Bijdragen tot de Dierkunde, 59 (3) 141-158 (1989) SPB Academie Publishing bv, The Hague the Delta Sublittoral hard substrate communities of southern area, SW Netherlands M.J. de Kluijver Institute of Taxonomie Zoology, University of Amsterdam, P.O. Box 4766, 1009 AT Amsterdam, The Netherlands; SBNO; P.O. Box 16915, 1001 RK Amsterdam, The Netherlands Keywords: sublittoral, hard substrate, communities, environmentalparameters, Netherlands Abstract Introduction During 1985 and 1986, sublittoral communities on hard sub- Recent pollution and human maritime manipula- strates in the southern Delta SW Netherlands, were inves- area, tions are characteristic for the pressure the marine tigatedat 79 stations. The stations were distributed over 20 local- ecosystem is subjected to in the SW Netherlands. ities situated in the saline Lake Grevelingen, the Oosterschelde Perkins (1974) already mentioned the importance estuary and the SE North Sea. The percentage cover of all sessile of estuaries and coastal waters for commercial fish- organisms were estimated using quadrat sampling techniques; data were processed using cluster analysis. The stations were eries and other types of exploitation of the sea. The characterized by the assessment ofthe most important environ- contributionof hard substrate benthic communities mental parameters: available light, hydrodynamics and sedi- this is be to ecosystem certainly not to underesti- ment characteristics. Eight sublittoral communities on hard sub- mated. Although the total surface of hard substrate strates are described by characteristic and dominant species. is a small fraction of the total sublittoral bot- Three communities are subdivided into variants on account of only in differences in abundance of the dominant species. This quantita- tom surface the Oosterschelde estuary, the hard tive approach leads to reproduceable results. substrate sessile animals stand for 32.7% of the to- tal benthic biomass (Leewis & Waardenburg, in prep.). To use these hard substrate communitiesfor Résumé ecological monitoring, a reproduceable description of both the communities and the environmental En 1985 et 1986, les communautés sublittorales sur substrats parameters must be available. Reproducibility de- durs ont été étudiées dans 79 stations de la partie méridionale de mands some conditions of the investigation. In the la zone du Delta (SO des Pays-Bas). Ces stations ont été choisies first communities place, the must be studied as a dans unevingtaine de localités du lac salé Grevelingen, de l’estu- whole. on marine hard sub- aire d’Oosterschelde, et de la partie SE de la Mer du Nord. Le Many investigations de les sessiles été estimé utili- strate communities deal with taxo- pourcentage tous organismes a par only a particular sation de techniques d’échantillonnagesur surfaces carrées; les nomie group, for example algae (Den Hartog, données ont été traitées par “cluster analysis”. Les stations sont 1959; Nienhuis, 1980; Coppejans, 1980), sponges caractérisées par évaluation des paramètres les plus importants (Pansini et al., 1977), Polychaeta (Bianchi & Morri, du milieu: lumière accessible, hydrodynamique, particularités and Octocorallia du sédiment. Huit communautés sublittorales sur substrats durs 1985) (Weinberg, 1978b). Second, sont décrites en termes d’espèces caractéristiques et dominantes. the data must be quantified as much as possible. Pour trois de ces communautés on reconnaît des variantes, Studies on sublittoral hard substrate communities compte tenu de différences dans l’abondance des espèces as a whole are often qualitative (Stephenson & dominantes. Cette approche quantitativeaboutit à des résultats Stephenson, 1972; Hiscock & Hiscock, 1980; Kön- reproductibles. necker & Keegan, 1983). The main benefit of quan- Downloaded from Brill.com10/09/2021 05:47:16AM via free access - 142 M.J. de Kluijver Hard substrate communities ed. Although intended to be closed off too, it was decided later, owing to theefforts of environmental hinterland pressure groups, to protect the by a with that storm surge barrier open floodgates, can be closed with steel slides during extreme spring tides and bad weather conditions (Leemans & been Geers, 1983). The artificial opening has re- 2 stricted to m The natural opening of the 14,000 . 