Food web interactions at the Belgian Continental Shelf

By Travis Greene,2014-04-16 21:17
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Food web interactions at the Belgian Continental Shelf

    Diensten van de Eerste Minister

    Federale diensten voor wetenschappelijke, technische en culturele aangelegenheden

Tweede plan voor wetenschappelijke ondersteuning van

    een beleid gericht op duurzame ontwikkeling

Deel II: "Global change, Ecosystemen en Biodiversiteit"

    Netwerkovereenkomst EV/02/25A



    Universiteit Gent

    Sektie Mariene Biologie


    Instituut voor Natuurbehoud


    Katholieke Universiteit Leuven

    Laboratorium voor Aquatische Ecologie


    voor de periode van 01/02/2002-31/01/2003

    Food web interactions at the Belgian Continental Shelf

    1221 Jan Vanaverbeke , Leon Moodley, Karline Soetaert & Magda Vincx

1 Ghent University, Biology Department, Marine Biology Section



    Based on results obtained in a previous OSTC-programme (Functional and structural biodiversity of North Sea ecosystems), the existence of two different food webs on the Belgian Continental Shelf (BCS) was hypothesized. A comparison of the response of nematode communities at an “open” sea station (Station 330) and a coastal „accumulation” station (Station 115 bis) (Fig. 1) to the deposition of phytodetritus during a spring phytoplankton bloom revealed completely different reactions in terms of nematode densities, vertical distribution and diversity (Steyaert et al. subm, Vanaverbeke et al., in prep).



    Longitude (N)Zeebrugge


    115bis-5 m-10 mNieuwpoort-20 m

    Dunkerque51. (E)

    Figure 1 Map of the Belgian continental shelf with indication of the samplin stations

    Within the framework of TROPHOS, we aim to unravel the differences in the benthic food webs at these two target locations. In a first step, all biota and structuring variables


    at both stations are examined in order to quantify and understand the differences in primary and secondary production at both locations at the BCS.

General sampling scheme

Both stations are visited monthly with RV Belgica or Zeeleeuw and sampled according to

    the scheme presented in Fig. 2. The concentration and organic matter content of suspended particulate matter (SPM) will provide necessary insight into trophic status of the stations, whilst their stable isotope ratios (carbon and nitrogen) together with phytopigment concentrations will help track changes and blooms of primary producers. Similarly, the isotope ratios and pigment concentrations of surface sediment is analysed to follow organic matter transfer to the sediment (benthic-pelagic coupling). The amount of incoming organic matter channelled into benthic fauna will be traced through quantification of the biomass, standing stock and nitrogen and carbon isotope signatures of major benthic components (micro-, meio- and macro-fauna). Bulk remineralization of organic matter is followed by monthly sediment oxygen consumption (SOC) measurements

    SurfacewaterSurfacewater Pigments (UG + ULB)Pigments (UG + ULB)Pigments (UG + ULB)Pigments (UG + ULB)

    Nutrients (UG)Nutrients (UG)Nutrients (UG)Nutrients (UG)

    DOC (UG)DOC (UG)DOC (UG)DOC (UG) Phytoplankton (ULB)Phytoplankton (ULB)Phytoplankton (ULB)Phytoplankton (ULB)


    Stable isotopes (NIOO-CEME)Stable isotopes (NIOO-CEME)Stable isotopes (NIOO-CEME)Stable isotopes (NIOO-CEME)


    Meiobenthos (UG + NIOO-CEME)Meiobenthos (UG + NIOO-CEME)Meiobenthos (UG + NIOO-CEME)SedimentSediment Pigments (UG)Pigments (UG)Pigments (UG)

     C/N (UG)C/N (UG)C/N (UG)

     Macrobenthos (UG)Macrobenthos (UG)Macrobenthos (UG)Bacteria: diversity (UG)Bacteria: diversity (UG)Bacteria: diversity (UG)


    Stable isotopes (NIOO-CEME)Stable isotopes (NIOO-CEME)Stable isotopes (NIOO-CEME)Slurry incubationsSlurry incubationsSlurry incubations

    Figure 2 General sampling scheme 2

Preliminary results

    The sampling campaigns, initiated in September 2002, have been very successful and analyses on the way. Here we present some preliminary data obtained in November 2002 during a cruise with the RV Zeeleeuw.

    Sediment oxygen consumption (SOC) is a good indicator of total benthic activity and in accordance with the hypothesis, station 115 bis is characterized by higher metabolic activity. SOC at station 115 bis is more that twice that found at the “open” sea station

    (Fig. 3), reflecting a larger input of reactive organic matter to the former station.

