Dimethylsulphoniopropionate Production Research Articles

Different dimethylsulphoniopropionate-producing ability of dinoflagellates could affect the structure of their associated bacterial community

Dinoflagellate plays an important role in the production of dimethylsulphoniopropionate (DMSP) in marine ecosystem. DMSP derived from dinoflagellates is an important reducing sulfur and carbon source for heterotrophic bacterioplankton. Although dinoflagellates have outstanding ability in DMSP biosynthesis, and the inter-specific variation of cellular DMSP concentrations in different species and strains has been well described, the effects of DMSP level on microbial community structure are still unclear. In this study, the ability of seven dinoflagellates to synthesize DMSP and their effects on the composition of associated bacterial community were investigated. Total concentration of DMSP (2397.25 ± 187.17 μM) and single cell DMSP content (34.25 ± 2.67 pmol cell−1) were the highest in Protoceratium reticulatum, while the DMSP contents of Prorocentrum texanum and Amphidinium carterae were significantly lower than those of other dinoflagellates. Bacterial community structure in dinoflagellate culture was determined by cultivation-dependent and cultivation-independent approaches. There were significantly differences in the richness and diversity of bacteria in different dinoflagellate cultures with different DMSP contents. In addition, abundant of Roseobacter-clade bacteria (well-known DMSP degraders) were found in the cultures of six dinoflagellates. Genomic analysis indicated that the Roseobacter-clade bacteria isolated from dinoflagellate could degrade DMSP by cleavage pathway. The results demonstrated that DMSP could be an important factor affecting the abundance and composition of bacterial community in phycosphere of dinoflagellates.

Local environment shapes adaptation of Phaeocystis antarctica to salinity perturbations: Evidence for physiological resilience

The Southern Ocean (SO) is a fragile ecosystem as judged by changes in the timing of the advance and retreat of its ice cover. In the SO, the Antarctic Circumpolar Current (ACC) and the near shore gyres (Weddell Sea and Ross Sea) provide local environments with distinct temperature and salinity attributes associated with varying sea ice history. Phaeocystis antarctica is a prymnesiophyte often dominating polar phytoplankton blooms in the (SO) and is a keystone species there because its abundance can have negative effects on higher trophic levels and it can influence air/sea gas exchange involved in DMSP production, Thus, its ability to survive in response to perturbations in the environments may be linked to its genetic diversity within its populations as they move around the SO. Here we apply increased (70 PSU) and decreased (18 PSU) salinity treatments to five genetically different P. antarctica strains isolated from three different water masses to test whether genetic similarity or water mass physical features were more important in determining responses to salinity changes, such as those encountered by inclusion into sea ice brine channels and/or its subsequent melt water in those water masses that have annual ice cover. Strains that were geographically close (isolated from the same water mass), but genetically distinct (ca. 30% similar and from different gene pools as judged by microsatellite (MS) and amplified fragment linked polymorphisms (AFLP) analyses responded similarly to higher and lower salinity regimes, whereas genetically close strains (ca. 95% identical or from the same gene pool) that originated from different water masses and hence different environmental conditions responded differently. Dimethylsulphoniopropionate (DMSP) production in response to these salinity changes were not significantly different between any of the strains/treatments. Considering the presence of highly similar genotypes in ice-free as well as seasonally ice covered sampling sites, the observed phenotypic differences most likely result from rapid local adaptation between both habitat types or a hybridization of isolates from the two gene pools with the resultant genotype for salinity tolerance being that from which the isolate originated, suggesting that the selective effect of seasonal presence or year-round absence of sea ice overrides gene flow between these habitats to adapt the physiology of cells to the environment in a relatively short period of time.

