Although blooms of opportunistic fast-growing macroalgae now occur frequently in coastal ecosystems affected by eutrophication, their initiation and control is little understood. Most previous studies have focused on the ecophysiology of adult algae only. We show that spores and/or germlings may represent critical stages in the life cycles and mass-developments of co-occurring opportunistic macroalgae in the Baltic (Pilayella littoralis and Enteromorpha spp.). We investigated the overwintering of spores, timing of germination, subsequent growth, and grazing on spores and germlings, in order to explain the initiation of mass blooms and species dominance patterns. In the field, Enteromorpha spp. showed 10- to 50-fold higher abundances of overwintering microscopic forms (up to 330 individuals cm) than P. littoralis. Moreover, we found continuous production of spores (up to 1.2 million settling spores m h) from April to October in Enteromorpha spp., while there was evidence of only a short reproductive period in Pilayella. However, in spring, germlings and adults of P. littoralis appeared earlier in the field and reached a 10-fold higher biomass than Enteromorpha spp. In factorial laboratory experiments including temperature and light, there were clear differences in timing of germination. P. littoralis germinated at 5°C whereas Enteromorpha spp. required temperatures of 10-15°C for germination. In contrast, we detected only minor differences in growth response among adults of P. littoralis and Enteromorpha spp. Germination, not growth of adults, appeared to be the ecophysiological bottleneck for initiating mass spring development. Following the spring Pilayella bloom, Enteromorpha germlings occurred massively in the field (April-September), but rarely developed into adults. In laboratory feeding experiments we tested whether crustacean mesograzers common in summer may control development of Enteromorpha germlings. Both germination of settled spores and growth of germlings were reduced by 93-99% in the presence of grazers (Idotea chelipes and Gammarus locusta). Thus in addition to ecophysiological constraints, grazers, if present, may play a decisive role in the early life stages of macroalgal mass developments. These results mirror patterns of overwintering of seeds, germination control, seed and seedling predation in terrestrial plant communities.

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Large quantities of filamentous green algae (Enteromorpha sppl) have regularly occurred on muddy and sandy tidal flats in K6nigshafen, on the island of Sylt (North Sea), since 1979 -covering the sediments in thick mats during the summer months. While spores of Enteromorpha were encountered in both mud and sand, germ~g formation was restricted to sand: However, mud snarls (Hydrobia ulvae Pennant) were overgrown with small Enteromorpha filaments in both habitats, about 50% of them at a muddy site and 20% at a sandy one. Filaments, several cm in length and still adhering to the snails, became tangled into clusters. At the sandy site, with abundant Arenicola marina L., these clusters slid into the feeding funne!s of lugworm burrows; the importance of this Secondary anchorage is demonstrated by afield experiment. We suggest that the primary and secondary attachment of Enteromorpha filaments provided by benthic fauna is an essential step in the development of green algal mats on sedimentary tidaI flats.

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H i s t o r i c a l c h a n g e s a n d i n v e n t o r y of m a c r o a l g a e f r o m K 6 n i g s h a f e n B a y in t h e n o r t h e r n W a d d e n S e a

Antarctic sea anemones, with few exceptions, are known mainly from dredged or trawled samples while the shallow water anemone fauna of this region is poorly known. In the present paper, we present records of 10 species of sea anemones collected and photographed in situ on diver accessible depths (down to 40 m) on King George Island. Three species, Edwardsia inachi sp.n., Armactinia antarctica gen.n. sp.n. and Corallimorphus karinae sp.n. are described as new. The remaining species are briefly described and discussed. Descriptions include new data on nematocysts and shape of spermatozoa. How to cite this article: