Tidal variation in bacteria, phytoplankton, zooplankton, mysids, fish and suspended particulate matter in the turbidity zone of the Elbe estuary; Interrelationships and causes

Abstract

In June 1992, an extensive investigation programme was carried out in the turbidity zone of the Elbe river. Special attention was paid to salinity and suspended particulate matter (SPM) and their influence on bacteria, phytoplankton, zooplankton, mysids and fish. SPM was separated into three fractions of different settling velocities. Mean settling velocity (Ws) was 0.05 cm s -1. The major part of SPM belonged to the slow settling fraction (w s <0.02 cm s-l).Bacterial exoenzymatic activity showed a positive correlation with SPM and chlorophyll-a content, and also to total dissolved free amino acids.Phytoplankton biomass reached maximum values of 5.7 pg chlorophyll-a 1-1 at ebb tide. Chlorophyll-a correlated negatively with salinity, indicating riverine input of phytoplankton. A positive correlation was found between chlorophyll-a and dissolved oxygen.Abundance of zooplankton species and their developmental stages varied over the tidal cycles; abundance of cirriped larvae and copepodite stages of the dominant species Eurytemora affinis (Copepoda, Crustacea) was positively correlated with salinity. Individual filtering rates (IFR) of Eurytemora affinis were negatively affected by the SPM content of the water. Maximum IFR for adults was 7.2 ml h -1. Community grazing reached maximum rates of 30.3 ml 1-1 h -1 (Le. 72.7% d-l).The dominant mysid Neomysis integer showed maximum abundance at night, possibly resulting from diel vertical migration. Abundance of N. integerwas positively correlated with SPM content.The fish community, consisting of 17 fish species, was characterised by high densities of smelt (Osmerus eperlanus). A positive correlation was found between salinity and abundance of typical marine fish species, such as sprat (Sprattus sprattus). Similar temporal variation of abundance of smelt, sprat, and Eurytemora copepodites indicates processes of habitat preference of these planktivorous fish in relation to optimal food supply.SPM was the factor controlling both distribution of organisms and the turnover of nutrients. Salinity only was important for the distribution of organisms.

Dominance of particle-attached bacteria in the Columbia River estuary, USA

“…In the turbidity maxima region of the Elbe Estuary, Germany, proteolytic enzyme activity was found to correlate with the concentration of SPM and dissolved free amino acids (Bernat et al 1994). In the Columbia River estuary, extracellular enzyme activity was detected principally on particles (Flg.…”

A Conceptual Model of the Aquatic Food Web of the Upper San Francisco Estuary

“…Phytoplankton, particularly diatoms, support zooplankton (such as the calanoid copepods E. affinis and P. forbesi) (Sautour et al 1996;Breitburg et al 1999;Tan et al 2004) and mysid larvae (including the once dominant N. mercedis) (Linkage 3.11) (Siegfried and Kopache 1980;Bernát et al 1994;Froneman 2001). These planktonic invertebrates in turn support planktivorous fishes (such as delta smelt) and filter-feeding fishes (such as threadfin shad) (Linkage 5.11) (Kjelson 1971;Domermuth and Reed 1980;Bernát et al 1994;Lott 1998;Feyrer et al 2009). This pelagic web also supports larvae of fishes at the critical period in their ontogenetic development when they are transforming from the yolk stage to the first feeding stage (Nobriga 2002;Nobriga and Feyrer 2007).…”

Effects of the river discharge management on the nursery function of the Guadalquivir river estuary (SW Spain)

“…Although estuarine recruits of marine species are typically euryhaline, it is likely that most of them have an optimal salinity (Rakocinski et al, 1992;Jassby et al, 1995). Indeed, there are examples of other estuaries in which the largescale salinity gradient seems to be the primary factor determining the spatial distribution of estuarine species, with biotic interactions being secondary (Peterand & Ross, 1991;Berná t et al, 1994 ;Thiel et al, 1995;Maes et al, 1998;Marshall & Elliot, 1998;Wagner & Austin, 1999;Barletta et al, 2005, among others). That is, in addition to other possible indirect effects, the river management from the upstream dam has an immediate effect on its nursery function: a reduction or enlargement of the estuarine nursery area depending on the magnitude (higher or lower, respectively) of the freshwater input to the estuary.…”