Influence of salinity on the dimethylsulphoniopropionate production from Prymnesium simplex

Dimethylsulphoniopropionate (DMSP) is a tertiary sulphonium compound which has received a considerable attention over recent years for acting as a principal intermediate in the production of dimethylsulphide, which is mostly noted as odour causing substance and it acts as a potential key player for climate regulation. The synthesis of DMSP is confined to some species of microalgae especially, prymnesiophytes and dinophytes and its concentration level varies with some environmental factors. In this context, this research work applies an experimental approach to assessing the production rate of DMSP under varying salinity (28, 30, 32 PSU) across distinctive growth phases. For this purpose, estuarine isolated microalgae, Prymnesium simplex (prymnesiophyceae) was selected as a model organism. The results showed that the growth rate response of P. simplex was significantly reduced at lower salinity (28 and 30 PSU) compared to higher salinity in this range (32 PSU). The concentration of DMSP and particulate fraction of DMSP was also elevated at higher salinity in the exponential phase of growth and lower at lower salinity. In contrast, the maximum production of dissolved DMSP was seen at lower salinity. Essentially research is to determine a maximum contribution of the regionally important prymnesiophyte family in the process of biogeochemical sulphur cycling.

Soft corals are significant DMSP producers in tropical and temperate reefs

Corals synthesise large quantities of the sulphur metabolite dimethylsulphoniopropionate (DMSP), which contributes to key roles in coral reef ecology including the capacity of corals to withstand various stressors. While closely related to scleractinian corals and often occupying similar ecological niche space, it is currently poorly defined to what extent soft corals produce DMSP. We, therefore, examined DMSP content within four key species of soft coral in February and July–August of 2017, including two temperate species from Sydney Harbour (Erythropodium hicksoni, Capnella gaboensis) and two tropical species from the Great Barrier Reef (Sinularia sp., Sarcophyton sp.). We compared DMSP content of these soft coral species to that of commonly occurring temperate (Plesiastrea versipora) and tropical (Acropora aspera) scleractinian coral species. DMSP content was normalised to coral protein content, with soft coral DMSP content highly variable across species and locations [56–539 nmol (mg protein)−1], and lower than for the tropical [1242–4710 nmol (mg protein)−1], but not temperate [465–1984 nmol (mg protein)−1] scleractinian species. Further comparison with previously published values demonstrated that soft coral DMSP content falls within the “low–mid range” of scleractinian corals. Notably, DMSP content was also higher in summer samples than winter samples for the scleractinian corals, but did not differ between seasons for soft corals. Such contrasting dynamics of DMSP production by soft corals compared to scleractinian corals indicates that the regulation of DMSP content differs between these two important benthic cnidarian groups, potentially as a consequence of dissimilar ecophysiological roles for this compound.

Comparative response of DMS and DMSP concentrations in Symbiodinium clades C1 and D1 under thermal stress

Coral-associated Symbiodinium are known to produce dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP), two biogenic sulphur compounds that potentially play a role in the algal antioxidant system and climate regulation. Coral resistance to bleaching and oxidative stress partly depends upon the capacity of their symbionts to respond to environmental stressors, with DMS and DMSP possibly contributing to this response. Under increasing sea surface temperatures, zooxanthellate corals might dominantly associate with more thermally tolerant clades of Symbiodinium, of which the nutritional and biochemical contribution to the holobiont remains unknown. Here, the production of DMS and DMSP under increasing temperature (from 26°C to 31°C) was investigated over 6days in axenic cultures of two Symbiodinium clades (C1 and D1) that are known to exhibit different thermal tolerances. Regardless of the temperature treatment, clade C1 was a greater producer of DMS and DMSP. An increase in temperature of up to 5°C did not substantially affect DMS and DMSP production in the thermo-tolerant clade D1. However, thermal stress induced enhanced consumption of both DMS and DMSP in the more thermo-sensitive clade C1, potentially indicating the use of sulphur compounds as antioxidants. Together, these results suggest that thermal stress differentially affects the biogenic sulphur cycle of Symbiodinium clades that exhibit different thermal tolerances, with possible consequences for reef-building corals under future climate change scenarios.