2 mouth of the amounted to 80,000 m estuary , which caused tidal of 3.7 in the a range m eastern tidal of 2.75 after part. To ensure a range m com- pletion (October 1986) of the storm surge barrier, two compartmentalisation-dams were constructed (Oesterdam, October 1986, and Philipsdam, April tidal is 1987). The surface area of the region 2 2 reduced from 400 km to 310 km implying a , 6 3 reduction of the volume from 1230.10 m to 6 3 820.10 m This caused a reduction of the stream . to in the other environ- 1. velocity leading changes Fig. Map of the study area with dates of the main closure works of the “Delta Plan”. mental parameters (sediment load, submarine day- light and salinity). this the results are of the titative studies is, that it becomes possible to In paper presented study of of the of the Oosterschelde describe communities by means characteristic original communities tideless Lake species (common species, but restricted to just one estuary, the communities of the community) and dominant species (occurring in Grevelingen, and the coastal communities of the dikes in the southern Delta more communities, but abundant in just a few com- neighbouring North Sea munities). Examples of quantitative studies on ma- area. The environmentalparameters are quantified much In rine hard substrate communitiesare: Gislen (1930), as as possible. forthcoming papers changes Van Soest & Weinberg (1981), Kaandorp (1986), De in species composition and community structures, environmental Kluijver (1986), De Kluijver et al. (in prep.) and caused by changes in the parame- Leewis & Waardenburg (in prep.). ters, will be discussed. Although all hard substrate in the Netherlands is artificial, the southern Delta area is suitable for the study of the structure of sublittoral communitiesin Materials and methods this relation to the environmental parameters. In is availabe the of 1985 and 1986 79 stations 20 area a diverse scale of differenthabitats During years at (Anonymous, 1982). After the disastrous inunda- localities were investigated along the dikes of the tions of 1953 it was decided to close off the main es- southern Delta area (fig. 2). Not only the sublittoral communities but tuaries (Delta Plan). The situation and dates of the hard substrate were quantified, also the environmental main closure works are shown in fig. 1. In 1971 the most important parameters. tide- Grevelingen estuary was closedand became a 2 less salt water lake with a water area of 108 km . Sampling Morphometrical, hydrochemical and hydrophysi- The communities were sampled using the "In- cal Estimate" data of this lake are enumerated by Bannink et dividual Counting and Cover (ICCE) al. (1984). To the south, in the Oosterschelde estu- method described by Weinberg (1981). The percent- of the vertical of all sessile ary the original (uninfluenced) structure of sublit- ages cover projection communitiesof the of 32 x toral estuaries can be investigat- organisms were estimated, using a quadrat Downloaded from Brill.com10/09/2021 05:47:16AM via free access Bijdragen tot de Dierkunde, 59 (3) - 1989 143 the Fig. 3. Bray-Curtis coefficient (SI) as a function of sampled surface (A) for Station 34 (Ouddorp-9.0 m depth). Fig. 2. Map of the study area showing the localities. 32 cm. In order to obtain comparable data the or- ganisms were not counted, but only percentages cover were estimated. Underwater it was not possi- ble to quantify the different species of tubicolous organisms. These species belong to differenttaxaof 4. Crustacea (Amphipoda) and Polychaeta (Terebelli- Fig. Bray-Curtis coefficient (SI) as a function of the sampled surface (A) for Station 36 (Schelphoek — 10.5 m depth). dae and Spionidae). In the results these species are of taken together. Because thepoor visibility of the 2 water, vagile organisms were not included. In both (10.2 dm ). In fig. 4 the curve for Station 36, is shown. The years and during differentseasons, the same locali- Schelphoek, depth 10.5 m (n = 21), level is reached within ties were sampled. 0.70 similarity 3 quadrats 2 (30.7 dm ). Fig. 5 shows the curve for Station 40, Minimal area Wemeldinge, depth 8.0 m (n =23). Again the 0.70 In order to take a representative sample, usually 3 level is reached within 1 quadrat. In the southern station. to 4 quadrats were sampled at each The Delta area the mosaic distribution of the compo- minimal determined for different of the communities be area was 3 com- nents appears to very munities (De Kluijver, 1986), using the program homogeneous compared to the sublittoral commu- MINAR (Kaandorp, 1986) with logarithmically nities of the Atlantic coasts, where a minimal area of dm2 found in transformed data. In fig. 3 the curve for Station 34, 150 was (De Kluijver et al., prep.). Ouddorp, depth 9.0 m (number of species, n = 27), is shown. Weinberg (1978a) suggested a similarity Environmentalparameters level of 0.70 at which the minimal area is reached. In a diverse area as the southern Delta area, with a This level is reached at this station within 1 quadrat saline lake, an estuary and the open North Sea, it Downloaded from Brill.com10/09/2021 05:47:16AM via free access - 144 M.J. de Kluijver Hard substrate communities of classes sediment one 6 (-: no available, with sedi- + + + + : all bare substrate covered sediment ment). In order to get the characteristics all locali- the top cm layer was investigated at nearly ties. The sediment samples were sieved through 6 graded sieves (2.9—0.09 mm). The sediment char- contri- acteristics are expressed as the proportional bution of the dry weight of the different sieved fractions. The contribution of the various frac- the tions were analyzed using computer programs CLUSTAN1C2 (Wishart, 1978) and SRTORD (Kaandorp, 1986; in prep.).