Regulation of zooplankton by suspension-feeding bivalves and fish in estuarine enclosures

Abstract

Enclosure experiments were conducted during April. June/July and September in the eutrophc estuary Roskilde Fjord, Denmark, to reveal the effects of inorganic nutrients, suspensionfeedng bivalves Mytilus edulis and planktivorous fish (three-spined sticklebacks Gasterosteus aculeatus) on the zooplankton community > 45 pm. The additlon of inorganic nutrients did not increase zooplankton biomass although it did increase the chlorophyll level, indicating that zooplankton production was not food hmited. Filtration by M. edulis reduced the number of tintinnid ciliates and rotifers during all 3 experiments, but not the abundance of the larger zooplankton species. Additions of planktivorous fish reduced the densities of larger zooplankton species Acartia tonsa and Pleopis polyphernoides but not of smaller species. An immense increase in numbers of A. tonsa and P. polyphernoides was observed in enclosures without fish, indicating that the larger crustacean zooplankton is strongly predator controlled. Thus, the qualitative and quantitative development of the zooplankton community in the enclosures was controlled in 2 ways; from the top of the size spectrum by G. aculeatus and from the bottom of the size spectrum by M. edulis.

Impact of introduced juvenile mussel cultures on the pelagic ecosystem of the western Wadden Sea, The Netherlands

“…This study confirmed the removal of heterotrophic organisms by juvenile mussels (e.g. Horsted et al 1988, Kreeger & Newell 1996. Assuming that heterotrophs, like phytoplankton, also serve as a food source for mussels (e.g.…”

“…Within the plankton community, 4 groups were distinguished; bacteria, picophytoplankton (defined here as 0.2 to < 3 µm), nanophytoplankton (3−20 µm), and ciliates (20−200 µm). Larger zooplankton were not included in the current study, as we assumed that juvenile mussels do not effectively filter out larger heterotrophs (Horsted et al 1988). …”

“…From previous studies, it was already known that adult mussels are not very efficient suspension feeders on small planktonic components like bacteria and picophytoplankton (< 2 µm), while they are generally assumed to better retain larger organisms like nanoand microsized plankton (> 2 µm) including both autotrophs and heterotrophs (Lucas et al 1987, Horsted et al 1988, Matthews et al 1989, Kreeger & Newell 1996, Ward & Shumway 2004, Trottet et al 2008a, Strohmeier et al 2012. Using a mesocosm set-up in which natural plankton was exposed to mussel filtration, we confirmed for juvenile mussels (< 25 mm) that filtration mainly affected the larger components of the plankton community (3−200 µm).…”

“…Heterotrophic organisms can serve as an important food source for bivalves, and filtration can thus result in (local) depletion of heterotrophs like rotifers, heterotrophic nanoflagellates and ciliates (Horsted et al 1988, Kreeger & Newell 1996, Wong et al 2003, Trottet et al 2008a. Since these heterotrophs are the main predators on bacteria and small phytoplankton, the removal of these predators by bivalves might alter the competitive outcome between small and larger algae.…”

Length- and weight-dependent clearance rates of juvenile mussels (Mytilus edulis) on various planktonic prey items

“…Although phytoplankton was traditionally considered the main food source (Nielsen and Maar 2007), several studies have stated the importance of other food particles like dead organic material (Dame and Dankers 1988) and bacteria attached to this (Newell et al 1989), microzooplankton (Horsted et al 1988;Kreeger and Newell 1996;Trottet et al 2008) and, for larger mussels ([22 mm;Horsted et al 1988), mesozooplankton (Davenport et al 2000;Wong and Levinton 2006;Lehane and Davenport 2006).…”