Browsing by Author "Lillebo, A. I."
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- Flagging greens: hydrobiid snails as substrata for the development of green algal mats (Enteromorpha spp.) on tidal flats of North Atlantic coastsPublication . Schories, D.; Aníbal, J.; Chapman, A. S.; Herre, E.; Isaksson, I.; Lillebo, A. I.; Pihl, L.; Reise, K.; Sprung, Martin; Thiel, M.During the past 3 decades, dense mats of green algae (especially Enteromorpha spp.) have been recorded regularly from tidal flats worldwide. The development of green algal mats on tidal flats may be initiated by overwintering and regrowth of adult plants or by the formation and release of small propagules, i.e. vegetative fragments, zoospores and zygotes. On soft sediments, macroinvertebrates may constitute prime substrata for germination of algal spores. Hydrobud (mud-) snails are widespread along North Atlantic soft sediment shores and were identified previously as important substrata for Enteromorpha spp. germlings in 1 of our study areas. To test the generality of this phenomenon, we investigated the presence of Enteromorpha spp. gerrnlings attached to hydrobud snails from November 1995 to December 1996 on 6 tidal flats of North Atlantic coasts (Tralebergslule, Sweden; Konigshafen Bay, Germany; Mondego Estuary, Portugal; Ria Formosa, Portugal; Cole Harbour, Nova Scotia, Canada; Lowes Cove, Maine, USA). With 1 exception, hydrobiid snails were present in all areas studied, and intensive growth of Enteromorpha spp. occurred during summer. Throughout winter 1995/96, hardly any Enteromorpha spp. gerrnlings were found on snail shells, but over the following months germlings developed on up to 60% of the hydrobiid snails present. In 2 areas (Konigshafen, Germany; Lowes Cove, USA), germhng abundance on hydrobuds began to rise before the peak of green algal mat development. In Tralebergskile, Sweden, high mat abundance occurred simultaneous to and after increased germling abundance on Hydrobia ulvae. Densities of snails were very low, however, and hydrobuds appeared to be unimportant as substratum. No clear temporal pattern between high germling abundance on snails followed by mat development was found in the other 3 study areas (Ria Formosa, Portugal; Mondego Estuary, Portugal; Cole Harbour, Canada). In Lowes Cove, USA, gerrnlings and juveniles of Enteromorpha spp. first grew at the site with high Hydrobia abundance and were subsequently drifted to another site where they developed into full mats. We conclude that initiation of green algal mats by germination on Hydrobia spp. may be a general phenomenon, but that other modes of development also occur frequently. Pelagic dnft of overwintering thalli to new sites, followed by prolific growth, might be of similar or greater importance.
- Hydroiid snails conditioning green algae mats (Enteromorpha spp.) in the Northern HemispherePublication . Schories, D.; Albrecht, A.; Aníbal, J.; Fletcher, R.; Isaksson, I.; Lillebo, A. I.; Pihl, L.; Pye, K.; Reise, K.; Sprung, Martin; Thiel, M.For the last decades dense mats of filamentous green algae Enteromorpha spp. have regularly occurred worldwide on tidal Àats. The development of green algal rnats on intertidal Àats is commonly achieved by overwintering and regrowth of adult plants or by the formation and detachment of propagules. Up to now the study of germlings as initiators of algal mats have received relatively little attention. It was known from one of our study sites (Konigshafen Bay, Germany) that shells of living mudsnails (Hydrobia ulvae) serve as the main substrate of overwintering Enteromorpha spores and initiate in this way extensive growth of Enteromorplza mats in spring. We investigated the presence of Enteromorpha germlings attached on hydrobiid snails in different places of Canada, England, Germany, Portugal, Sweden and the United States between November 1995 and November 1996. At all investigation sites huge amounts of hydrobiid snails were present during the last years and and intensive growth of Enteromorplm occurred during the course of the season. - During winter 1995 /96 hardly any Enteromorpha germlings were found on the snail houses, but depending on the site, germlings developed on up to 60 % of hydrobiid snails during spring. It is obvious, that at least in some areas the germling development was related to overwintering of spores on snails, due to poor biomass of adult Enteromorpha plants during winter. In our study we could demonstrate that hydrobiid snails can play an important role in soft sediments for the successfull development of green algal mats in soft sediments.