Journal of Plankton Research - current issue

An advanced laser-based fluorescence microstructure profiler (TurboMAP-L) for measuring bio-physical coupling in aquatic systems

Doubell, M. J., Yamazaki, H., Li, H., Kokubu, Y. — Wed, 04 Nov 2009 06:08:08 PST

An advanced model of the Turbulence Microstructure Acquisition Profiler, TurboMAP-L, to investigate the coupling between phytoplankton and turbulence in aquatic systems is described. The profiler provides simultaneous measurement of turbulence, hydrographic and biological parameters at sampling rates between 64 and 512 Hz. Specifically, the addition of a new laser fluorescence-based sensor extends the measurement of in situ chlorophyll fluorescence distributions to millimeter scales. Complementary information on phytoplankton patch and particulate matter size and spatial structure are obtained through the attachment of a separate CMOS mini-camera system. Images of the TurboMAP-L LED fluorescence/turbidity sensor sample volume are obtained with 330 x 330 µm resolution. Results with respect to the performance of the laser sensor and camera system are presented from laboratory tests and field experiments conducted in coastal waters off Tokyo, Japan.

Regulation of filter-feeding house components in response to varying food regimes in the appendicularian, Oikopleura dioica

Wed, 04 Nov 2009 06:08:08 PST

The frequent repetitive secretion of filter-feeding houses of the tunicate, Oikopleura dioica represents investment of a substantial proportion of total body carbon. Despite this investment, the filter-feeding strategy of pelagic tunicates has been proposed as an adaptation to oligotrophic environments. Here, we examined the capacity of O. dioica to modify its house renewal rate (HRR) and expression of component proteins, oikosins, as well as ingestion rates of different sized particles in response to varying food regimes. There were no significant changes in HRR (0.26 ± 0.07 SD house h^–1) with age or food concentration throughout the life cycle. Our data suggest that the complex pattern of endoreduplicating cycles in the oikoplastic epithelium probably limits the capacity to reduce the energetic output of house replacement as a response to a limiting food environment. On the other hand, at the molecular level, there was differential regulation of component house proteins when animals were cultured in standard versus limiting food regimes. Animals pre-conditioned in each of these regimes and subsequently challenged with an identical mixture of large and small particles exhibited different retention efficiencies of larger food particles. Taken together, these results raise the possibility that a limited ability to modulate house architecture may underlie the differential particle retention efficiencies observed.

Evaluation of DNA extraction and handling procedures for PCR-based copepod feeding studies

Wed, 04 Nov 2009 06:08:08 PST

Molecular methods are becoming increasingly common for taxonomic and ecological studies of marine and freshwater plankton. Recently, nucleic acids have been used as target molecules for identification and quantification of prey species in studies of trophic interactions. A critical step in the quantification of mesozooplankton feeding by molecular analysis is the isolation of microalgal DNA from predator guts and in the food environment. It is essential that total genomic DNA extraction provides maximum quantitative yield suitable for downstream analysis. In this study, we compared the efficacy and experimental variability of eight different protocols for total genomic DNA extraction from free-living microalgae and microalgae within the gut of copepods. We also developed and evaluated different sampling procedures for copepods prior to genomic extraction. The optimal protocol was evaluated using real time quantitative polymerase chain reaction (qPCR) and the integrity of the genomic DNA was determined by amplifying PCR targets of increasing size. Considerable variability was observed between purification protocols. Qiagen DNeasy® Blood & Tissue kit was the most efficient of the tested methods for genomic extraction from both free-living microalgae and microalgae inside copepod guts. Furthermore, the appropriate handling of predator copepods prior to genomic extraction was essential for quantitative gut content estimates.

Seasonal succession and composition of the zooplankton community along an eutrophication and salinity gradient exemplified by Danish waters

Zervoudaki, S., Nielsen, T. G., Carstensen, J. — Wed, 04 Nov 2009 06:08:08 PST

The seasonal distribution of the major components of the zooplankton community, protozooplankton, copepods and cladocerans, along a eutrophication gradient were examined in order to establish if eutrophication through increases in phytoplankton biomass and productivity has an impact on biomass and composition of the zooplankton community. Data on salinity, temperature, inorganic nutrients, chlorophyll a, phytoplankton biomass and production, protozooplankton and mesozooplankton biomass were collected during routine sampling at seven stations representing a eutrophication gradient from open to estuarine waters. Mesozooplankton biomass varied seasonally in all areas with a unimodal pattern characterized by a peak between mid-spring and mid-summer. Total mesozooplankton biomass as well as copepod and cladoceran biomass, decreased with DIN concentration. Salinity and the type of ecosystem (well-mixed shallow estuaries versus stratified open waters) were the major factors controlling the biomass proportion of copepod species. Annual production of the total copepod community as well as the total grazing impact of copepods on primary production was higher in open waters than in estuarine waters. In estuarine type ecosystems, phytoplankton production is underexploited by copepod grazing, whereas in the open type ecosystems, the phytoplankton production alone could not satisfy the carbon demand of copepods stressing the potential importance of protozoans in the copepod diet.

