Influences of bag dimensions on the development of enclosed plankton communities during POSER

Abstract

During POSER (Plankton Observations with Simultaneous Enclosures in Rosfjorden) natural plankton communities were enclosed by large plastic bags anchored in situ. Enclosures of different dimensions, ranging in depth from 3 to 40 m and containing 1.5 to 30 m3 of water, facilitated the study of dimension effects of the enclosure on the development of the plankton inside. When comparing mean values in small bags with those of the total mixed layer of large bags, phytoplankton development was very similar in large and small enclosures. Although large and small enclosures had been filled simultaneously, bacterial numbers increased faster in small than in large enclosures, probably because of closer contact with the substrate. Copepod populations suffered high mortalities, in particular in small bags. Their mortality may have been influenced by the extremely cold weather prevailing during the experiment. It appeared that fluctuations in environmental factors (temperature, light, nutrients, etc.) were much more important for plankton development than the dimensions of the enclosure. The suitability of enclosures for studylng natural plankton ecosystem is discussed. It is concluded that optimum dimensions depend on the aim of the experiment, number of trophic levels enclosed, population density at these levels and on the species present at these levels. For ecotoxicological experiments with marine phyto-and zooplankton communities in eutrophic waters, enclosures of 1 to 2 m3 are sufficiently large, and for practical reasons should be preferred over larger ones. In more oligotrophic waters, enclosures with a volume of ca. 10 m3 are to be preferred, so that larger zooplankton samples can be taken.

Technical Note: A mobile sea-going mesocosm system – new opportunities for ocean change research

“…fish, seabirds and mammals), and to approximate vertical mixing of water column and small-scale shear occurring in nature (Menzel and Steele, 1978;Carpenter, 1996). Enclosure effects may also influence food web dynamics to varying degrees, creating trophic interactions that can differ with mesocosm dimension and which may deviate from those of the natural system intended to be mimicked (Kuiper et al, 1983;French andWatts, 1989, Petersen et al, 2009). Despite these difficulties and the intense debate they have spurred over the past decades (e.g.…”

Turbulent mixing in experimental ecosystem studies

“…Many of these are little more than common sense, bul they should be enumerated both for completeness and because they impose constraints on the design of a mixing system. The most important are (1) Size: There are minimum dimensions for mesocosms based on organism size and behavior (Guanguo 1990), light extinction (Menzel & Case 1977), trophic complexity (Kuiper et al 1983), and sampling requirements. Size also is an issue with regard to the state of the turbulence (Osborn & Scotti 1996).…”

Fluctuations in heterotrophic bacterial community structure, activity and production in response to development and decay of phytoplankton in a microcosm

“…Recent studies have shown that particularly surface or wall effects in enclosures tend to increase bacterial growth and activity, and that these effects are more pronounced in small volumes (<3 1) than in larger enclosures (30 m3; Kuiper et al 1983, Ferguson et al 1984, see also Grice & Reeve 1982. In addition, Ferguson et al (1984) found that manipulation of natural seawater by filtration (3 pm) increased the growth rate of bacteria.…”