DMSP biosynthesis by an animal and its role in coral thermal stress response

Globally, reef-building corals are the most prolific producers of dimethylsulphoniopropionate (DMSP), a central molecule in the marine sulphur cycle and precursor of the climate-active gas dimethylsulphide. At present, DMSP production by corals is attributed entirely to their algal endosymbiont, Symbiodinium. Combining chemical, genomic and molecular approaches, we show that coral juveniles produce DMSP in the absence of algal symbionts. DMSP levels increased up to 54% over time in newly settled coral juveniles lacking algal endosymbionts, and further increases, up to 76%, were recorded when juveniles were subjected to thermal stress. We uncovered coral orthologues of two algal genes recently identified in DMSP biosynthesis, strongly indicating that corals possess the enzymatic machinery necessary for DMSP production. Our results overturn the paradigm that photosynthetic organisms are the sole biological source of DMSP, and highlight the double jeopardy represented by worldwide declining coral cover, as the potential to alleviate thermal stress through coral-produced DMSP declines correspondingly.

Spatiotemporal Variability of Dimethylsulphoniopropionate on a Fringing Coral Reef: The Role of Reefal Carbonate Chemistry and Environmental Variability

Oceanic pH is projected to decrease by up to 0.5 units by 2100 (a process known as ocean acidification, OA), reducing the calcium carbonate saturation state of the oceans. The coastal ocean is expected to experience periods of even lower carbonate saturation state because of the inherent natural variability of coastal habitats. Thus, in order to accurately project the impact of OA on the coastal ocean, we must first understand its natural variability. The production of dimethylsulphoniopropionate (DMSP) by marine algae and the release of DMSP’s breakdown product dimethylsulphide (DMS) are often related to environmental stress. This study investigated the spatiotemporal response of tropical macroalgae (Padina sp., Amphiroa sp. and Turbinaria sp.) and the overlying water column to natural changes in reefal carbonate chemistry. We compared macroalgal intracellular DMSP and water column DMSP+DMS concentrations between the environmentally stable reef crest and environmentally variable reef flat of the fringing Suleman Reef, Egypt, over 45-hour sampling periods. Similar diel patterns were observed throughout: maximum intracellular DMSP and water column DMS/P concentrations were observed at night, coinciding with the time of lowest carbonate saturation state. Spatially, water column DMS/P concentrations were highest over areas dominated by seagrass and macroalgae (dissolved DMS/P) and phytoplankton (particulate DMS/P) rather than corals. This research suggests that macroalgae may use DMSP to maintain metabolic function during periods of low carbonate saturation state. In the reef system, seagrass and macroalgae may be more important benthic producers of dissolved DMS/P than corals. An increase in DMS/P concentrations during periods of low carbonate saturation state may become ecologically important in the future under an OA regime, impacting larval settlement and increasing atmospheric emissions of DMS.

Contrasting responses of DMS and DMSP to ocean acidification in Arctic waters

Abstract. Increasing atmospheric CO2 is decreasing ocean pH most rapidly in colder regions such as the Arctic. As a component of the EPOCA (European Project on Ocean Acidification) pelagic mesocosm experiment off Spitzbergen in 2010, we examined the consequences of decreased pH and increased pCO2 on the concentrations of dimethylsulphide (DMS). DMS is an important reactant and contributor to aerosol formation and growth in the Arctic troposphere. In the nine mesocosms with initial pHT 8.3 to 7.5, equivalent to pCO2 of 180 to 1420 μatm, highly significant but inverse responses to acidity (hydrogen ion concentration [H+]) occurred following nutrient addition. Compared to ambient [H+], average concentrations of DMS during the mid-phase of the 30 d experiment, when the influence of altered acidity was unambiguous, were reduced by approximately 60% at the highest [H+] and by 35% at [H+] equivalent to 750 μatm pCO2, as projected for 2100. In contrast, concentrations of dimethylsulphoniopropionate (DMSP), the precursor of DMS, were elevated by approximately 50% at the highest [H+] and by 30% at [H+] corresponding to 750 μatm pCO2. Measurements of the specific rate of synthesis of DMSP by phytoplankton indicate increased production at high [H+], in parallel to rates of inorganic carbon fixation. The elevated DMSP production at high [H+] was largely a consequence of increased dinoflagellate biomass and in particular, the increased abundance of the species Heterocapsa rotundata. We discuss both phytoplankton and bacterial processes that may explain the reduced ratios of DMS:DMSPt (total dimethylsulphoniopropionate) at higher [H+]. The experimental design of eight treatment levels provides comparatively robust empirical relationships of DMS and DMSP concentration, DMSP production and dinoflagellate biomass versus [H+] in Arctic waters.