Distribution of hyperiid amphipods (Crustacea) of the southern Gulf of Mexico, summer and winter, 1991

Gasca, R., Manzanilla, H., Suarez-Morales, E. — Wed, 04 Nov 2009 06:08:08 PST

The distribution and abundance of the hyperiid amphipods of the southern Gulf of Mexico was analyzed from zooplankton samples collected during summer and winter 1991. We evaluated the effect of the local hydrographic conditions, characterized by mesoscale eddies, on the hyperiid community. We explored the presumed correlation of hyperiids with siphonophores, one of the groups of gelatinous zooplankton to which they are symbionts. It was expected that hyperiids were more abundant in areas related to cyclonic eddies and less abundant in the anticyclonic eddies than in the surrounding waters, but most differences were not significant. Both our data set and previous observations are not conclusive because they are based on low resolution sampling grids. Hyperiids were significantly more abundant at night. Of the 57 species of hyperiids recorded, Lestrigonus bengalensis was widely dominant in both seasons. It was significantly correlated (Spearman r) with the siphonophore Muggiaea kochi during the winter and with Diphyes dispar in the summer, when this siphonophore was most abundant. It is suggested that the association takes place and is detectable when and where both species are highly abundant. There are other significant siphonophore/amphipod correlations; most are not likely to represent symbiotic associations. Variations of the gulf hyperiid community are related to: (i) the dominance of L. bengalensis, (ii) the seasonal abundance of the siphonophore D. dispar, mainly in relation to L. bengalensis, (iii) the anomalous occurrence of deep-living forms and (iv) day/night variations. The presumed influence of mesoscale eddies on the gulf hyperiid community deserves further study.

Comparison between automated analysis of zooplankton using ZooImage and traditional methodology

Gislason, A., Silva, T. — Wed, 04 Nov 2009 06:08:08 PST

The objective of this study was to evaluate the accuracy of the ZooImage image analysis system for taxonomic classification of zooplankton samples. For this purpose, automated analysis with the ZooImage software was compared with traditional analysis, using zooplankton samples collected in the Iceland Sea in July 2006. When compared with the traditional methodology, ZooImage was able to classify zooplankton into main taxonomic entities (size classes and families or genera in some cases), while being less successful in identifying the zooplankton into species. Other important information, that is difficult and time consuming to obtain by traditional methods such as biomass and size distributions are, however, easily obtained with ZooImage. The automated analysis takes much less time than the traditional methods. While the study confirms that ZooImage is a promising tool for rapidly analysing zooplankton samples, it is also clear that the traditional approach will be needed in future investigations, particularly studies addressing zooplankton community structure, development and life history.

The effects of light availability in shallow, turbid waters: a mesocosm study

Wed, 04 Nov 2009 06:08:08 PST

Seasonal patterns of water transparency in turbid Pampean lakes suggest that the amount of seston is strongly influenced by incident solar radiation. However, the unequivocal identification of light as the major forcing variable is precluded due its co-variation with several potentially confounding variables. In order to specifically investigate the role of light, we performed a mesocosm (3000 L) experiment aimed at investigating the effects of different degrees of light availability on planktonic community structure and metabolism. The experimental setup successfully mimicked the light limiting conditions prevailing in Pampean turbid lakes. We used neutral density filters to create four light treatments, approximately covering the natural annual range of incident irradiance. Our results are consistent with field patterns and light-limitation theory: (i) light attenuation and (ii) primary production increased with light availability. In contrast, the abundance of most grazers displayed negative relationships with light availability. The decreases in the density of grazers could have resulted from changes in the nutritional value of the food. This possibility is also supported by (iii) decreases in seston P-content and (iv) increases in community respiration with increasing light availability.

