MACROBEL
Long term trends in the macrobenthos of the Belgian Continental Shelf
Introduction Methods Taxonomy Distribution Project info Atlas

MACROBEL project goals and database

The general aim of this research project is to deliver a substantial contribution to the knowledge of the long-term variability within the biodiversity and density patterns of the macrobenthos and its relation to anthropogenic activities.

In detail:

  • Spatial distribution and long-term variation (on a large scale) of the macrobenthos
    • Making of a distribution atlas of the macrobenthos on the BCS for the periods 1977-1986 and 1994-2001 (by collating already existing data with newly gathered ones)
    • Evaluation of long-term variation of the macrobenthos on the BCS (1977-1986 versus 1994-2001)
    • Evaluation of the different influences on macrobenthos, caused by anthropogenic activities
  • Detailed long-term variation of the macrobenthos on the BCS
    • Detailed study of the long-term variation of the macrobenthos on the BCS in 4 stations stressed by anthropogenic activities
    • Detailed evaluation of the influences of a selection of anthropogenic activities on macrobenthos of the BCS (study on causal connections)

MACROBEL

The database is derived from an existing relational Access database MACRODAT (developed by Drs. Tim Deprez, SMB), which combines taxonomy, geography, and biotic and abiotic data. MACROBEL will contain a full compilation of all available macrobenthos data of the BCS from the periods 1976-1986 en 1994-2001 and will be hosted by VLIZ (Flanders Marine Institute).

Quality control identifications

Overview of used identification manuals:
Polychaeta:Hartmann-Schrder (1996). Die Tierwelt Deutschlands: Annelida, Borsten wrmer, Polychaeta, Teil 58. IMIS
Amphipoda:Roger J. Lincoln (1979). British Marine Amphipoda: Gammaridae. IMIS
Cumacea:N.S. Jones (1976). British Cumaceans. IMIS
Brachyura:J.P.H.M. Adema (1991). Krabben van Nederland en Belgi. IMIS
Pycnogonida:P.E. King (1974). British Seaspiders. IMIS
Isopoda:E. Naylor (1972). British Marine Isopods. IMIS
Bivalvia:Norman Tebble (1976). British Bivalve Seashells. IMIS
R.H. de Bruyne (1994). Schelpen van de Nederlandse kust. IMIS
Decapoda:G. Smaldon (1979). British coastal shrimps and prawns (Caridea). IMIS
P.J. Hayward & J.S. Ryland (1996). General Handbook of the Marine Fauna of North-West Europe. IMIS

Sampling methodology (period 1976-1986)

ScientistVan Veen(m)Volume sample (l)Immediately fixedFixation (% formalin)ReplicatesSieve mesh size mGutterSediment # sieves
Vanosmael, C. (1977)0.1026min. 5Yes7387019
Van Steen, E. (1978)0.1026min. 5Yes73870Yes17
Rapp, G. (1978)0.1026min. 5Yes7387017-18-19
Kerckhof, F. (1980)0.1026min. 5Yes73-287015
Meheus, L. (1981)0.1026min. 5Yes73250Yes9
De Rycke, R. (1982)0.1026min. 5Yes73870Yes9
Vanosmael, C. (1982)0.1026min. 5Yes73250
Waeterschoot, H. (1984)0.1026min. 5Yes73870Yes8
Brendonck, L. (1985)0.1026min. 5Yes73870Yes15
Wittoeck, J.0.1026min. 5Yes71-31000
(0.12)min. 5Yes71-101000Yes7

Sampling methodology (period 1994-2001)

ScientistVan Veen(m)Volume sample (l)Immediately fixedFixation (% formalin)ReplicatesSieve mesh size mGutterSediment # sieves
Coenjaerts, J. (1997)0.1026min 5cmno711000noCoulter
Philips, F. (1998)
Degraer, S. (1999)0.10265no811000noCoulter
Taverniers, K. (2000)0.12min 5no811000noCoulter
Deneudt, K. (2000)0.1026
Erdey, M. (2000)0.1026no811000noCoulter
Van Hoey, G. (2000)0.1/0.125yes851000noCoulter

General sampling info

Van Veen Grab

All samples were taken with a Van Veen Grab (+/- 50 kg) with a sampling surface of 0.1026 m, or in some cases 0.12 m. This grab enables fast sampling. The variability within replicates corresponds to about 13 %, what gives a difference in depth of 0.7 to 1.2 cm (Lie & Pamatmat, 1965).

Picture: Van Veen Grab - Desmet, G.

