Derek Harbour

Copepod hatching success in marine ecosystems with high diatom concentrations

Diatoms dominate spring bloom phytoplankton assemblages in temperate waters and coastal upwelling regions of the global ocean. Copepods usually dominate the zooplankton in these regions and are the prey of many larval fish species. Recent laboratory studies suggest that diatoms may have a deleterious effect on the success of copepod egg hatching. These findings challenge the classical view of marine food-web energy flow from diatoms to fish by means of copepods. Egg mortality is an important factor in copepod population dynamics, thus, if diatoms have a deleterious in situ effect, paradoxically, high diatom abundance could limit secondary production. Therefore, the current understanding of energy transfer from primary production to fisheries in some of the most productive and economically important marine ecosystems may be seriously flawed. Here we present in situ estimates of copepod egg hatching success from twelve globally distributed areas, where diatoms dominate the phytoplankton assemblage. We did not observe a negative relationship between copepod egg hatching success and either diatom biomass or dominance in the microplankton in any of these regions. The classical model for diatom-dominated system remains valid.

Retrieval of coccolithophore calcite concentration from SeaWiFS Imagery

We examined blooms of the coccolithophorid E. huxleyi, observed in SeaWiFS imagery, with a new algorithm for the retrieval of detached coccolith concentration. The algorithm uses only SeaWiFS bands in the red and near infrared (NIR) to minimize the influence of the absorption by chlorophyll and dissolved organic material. We used published experimental determinations of the calcite specific backscattering and its spectral dependence, and assumed that the absorption coefficient of the medium was that of pure water, to estimate the marine contribution to the SeaWiFS radiance. The aerosol (and Rayleigh-aerosol interaction) contribution to the radiance was modeled as an exponential function of wavelength. These allow derivation of the coccolith concentration on a pixel-by-pixel basis from SeaWiFS imagery. Application to a July 30, 1999 SeaWiFS image of a bloom south of Plymouth, UK indicates that the SeaWiFS estimates are in good agreement with surface measurements of coccolith concentration.

Using HPLC pigment analysis to investigate phytoplankton taxonomy: the importance of knowing your species

Phytoplankton microscopic enumerations and HPLC analyses of their pigments were performed weekly for a complete year at a coastal station in the English Channel. The taxonomic composition of the phytoplankton community was assessed using the HPLC results combined with the mathematical tool CHEMTAX in two different ways. Firstly, without using the species level taxonomic information obtained at the microscopic level (blind analyses), and secondly by including the information from the microscopic taxonomic analysis (directed analyses). The results indicate that, due to the particular pigment composition of some species (for example, the dinoflagellate, Karenia mikimotoi and the haptophyte, Phaeocystis pouchetii), a blind analysis would result in very significant errors in the taxonomic determination of the bloom events at this station. Major blooms of Karenia mikimotoi and P. pouchetii were mistaken for blooms of diatoms on the basis of a blind HPLC-CHEMTAX analysis. Only with the information from the microscopic observations was it possible to obtain an accurate representation of the phytoplankton community.

Variability and seasonality of physical and biological fields at the Great Meteor Tablemount (subtropical NE Atlantic)

Abstract Five oceanographic surveys were conducted at the Great Meteor Tablemount (subtropical NE Atlantic; 30.0oN, 28.5oW) throughout the 1992–1999 period to investigate temporal variability in the relationship between the physical structure of the water column associated with the seamount and phytoplankton biomass and/or production rates. Local increases in chlorophyll a , enhanced carbon incorporation rates and changes in phytoplankton species composition were associated with the seamount. These effects were subjected to a large degree of temporal and spatial variability both at seasonal and shorter time scales.

