Journal of Plankton Research - current issue

Temporal and vertical distributions of three appendicularian species (Tunicata) in Conception Bay, Newfoundland

Choe, N., Deibel, D. — 2008-08-21

Temporal and vertical distributions of the boreal appendicularian species Oikopleura vanhoeffeni, Fritillaria borealis and O. labradoriensis were observed in Conception Bay, Newfoundland, over a 1-year period in order to determine whether they share the same environmental niche. Total abundance of the three species together peaked after the spring maximum of chlorophyll a concentration, indicating that appendicularian abundance was generally related to the biomass of phytoplankton. The seasonal peak abundance of the three species did not overlap in time. The maximum abundance of O. vanhoeffeni occurred in May and June during the spring phytoplankton bloom, that of F. borealis occurred in July and August as upper mixed layer temperature increased and salinity decreased and that of O. labradoriensis occurred in October when salinity was at its annual minimum. Vertical distribution also differed among the species. Oikopleura vanhoeffeni occurred primarily below the surface layer and remained below the thermocline in summer. The vertical distribution of F. borealis was not correlated with the observed environmental variables, whereas O. labradoriensis occurred primarily at depths of minimum salinity. Each species displayed a distinct niche based on temperature and salinity. Oikopleura vanhoeffeni was a cryophile with a stenothermal and stenohaline niche, F. borealis was eurythermic and euryhaline and O. labradoriensis inhabited a mesothermal and mesohaline niche. These results indicate physical niche separation among these three sympatric, arcto-boreal appendicularian species and provide information from which future changes in their abundance and spatial distribution can be predicted given likely climatic variation.

Life history trends of copepods Drepanopus forcipatus (Clausocalanidae) and Calanus australis (Calanidae) in the southern Patagonian shelf (SW Atlantic)

Sabatini, M. E. — 2008-08-21

The copepods Drepanopus forcipatus and Calanus australis are key species in the mesozooplankton community over the southern Patagonian shelf. Their population abundance, stage composition and vertical distribution within the region were studied during late summer 2000. Individual size of adult females was also examined. Maximum abundances of D. forcipatus were recorded in outer waters of Grande Bay at ca. 51°S and decreased noticeably towards the northern and southern parts of the study area. Calanus australis was much less abundant but rather uniformly distributed over the entire study area. Highest numbers were recorded in the inner area of the Grande Bay and lowest in shelf waters offshore. Both populations were also differently distributed in the water column. Drepanopus forcipatus were concentrated mainly within the upper layers down to ca. 50 m, whereas C. australis were deeper close to the bottom. Late copepodids were dominant in both populations over most of the shelf. Size variation of adult females was much larger in D. forcipatus than in C. australis. Overall, these preliminary data suggest that both copepod species have developed different life-cycle strategies to contend with the suboptimal food conditions that typically follow the spring net-phytoplankton bloom in high latitude ecosystems.

An evaluation of methods to study the gut bacterial community composition of freshwater zooplankton

Peter, H., Sommaruga, R. — 2008-08-21

The occurrence of gut bacteria in freshwater and marine zooplankton has long been recognized, but knowledge about the composition of the gut "microflora" and its permanent presence in different zooplankters is still inadequate. In this study, we tested the suitability of fluorescence in situ hybridization (FISH), catalysed reporter deposition (CARD)-FISH, cultivation and transmission electron microscopy (TEM) on homogenates and whole-specimen sections to assess the presence and identity of gut bacteria in several freshwater copepod and cladoceran species. Unambiguous results about the presence of a permanent gut "microflora" were obtained for freshly caught Daphnia pulex by TEM. CARD-FISH on gut homogenates from Acanthodiaptomus denticornis and D. pulex revealed a very similar bacterial composition to that present in the water column. Major bacterial groups found in cladocerans and copepods were alpha-, beta-, gamma-Proteobacteria and Cytophaga–Flavobacteria. The high contribution of alpha-Proteobacteria in A. denticornis suggested a specific niche for this group, but probably in association with its carapace. FISH on paraffin semithin sections had the potential to provide quantitative and qualitative information about the composition of the gut "microflora", but loss of bacteria and gut content was significant.

