Martien Baars Senior Scientist	ROYAL NETHERLANDS INSTITUTE FOR SEA RESEARCH   Postal address: P.O. Box 59, NL-1790 AB Den Burg (Texel) The Netherlands   Visiting address: Landsdiep 4 NL-1797 SZ ’t Horntje (Texel) The Netherlands   Phone: (+31) (0)222-369300 Fax: (+31) (0)222-319674
E-mail: baars@nioz.nl   Phone: (+31) (0)222-369511
General
Martien A. Baars (born 1948) received his masters in zoology from the University of Groningen in 1972. His PhD thesis 'Running for life' (Free University Amsterdam, 1982) was on population dynamics of ground-beetles on moorland, Agricultural University Wageningen, 1972-1976. Baars was appointed for zooplankton studies at NIOZ in 1977. Work gradually extended to all aspects of pelagic ecosystems and cruise programs were both in the North Sea and in tropical upwelling areas: near West-Africa 1977-1982, Eastern Indonesia 1984-1987, and in the Arabian Sea 1992-1995. International relations involved membership of the JGOFS Indian Ocean Planning Group 1991-1997. Current activities in temperate waters are more related to GLOBEC and LOICZ, other IGBP/SCOR core projects. International cooperation also comprised a twinned Dutch-UK program on nutrient dynamics in the offshore part of the southern North Sea. The cruise program ‘Transport and Fate’ by Cefas (Lowestoft) focused on the physical transport patterns, whereas the NIOZ program 'Plume & Bloom' studied phyto- and zooplankton distributions in relation to hydrography. The Dutch cruises led by Baars discovered the presence of a 'river' of English Coastal Water, hidden in the East Anglian Silt Plume. The water mass pattern is very robust but the significance of the eutrophication effects by this ‘river’ for the Dutch EEZ is still being debated *). The Dutch data base comprises 7 major cruises plus 8 additional cruises during 1999-2002, with reasonable coverage of the seasonal pattern. *) An overview of the Dutch findings is given by http://www.nioz.nl/public/annual_report/2002/noordzee3.pdf Baars, M., S. Oosterhuis, & B. Kuipers, 2003. Plume & Bloom: water mass patterns and nutrient dynamics in the central part of the Southern Bight. Annual Report 2002, Royal Netherlands Institute for Sea Research, Texel: 11-13
Current Projects
1) ToRSMoN – Towards Remote Sensing supported Monitoring of the North Sea  A project carried out in the framework of the National User Support Programme 2001-2005 (NUSP-2) under responsibility of the Netherlands Agency for Aerospace Programmes (NIVR). To be completed summer 2007.   2) MEC – Marine Ecosystem Connections  (Cefas-NIOZ collaboration) Cruise program 2007-2008 by RV Cefas Endeavour (Lowestoft), funded by Defra (London), with an important contribution by the NIOZ departments Biological Oceanography and Marine Ecology. There will be 3 main study sites in the North Sea (in the Silt Plume, in the Oyster Ground and north of the Dogger), which will be visited 5 times per year for detailed process-orientated research in both the water column and the bottom, with special focus on the benthic boundary layer.   3) Free chitobiase, a marker enzyme for the growth of crustaceans An internal project by Martien A. Baars & Swier S. Oosterhuis (Below the text of a chapter in the NIOZ Annual Report 2006, that will appear in May 2007) Copepods are the most abundant animals in the plankton. These crustaceans undergo a series of moults during their development from egg to the adult stage. We developed a new method to measure growth of copepods in the open sea by using the enzyme chitobiase. The enzyme breaks down the old chitin exoskeleton and is released in the ambient water during the moult. Experiments showed that the free chitobiase in water samples can be used quantitatively to calculate copepod production in the sea. Field surveys in the North Sea indicated that copepod growth varied from less than 10% of body weight per day in autumn and winter, up to more than 30% in spring and summer. The chitobiase method could also be a relevant tool to estimate the production by other crustaceans like shrimps and crabs living on the bottom of the Wadden Sea. The measurement of production is a key variable in ecological research, especially if the focus is on the transfer of carbon and energy through the pelagic food web from algae via animal plankton to fish. The 14C-bicarbonate incorporation method for estimating primary production and tritium labelled amino acids for estimating bacterial production are used in aquatic studies. To estimate zooplankton production, there is no such method available using the incorporation of a specific substrate during short-time incubations. Copepods, small crustaceans, representing the most dominant group of the marine zooplankton, have generation times of several weeks to months. Theoretically, the growth of copepods can be deduced from the changes in abundance and size in time series sampling. However, in the open sea the tracking of populations over sufficiently long time spans is hampered by logistic constraints and by advection, patchiness and vertical migration. Consequently, estimates of secondary production in open marine waters are mainly based on plankton net catches combined with growth rates measured in laboratory experiments. Thus, there is still need for an easy field method to measure copepod growth more directly.   Fig. 1. Left panel: The release of the enzyme chitobiase (red dots) in the ambient water during the moult of a copepodite. Right panel: Relation between the increase in body weight and the released chitobiase activity for moults of different stages of three copepod species. Calanus finmarchicus (green), Temora longicornis (red) and Pseudocalanus elongatus (brown).   