Photosynthetic picoplankton in Lake Tanganyika: biomass distribution patterns with depth, season and basin

Wed, 04 Nov 2009 06:08:08 PST

Photosynthetic picoplankton (PPP), particularly picocyanobacteria (PCya), are known to be a major component of phytoplankton in oligotrophic waters. We investigated the dynamics of PPP and heterotrophic bacteria (HBact) in Lake Tanganyika during the dry and rainy seasons of 2004 to 2007, in the two basins of this large lake. Flow cytometry analyses showed that PPP was mainly composed by PCya of the phycoerythrin-rich Synechococcus type, with maximal abundances (2.3 x 10⁴–8.2 x 10⁵ cells mL^–1) found in the mixolimnion (10–20 m depth). PPP biomass integrated over the water column depth ranged between 0.41 and 3.09 g C m^–2, with maximal values in the south basin during the dry season (2.28 ± 0.62 g C m^–2 on average). The contribution of PPP to total phytoplankton biomass ranged from 41 to 99%, with highest values in the south basin in the dry season. Cellular measurements by image analysis of epifluorescence microscopy images showed a significant increase of the cell volume of the PCya during this period. Flow cytometry also allowed enumeration of photosynthetic picoeukaryotes. Assuming a conversion factor of 530 fg C cell^–1, they contributed on average to 6% to PPP biomass, except during the dry season in the south basin, where their contribution increased to up to 20% of PPP biomass. Integrated over a 100-m water column depth, PCya biomass was on average 1.4 times higher than HBact biomass. This study establishes reference values for the biomass contribution of this part of the microbial food web, covering for the first time, spatial (different sites), vertical (profiles at different depths) and seasonal variations on a multi-year basis. The results strengthen the view of a major role of PPP in the pelagic food web of large tropical Lake Tanganyika.

Short-term variability of abundance, diversity and activity of estuarine bacterioneuston and bacterioplankton

Wed, 04 Nov 2009 06:08:08 PST

Short-term variability in abundance, heterotrophic activity and structural diversity of bacterioneuston and bacterioplankton were assessed over 24-h cycles at a fixed point in the estuarine system of Ria de Aveiro (Portugal). Lipase activity was the only descriptor of bacterial activity significantly different in samples collected during the day and the night (up to 40% higher during the night) at equivalent tidal conditions. The lack of diel patterns in other microbiological parameters indicates uncoupling of estuarine bacteria from primary production, pointing to the relevance of allochthonous nutrient sources for heterotrophic bacteria in this mesotrophic system. Occurrence of strong positive correlations between the values of microbiological parameters (total bacterial abundance, chlorophyll a concentration, leucine-aminopeptidase, lipase, phosphatase, sulphatase and acetate and glucose incorporation) in bacterioneuston and bacterioplankton suggests that the surface community may originate from the underlying waters (UWs) concentrating at the surface through upward passive transport, and that bacterioneuston and bacterioplankton are subjected to similar environmental regulation. The results also indicate that the microbial enrichment of the surface microlayer relative to the UW is highly variable during the day, pointing to the importance of the sampling time for the outcome of comparative analyses of bacterioneuston and bacterioplankton dynamics.

Bacterial chemotaxis towards the extracellular products of the toxic phytoplankton Heterosigma akashiwo

Seymour, J. R., Ahmed, T., Stocker, R. — Wed, 04 Nov 2009 06:08:08 PST

Marine bacteria exhibit positive chemotactic responses to the extracellular exudates of the toxic phytoplankton Heterosigma akashiwo. In the environment, this will support bacteria–algae associations with potential implications for harmful algal bloom dynamics.

Uptake of dissolved organic matter by ephyrae of two species of scyphomedusae

Skikne, S. A., Sherlock, R. E., Robison, B. H. — Wed, 04 Nov 2009 06:08:09 PST

Ephyrae of Aurelia labiata given dissolved organic matter (DOM) in seawater had higher carbon content than starved ephyrae. DOM-fed ephyrae of Chrysaora colorata did not have significantly higher carbon content than starved ephyrae, although the mean trend was higher. DOM-fed ephyrae of A. labiata developed aberrant morphologies similar to starved ephyrae, and neither starved nor DOM-fed ephyrae of either species developed into medusae. In addition to higher carbon content, there was evidence for DOM utilization by A. labiata shown through uptake of and increased ammonium production after exposure to a fluorescently labeled lysine polymer.

Predictability of patches of neritic salps and doliolids (Tunicata, Thaliacea)

Deibel, D., Paffenhofer, G.-A. — Wed, 04 Nov 2009 06:08:09 PST

The occurrence of large patches of gelatinous zooplankton has for decades been considered to be unpredictable. An evaluation of our own data and published results on abundances of doliolids and salps from ocean margins reveals that a considerable degree of prediction is possible, based upon meteorological and boundary current intrusion dynamics.

Lipids in Aquatic Ecosystems

Pond, D.W. — Wed, 04 Nov 2009 06:08:09 PST