Meereswissenschaftliche Berichte MARINE SCIENCE REPORTS No. 18 The ecology of macrozoobenthos and sea ducks in the Pomeranian.Bay Jan Kube Institut fürOstseeforschung Warnemünde 1996 Die vorliegende Arbeit ist die inhaltlich unveränderte Fassung einer Dissertation, die am Institut für Ostseeforschung Warnemünde angefertigt und im September 1996 von der Mathematisch­ Naturwissenschaftlichen Fakultät der Universität Rostock angenommen wurde. Diese Arbeit wurde mit Mitteln des.Bundesministeriums ·:tUr .Bildung, Wissenschaft, Forschung und Technologie (Projekt 03F0105B) gefördert. Die Verantwortung für den Inhalt dieser Veröffentli• chung liegt beim Autor. Contents pages Summary 1. Introduction An assessment ofenvironmental changes in the Pomeranian Bay 1 2. Methodological approach Designing a sampling programme: collection and treatment ofdata 7 3. Benthic macrofauna communities of the Pomeranian Bay and their variations in space and time Coastal sublittoral sands in the southem Baltic Sea as a habitat for benthic 17 fauna paper 1: The importance ofhydrodynamic processes and food availability for 18 the structure of macrofauna assemblages in the Pomeranian Bay (Southem Baltic Seal J. Kube, M Powilleit & J. Warzoeha Arch.. Hydrobiol. in press paper 2: Long-term changes in the benthic communities of the Pomeranian 28 Bay (Southem Baltic Seal J. Kube, F. Gosselek, M Powilleit & J. Warzoeha submitted for publication 4. Spatial and temporal variations in the population structure of benthic filter-feeders . Functional implications: the analysis ofpopulation structure and dynamicsas 43 a baseline study paper 3: Spatial and temporal variations in the population structure of the 47 soft-shell clam, Mya arenaria, in the Pomeranian Bay (Southem Baltic Seal J. Kube J. Sea Res. 35: 335-344 paper 4: Spatial variation in growth ofMacoma balthiea and Mya arenaria 57 (Möllusca: .Bivalvia) .inrelation toenvironmental .gradients the Pomeranian Bay· (Southem Baltic Seal Jan Kube, Christine Peters &MartinPowilleit Arch.· Fish. Mar.. Res. in press paper 5: Distribution ofMai'enzelleria viridis (Polychaeta: Spionidae)in the 65 southwestem Baltic Sea Ü1 1993/94 - ten years after introduction J. Kube~ ML. Zettler, F. Gosselek, S. Ossig & M Powilleit Sarsia 81: 131-142. pages 5. The feeding ecology ofwintering sea ducks The importance ofpredatioll: trophic interactions between sea ducks and their 77 invertebrate prey paper 6: Habitat selection, feeding characteristics, and food consumption of 83 long-tailed ducks, Clangula hyemalis, in the southem Baltic Sea J. Kube & H. Skov Manuscript 6. Conclusions Benthic filter-feeding: a natural eutrophication control ? 101 Acknowledgements 110 References 111 Summary I. The Pomeranian Bay (southem Baltic Sea), a large shallow offshore bay, is the transition zone between the Oder Estuary and the Baltic Proper. Sandy bottoms, between 0-20 m water depth, cover 2 3 1 an area of 8.800 km • The' rivers Oder and Peene transport about 20 km a- freshwater into the bay. In the last decades the area has been influenced by increasing anthropogenie discharges. The study area has undergone significant eutrophication. Riverine nitrogen loads were five times higher in the 1990s than in the 1960s. Phytoplankton and primary production have roughly doubled during the last 20 years. Accumulation oforganie matter was observed in sediments locally. A joint Polish and Gennan research project (TRUMP) was started in 1993 to evaluate the impact of the riverine material on the ecosystem ofthe Pomeranian Bay. Investigations focus on the distribution, transport, and modification of biogenie and anthropogenie inputs from the Oder River. Benthic macrofauna studies form a major part ofthese investigations. 2. This phD thesis aimed at 1) describing the recent distribution of macrozoobenthos communities and sea ducks in the Pomeranian Bay in relation to the prevailing abiotic and biotic factors, 2) developing and applying efficient methods for the analysis of low diverse sublittoral benthic communities, 3) ·to analyse short-term and long-te~ changes in the macrozoobenthos in relation to fluctuations and long-term trends in the environmental conditions. 3. Quantitative sampIes ofbenthic macrofauna were taken at 34 stations (6 to 30 m water depth) in the Pomeranian Bay in the period April 1993 to April 1995. Two different sampling methods were 2 applied: 1) Van Veen grab (23kg/70 kg, 0.1 m , 1.0 mm mesh size) and 2) modified 'Reineck' box 2 corer (190 kg, 0.0225 m , 0.5.mm mesh size). Methodological comparisons between both methods were performed..Species distribution patterns, species numbers, abundances, and biomasses were analysed. Univariate and multivariate statistics were used to compare the precision ofresults ofboth procedures . in terms of species .. richness, abundance, biomass .and size-frequency distribution. Conclusions are made about the applicability and efficiency of the two methods. Five replicate are demonstrated to .. be the most efficientmethod .for routine monitoring ata precision and laboratory sortin . endations are given for the . epifauna species, whichcannot be sampled . ~. ss than ten e identification of oligochaetes to species leve seems 0 e renouncable cal analyses ofcommunity structures. 