nutricline (Pingree et al 1977;Hickman et al 2009) is a well-known phenomenon. Smaller-celled phytoplankton tend to dominate here due to competition for nutrients and include prymnesiophytes, pelagophytes and the cyanobacteria Synechococcus (Hickman et al 2009). …”