AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS

Aquatic Conser6: Mar. Freshw. Ecosyst. 9: 541–544 (1999)

The conser7ation 7alue of artificial habitats in the marineen7ironment: a case study of the artificial rocky shores of

The Netherlands

WIM J. WOLFF*Department of Marine Biology, Uni6ersity of Groningen, Haren, Netherlands

KEY WORDS: artificial habitats; The Netherlands; rocky shores; North Sea

INTRODUCTION

Man’s impact on the marine environment continues to increase. This is also true for the presence ofartificial structures, illustrated by the abundance of wrecks and all types of waste on the sea bottom.Along the seashore man has changed the coastal habitats through reclamation, harbour construction andurbanization. This trend can be expected to continue into the next millennium. Artificial structures at seaand along the coast often form new types of habitat, thus providing opportunities for numerous speciesof plants and animals, many of which would not otherwise occur in these localities. An example is thenumerous ship wrecks lying on the predominantly mobile, soft sediment seabed of the North Sea. Theprovision of hard substrates in the form of wrecks creates living conditions for hard-bottom organisms;in fact, the only living conditions for these species in this type of area. Hence, many believe that thepresence of wrecks creates a welcome addition to the biodiversity of the North Sea.

There is a rich literature on the creation of artificial reefs for conservation or fisheries purposes. Thispaper, however, will discuss the conservation value of artificial habitats created for other reasons in themarine environment. As a case study I describe the development of artificial rocky shores along the coastof The Netherlands, giving a short description of their flora and fauna and, finally, focusing on theconservation value of this new habitat. Do such habitats have any conservation value and, if so, does thisvalue warrant conservation measures? This discussion might pave the way for a closer examination ofother artificial structures at sea and along the coast, in order to determine whether conservation measuresshould also apply to other artificial habitats.

ARTIFICIAL ROCKY SHORES ALONG THE COAST OF THE NETHERLANDS

Originally the coast of The Netherlands consisted of sand, mud and peat, with stones and boulders,imported by the Pleistocene Ice Age glaciers, occasionally being found in the northern part of the country.Especially in the south, no suitable habitat existed for sessile rocky shore species, although some of thesespecies are able to live on submerged peat or wood.

* Correspondence to: Department of Marine Biology, University of Groningen, PO Box 14, 9750 AA Haren, Netherlands.

CCC 1052–7613/99/060541–04$17.50Copyright © 1999 John Wiley & Sons, Ltd.

Received 7 May 1999Accepted 5 August 1999

W.J. WOLFF542

Probably at about the end of the first millennium the Flemish, Dutch and Frisians discovered the artof land reclamation through building dikes around saltmarshes (Van Veen, 1962; Wolff, 1992). Thus,embanked saltmarsh islands originated in the coastal landscape. Originally, the seawall was constructedwell away from the margin of the saltmarsh. However, at that time the estuaries and tidal channels maybe assumed to have frequently changed their position and more than likely it was not very long before thefirst tidal channel approached a dike. Undoubtedly, this meant disaster in many cases. However, in theMiddle Ages stone had already been discovered to be a means of protecting the eroding dikes. In the 16thcentury, magistrates from the Zeeland area in south-west Netherlands frequently travelled to Vilvoorde,Belgium, to order stones from the local quarries for dike protection (Dekker, 1971). These stones wereused to construct groynes or were dumped at the eroding side of the channel. This practice continuestoday.

Originally, stones were mainly used subtidally. However, in 1827 Vilvordian limestone was used for thefirst time to construct revetments on the intertidal slope of the seawall (Wilderom, 1964). In 1858, basaltfrom German quarries was used for the same purpose (Wilderom, 1964). This use of stone rapidlyincreased. Concrete was used intertidally for the first time in 1905. Until the 1950s, the types ofreinforcement used proved to be suitable for colonization by marine flora and fauna. In 1954, however,bitumen was used for the first time and then in 1961 copper slag was introduced as a dike-protectionmaterial (Wilderom, 1964). Later, other types of toxic slag were also used until this practice wasterminated for environmental reasons. Wilderom (1973) summarizes the amount of stone used until about1970. At that time in the Dutch province of Zeeland 6236000 tons of stones had been dumped in orderto protect the dikes against subtidal erosion. This amount covered 6.8 km2 of seabed. In the sameprovince, 4.6 km2 of intertidal dike slopes had been covered by stone revetments. Thus, more than 300 kmof coastline were covered to some degree with stones.

In addition, elsewhere in The Netherlands stones have been used to protect and reinforce seawalls. Inthe northern part of the country, this occurred especially in the vicinity of Den Helder, near Harlingen andon the islands of Texel and Terschelling. Smaller areas of stone-covered seawalls occur at several otherplaces.

