A tentative field experiment on population dynamics of macrobenthos in the western Baltic

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

Sediment geochemistry of Neustadt Lagoon, north Germany

In the brackish water lagoon of Neustädt (Lübeck Bay/Southern Baltic Sea) hydrological, sedimentological and geochemical measurements were carried out to quantify the retention of nutrients and harmful substances. The exchange of water masses between Neustädt Kanal and the lagoon is dominated by aperiodic sea level fluctuations of the Baltic Sea. In the contact zone saltwater/freshwater muddy sediments occurred. The distribution of heavy metals in the surface sediments in the S part of the lagoon can be referred to the vicinity of the harbour, in the N part to the influence of the sewage plant

Zonierung von Mollusken und Schill im Rinnensystem der Kieler Bucht (Westliche Ostsee)

Great Belt, Vejsnäs Rinne and Boknis Rinne form a major interconnected channel System of approximately 80 km length and 30 m depth on the Kiel Bay sea floor, which generally is only some 10 to 20 m deep. 1971 to 1973, 32 transects were sampled across the channel slopes using narrow Station distances and systematically adding data (T°, S°/oo) from 5 hydrographic cross sections over a one and a half year period. A quantitative, combined study of the molluscan fauna, dead shells and Sediments yielded the following results. 30 species of bivalves and 19 of gastropods were sampled as livingspecimens. According to their long life span, Cypritta islandica is dominant in the deep and the Astarte species on the upper part of the channel slope. Macoma baltica is dominantin a third, more shallow Zone, which is actually outside of the channels. Abra alba is the most persistent species of the channels being present in 86% of all samples. Except for Hydrobia, gastropods display low numbers of presence and abundance and are almost never dominant. The bottom level of the thermohaline pycnocline impinges on the channel slope as a rule between (15-)18 and 22 (-25) m depth. This boundary layer is clearly reflected by the fauna, i.e. by maximum numbers of species and species richness, of species presence and abundance, as well as of the biomass of total molluscs and of most of the single mollusc species. The faunal Optimum is explained by the favourable combination of a suite of factors, such as relatively stable temperatures and increased salinity, sufficient aeration, and a strong “rain” of larvae and nutrition where the upper water mass is barred by the pycnocline. Substrate conditions (± 50 % of Sediment < 63 p) might be favourable as well. The deeper water mass of the channel System is increasingly plumbed by the pycnocline and correspondingly poor in oxygen concentration towards the inner end of the bay. The oxygen deficiency more and more confines the Optimum beit of the molluscs from below, and causes a distinct elevation of the maximum numbers of species, species richness, species dominance and biomass from the entrance towards the inner part of the bay from 20-24 to 15 -20 m depth. Increasing distance from the bay ’s entrance , (the Great Belt) does not exert any other influence on the molluscan fauna. Averaging the whole transects, the mean numbers of species, species richness, species presence and biomass stay constant in line with constant T-S conditions. The molluscan Optimum belt is widened on the slope towards the deep and partly doubled at current and water exposed parts of the slope, where it also achieves its absolute maximum numbers. No molluscan species is bound to a specific type of Sediment, though eventually certain Sediments may be preferred. Mud forms an exception in showing a clear decrease of the number of specimens (by an overlap with the factor oxygen deficiency). Except for the well known general reduction of species in the Kiel Bay, the distribution pattern of temp erature and salinity exerts only minor influences on the fauna. The dead-shell species as semblage generally reflects the living one. On the whole, they correspond with their composition of species, the zonation of dominant species (middle, emergent Astarte beit) and the distribution and elevation pattern of the maxima of species, species richness and dead-shell quantities. A downslope transport of shells is inferred, among other things, from a stronger presence of (dead-shell) species in the deeper part of the channel. As measured by the lateral displacement of the mollusc maximum belts, the transport amounts 1 to 3 m in vertical distance, rarely up to 7 m at current exposed slopes. These numbers correspond to 30-75 m horizontal distance. Besides currents, extreme wave action is a possible cause. Current induced long-distance transport of dead shells generates increased numbers of species, species presence and dead-shell quantities at the channel bottom, especially behind narrow passes. Hotvever, taking into account the undisturbed distribution of dominant species, the quantity of reworked shells must be insignificant. First indications of the shell production can be derived from the living-dead ratio of shell samples — notwithstanding the varying amounts of carbonate dissolution. For instance, the production of Astarte species is some 13 times smaller than the one of Abra alba and 7 times smaller than that of Cyprina islandica. — A general strong change from living to dead-shell dominance occurs below the pycnocline at 20 to 24 m depth. In the case of a fossil analogue of a Baltic Sea channel, marked shell horizons with a broad species spectrum most probably correspond to a molluscan zone at the level of the mean pycnocline Position