[1] Univ Copenhagen, Marine Biol Sect, DK-3000 Helsingor, Denmark
[2] NIOZ Royal Netherlands Inst Sea Res, Dept Marine Microbiol & Biogeochem, POB 59, NL-1790 AB Den Burg, Texel, Netherlands
[3] Univ Utrecht, POB 59, NL-1790 AB Den Burg, Texel, Netherlands