Production and turnover of particulate dimethylsulphoniopropionate during a coccolithophore bloom in the northern North Sea

Abstract

Dimethylsulphoniopropionate (DMSP) synthesised by phytoplankton is the principal precursor of the climatically active gas dimethyl sulphide (DMS). The rates of production of particulate DMSP (DMSPp) and turnover by microzooplankton were determined in surface waters of the northern North Sea, using a dilution approach. The phytoplankton communities were characterised by DMSPrich taxa including Emiliania huxleyi and Prorocentrum minimum and DMSPp:chlorophyll a (chl a) ratios of 64 to 162 nM µg -1 . Microzooplankton biomass varied from 25.5 to 56.7 µg C l -1 and was dominated by oligotrich ciliates and heterotrophic dinoflagellates. DMSPp production rates ranged from 14.8 to 45.6 nM d -1 and represent a doubling time of the ambient DMSPp pool of between 1.2 and 3.1 d. Consumption rates of DMSPp by microzooplankton varied between 11.4 and 59.9 nM d -1 and were equivalent to turnover rates of the ambient DMSPp pool of between 16 and 43% d -1 . In general, production rates of DMSPp were lower than those of chl a and E. huxleyi, with respective mean doubling times of 1.9, 1.5 and 1.3 d. Loss rates due to grazing were similar for DMSPp and E. huxleyi but generally significantly lower than those of the bulk phytoplankton, with mean turnover rates of 31, 30 and 40% d -1 of the standing stock of DMSPp, E. huxleyi and chl a, respectively. E. huxleyi contributed an estimated 2 to 25% of the total DMSPp production and 6 to 23% of the DMSPp ingested by microzooplankton, indicating the importance of other phytoplankton to DMSPp dynamics in 'E. huxleyi blooms'. At the depths sampled, DMSPp production was closely coupled to primary production and was equivalent to approximately 11% of the carbon fixation. DMSPp may be an important component of the diets of microzooplankton. Ingested DMSPp could have provided 2 to 3% of the microzooplankton carbon demand and 26 to 44% of their sulphur demand. DMSPp production and turnover rates were closely matched and suggest that in these waters microzooplankton grazing may be the principal determinant of the fate of DMSPp. The quantity of 'DMSP' excreted by microzooplankton, calculated from ingestion rates, biomass and assumed growth rates and growth efficiencies, ranged from 8.0 to 41.9 nM d

Environmental constraints on the production and removal of the climatically active gas dimethylsulphide (DMS) and implications for ecosystem modelling

“…In grazing experiments with another heterotrophic dinoflagellate, Gyrodinium dominans, Tang and Simo (2003) calculated that 32% and 44% of ingested prey DMSP was retained in the grazer, irrespective of the lyase activity of the prey (Table 4). This would roughly comply with a growth efficiency of 0.3 as has also been suggested by Archer et al (2001b).…”

“…However, it was recently suggested that DMSP rather than acrylate is the active deterrent of microzooplankton grazing (Strom et al 2003b) and readers are directed to the paper presented by Nejstgard et al (this issue) for a discussion on this subject. A few field experiments have combined the determination of microzooplankton grazing rates (the Landry-Hassett dilution technique) with DMS(P) analyses and have shown that DMSP-containing algal species may be proportionally less grazed than total algal biomass (Archer et al 2001b;Olson and Strom 2002;Wolfe et al 2000). However, several problems are associated with this technique and we refer to Archer et al (2001b) for a discussion on the potential pitfalls.…”

“…A few field experiments have combined the determination of microzooplankton grazing rates (the Landry-Hassett dilution technique) with DMS(P) analyses and have shown that DMSP-containing algal species may be proportionally less grazed than total algal biomass (Archer et al 2001b;Olson and Strom 2002;Wolfe et al 2000). However, several problems are associated with this technique and we refer to Archer et al (2001b) for a discussion on the potential pitfalls. Nevertheless, the emerging picture is that generally 20% to 70% of the ingested DMSP p is released to the dissolved phase (Table 4).…”

Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel

“…These workers suggested that microzooplankton grazing contributed more signi¢-cantly than viruses to E. huxleyi loss processes during the developing stages of a bloom, particularly since Archer et al (2001) calculated that grazing accounted for between 22%^39% of E. huxleyi turnover in that same bloom. During a parallel study in the Plymouth bloom, Fileman et al (2002) demonstrated that protozoan abundances were higher in the high re£ectance area than Station 1.…”

Structures of dimethylsulfoniopropionate‐dependent demethylase from the marine organism Pelagabacter ubique

“…1,2 Although DMSP is used primarily as an intracellular osmolyte by phytoplankton, the compound has also been recognized as an antioxidant and predator deterrent. 3,4 While some phytoplankton can convert DMSP to dimethyl sulfide (DMS), upon phytoplankton lysis a considerable amount of DMSP is released and rapidly metabolized by the marine microbial food web.…”