Comparative study of phosphorus strategies of three typical harmful algae in Chinese coastal waters

Ou, L., Wang, D., Huang, B., Hong, H., Qi, Y., Lu, S. — 2008-08-21

A series of batch culture experiments were carried out to compare the specific eco-physiological responses of three typical harmful algae of Chinese coastal waters to environmental phosphorus (P) variations. Results showed that Skeletonema costatum, when compared with Prorocentrum donghaiense or Alexandrium catenella, was a better growth strategist in nutrient-rich condition. Although S. costatum had a greater advantage in phosphate affinity and could save more internal P, it also had a higher P demand for growth and it used up all its resources to sustain a high growth rate. The growth of S. costatum collapsed soon after phosphate depletion. P. donghaiense and A. catenella, with lower growth rates, could survive well under P-limited conditions. With higher affinities for dissolved organic phosphorus (DOP), P. donghaiense and A. catenella might likely make good use of the metabolized DOP in the water after the collapse of S. costatum blooms to sustain their growth.

Dynamics of phosphorus in the Venice lagoon during a picocyanobacteria bloom

Sorokin, Yu. I., Dallocchio, F. — 2008-08-21

The lagoon of Venice experienced dense blooms of picocyanobacteria in the summer of 2001. The dynamics of soluble reactive inorganic phosphorus (DIP) was studied in these blooms in the lagoon. DIP uptake and regeneration rates were measured in situ using a ³²P-radiotracer. DIP content remained high even during the bloom (0.2–0.7 µM), at P_tot concentrations from 4 to 8 µM. The DIP uptake rate by microplankton varied between 20 and 73 nM min^–1, depending mainly on the bloom density. The DIP residence time varied from 5 to 20 min, whereas in the waters of the coastal Adriatic, where picocyanobacteria were also present, it was 2.5 h. The DIP regeneration rate varied from 18 to 59 nM min^–1. The picocyanobacterial bloom assemblage was able to consume and to store in its biomass up to 10 µM of phosphorus in the samples of lagoon water enriched with DIP at up to 17 µM. The results demonstrate the capability of picocyanobacterial blooms to recycle DIP rapidly and to accumulate high stocks of phosphorus in their biomass. This feature of their physiology enables assemblages of picocyanobacteria to produce dense blooms in shallow marine basins experiencing the impact of eutrophication.

Short-term variation of phytoplankton assemblages in Mediterranean coastal waters recorded with an automated submerged flow cytometer

Thyssen, M., Mathieu, D., Garcia, N., Denis, M. — 2008-08-21

Short-term variations of phytoplankton communities are poorly documented. To overcome these limitations and make observations on a short-time (hours) scale, we moored a submersible flow cytometer (CytoBuoy b.v.) in the Bay of Marseille. The CytoSub monitored phytoplankton every 30 min at a fixed site (2 m depth) during summer 2005. The data treatment, conducted on the basis of pulse-shape analysis, resolved seven clusters. Daily sampling of nutrients and continuous information on salinity, temperature and wind speed allowed distinction between diel cycles and the impact of environmental factors on phytoplankton communities. Autocorrelation of the time series showed a significant periodicity of ~24 h for most of the clusters during undisturbed meteorological conditions. Two clusters had regular daily abundance variations in the range 0–>10³ cells cm^–3. Two strong wind events revealed similar cluster succession patterns occurring over several days after the wind events. These results provided by the high frequency in situ analysis suggest that the flow cytometry resolved clusters, showing independent behaviour and distinct environment-correlated variations, which may be considered as functional groups. We point out its potential for global oceanic observing systems for which such systems could provide real biological information.