4... Fourty-five macrofauna species. were. identified.· Mya arenaria, Macoma .balthica and Marenzelleria viridis are the most important species with respect to biomass. Mean total biomass values decreased from about 100 g AFDW'm-2 in the Southwest of the bay to only· about 10 g AFDW'm-2 in the North. Multivariate analyses suggest distinct assemblages within the shallow bay and at the slope to the adjacent deeper zones.Loose· .. of the shallow parts. They are all dominated. by filter-fee the northern .boundary of the study area adjacent to the Arkona Basin. The smallrange of sediment variation could not explain distribution pattern of species .with a large tolerance for sediment parameters. Physical disturbance and available food supply are proposed to be important in structuring the benthic community.. 5. The population structure of Mya arenaria has been investigated during a 1.5-year period in 1993/94 to follow changes in the size and age structure ofthe clam populations in different parts of the study area. Large spatial differences in the population structure were found between the sheltered Southwest ofthe bay and the shallow and exposed Oder Bank in the centre. The clam stock ofthe Oder Bank was formed by two different clam types. A slow growing cohort was assumed to be autochtonous on the Oder Bank. A fast growingonewas assumed to have been introduced from the surrounding area. Their contribution to the total density varied seasonally and was probably denpendent on the intensity of bedload transport events. Erosion was supposed tQ be of minor importance in the Southwest ofthe Pomeranian Bay. High mortality rates during the first two years oflife were assumed to be ~aused by predation. Mortality rates ofolder cohorts remained stableuntil old age. Variations in the density of cohorts were related to interannual differences in the reproductive success. A mild winter presumably lowers the reproductive success in the subsequent summer. 6. Spatial variations in individual growth rates of Macoma balthica and Mya ·arenaria were investigated in the Pomeranian Bay in 1993/94. Compared to full marine environments, growth rates of bivalves were considerably lower in this brackish area (salinity about 8%0). Growth of M balthica correlated significantly with phytoplankton concentration. Growth of M arenaria was assumed to be negatively effected by intensive physical disturbances. It is supposed that reduced salinities affect the growth ofM arenaria more than that ofM balthica. 7. The distribution and abundance ofMarenzelleria viridis, a North American spionid polychaete which was first recorded in the Pomeranian Bay in' the late 1980s, was studied in the southwestern part ofthe Baltic Sea in 1993/94 in relation to environmental factors. All available macrozoobenthos sampies from· German Baltic waters were used to construct a general distribution map. Highest abundances and biomasses were found in senri-enclosed lagoons (39.000 ind. m-2 and 70 g ash free 2 dry weigth m- ). The western horizontal distribution border and the vertical distribution range were following the 15 %0 isohaline. Neither a horizontal nor a verticallimit was found to the East. Dense settlement was restricted to sediments with an organic content ofless than 5 % and a silt content of less than 10 %. Simultaneous population studies were carried out in the Pomeranian Bay, the Oder Estuary and the Darss-Zingst Bodden from April 1993 to April 1994. Three different age groups were identified throughout the year. Settlement of larvae took place in aututnn. Successful larval settlement was restricted to areas with a salinity above 5 %0 and a winter phytoplankton 3 concentration above 5 g ChI a m- • Benthic stages were found to be higWy motile. Adults occurred up to 50 km away from recruitment areas. 8. Long-term changes in the macrofauna ofthe Pomeranian Bay were studied by comparing survey data from the 1950s, 1980s and 1990s. Biomass of filter-feeding bivalves increased significantly. Spatial . of the investigated species have changed. Strong decreases in species richness were caused by oxygen depletion at stations deeper than 15 m. Saduria entomon, Monoporeia affinis and Pontoporeiafemorata vanished entirely between 19 3. Although a causal re eous increases of nutrient levels