Phytoplankton production and biomass estimates in the northeast Atlantic Ocean, May-June 1990

Time series measurements of size-fractionated chlorophyll a concentrations and primary production were made over the course of the spring bloom in and adjacent to a mesoscale eddy in the N.E. Atlantic as part of the U.K. Biogeochemical Ocean Flux Study 1990 Lagrangian Bloom Experiment. Substantial production, dominated by the >5μm and >1–5,μm fractions, was recorded before the main growth phase of the bloom, although total chlorophyll a concentrations varied little over this period. The main growth phase of the bloom, which occurred over approximately one week, was dominated by the > 1–5 μm fraction; a principal constituent was the small diatom Nanoneis hasleae, which almost entirely displaced larger diatoms more typical of a spring bloom population. The >5 um phytoplankton fraction became dominant for approximately two weeks following the main bloom growth phase but was replaced at the end of the observation period by the > 1–5 μm and 0.2-1 μm fractions. Phytoplankton taxonomic data for the 1990 bloom period were very different to the more typical bloom conditions of 1989. An intercomparison of14C production measurements made by U.K. and Dutch participants during the period of the Experiment using common samples gave total column productivities differing by <4%.

The relationship between suspended particulate material, phytoplankton and zooplankton during the retreat of the marginal ice zone in the Bellingshausen Sea

Abstract The distribution, abundance and composition of suspended particulates, phytoplankton and zooplankton biomass were investigated for the marginal ice zone in the Bellingshausen Sea during the Austral spring of 1992. Marked changes were observed between the amount and composition of particulates under the sea-ice and those in open waters. Measures of phytoplankton abundance (chlorophyll) ranged from ∼0.05 μg l −1 under the ice to 3 μg l −1 in the open waters to the north. The high nutrient concentrations and low level of phytoplankton under the ice suggest that this region is typical of over-wintering conditions and provides a suitable background comparison to the development of more productive, recently ice-free waters, further north. Nearly all basic measurements of particulate material showed a gradient from south to north. However, the biochemistry of particulates (lipid in particular), a more sensitive measure of environmental growth conditions, showed the area as a whole to be broadly split into two; under ice (light limited) and open water (no light limitation). Total particulate carbon was almost entirely composed of inorganic carbon under the ice; waters away from the ice edge also contained significant levels of inorganic carbon. Hence, C:chlorophyll was estimated from POC or phytoplankton carbon. There was no evidence of nutrient limitation at any of the stations investigated. Integrated phytoplankton carbon for the upper 100 m ranged from 0.1 gC m −2 under the ice to 11.5 gC m 2 in the diatom dominated bloom in open waters. The mesozooplankton biomass in the same depth interval increased from 0.02 gC m −2 under the ice to 0.21 gC m −2 in open waters. However, zooplankton biomass in the upper 600 m changed little from under the ice out to open waters north of the ice edge; although the northernmost station, in the region of highest chlorophyll, had approximately three times more zooplankton carbon (0.67 gC m −2 than the other stations. There is some evidence, however, that the northern station may be associated with a frontal feature, and that conditions observed may not be solely related to previous ice edge processes.

Temporal variability of viruses, bacteria, phytoplankton and zooplankton in the western English Channel off Plymouth

The temporal distribution of autotrophic and heterotrophic components of the planktonic community was studied from samples collected weekly at station L4, located to the south of Plymouth, UK, from October 1992 to January 1994. Phytoplankton succession followed the typical pattern of temperate waters, the development of a summer Gyrodinium aureolum bloom being the most prominent feature. Bacterial numbers were significantly correlated with temperature during autumn and winter, whereas resource availability and predation, including viruses, appear to be the most important controlling factors in spring and summer. High mesozooplankton densities, mainly copepods, were observed throughout most of the study associated with a series of diatom blooms, and also during autumn when low phytoplankton biomass was measured. This data set was analysed in order to build up conceptual trophodynamic models whereby the role of biological communities on the cycling of organic matter could be inferred. The results obtained in this study provide empirical evidence supporting the existence of a sucession of trophic organization patterns in a coastal temperate environment. Classical models (herbivorous or microbial webs) appeared episodically whereas transition models (multivorous web) dominated throughout most of the seasonal cycle.