Axial variability in the relationship of chlorophyll a with climatic factors and the North Atlantic Oscillation in a Basque coast estuary, Bay of Biscay (1997-2006)

Villate, F., Aravena, G., Iriarte, A., Uriarte, I. — 2008-08-21

The relationships between chlorophyll a concentration and environmental (climatic and associated hydrographical) factors were investigated in the estuary of Urdaibai (Bay of Biscay) in different salinity zones of the euhaline region, using time-series for the period 1997–2006. Transfer function (TF) models were used on quarterly data (3 month mean values) to establish possible relationships between time-series. In the non-nutrient limited waters with salinities of 30 and 33 PSU, a chain of effects from the North Atlantic Oscillation (NAO) to chlorophyll a was established, where air temperature followed inversely the NAO index, water temperature followed air temperature and chlorophyll a followed water temperature. Each of the steps occurred with a lag of 0 (within the 3 month period); however, the effect from NAO to chlorophyll a showed a lag of 1 (a mean of 3 months delay). Consistent with this result, annual mean chlorophyll a biomass in the 30 and 33 PSU salinity zones showed a significant positive relationship with annual mean water temperature and a significant negative relationship with the 12 month mean NAO index from October of the previous year to September. In the 35 PSU salinity zone, no significant relationship between chlorophyll a and NAO or water temperature was observed. It is suggested that nutrient limitation distorts the effect of temperature on phytoplankton biomass enhancement in the outer estuary (35 PSU salinity zone).

The role of temperature on the growth and survival of early and late hatching Pacific cod larvae (Gadus macrocephalus)

Laurel, B. J., Hurst, T. P., Copeman, L. A., Davis, M. W. — 2008-08-21

Fish larvae hatch asynchronously from egg batches despite experiencing a common environment during their development. The consequences for growth and survival of early and late hatching larvae were examined in pre-feeding Pacific cod larvae under varying temperatures (i.e. 0–8°C) in the laboratory. As expected, time-to-first hatch and variation in time-to-hatch were negatively correlated with temperature. Larvae successfully hatched in the 0°C treatment, but hatch rates were poorer at this temperature relative to other temperature treatments. Size-at-hatch and the maximum size achieved during the pre-feeding larval stage were highest in the 0–4°C treatments, indicating that these temperatures are likely optimal for the conversion of endogenous resources to growth. At all temperatures, early hatching larvae were smaller but had more lipid reserves and survived longer after hatch in the absence of food than late hatching larvae. Together these data suggest that temperature fluctuations in the North Pacific have direct potential to impact the size, growth and endogenous reserves of Pacific cod larvae, which in turn, will likely influence survival through interactions with the prey and predator field.

Synchronicity between zooplankton biomass and larval fish concentrations along a highly flushed Tasmanian estuary: assessment using net and acoustic methods

Lara-Lopez, A., Neira, F. J. — 2008-08-21

We examined the spatio-temporal synchronicity between zooplankton biomass and larval fish concentrations within a highly flushed system in northern Tasmania, Australia, combining the data from nets and acoustic methods obtained between October 2001 and November 2002. Zooplankton and larval fish data from nets were analysed in terms of water temperature, salinity and freshwater flow, while backscatter strength from an Acoustic Doppler Current Profiler (ADCP) was employed to complement zooplankton–net data and identify the likely areas of high secondary productivity. Zooplankton and fishes varied significantly across months, peaking simultaneously during late spring (November) at an average temperature of ~15°C. Maximum zooplankton (20.5 mgC/m³) and fishes (874 larvae/100 m³) were recorded within mesohaline (5–17) and polyhaline (18–29) zones, respectively, also in spring. Peaks in zooplankton and larval fish occurred a month after peak freshwater flow, with temperature explaining variability better than did flow or salinity. The coupling of spring peaks in zooplankton biomass and larval fish implies that estuary-spawning fishes may have a fixed spawning period timed to increasing temperatures to ensure a match with abundant microplankton food supply. Backscatter strength complemented zooplankton biomass from nets, and could arguably be used as a proxy for zooplankton abundance even within "noisy" estuarine systems.

Using plankton nets as light traps: application with chemical light

Kehayias, G., Antonou, M., Zerva, M., Karachalios, I. — 2008-08-21

Plankton nets equipped with chemical light showed increased abilities in capturing zooplankton and ichthyoplankton and proved effective for the collection of rare organisms not usually caught in nets.