Spatial distribution of living coccolithophores in the southwestern Gulf of Mexico

Karl-Heinz Baumann,Babette Boeckel

doi:10.1144/jmpaleo2011-007

Abstract

Abstract. The present study was conducted to provide information about the upper water column distribution of living coccolithophores in the subtropical Gulf of Mexico. In total, 52 plankton samples from 6 stations collected in March 2006 were analysed. Coccolithophore standing crops range from zero in deep-water samples (200 m) to about 23 000 to 46 500 coccospheres per litre at intermediate water depths. From 39 identified taxa, only nine species contribute significant cell numbers of more than 1000 cells 1–1 and comprise more than 5 % of the communities in at least one sample. Emiliania huxleyi was the most abundant species throughout the stations with concentrations of up to 22 700 cells l–1. At all stations, a vertical succession of coccolithophore species was found. Umbellosphaera tenuis (type IV), Discosphaera tubifera, Rhabdosphaera clavigera and, as a minor component, species of the genus Syracosphaera, were mainly restricted to surface waters (≤50 m), all adapted to lower nutrient levels. The assemblage in the deep photic zone (50–150 m water depth) was composed mainly of abundant Florisphaera profunda, Gladiolithus flabellatus and Algirosphaera robusta indicating a tolerance of lower light availability. Thus, the vertical distribution of all coccolithophorid taxa, except the placolith-bearing species, in particular E. huxleyi, was probably controlled by upper photic-zone water temperature and stratification of the water column.

Highlights

The Gulf of Mexico (GoM) has been the focus of numerous physical oceanographic studies (e.g. Vidal et al, 1994; Sturges & Leben, 2000; Sturges & Lugo-Fernandez, 2005; Zavala-Hidalgo et al, 2006), but relatively little is still known about the biological oceanography of the region (e.g. Müller-Karger et al, 1991)
Material and Methods Fifty-two water samples were taken during Meteor Cruise M67/2 in 2006 (Table 1) using a Rosette sampler attached to a Conductivity Temperature Depth (CTD) device at 6 stations from distinct water depths
Highest numbers of no more than 48 000 cells l–1 were generally reached in intermediate water depths (50–75 m), except at station GeoB 10604, where highest numbers (23 700 cells l–1) occurred at 120 m water depth

Summary

Introduction

The Gulf of Mexico (GoM) has been the focus of numerous physical oceanographic studies (e.g. Vidal et al, 1994; Sturges & Leben, 2000; Sturges & Lugo-Fernandez, 2005; Zavala-Hidalgo et al, 2006), but relatively little is still known about the biological oceanography of the region (e.g. Müller-Karger et al, 1991). High production rates and large stocks of phytoplankton, mainly dominated by diatoms, raphidophytes and dinoflagellates, are commonly observed in discharge plumes of the Mississippi and other river-dominated estuaries Lohrenz et al, 1990; Dagg, 1995; Strom & Strom, 1996; Livingston, 2007) They occur because riverine waters, which are turbid but rich in nutrients, become ideal for high rates of phytoplankton growth when they spread out over the receiving oceanic waters. Okolodkov, 2003; HernándezBecerril et al, 2008) Many of these studies have traditionally considered the microplankton fraction, especially large diatoms and dinoflagellates, as the main contributors to primary production Many of these studies have traditionally considered the microplankton fraction, especially large diatoms and dinoflagellates, as the main contributors to primary production (e.g. Hernández-Becerril & Flores, 1998; Licea et al 2004, Hernández-Becerril et al, 2008)

Objectives

Methods

Results

Discussion

Conclusion