Description: Die Beobachtung von Barnea-Populationen auf den Schwebesubstraten (verankerte Unterwasserversuchsplattformen) und vor Boknis Eck (Kieler Bucht) erbrachte, daß isolierte Substratflächen von frei schwimmenden Barnea-Larven besiedelt werden, die Bohrmuschel bei geeignetem Substrat auch in größeren Tiefen zu finden ist und auch dort gutes Wachstum zeigt (durchschnittlich 54,2 mm/30 Monate im Experiment). Bei einer Siedlungsdichte von 162 Exempl./m2 ergibt sich auf den Schwebesubstraten in 19 m Wassertiefe ein Flächenabtrag von 5,2 mm/m2/30 Monate. Aufgrund der weit größeren lndividuenzahl im Flachwasser dürfte der Betrag dort um das 3-6fache höher liegen. Ihr Vorkommen scheint in der Ostsee an besondere Küstenformen gebunden zu sein (Kliff mit submariner Abrasionsplattform mit freiliegendem Geschiebemergel oder Ton). Observations of Barnea populations on submerged substrate platforms and off Boknis Eck (Kiel Bight) showed that isolated substrate patches are colonized by free swimming Barnea larvae. This boring clam is also found in deeper regions when suitable substrate is available, and it also shows good growth (mean 54,2 mm/30 months under experimental conditions). There is an abrasion of 5.2 mm2 30 months on the 19 m depth substrate platforms accompanied by a density of 162 individuals/m2. Due to a far denser population in shallower water the abrasion might be 3-6 times larger than in 19 m depth. In the Baltic the occurrence of Barnea candida seems to be linked to certain features of the coast (cliffs with free patches of till or clay on their submarine abrasion platforms).

Description: In the scope of our investigations on the basic processes in a soft-bottom macrobenthos community, as a preliminary test, a series of five 1 m2 metal boxes filled with sterilized sediment from the surrounding habitat was exposed in an enclosed area in the western Kiel Bight at a depth of 20 m from September 1972 until July 1975. The establishment and succession of the soft bottom association in the boxes was followed and compared to the association on the surrounding sea floor by monthly to bimonthly sampling by the diving group of SFB 95. While the number of species increases continuously until a final level of about 20 per 0.1 m2 is reached in January 1974, the values of total biomass (the starfish excluded) fluctuate seasonally being high in autumn and early winter and low in March and April. In a late experimental stage in January 1975, before or just in the beginning period of the regression of the bivalve populations, the association in the boxes (80g wet wt./m2) has only reached 50% of the biomass of the assemblage outside where large long-lived and slowly growing bivalve species contribute 75% of macrobenthos weight. The data of total specimen number fluctuate widely due to oxygen deficiency in late 1973 followed by a high colonization activity by opportunistic spionid species immediately after. According to the dominance in specimen numbers of the major taxononomic groups, three phases can be distinguisted: crustacea (mainly Diastylis rathkei) - sedentary polychaetes (spionids, Pectinaria koreni) - bivalves (Abra alba) together with errant polychaetes (Nepthys spp.). In terms of biomass, however, there is an additional phase of echinoderm prevalence (Asterias rubens) during the last five months. The starfish obviously utilize the bivalve production to a high extent: between 94 and 75 % mortality for the three most abundant bivalve species within six months. For the last six months of the experiment, the net production of all bivalve species is calculated as 24g wet wt./m2, i.e. 0.61 g organic carbon of living tissue, most of which is produced by only three species (Abra alba, Cardium fasciatum and Mya truncata: 22g wet wt/m2.) lt is suggested that predators are of eminent importance in controlling succession and production of the new association. The effects of the experimental conditions on the findings is discussed, and a design for extended interdisciplinary in situ experiments to be carried out from 1976 on, based on the experiences of this first test, is presented.