     Sediment Oxygen Consumption


    .day15 -2



    0mmol O 115 bis330


    Figure 3: Sediment Oxygen Consumption at Station 115 bis and Station 330 (data from November 2002)

    Similarly, surficial sediment bacterial biomass was also significantly higher at station 115 bis compared to station 330 (Fig. 4). Trends in SOC and bacterial biomass highlight the large differences in trophic status of the target locations.

     Bacterial Biomass (0-1 cm)





    0 115 bis330


     3 Figure 4. Bacterial biomass at Station 115bis and Station 330

    (data from November 2002)

    These measurements confirm the already observed differences between both locations during the spring phytoplankton bloom in 1999 (Steyaert et al. subm., Vanaverbeke et al. in prep). Using chl a concentrations in the sediment as a proxy for the labile organic matter pool in the sediment (Boon & Duineveld 1998), it became clear that the amount of mineralisable organic matter at Station 115bis was considerably higher. This results in a higher bacterial biomass as observed in the November measurements of 2002.


    Evolution, foraging behaviour and reproductive output of coastal breeders at Zeebrugge

Eric.W.M. Stienen & Jeroen van Wayenberge

Institute of Nature Conservation

    The creation of new land in the outer harbour of Zeebrugge in 1985 attracted large number of coastal breeding birds. Each species shows its own specific evolution in breeding numbers since the creation of new suitable nesting habitat. As a pioneer species the population of Little Tern initially increased up to a maximum of 425 pairs in 1997. Because of habitat loss and succession of the vegetation numbers decreased afterwards. The Common Tern population shows a gradual increase up to 2446 pairs in 2002, while the number of Sandwich Terns strongly fluctuated. The latter species shows peaks in occurrence in 1993 and 2000. The reasons for these strong fluctuations are not clear. All three species of gulls (Black-headed Gull, Herring Gull and Lesser Black-backed Gull) show a strong increase up to 2001. The Lesser Black-backed Gull further increased in 2002, but the number of Black-headed and Herring Gull slightly decreased, probably because of competition for nesting habitat with Lesser Black-backed Gull. For all species the outer harbour of Zeebrugge is by far the most important site within Flanders. Also at the international level, the numbers of Little Tern, Common Tern, Sandwich Tern and Lesser Black-backed Gull are extremely important (1.9% - 3.9% of the total geographical population!). European law protects all the three tern species because their populations are vulnerable for extinction. So, the Zeebrugge harbour has a unique and internationally important ornithological value, but unfortunately this is not translated into any protection of the breeding sites at the national level.

    Being highly specialised piscivorous birds, terns are often used as bio-indicators for example to predict the abundance of specific species of fish or the presence of toxicants in the coastal marine environment. To serve as bio-indicator one must, however, know precisely how fluctuations in the marine environment translate into changes in the


    biology of the investigated species. This requires the monitoring of a range of parameters for several years. For this reason the reproductive output of Common Terns at Zeebrugge is monitored since 1997 by enclosing a part of the colony with chicken wire to prevent the chicks to walk away from the study site. Up to and including 2001 clutch size (i.e. the average number of eggs per nest), hatching success (i.e. the proportion of eggs that actually hatched) and fledging success (i.e. the proportion of hatched eggs that actually fledge) of the Zeebrugge Common Terns was high. This resulted in a high reproductive output averaging 1.2 fledglings/pair during the period 1997-2001. Such output is by far sufficient to maintain a stable population and is high when compared to foreign colonies. The high reproductive success suggests a high availability of food at Zeebrugge. Surprisingly in 2002 none of the parents were able to fledge a chick. Clutch size and hatching success in 2002 were comparable to those in earlier years, but chick mortality was exceptional high. Data on food composition, food intake rate and growth of the chicks were gathered, but were not yet analysed. However, we got the impression that a combination of food shortage during the chick rearing period and high predation rates by Herring and Lesser Black-backed Gull caused the failure of the 2002-breeding season. Poor breeding success was also recorded in nearby colonies in the Dutch Delta area, suggesting a lack of clupeids in the entire southern North Sea. After all, clupeids are the major food source for Common Tern chicks.