FLORA AND FAUNA OF THE ARTIFICIAL ROCKY SHORES OF THE NETHERLANDS

Many species of plants and animals detached in some way from the natural rocky shores of the Channelare transported to the Dutch coast by water movements in the Channel and in the North Sea. IJzerman(1937) identified rock fragments attached to algae washed ashore in The Netherlands as originating fromNormandy and southern England. Den Hartog (1959) lists 57 plant and animal species washed ashore onDutch beaches which have never been found as indigenous organisms in Dutch coastal waters and whichmay be deduced to have arrived from the Channel coasts. Some of these species, e.g. the brown algaHimanthalia elongata, are frequently encountered on Dutch beaches. Den Hartog (1959) also records sevenspecies which are likely to have arrived from the shores of the northern North Sea. Another four speciesare believed to have arrived from the central Atlantic or even the West Indies. Thus, apparently there isa continuous immigration of ‘foreign’ algae and animals into the coastal waters of The Netherlands.

Both Den Hartog (1959) and Stegenga and Prud’homme van Reine (1999) point out that thiscontinuous import of ‘foreign’ organisms results in the colonization of Dutch shores by new species. Thus,the number of marine algal species in The Netherlands shows a steady increase from 106 species at thebeginning of this century to 229 species in 1998 (Stegenga and Prud’homme van Reine, 1999). Of course,part of these new species numbers are the result of taxonomic revisions and more detailed field work, butthese authors also make clear that there are numerous examples of new species for which the colonizationprocess can be followed.

Copyright © 1999 John Wiley & Sons, Ltd. Aquatic Conser6: Mar. Freshw. Ecosyst. 9: 541–544 (1999)

THE CONSERVATION VALUE OF ARTIFICIAL HABITATS 543

Den Hartog (1959) and Nienhuis (1980) describe the algal vegetation of the Dutch ‘rocky shores’. DenHartog (1959) lists about 100 species occurring in 33 floristic communities. Nienhuis (1980) lists about 200epilithic species but includes microalgae and estuarine freshwater species. De Kluijver (1989, 1997) andLeewis and Waardenburg (1989) describe the sublittoral hard-bottom communities of plants and animalsin the south-west Netherlands. Together, these authors make clear that the Dutch coast nowadaysharbours a rocky shore community characteristic for localities sheltered from wave-action, althoughcompared with the natural rocky shores of the Channel and elsewhere in Europe the Dutch communitiesmight seem impoverished.

CONSERVATION VALUE OF ARTIFICIAL ROCKY SHORES IN THE NETHERLANDS

Boddeke (1957), Smits (1957), Den Hartog (1971) and Wolff (1974) drew attention to the conservationvalue of the artificial rocky shores of the Dutch coast. Before that time, several professional and amateurbiologists were aware of these interesting communities, but apparently they never realized thatconservation work was necessary for their preservation. But during the 1970s the presence of an artificialrocky shore community was one of the arguments used to prevent the closure of the Oosterschelde estuary(Wolff, 1992, 1997).

However, once it had been decided not to close the Oosterschelde estuary, measures had to be taken toreinforce the existing seawalls. Unfortunately, the execution of these measures, such as the reinforcementof the stone revetments by bitumen, proved to be a negative factor for the further development of therocky shore communities (Leewis et al., 1989).

Nevertheless, when in 1990 the Dutch Government decided to protect the Oosterschelde estuary as astatutory nature reserve, the presence of ‘artificial rocky shore communities’ provided one of thearguments to do so. However, did this result in a policy to preserve and to further the richness of thesecommunities? In general, the answer is no. It is true that for environmental reasons the use of toxic copperand phosphorus slags for dike protection was ceased and this no doubt had a positive effect on the furtherdevelopment of these communities (Leewis et al., 1989). It is also true that for educational purposes a‘dike garden’ was created to demonstrate the variety of organisms, especially macroalgae, on the stonerevetments of the dikes. But, on the other hand, in 1992 a special issue of the Dutch conservationmagazine De Le6ende Natuur (93, 129–170), which is devoted to the conservation of the estuaries of thesouth-west Netherlands, did not even mention these artificial rocky shores.

DISCUSSION

I have shown that in Dutch coastal waters a previously lacking ‘rocky shore community’ was able todevelop thanks to the provision of hard substrate through coastal protection measures. On land, humanactivities have also resulted in the creation of new habitats, colonized by new communities of plants andanimals. Examples within the territory of The Netherlands are heath lands, species-rich meadows and theflora of stone and brick walls. In all cases such communities have been preserved in nature reserves orhave been the subject of special conservation measures by both the Dutch government and privateconservation organizations. Hence, it is remarkable that Dutch rocky shore communities have beenlargely overlooked by the conservation organizations. So far, no effective preservation policy has beendeveloped for this type of habitat.