The effect of chronic and acute low pH on the intracellular DMSP production and epithelial cell morphology of red coralline algae

The release of dimethylsulphoniopropionate (DMSP) by marine algae has major impacts on the global sulphur cycle and may influence local climate through the formation of dimethylsulphide (DMS). However, the effect of global change on DMSP/DMS (DMS(P)) production by algae is not well understood. This study examined the effect of low pH on DMS(P) production and epithelial cell morphology of the free-living red coralline alga Lithothamnion glaciale. Three pH treatments were used in the 80-day experiment: (1) current pH level (8.18, control), (2) low, chronic pH representing a 2100 ocean acidification (OA) scenario (7.70) and (3) low, acute pH (7.75, with a 3-day spike to 6.47), representing acute variable conditions that might be associated with leaks from carbon capture and storage infrastructure, at CO2 vent sites or in areas of upwelling. DMS(P) production was not significantly enhanced under low, stable pH conditions, indicating that red coralline algae may have some resilience to OA. However, intracellular and water column DMS(P) concentrations were significantly higher than the control when pH was acutely spiked. Cracks were observed between the cell walls of the algal skeleton in both low pH treatments. It is proposed that this structural change may cause membrane damage that allows DMS(P) to leak from the cells into the water column, with subsequent implications for the cycling of DMS(P) in coralline algae habitats.

Effect of elevated pCO2 on the production of dimethylsulphoniopropionate (DMSP) and dimethylsulphide (DMS) in two species of Ulva (Chlorophyceae)

Concentrations of the secondary algal metabolite dimethylsulphoniopropionate (DMSP) and its breakdown product, the climate-active trace gas dimethylsulphide (DMS), are sensitive to changes in pCO2. Data on the response of marine macroalgae to future pCO2 levels are lacking. Here we report the first measurements of DMSP and DMS production in two species of chlorophyte macroalgae (Ulva lactuca and U. clathrata). Laboratory cultures were grown in pH–stated medium that received pulses of CO2 to create pCO2 conditions ranging from ambient (432 μatm) to future (1514 μatm). Intracellular concentration of DMSP remained unaffected in both species (101 ± 21 and 69 ± 20 mmol g−1 FW in U. lactuca and U. clathrata, respectively) but significant differences in extracellular production of DMSP and DMS were observed for U. lactuca: Whilst production of total DMSP (the sum of external DMSP and DMS) was different between replicated experiments, the percentage of total DMSP produced throughout each experiment increased significantly by up to 65% with increasing pCO2 to 1514 μatm. In contrast, DMS production decreased from 0.4 to 0.25 nmol g−1 FW h−1. This decrease was not a linear function of pCO2 but an almost 50% step-wise loss of DMS production was indicated between 635 and 884 μatm, a pCO2 predicted for the next 100 years. Since Ulva spp. form massive harmful blooms (‘green tides’) that can occur free-floating and faraway (>100 km) from the coast, they may provide a locally significant source of DMS to the remote marine boundary layer.

