Introducing “plankton responses to environmental variability”

Acta Oecologica 24 (2003) S1 www.elsevier.com/locate/actoec

Editorial

Introducing “plankton responses to environmental variability” What governs plankton abundance and variability? In aquatic pelagic systems, structure and function are controlled to a large extent by physical forcing. The interaction between physical and biological processes occurs at a wide range of temporal and spatial scales. Plankton exhibits complex responses to environmental variability through changes at the individual (e.g. physiological growth and condition), population (migration, reproduction, and mortality), and community (species composition) levels of organization. These processes have important consequences for the dynamics of aquatic systems. Plankton clearly influences biogeochemical cycling in aquatic systems, but our knowledge of the underlying processes remains fragmentary. Plankton affects the elemental stoichiometry and material fluxes. The degree of coupling between zooplankton and primary producers gives rise to spatial and seasonal variations in the producer’s standing stocks, nutrient utilization and recycling efficiencies, and elemental export ratios. Hence, there is a growing recognition of the essential role played by plankton communities in aquatic ecosystems, and a thorough assessment of variables that still need to be quantified is required to obtain a clearer understanding of plankton contributions to biogeochemical cycling. Ongoing studies should lead to a more comprehensive insight of the mechanisms governing the occurrence and abundance of dominant plankton taxa, and of which factors control plankton biodiversity and bio-complexity. Furthermore, efforts should be promoted within the plankton researchers community focusing on the development of predictive capabilities regarding major biological processes in the aquatic systems. In this special issue, we present the main results proceeding from an International Plankton Symposium held in Portugal in September 2001, which was organized on behalf of the Institute of Marine Research, IMAR, Portugal. The volume is organized in five sections. The first section deals with “Microplankton and phytoplankton studies”, including 15 papers. Freshwater studies, namely on cyanobacteria, which are still a poorly known group from the ecological viewpoint, are addressed. Moreover, several contributions include studies on bacterioplankton on tidal systems, and the section ends presenting a few studies on phytoplankton ecology in coastal waters, emphasizing the role of bacteria in the metabolism of aquatic ecosystems and its contribution to total biomass and primary productivity. Also the interplay © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. DOI: 1 0 . 1 0 1 6 / S 1 1 4 6 - 6 0 9 X ( 0 3 ) 0 0 0 4 1 - 9

between biological, chemical, meteorological, and physical processes involved in the control of aquatic systems functioning is overviewed. The second section presents “Zooplankton studies” and includes 13 papers. Zooplankton plays a quantitatively important role in pelagic ecosystems, namely through grazing, nutrient cycling, trophic transfer and, obviously, secondary production. This section includes contributions on zooplankton distribution and zooplankton community’s structure, addressing issues like the relation between nycthemeral, tidal, and lunar dynamics and larval transport, and zooplankton population dynamics. In the third section, we may find four contributions on “Food webs and benthic-pelagic coupling”. Physically driven changes in top-down and/or bottom-up processes and the role of plankton in food webs are addressed. No topic within aquatic ecology has changed more in the last years than our notions about components and structure of planktonic food webs. The fourth section addresses “Toxicology and Contamination”, including five contributions. Contamination with diverse classes of toxic chemical substances is most pronounced in coastal ecosystems. In this section, besides plankton responses to different food levels under laboratory conditions, metal inputs and its effects are addressed, as well as ecological problems related with PCBs impact on plankton communities. Finally, the fifth and shorter section deals with Modelling, including two contributions. The potential value of modelling as a powerful tool is exemplified with two case studies, showing how it can be used to conduct novel experiments and test hypothesis that are otherwise too expensive or too difficult to test in situ. Plankton research as a whole plays an essential role in regional environmental health and quality assessment (e.g. eutrophication, harmful algal blooms, and environmental contamination), as well as with regard to global environmental problems (e.g. climate change and biodiversity, among others). This special issue represents a contribution to a more sound knowledge on plankton responses to changes in environmental conditions, and intends as well to be useful as a tool to researchers from other scientific areas within Biology. Ulisses Miranda Azeiteiro, João Carlos Marques