Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research

The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean. Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem.info:eu-repo/semantics/publishe

Composition and biomass of plankton in spring on the Cape Hatteras shelf, with implications for carbon flux

The Ocean Margins Program, an interdisciplinary study focussed at Cape Hatteras, is evaluating whether this region is a net source or sink for carbon, while concurrently developing a mechanistic understanding of the production, cycling and fate of organic carbon. Preliminary to a large multi-ship field program in 1996–1997, the first of several short cruises surveyed Cape Hatteras in May 1993. High concentrations of chla occurred across the shelf. Stations and depths at which chla was highest also showed elevated concentrations of large phytoplankton, predominantly chained diatoms, but also single-celled dinoflagellates and obligately photosynthetic ciliates. These populations occurred in deeper waters, however, and their abundance was poorly correlated with proxies of community photosynthesis. Instead, small phototrophic nanoplankton, abundant in surface waters, were positively correlated with primary production. Carbon budgets indicated that inner shelf waters containedca 50% more living POC than outer shelf waters. The relative importance of large phytoplankton and grazers decreased with distance offshore, and they were replaced by photosynthetic nanoplankton and microzooplankton. Even greater changes in living POC occurred in the alongshore direction due to the dramatic reductions in diatoms in southern waters. Estimated herbivory wasca 2–4 gC m−2 d−1. The ratio of heterotrophic : autotrophic POC increased from 38% in northern waters to 137% in southern waters, suggesting that phytoplankton was being converted into consumer carbon as shelf waters advected south. The dominant consumers at most stations were single-celled protozoan zooplankton and small copepods, whose fecal products remain in suspension in energetic shelf environments, suggesting that much of the non-diatomaceous POC was exported as shelf waters exited at Cape Hatteras

Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements

The ubiquitous marine microalgal species Phaeocystis plays an important role in biogeochemical cycles. Phaeocystis has a complicated life cycle, which makes it hard to decipher the role of this organism in ecosystem dynamics and hence its role in elemental cycles. This volume offers a selection of papers that have been presented at the final meeting of Working Groupinfo:eu-repo/semantics/publishedChristiane Lancelot: Author and series editor Reprinted from Biogeochemistry Volume 83 1-3, 2007 2007, VI, 330 p. Hardcover ISBN: 978-1-4020-6213-

Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements

reprinted from Biogeochemistry, volume 83info:eu-repo/semantics/publishe

Microzooplankton along a transect from northern continental Norway to Svalbard

In the framework of the Italian International Polar Year project entitled Evolution of a Glacial Arctic Continental Margin: the Southern Svalbard Ice Stream-dominated Sedimentary System, a study was carried out on microzooplankton distribution and biomass along a south-to-north transect extending from northern Norway to the Svalbard Archipelago, from 65° to 78°N. Tintinnids, heterotrophic dinoflagellates, aloricate cilates and micrometazoans were the main groups observed in the samples collected at 17 surface stations from 9 to 13 July 2008. Total microzooplankton abundance ranged from 17 to 438 ind l−1. Tintinnids and heterotrophic dinoflagellates were the most abundant organisms, ranging from 1.5 to 292.5 ind l−1 and from 0 to 232 ind l−1, respectively. Micrometazoans (mainly copepod nauplii) reached a maximum of 45.5 ind l−1, whereas aloricate ciliates were scarce at all stations. Microzooplankton carbon content ranged from 0.87 to 5.18 µg C l−1. In particular, tintinnids and micrometazoans made up the largest part of the microzooplankton biomass. Parafavella denticulata, Parafavella gigantea, Acanthostomella norvegica and Ptychocylis obtusa were the most common species among tintinnids, whereas Leprotintinnus pellucidus was recorded in only one station close to Svalbard. Protoperidinium was the most representative genus among heterotrophic dinoflagellates. The community of naked ciliates was dominated by Strombidiidae and Holotrichia. A clearly increasing gradient in both abundance and number of taxa was observed from south to north, with the temperature decreasing from 13.3 to 2.5°C

Future marine zooplankton research - a perspective

During the Second Marine Zooplankton Colloquium (MZC2) 3 issues were added to those developed 11 yr ago during the First Marine Zooplankton Colloquium (MZC1). First, we focused on hot spots, i.e., locations where zooplankton occur in higher than regular abundance and/or operate at higher rates. We should be able to determine the processes leading to such aggregations and rates, and quantify their persistence. Second, information on the level of individual species, even of highly abundant ones, is limited. Concerted efforts should be undertaken with highly abundant to dominant species or genera (e.g., Oithona spp., Calanus spp., Oikopleura spp., Euphausia superba) to determine what governs their abundance and its variability. Third, zooplankton clearly influence biogeochemical cycling in the ocean, but our knowledge of the underlying processes remains fragmentary. Therefore a thorough assessment of variables that still need to be quantified is required to obtain an understanding of zooplankton contributions to biogeochemical cycling. Combining studies on the 7 issues from MZC1 with the 3 from MZC2 should eventually lead to a comprehensive understanding of (1) the mechanisms governing the abundance and existence of dominant zooplankton taxa, and (2) the control of biodiversity and biocomplexity, for example, in the tropical ocean where diversity is high. These recommendations come from an assemblage of chemical, physical and biological oceanographers with experience in major interdisciplinary studies, including modeling. These recommendations are intended to stimulate efforts within the oceanographic community to facilitate the development of predictive capabilities for major biological processes in the ocean