Physical, chemical and biological features of a cyclonic eddy in the region of 61°10'N 19°50'W in the North Atlantic

Abstract The second leg (CD61) of a two cruise investigation of coccolithophore biogeochemistry in the NE subarctic Atlantic provided the opportunity to make a detailed study of a cyclonic eddy in the vicinity of 61°N 20°W. The eddy field in the NE Atlantic is thought to be particularly important with regard to the physics of this region, and may influence the resulting chemical and biological properties of subarctic Atlantic waters. This eddy was ca. 50 km in diameter, moved at ca. 1.5 km d −1 to the north of east, with a geostrophic circulation around the feature of ca. 25 cm s −1 and probably extended as far as the ocean floor, where it may have interacted with the bottom topography. The horizontal salinity, nitrate and biological gradients between adjacent waters and the eddy were less marked in the present study than in a previous investigation of a cyclonic eddy in the vicinity of 48N 22°W (Mittelstaedt, 1987), possibly due to the surface waters of the eddy mixing with surrounding waters. Satellite image sequences clearly link this feature with those studied in a mesoscale coccolithophore bloom studied in the same region on a previous cruise (CD60). Rates of primary production within the eddy were almost twice the mean values reported for Ocean Weather Station India (OWSI) at this time of year, but were similar to those noted during studies at the MLML site to the SE of the eddy location. Other biological rate measurements also indicated that the NE sub-polar Atlantic in mid-summer is more active than previously thought. Despite the extensive coccolithophore bloom studied immediately previously by CD60, there was no measurable coccolithophore calcification in the waters within the eddy in the present study. This is consistent with phytoplankton taxonomic data, which demonstrates that coccolithophore abundance was almost one hundred fold lower at this location on CD61 relative to CD60 and that lith and coccolithophore abundances were grestest in the water column beneath the mixed layer, suggesting sinking. These observations suggest that the decline of the bloom had occurred in the period between the two cruises.

Effects of the diatom-Emiliana huxleyi succession on photosynthesis, calcification and carbon metabolism by size-fractioned phytoplankton

Changes in the species composition, photosynthesis, calcification and size-fractionated carbon metabolism by natural phytoplankton assemblages were monitored in three mesocosms under different nutrient conditions during May 1993. In the 3 enclosures, the decline of the diatom-dominated assemblages was followed by the development of a bloom of the coccolithoporid Emiliania huxleyi. Highest growth of E. huxleyi was observed in the mesocosm with a high N : P ratio, suggesting this species is a good competitor at low phosphate concentrations. The transition from diatom- to E. huxleyi-dominated assemblages brought about a sharp reduction of the phytoplankton standing stock and carbon-specific photosynthetic rate. The relative contribution of the smaller size fraction to total photosynthesis increased as the succession progressed. Calcification rate and E. huxleyi cell-specified calcite production were highest during the early stages of development of the E. huxleyi bloom. Distinct changes in the patterns of 14C allocation into biomolecules were noticed during the diatom-E. huxleyi succession. The diatom-dominated assemblage showed high relative 14C incorporation into low molecular weight metabolites (LMWM), whereas proteins and, specially, lipids accounted for the largest proportion of carbon incorporation in the E. huxleyi bloom. The patterns of photoassimilated carbon metabolism proved to be strongly dependent on cellular size, as protein relative synthesis was significantly higher in the smaller than in the larger size fraction, irrespective of the nutrient regime and the successional stage. These results are discussed in relation to the ecological and physiological features of small phytoplankton.

Marine microplankton diversity database.

Many macroecological theories have been developed to study the diversity on our planet. All these theories require the existence of consistent databases to test their predictions. In this work, we compiled a data set of marine microplankton species abundances at 788 stations with an extensive geographical coverage. Data were collected on different oceanographic cruises between 1992 and 2002. This database consists of abundances (cells/mL) for each species at each station and depth, together with estimates of the biomass and biovolume for each species. One of the key strengths in this database is that species identifications were made by the same taxonomist, which provides greater strength to the collection and ensures that estimates of species diversity are reliable. Environmental information has also been compiled at each station (chlorophyll, temperature, photosynthetically active radiation [PAR], nutrients) in order to have a characterization of the study area and to be used in studies on the environmental and biological controls of marine biodiversity.