    Earlier research on terns in The Netherlands suggests that foraging trip duration (i.e. the time it takes a parent from leaving the colony until it returns with a fish) is a good indicator for the amount food available to the terns. In 2001 and 2002 foraging trip duration was measured at the Zeebrugge Sandwich Tern colony. It appears that the time a parent is absent from the nest is positively related to the size of the prey it brings back to colony (Fig. 1). Compared to Europe‚Äüs largest colony, which is established at the isle of

    Griend in The Netherlands, it took parents at Zeebrugge less time to return with a fish. At Zeebrugge in particular small clupeids were brought to nest in a relatively short time. Even compared to a colony at Hirsholm (Denmark) where the availability of clupeids appeared to be very high, foraging trip duration of small clupeids was even shorter at Zeebrugge. In other words: at Zeebrugge there seems to be a superabundance of small


    clupeids. There were no large differences in foraging trip duration between 2001 and 2002, suggesting that the availability of clupeids did not decline in 2002. This seems to be in contradiction with our above conclusions that for Common Terns the availability of clupeids has drastically decreased in 2002. There is, however, a major difference in the timing of breeding season between Common and Sandwich Terns, which can explain this seemingly contrast. The latter species hatches most chicks during the last week of May, while most Common Tern chicks hatch around the second half of June.


    Griend (NL)

    100Zeebrugge (B)

    Hirsholm (DK)75



    0Foraging Trip Duration (min)01234

    Prey Length (BL)

    Figure 1 Foraging trip duration in relation to the length of the clupeids brought to Sandwich Tern

    chicks at Griend, Hirsholm and Zeebruge

    Although we have no evidence for this, it seems that in 2002 the population of small clupeids collapsed somewhere in June when Sandwich Tern chicks did no longer depend on these small prey. On the other hand, Common Tern chicks heavily depend on small clupeids from hatching until fledging. In the next period we will further analyse data gathered in 2002 on chick growth will be linked to the rate of food transport to the chicks. During the coming breeding season also new data will be collected. This will lead to a better understanding of the local food situation and fluctuations therein.


Peer reviewed publications:

    Stienen, E.W.M. & Brenninkmeijer, A. 2002. Foraging decisions of Sandwich Terns in the presence of kleptoparasitising gulls. Auk 119: 473-486.

Stienen, E.W.M., van Waeyenberge, J, Vercruijsse, H.J.P. 2002. Zilvermeeuw Larus

    argentatus en Kleine Mantelmeeuw Larus fuscus als broedvogels in Vlaanderen.

    Natuur.Oriolus 68: 104-110.

    Van Waeyenberge, J, Stienen, E.W.M., Vercruijsse, H.J.P. 2002. Kleurringproject van Zilvermeeuw Larus argentatus en Kleine Mantelmeeuw Larus fuscus aan de Belgische

    kust: overzicht van algemene resultaten. Natuur.Oriolus 68: 146-156.

Vercruijsse, H.J.P., Stienen, E.W.M., van Waeyenberge, J, 2002. Geelpootmeeuw Larus

    michahellis als nieuwe broedvogel in België. Natuur.Oriolus 68: 120-122.

    Vercruijsse, H.J.P., Stienen, E.W.M., van Waeyenberge, J, 2003. First pure pairs of Yellow-legged Gull Larus [cachinnans] michahellis along the North Sea coasts. Atlantic

    Seabirds 4: 127-129.


Life History and dispersal of selected key species

    11 Filip Volckaert , Thomas Remerie?, Bart Hellemans & Christophe


1 Catholic University of Leuven, Laboratory of Aquatic Ecology

    ? Ghent University, Biology Department, Marine Biology Section


    Although the North Sea is a relatively small basin, its hydrodynamical range varies from fully mixed to stratified, with tidal regimes up to 6 m. Tidally induced currents and wind stress generate a complex pattern of local currents. Marine invertebrates and fish, inhabiting this environment, are characterized by a high potential for dispersal. However, the realized dispersal depends on how they behaviourally deal with the current dynamics they experience. Here we report on how dispersal patterns of a mysid and two fishes, all common inhabitants of the North Sea, are reflected in their life-history and in their genetic variation.

Material and methods


    Specimens of Mesopodopsis slabberi were collected from 5 Northeastern Atlantic

    (Westerschelde, Belgian Continental Shelf, Seine, Mondego, Guadalquivir) and one Mediterranean population (Ebro). Samples from each location were collected with a hand net or a hyperbenthic sledge (mesh size 1 mm). After collection, the samples were stored in ethanol (70 95%) or aceton at 4?C. Ten specimens were analysed from each location. DNA was extracted using a modified CTAB protocol (Kocher et al. 1989). Small aliquots of extracted nucleic acids (1 µl) were used as template for polymerase chain reaction


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