Possible disadvantages of the Van Veen grab:

  • Fast moving organisms (e.g. some Brachyura, Mysida) can easily escape from the closing grab. Hence, the number of mobile species that is found in the samples never constitutes the number of species actually present on the sampled site.
  • The maximum penetration depth in the sediment of the Van Veen grab is about 15 cm. This limited depth range biases the sampling of bigger and deeper burrowing macrobenthos species such as Ensis sp., Lanice conchilega, Venerupis senegalensis, etc).
  • On harder substrates (e.g. very fine sands, places with large gravel fraction) the penetration is sometimes limited to the upper centimetres of the sediment. As the catch efficiency is related to the penetration depth of the grab, it is from the utmost importance that with every sample that is taken the penetration depth should be kept to at least 5 cm. The latter corresponds with a minimum sediment volume of 5 l as was assumed in former studies (see sampling methodology).
  • The ideal impact position of the grab just before a sample is taken should be perpendicular to the bottom surface. Strong currents or drifting of the vessel can jeopardise a good sampling. It is therefore advised that in such cases the ship would cast anchor. Nevertheless it is imperative to check the contents of the grab with every sampling and to repeat the sampling when falling short of the mentioned criteria.
  • On every sampling occasion a sediment sample is taken (using a plastic tube or core)
  • The entire contents of the Van Veen grab ends up on a PVC tray with a funnel like opening and is washed into a bucket using seawater. That bucket is then emptied over a 1000 m sieve and rinsed with seawater until only the coarse sediment and the macrobenthos organisms remain. This residue is transferred into a recipient and fixated with a neutralised (with seawater) formalin solution to a concentration of 7-8 %. As noticed in tables 1 and 2 the described technique differs from the one used during the period 1977-1986. In the latter the samples were firstly fixated in the buckets before pored over the 1000 m (or 870 m) sieve. A gutter was often used for a better separation of biota and sediment.

Processing samples

Every sample (already stained with a Bengal Rose or eosin solution) is decanted (10 times) on a 1000 m sieve in order to separate the present fauna from the sediment. With this technique the residue of coarse sediment and fauna is pored into a measuring cup (5 l) and is brought into suspension with a strong jet of water. During this process the smaller and lighter organisms will go into suspension, whereas the heavier sediment and organisms remain on the bottom. The water containing the organisms is there after pored over a 1000 m sieve. All retained fauna is stored in a 4-8 % neutral formalin solution and stained with Bengal-Rose of eosin (if not done earlier). Both solutions colour all organic material. This enables easier sorting of the animals. After decantation the residue is checked for bigger and heavier organisms (e.g. Mollusca, Actinaria). Decantation must not be applied to fine sediment samples (< 1000 m) as all sediment is directly rinsed through the 1 mm sieve and what remains on the sieve can directly be fixated.

Identification

All organisms are counted and identified, if possible to species level. For some animal groups however this is not the case:

  • Nematoda, Nemertinea, Sipunculida, Turbellaria, Actinaria, Oligochaeta and Copepoda are never identified to a higher level because they are not representative for the macrobenthos community. The sampling technique is not suited to quantify these groups neither.
  • The identification of some taxa is still under discussion. Whether they should be identified up to species level or grouped into complexes is still not clear due to uncertain taxonomy (e.g. Phyllodoce maculata of P. mucosa; Harmotho spp.; Bathyporeia spp.; Cirratulidae; Capitellidae).

Sediment analysis

Two standard methods were applied:

  • using sieves with different mesh sizes
    During the period 1976-1986 all sediment analyses were done using at least 7 sieves with different mesh size (see table 1). Approximately 25 g of homogenized substrate was used for grain size analysis of the sand fraction according to Buchanan & Kain (1971). The wet-sieved fraction smaller than 63 m was used as a measure for mud content.
  • using a Coulter LS 100
    From 1994 on all sediment samples were analysed using a Coulter counter. Within the measuring range of 2 m to 850 m the grain sizes are measured. The fraction larger than 850 m is separated and expressed as weighed percentage. The subdivision in sediment fractions follows the Wentworth scale (Buchanan, 1984).

Density

All densities are shown as the number of individuals per square meter (ind/m). Only the anterior parts of the organisms are counted.

Definition macrobenthos

Macrobenthos is considered to be all organisms living in the bottom of the sea and retained on a sieve with a mesh size of 1 mm. These organisms are mainly bristle worms (Polychaeta), bivalves (Mollusca), echinoderms (Echinodermata) and amphipods (Crustacea).