Atmospheric dimethysulphide production from corals in the Great Barrier Reef and links to solar radiation, climate and coral bleaching

Coral zooxanthellae contain high concentrations of dimethylsulphoniopropionate (DMSP), the precursor of dimethylsulphide (DMS), an aerosol substance that could affect cloud cover, solar radiation and ocean temperatures. Acropora intermedia a dominant staghorn coral in the Indo-Pacific region, contain some of the highest concentrations of DMSP reported in the literature but no studies have shown that corals produce atmospheric DMS in situ and thus could potentially participate in sea surface temperature (SST) regulation over reefs; or how production varies during coral bleaching. We show that A. intermedia from the Great Barrier Reef (GBR) produces significant amounts of atmospheric DMS, in chamber experiments, indicating that coral reefs in this region could contribute to an “ocean thermostat” similar to that described for the western Pacific warm pool, where significantly fewer coral reefs have bleached during the last 25 years because of a cloud-SST feedback. However, when Acropora intermedia was stressed with higher light levels and seawater temperatures DMSP production, an indicator of zooxanthellae expulsion, increased markedly in the chamber, whilst atmospheric DMS emissions almost completely shut down. These results suggest that during increased light levels and seawater temperatures in the GBR coral shut-down atmospheric DMS aerosol production, potentially increasing solar radiation levels over reefs and exacerbating coral bleaching.

Concentrations of dimethylsulphoniopropionate and activities of dimethylsulphide-producing enzymes in batch cultures of nine dinoflagellate species

Dinoflagellates are recognised as one of the major phytoplankton groups that produce dimethylsulphoniopropionate (DMSP), the precursor of the marine trace gas dimethylsulphide (DMS) which has climate-cooling potential. To improve the prospects for including dinoflagellates in global climate models that include DMSP-related processes, we increased the data base for this group by measuring DMSP, DMS-producing enzyme activity (DPEA), carbon, nitrogen and Chl a in nine clonal dinoflagellate cultures (1 heterotrophic and 8 phototrophic strains). Growth rates ranged from 0.11 to 1.92 day−1 with the highest value being for the heterotroph Crypthecodinium cohnii. Overall, we observed two orders of magnitude variability in DMSP content (11–364 mM) and detected DPEA in five of the nine strains (0.61–59.73 fmol cell−1 h−1). Cell volume varied between 454 and 18,439 μm3 and whilst C and N content were proportional to the cell volume, DMSP content was not. The first DMSP measurements for a dinoflagellate from Antarctic waters and a species with diatom-like plastids are included. Lower DMSP concentrations were found in three small athecate species and a dinoflagellate with haptophyte-like plastids. The highest concentrations and production rates tended to be in globally distributed dinoflagellates and the heterotroph. Photosynthetic species that are distributed in temperate to tropical waters showed low DMSP concentrations and production rates and the polar representative showed moderate concentration and a low production rate. Estuarine species had the lowest concentrations and production rates. These data should help refine the inclusion of dinoflagellates as a functional group in future global climate models.

Combining cell sorting with gas chromatography to determine phytoplankton group-specific intracellular dimethylsulphoniopropionate

An approach combining flow-cytometric fluorescence-activated cell sorting (FACS) of specific phytoplankton groups and subsequent quantification of dimethylsulphoniopropionate (DMSP) content by gas chromatography (GC) is introduced and applied to cultivated microalgae and natural seawater samples. The FACS-GC based method produces statistically robust estimates of the intracellular DMSP content of a variety of phytoplankton groups ranging from prokaryotic Synechococcus spp. to eukaryotic nanophytoplankton. Comparison between FACS and traditional filtration approaches to determine intracellular DMSP content of cultivated microalgae illustrates variable responses between species to the 2 methods. Natural photosynthetic nanoeukaryote populations contained high intracellular DMSP content; comparable to many cultivated prymnesiophyte taxa. A surprisingly high DMSP content was found in natural populations of Synechococcus spp., in contrast to previous values measured in cultivated strains, but possibly confirming the uptake and retention of DMSP by this photosynthetic prokaryote. When combined, the DMSP contributions of each phytoplankton group amounted to between 40 and 57 % of total DMSP in each water sample, with the bulk of the total comprising nanoeukaryote-DMSP. The approach has high potential to provide information that enables better parameterisation of phytoplankton functional types in mechanistic dimethyl sulphide models and to help elucidate the environmental controls that govern the extent and diversity of DMSP production in the oceans.

