Reef Balls in the Baltic Sea
The private company MariLim created the first artificial reef in the Baltic Sea, consisting of
Reef Balls on the 15th of June 2001. Reef Balls are half-round reef-modules having a central
cavity with several openings. They were made out of marine friendly concrete with a pHvalue
similar to seawater. Hereby a rapid settlement of organisms is possible.
The balls were deployed in an area off the Holtenau bathing facility (Kiel).
Four groups of Reef Balls were manufactured, which differ in concrete mixture and surface
texture to determine the most suitable mixture. All in all 12 Reef Balls were deployed. In a
first step each of them was lifted into shallow water by crane. After that the structures were
draged by boat to the desired area. Subsequently, the deployment was done randomly. A diver
was present all the time coordinating the work.
It is the aim of this study to monitor the speed of settlement and to determine the diversity of
the algal and animal community living on or associated to the balls. On the 4th of July 2001
the first samples of the surface community were taken by a diver. From each ball an area of
10 by 10 cm was sucked off using an underwater sucktion device. The remaining residue was
conserved for subsequent laboratory analysis. Additionally, samples for the determination of
the benthic microorganisms were taken. This kind of sampling will be continued on a two
weeks basis to get infromation about the succession of species. In order to incorporate larger
species in this study scuba census is performed regularly on each ball.
Figure 1: Only days after the deployment the settlement started.
The four different groups of Reef Balls will be tested statistically for differences in quality
and quantity.
Only a week after the deployment a check dive revealed that settlemet of the outer surface
had already begun. A macrophytic green algae of the genus Enteromorpha sp. and a sessile
polychaete worm (Polydora sp.) were found. The beach crab carcinus maenas was also very
present in the inner cavities of the structures.
Figure 2: Strong occurance of Enteromorpha sp. two weeks after deployment.
After three weeks the surface was colonised by a variety of invertebrate animals. Juvenile
Black mussles (Mytilus edulis) and barnackles (Balanus improvisus) occupies wide areas. The
carnivorous starfish Asterias rubens live in densities exceeding 100 individuals per ball.
The reef was also accepted by various fish species. The recorded species contain several
species of the genus gobiidae. Frequently, individuals were observed feedind on the reef
strucutres. Also “Sea skorpions” (Myoxocephalus scorpius) were found frequently in the
central cavity of the balls. Beeing acitve mainly during the night, this species might use the
reef as a resting area during the day.
Figure 3: Occupation of the whole surface area by a diverse algal and animal community four weeks after deployment.
The inner cavity of the balls is also occupied by sea squirds (Ciona intestinalis). These filter
feeders may find suitable current conditions here.
In the near future a further increase of species number and diversity is....
