Plankton development and trophic transfer in seawater enclosures with nutrients and Phaeocystis pouchetii added

Abstract

In high latitude planktonic ecosystems where the prymnesiophyte alga Phaeocystis pouchetii is often the dominant primary producer, its importance in structuring planktonic food webs is well known. In this study we investigated how the base of the planktonic food web responds to a P. pouchetii colony bloom in controlled mesocosm systems with natural water enclosed in situ in a West Norwegian fjord. Similar large (11 m 3 ) mesocosm studies were conducted in 2 successive years and the dynamics of various components of the planktonic food web from viruses to mesozooplankton investigated. In 2002 (4 to 24 March), 3 mesocosms comprising a control containing only fjord water; another with added nitrate (N) and phosphate (P) in Redfield ratios; and a third with added N, P, and cultured solitary cells of P. pouchetii, were monitored through a spring bloom cycle. In 2003 (27 February to 2 April) a similar set of mesocosms were established, but cultured P. pouchetii was not added. As expected, during both years, addition of N and P without addition of silicate resulted in an initial small diatom bloom followed by a colonial bloom of P. pouchetii (600 to 800 µg C l -1 ). However, the hypothesis that addition of solitary cells of P. pouchetii would enhance subsequent colony blooms was not supported. Interestingly, despite the large production of Phaeocystis colonial material, little if any was transferred to the grazing food web, as evidenced by non-significant effects on the biomass of micro-and mesozooplankton in fertilized mesocoms. Separate experiments utilizing material from the mesocosms showed that colonies formed from solitary cells at rates that required only ca. 1% conversion efficiencies. The results are discussed from the perspective of future research still required to understand the impact of life cycle changes of this enigmatic phytoplankter on surrounding ecosystems. KEY WORDS: Phaeocystis pouchetii · Mesocosms · Nutrients · Fjord · Biocomplexity Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 321: 2006 gelatinous polysaccharide 'skin' (Chen et al. 2002). Solitary cells may be either motile or non-motile, and are typically 3 to 9 µm in diameter (Rousseau et al. 1994). This unusually large range of sizes between colonies and solitary cells (ca. 6 to 11 orders of magnitude in biovolume) can significantly alter material flow among trophic levels and export from the upper ocean (Wassmann et al. 1990, Lancelot et al. 1998. Furthermore, each stage is thought to function in different ways in order to reduce losses to either small or large zooplankton and viruses, and thus Phaeocystis spp. effectively function as dual species (Weisse et al. 1994, Smaal & Twisk 1997, Hamm et al. 1999, Jacobsen 2000, Verity 2000, Jakobsen & Tang 2002, Tang 2003.The dual life history of colonial and solitary cell stages was described over 50 yr ago (Kornmann 1955), and the dominant morphology appears to alter the ecosystem function from a regenerative system (solitary cells) ...

Susceptibility of colonies and colonial cells of Phaeocystis pouchetii (Haptophyta) to viral infection

“…However, there is strong evidence that viral lysis does not terminate colonial blooms of P. pouchetii (Nejstgaard et al 2006) and that viruses do not infect colonial P. pouchetii cells (present study). At the peak of the P. pouchetii mesocosm blooms, flagellated cells were observed inside of the colonies, followed by proliferation of flagellated cells, which were possibly triggered by nutrient limitation (Whipple et al 2005).…”

“…Each of the 12 wells in the 5 Nunc culture plates was then inoculated with PpV-AJ96 corresponding to a final concentration of 10 The development of virus populations was followed along with blooms of Phaeocystis pouchetii in the mesocosm experiments in both years, except in the control mesocosm in 2002. Flagellated cells and colonies of P. pouchetii were counted as described in Nejstgaard et al (2006), and viruses were counted by means of FCM. For FCM analyses, seawater samples were fixed with glutaraldehyde (0.5% final concentration), frozen in liquid nitrogen and stored at -70°C (Marie et al 1999b).…”

The rise of Network Ecology: Maps of the topic diversity and scientific collaboration

“…Another cluster of co-authorships appears in the lower region of the plot and includes P. G. Verity, M. E. Frisher, and J. C. Nejstgaard. The publications that link these co-authors were a result of an NSF Biocomplexity award (Nejstgaard et al, 2006;Whipple et al, 2007). There is another cloud of co-authors plotted between Patten and Ulanowicz that is a result of a synthetic publication calling for improvement in food web construction co-authored by multiple investigators working on food webs at that time (Cohen et al, 1993).…”

Partition of planktonic respiratory carbon requirements during a phytoplankton spring bloom

“…A field-based mesocosm study was carried out at the Espegrend marine biological station, University Nejstgaard et al (2006), and a general overview of the experiment and its main results will be presented elsewhere. In short, 6 floating transparent (ca.…”

“…At the end of the experiment, a sample of ca. 7 m 3 from each mesocosm bag was collected with a submersible pump and filtered through 90 µm plankton gauze, and the retained material was preserved in 4% formaldehyde.The average mesozooplankton biomass at the start and end of the experiment was calculated as the sum of species-specific body mass, based on samples analyzed for species and stage distributions, size measurements and size/weight relationships (described in Nejstgaard et al 2006). Since respiration incubations of the 4 groups covered a period exceeding 1 d, we related the copepod and community response to the food variable measured over an average of 2 d (see 'Results').…”