But is the Dutch ‘rocky shore’ really eligible for conservation measures? I believe that there are at leasttwo reasons for an affirmative answer. First, these ‘rocky shores’ probably have the highest biodiversityof all coastal habitats in The Netherlands. Second, they are found in an area where until recently hard

Copyright © 1999 John Wiley & Sons, Ltd. Aquatic Conser6: Mar. Freshw. Ecosyst. 9: 541–544 (1999)

W.J. WOLFF544

substrates were almost absent. The nearest natural rocky shores occur in France and England along thecoasts of the Channel and at Helgoland in Germany.

I believe that the case of the Dutch ‘rocky shores’ shows the general neglect of the aquatic conservationcommunity for artificial habitats created for non-conservation purposes. Such an attitude may bewarranted in countries and regions with a large share of natural habitats, but in those areas where naturalmarine habitats have been modified to a large extent (e.g. Netherlands, Belgium, Hong Kong) artificialreplacements gain in value. This does not only apply to rocky shore habitats. For example, in TheNetherlands nearly all brackish lagoons are man made or at least heavily influenced by human activities.

I expect that, as a result of increasing human activities in the marine realm, artificial structures willbecome increasingly common in the marine environment. I suggest that in all cases the conservation valueof such structures should be investigated and that in relevant cases appropriate conservation measuresshould be taken.

This recommendation is not directed at the restoration of degraded existing habitats or at the creationof new artificial habitats for environmental reasons. In the former case, the conservation value usuallyforms the rationale for restoration. In the latter case, however, I seriously doubt whether a net gain ofconservation value can be demonstrated if all aspects are taken into account.

REFERENCES

Boddeke, D. 1957. ‘De zeewieren en het Deltaplan’ (Seaweeds and the Delta plan), Amoeba, 33, 127–130.Dekker, C. 1971. Zuid-Be6eland. De historische geografie en de instellingen 6an een Zeeuws eiland in de Middeleeuwen

(Zuid-Beveland. The historical geography and the institutions of a Zeeland island in the Middle Ages), VanGorcum, Assen.

De Kluijver, M.J. 1989. ‘Sublittoral hard substrate communities of the southern Delta area, SW Netherlands’,Bijdragen tot de Dierkunde, 59, 141–168.

De Kluijver, M.J. 1997. Sublittoral communities of North Sea hard substrata, PhD Thesis, University of Amsterdam,Amsterdam.

Den Hartog, C. 1959. ‘The epilithic algal communities occurring along the coast of The Netherlands’, Wentia, 1,1–241.

Den Hartog, C. 1971. ‘De natuurwetenschappelijke betekenis van het Oosterscheldegebied’ (The scientific significanceof the Oosterschelde area), Waddenbulletin, 6, 6–10.

IJzerman, R. 1937. ‘Transporteerend zeewier’, De Le6ende Natuur, 42, 149–150.Leewis, R.J. and Waardenburg, H.W. 1989. ‘The flora and fauna of the sublittoral part of the artificial rocky shores

in the south-west Netherlands’, Progress in Underwater Science, 14, 109–122.Leewis, R.J., Waardenburg H.W. and Meijer, A.J.M. 1989. ‘Active management of an artificial rocky coast’,

Hydrobiological Bulletin (Amsterdam), 23, 91–99.Nienhuis, P.H. 1980. ‘The epilithic algal vegetation of the SW Netherlands’, No6a Hedwigia, 33, 1–93.Smits, H. 1957. ‘Deltaproblemen rond de verandering van de dierenwereld in het water’ (Delta problems and the

change of the aquatic fauna), Amoeba, 33, 133–145.Stegenga, H. and Prud’homme van Reine, W.F. 1999. ‘Changes in the seaweed flora of The Netherlands’, in Scott,

G.W. and Tittley, J. (Eds), Changes in the marine flora of the North Sea, CERCI, University College Scarborough,77–87.

Van Veen, J. 1962. Dredge, Drain, Reclaim. The Art of a Nation, Martinus Nijhoff, The Hague.Wilderom, M.H. 1964. Tussen Afsluitdammen en Deltadijken. II. Noord-Zeeland (Schouwen-Dui6eland, Tholen en St.

Philipsland) (Between Closing Dams and Delta Dikes II. Noord-Zeeland), Wilderom, Vlissingen.Wilderom, M.H. 1973. Tussen Afsluitdammen en Deltadijken. IV. Zeeuwsch Vlaanderen (Between Closing Dams and

Delta Dikes IV. Zeeuwsch-Vlaanderen), Wilderom, Vlissingen.Wolff, W.J. 1974. ‘De Oosterschelde in de Delta’ (The Oosterschelde estuary in the Delta), in Abrahamse, J. and

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Ambio, 21, 287–291.Wolff, W.J. 1997. ‘Development of the conservation of Dutch coastal waters’, Aquatic Conser6ation: Marine and

Freshwater Ecosystems, 7, 165–177.

Copyright © 1999 John Wiley & Sons, Ltd. Aquatic Conser6: Mar. Freshw. Ecosyst. 9: 541–544 (1999)