At the NIOZ, a new approach to estimate crustacean production was developed. The principle is not based on the uptake of a substrate but on the release of a specific substance indicative for growth. In the pre-moult phase of crustaceans, the old chitin exoskeleton is degraded by the chitinolytic enzymes chitinase and chitobiase. The NAG-monomers (N-acetyl-b-D-glucosaminide) resulting from the cleavage of chitin by this combined enzyme action, are re-used as building blocks for the new chitin skeleton underneath the old exoskeleton. During the moult, the remnant of the old skeleton is shed and the chitinolytic enzymes are released into the ambient water (Fig. 1). In laboratory experiments, the release of chitobiase by juveniles during the moult was measured. The amount of enzyme was linearly related to the growth of the juveniles between moults. The relation was similar for three different copepod species, and the regression equation on the combined data (inset in Fig.1) is used to estimate the total daily growth in mixed copepod populations in the sea. The free enzyme is not accumulating in the water but steadily consumed by bacteria (Fig. 2). Thus, to estimate the total amount of chitobiase released per day, the rate of chitobiase decay over 24 hours has to be measured in addition to the amount of dissolved chitobiase present in the water. Fig. 2. Free chitobiase remains present in autoclaved, sterile seawater (blue dots) whereas the consumption by bacterioplankton causes an exponential decay of chitobiase in raw seawater (red dots).   The spatial distribution of copepod production was mapped with the new technique during surveys in the North Sea. A plume of turbid English Coastal Water with high concentrations of suspended matter and low salinity (see the contours in Fig. 3) crosses the Southern Bight in-between the more saline Central North Sea Water and Channel Water.   Fig. 3. Copepod production (black dots) estimated by free chitobiase in the southern North Sea plotted on contour maps of surface salinity (blue scales) and concentration of suspended matter (mg/litre, brown lines). Plume & Bloom cruise September 2000.    In September 2000, daily primary production was low inside compared to outside of the plume (0.5 versus 1 gram carbon per square metre) and mean copepod production showed a similar difference (150 versus 370 mg carbon per square metre). Highest copepod production was measured at the rim and downstream of the plume (Fig. 3) where water masses mixed. One particular station, at the southern, muddy slope of the Oyster Ground – the so-called Frisian Front – was visited during several cruises through the year. Copepod production was one order of magnitude higher in June and September than in December 2003 and April 2004. The production estimated via the free chitobiase method was compared with the biomass of copepods in the net catches. Production/biomass ratios ranged between 0.30-0.35 during late spring/summer to 0.05- 0.10 in winter/early spring. Free chitobiase was frequently markedly higher in near-bottom water samples than in water collected in the upper layer of the North Sea. This phenomenon indicates that copepods or other crustaceans concentrate near the bottom. The benthic boundary layer may form a special, productive habitat for crustaceans due to the constant sedimentation and resuspension of phytoplankton and detritus by the tidal movement.   Fig. 4. Seasonal pattern of free chitobiase activity (upper panel) and the calculated crustacean production (lower panel) in the water column at the NIOZ jetty and at the mud flat near the NIOZ harbour, April – December 2006. Enzyme activity (expressed in units substrate cleaved) per litre per hour; production (in mg carbon) per square metre per day.   High productivity of the crustacean community of the bottom was measured regularly at a small mudflat near the NIOZ. The free chitobiase signal in the water collected above the mudflat near the end of ebb was significantly stronger than the chitobiase signal in the first flood-water collected at the nearby jetty (Fig. 4 upper panel). The extra chitobiase originates from both the harpacticoid copepods, the crustacean component of the meiofauna in the bottom and from shrimps and crabs living on the bottom. An attempt was made to calculate the square metre crustacean production of the plankton in the mean water column near the jetty and of the mudflat (Fig. 4 lower panel). This pilot study suggests that the chitobiase approach may be a useful tool in field programs to estimate the productivity of all the different crustaceans in the Wadden Sea.
Student oportunities
There is the possibility for Master students to participate in a pilot study on the usefulness of chitobiase to estimate the secondary production by different components (plankton, crabs & shrimp, bottom meiofauna) in the Wadden Sea.
Publication list
Selected papers and reports since 1993 Smith, S.L. & M.A. Baars, 2002. Zooplankton. In: Report of the Indian Ocean Synthesis Group on the Arabian Sea Process Study. (SCOR/JGOFS, Bergen, Norway) JGOFS Report 35: 51-56. Oosterhuis, S.S., M.A. Baars & W.C.M. Klein Breteler, 2000. Release of the enzyme chitobiase by the copepod Temora longicornis: characteristics and potential tool for estimating crustacean biomass production in the sea. Mar. Ecol. Prog. Ser. 196: 195-206. Baars, M.A., M.J.N. Bergman & M.S.S. Lavaleye, 1999. The Frisian Front Revisited. New observations on the benthic and pelagic communities in the transition zone between the Southern Bight and the Oyster Ground. NIOZ Report, Texel: 56 p. Baars, M.A., 1999. On the paradox of high mesozooplankton biomass, throughout the year in the western Arabian Sea: re-analysis of IIOE data and comparison with newer data. Indian Journal of Marine Sciences, 28: 125-137. Baars, M.A., P.H. Schalk & M.J.W. Veldhuis, 1998. Seasonal fluctuations in plankton biomass and productivity in the ecosystems of the Somali Current, Gulf of Aden and southern Red Sea. In: K.Sherman, E.N. Okemwa & M.J. Ntiba (Eds.). Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management. Blackwell Scientific, Malden: 143-174. Tett, P.B., I.R. Joint, D.A. Purdie, M. Baars, S. Oosterhuis, G. Daneri, F. Hannah, D.K. Mills, D. Plummer, A.J. Pomroy, A.W. Walne & H.J. Witte, 1993. Biological consequences of tidal stirring gradients in the North Sea. Phil. Trans. R. Soc. Lond. A 343: 493 -508.