Grazing suppression of dimethylsulphoniopropionate (DMSP) accumulation in iron-fertilised, sub-Antarctic waters

The impact of in situ iron fertilisation on the production of particulate dimethylsulphoniopropionate (DMSPp) and its breakdown product dimethyl sulphide (DMS) was monitored during the SOLAS air–sea gas exchange experiment (SAGE). The experiment was conducted in the high nitrate, low chlorophyll (HNLC) waters of the sub-Antarctic Southern Ocean (46.7°S 172.5°E) to the south-east of New Zealand, during March–April, 2004. In addition to monitoring net changes in the standing stocks of DMSPp and DMS, a series of dilution experiments were used to determine the DMSPp production and consumption rates in relation to increased iron availability. In contrast to previous experiments in the Southern Ocean, DMS concentrations decreased over the course of the 15-d iron-fertilisation experiment, from an integrated volume-specific concentration in the mixed layer on day 0 of 0.78 nM (measured values 0.65–0.91 nM) to 0.46 nM (measured values 0.42–0.47 nM) by day 15, in parallel with the surrounding waters. DMSPp, chlorophyll a and the abundance of photosynthetic picoeukaryotes exhibited indiscernible or only moderate increases in response to the raised iron availability, despite an obvious physiological response by the phytoplankton. High specific growth rates of DMSPp, equivalent to 0.8–1.2 doublings d −1, occurred at the simulated 60% light level of the dilution experiments. Despite the high production rates, DMSPp accumulation was suppressed in part by microzooplankton grazers who consumed between 61% d −1 and 126% d −1 of the DMSPp production. Temporal trends in the rates of production and consumption illustrated a close coupling between the DMSP-producing phytoplankton and their microzooplankton grazers. Similar grazing and production rates were observed for the eukaryotic picophytoplankton that dominated the phytoplankton biomass, partial evidence that picoeukaryotes contributed a substantial proportion of the DMSP synthesis. These rates for DMSPp and picoeukaryotes were considerably higher than for chlorophyll a, indicating higher cycling rates of the DMSP-producing taxa than for the bulk phytoplankton community. When compared to the total phytoplankton community, there was no evidence of selection against the DMSP-containing phytoplankton by the microzooplankton grazers; the opposite appeared to be the case. SAGE demonstrated that increased iron availability in the HNLC waters of the Southern Ocean does not invariably lead to enhanced DMS sea–air flux. The potential suppression of DMSPp accumulation by grazers needs to be taken into account in future attempts to elevate DMS emission through in situ iron fertilisation and in understanding the hypothesised link between levels of Aeolian iron deposition in the Southern Ocean, DMS emission and global albedo.

Strong linkages between dimethylsulphoniopropionate (DMSP) and phytoplankton community physiology in a large subtropical and tropical Atlantic Ocean data set

We present an extensive data set of dimethylsulphide (DMS, n = 651) and dimethylsulphoniopropionate (DMSP, n = 590) from the Atlantic Meridional Transect program. These data are used to derive representative depth profiles that illustrate observed natural variations and can be used for DMS and DMSP model‐validation in oligotrophic waters. To further understand our data set, we interpret the data with a wide range of accompanying parameters that characterize the prevailing biogeochemical conditions and phytoplankton community physiology, activity, taxonomic composition, and capacity to cope with light stress. No correlations were observed with typical biomarker pigments for DMSP‐producing species. However, strong correlations were found between DMSP and primary production by cells >2 μm in diameter and between DMSP and some photo‐protective pigments. These parameters are measures of mixed phytoplankton communities, so we infer that such associations are likely to be stronger in DMSP‐producing organisms. Further work is warranted to develop links between community parameters, DMS, and DMSP at the global scale.

Simulating dimethylsulphide seasonality with the Dynamic Green Ocean Model PlankTOM5

We study the dynamics of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) using the global ocean biogeochemistry model PlankTOM5, which includes three phytoplankton and two zooplankton functional types (PFTs). We present a fully prognostic DMS module describing intracellular particulate DMSP (DMSPp) production, concentrations of dissolved DMSP (DMSPd), and DMS production and consumption. The model produces DMS fields that compare reasonably well with the observed annual mean DMS fields, zonal mean DMS concentrations, and its seasonal cycle. Modeled ecosystem composition and modeled total chlorophyll influenced mean DMS concentrations and DMS seasonality at mid‐ and high latitudes, but did not control the seasonal cycle in the tropics. The introduction of a direct, irradiation‐dependent DMS production term (exudation) in the model improved the match between modeled and observed DMS seasonality, but deteriorated simulated zonal mean concentrations. In PlankTOM5, exudation was found to be most important for DMS seasonality in the tropics, and a variable DMSP cell quota as a function of light and nutrient stress was more important than a PFT‐specific minimal DMSPp cell quota. The results suggest that DMS seasonality in the low latitudes is mostly driven by light. The agreement between model and data for DMS, DMSPp, and DMSPd is reasonable at the Bermuda Atlantic Time Series Station, where the summer paradox is observed.

The distribution of DMSP in green macroalgae from northern New Zealand, eastern Australia and southern Tasmania

The sulphonium compound dimethylsulphoniopropionate (DMSP) is commonly found in temperate green macroalgae. To examine taxonomic and regional and local geographical patterns of DMSP production in Australasian algae, I collected 30 species of green algae from 14 sites in three regions, eastern Australia, Tasmania, Australia, and the North Island of New Zealand. The distribution of DMSP content was similar to that seen from other areas of the world. DMSP was found in high concentrations inUlvaandCodiumspp. It tended to be undetectable or in lower concentrations in other members of the orders Bryopsidales and Cladophorales. There was no evidence for differences in concentrations among the three regions in the generaCodiumandUlva; however, the invasive subspecies ofCodium fragile, C. fragilessp.tomentosoides, had significantly higher concentrations of DMSP than the non-invasivesubspecies.The herbivorous sea slugElysia maoriahad whole body concentrations that were not significantly different from those of its host algaC. fragilessp. tomentosoides. The distribution patterns of DMSP inCodiumspp. do not support the hypothesis that DMSP is used as an antioxidant in this genus. Based on the data collected here and previous reports from the literature, I speculate that one function of DMSP in these algae may be to deter herbivores.

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

Seawater concentrations of the climate-cooling, volatile sulphur compound dimethylsulphide (DMS) are the result of numerous production and consumption processes within the marine ecosystem. Due to this complex nature, it is difficult to predict temporal and geographical distribution patterns of DMS concentrations and the inclusion of DMS into global ocean climate models has only been attempted recently. Comparisons between individual model predictions, and ground-truthing exercises revealed that information on the functional relationships between physical and chemical ecosystem parameters, biological productivity and the production and consumption of DMS and its precursor dimethylsulphoniopropionate (DMSP) is necessary to further refine future climate models. In this review an attempt is made to quantify these functional relationships. The description of processes includes: (1) parameters controlling DMSP production such as species composition and abiotic factors; (2) the conversion of DMSP to DMS by algal and bacterial enzymes; (3) the fate of DMSP-sulphur due to, e.g., grazing, microbial consumption and sedimentation and (4) factors controlling DMS removal from the water column such as microbial consumption, photo-oxidation and emission to the atmosphere. We recommend the differentiation of six phytoplankton groups for inclusion in future models: eukaryotic and prokaryotic picoplankton, diatoms, dinoflagellates, and other phytoflagellates with and without DMSP-lyase activity. These functional groups are characterised by their cell size, DMSP content, DMSP-lyase activity and interactions with herbivorous grazers. In this review, emphasis is given to ecosystems dominated by the globally relevant haptophytes Emiliania huxleyi and Phaeocystis sp., which are important DMS and DMSP producers.

Significance of vertical flux as a sink for surface water DMSP and as a source for the sediment surface in coastal zones of northern Europe

In April 1997 and 1998 the significance of sedimentation as a sink for epipelagic dimethylsulphoniopropionate (DMSP) production and as a source for marine sediments was reassessed using a newly designed sediment trap. The behaviour of the traps in immersion was monitored continuously and the collection efficiency was evaluated with 234Th measurements. Net DMS(P) fluxes were corrected for some physical and biological losses during the whole sedimentation process providing reliable estimates of gross DMSP fluxes. It is shown that daily losses by sedimentation account for between 0.1% and 16% of seawater particulate DMSP (DMSPp) standing stocks, and between 3% and 75% of daily DMSPp production. In the Malangen fjord we observed temporal increases of DMSP production and standing stocks which resulted also in increases of DMSP vertical fluxes and DMS(P) concentrations at the sediment surface. This result illustrates how tight the coupling can be between pelagos and benthos, and confirms that DMS(P) concentration in the sediment was a reliable diagnostic indicator of vertical export from overlying waters in Malangen fjord. In Ullsfjord, however, DMS(P) concentrations in the sediment were poorly indicators of Phaeocystis pouchetii export during the early stage of growth of a bloom. The high load of DMS(P) in Balsfjord's sediments could neither be attributed to local vertical sedimentation nor to short-term lateral advection of fresh DMSP-containing phytoplanktonic material, and provides indication that this tracer sometimes also can be misleading. The highest loads of DMS(P) in sediments and the fastest rates of sedimentation occurred in the Southern Bight of the North Sea.

Profiles of dimethylsulphoniopropionate (DMSP), algal pigments, nutrients, and salinity in the fast ice of Prydz Bay, Antarctica

Total dimethylsulphoniopropionate (DMSPt), chlorophylla(Chla), and algal marker pigments were measured in 12 fast ice cores collected from Prydz Bay, eastern Antarctica (68°–69°S, 77°–79°E) in October 1997 and November 1998. Patterns of DMSPt distribution through the ice were similar on spatial scales of meters to tens of kilometers within ice sheets grouped according to growth history. This reflects the association of DMSP in fast ice with autotrophic biomass distribution, which is intrinsically linked with ice growth and differed between the ice sheets. The 12 fast ice cores were divided into three groups on the basis of ice thickness and year. Concentrations of DMSPt ranged widely from 9 to 1478 nM with marked peaks occurring within each core. Mean DMSPt concentrations were higher (200 nM) in the medium first‐year ice (0.7–1.2 m) than in the thick (>1.2 m) first‐year ice (90 nM), mainly because of a local surface algal assemblage that may be atypical. The fast ice algal assemblages in surface, interior, and bottom ice were dominated by diatoms (Fucoxanthin:Chlaconcentrations >80%). Dinoflagellates and haptophytes were generally small and variable components of the assemblages (Peridinin:Chla2–11% and 19′‐hexanoyloxyfucoxanthin:Chla2–4%, respectively). Our data support the important contribution of diatoms to DMSP production in sea ice. Nutrient (nitrate, silicate, phosphate) concentrations were measured for one group of cores. Silicate and Chlaconcentrations were significantly correlated (r = 0.30, P < 0.02, Pearson), implying that silicate availability may have regulated algal growth. The Si:P:N ratio in interior ice (27:1:10) was different to that in surface and bottom ice (46:1:23). We have summarized DMSP data reported from six Antarctic sea ice studies to investigate whether comparisons within the growing database need to consider differences in sea ice type, thickness, location, or season. Although concentrations from individual samples ranged over 4 orders of magnitude (<1 to >1000 nM,n= 410), the mean DMSP concentrations during spring/summer were within the range of 107–322 nM, with an overall mean of 178 nM. Mean DMSP concentrations in Antarctic sea ice appear to be comparable between studies and across the Antarctic sea ice zone. We estimate that the Antarctic sea ice zone may contain up to 9 Mmole sulphur as DMSP.