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Content archived on 2024-04-30

Long-term Changes in Baltic Algal Species and Ecosystems


Our analyses show that dispersal of macroalgae depends not only on salinity but also on favourable physical and chemical conditions, for example presence of suitable substrate. If such conditions are presnet good dispersal is ensured between species-rich communities and causes high stability of the ecosystem. However, when species disappear the remaining ecosystem tends to be unstable. Especially the community of perennial seaweeds dominated by fucoids (Fucus vesiculosus, F. serratus, F. spiralis, and F. evanescens disappears as a result of eutrophication being replaced by redundant green algae. The time scale for resilience of such a system is years and is only possible if viable nearby populations are present. Similar effects can be caused by other human activities, for example monumental constructions, which in periods may create enlarged sedimentation.

As the ecosystem is an important breeding area for some commercial fish species, the species richness must be taken into consideration and supervision by local environmental authorities. Along the Skagerrak, Kattegat, Baltic Sea (SKB) salinity gradient the number of species decreases from c. 325 to less than 100. The ecophysiological studies under Biobase show that some species show incipient adaptation to reduced salinity (cryptic species), but other species exhibit considerable morphological depauperization and also change their reproductive patterns. The species are thus often stressed by the reduced salinity and may experience change in their distribution by only minor oceanographic changes. Biobase has made considerable contribution to the understanding of the genetic diversity of the key species. Based on molecular data and crossing experiments it is now clear, that what was previously know under 4 names can be reduced to one name, Ceramium tenuicorne.

The results also show, that reproductive differences exist between Baltic and extra-Baltic populations reproduction being almost asexual or vegetative in the Baltic proper, but sexual outside the Baltic Sea. The RAPD-data show a clear geographic component of the mtDNA haplotypes in C. tenuicorne. The SKB populations of Fucus serratus reveal a remarkable similarity despite being separated by 933 km and spanning a salinity range from 7 to 33 psu. This is in contrast to populations in Brittany. They display 2-3 times more alleles per locus than any other area within the species range. In the other end of the spectrum two populations from the northern coast of Spain showed very little differentiation, but they were more different from each other although separated by only 140 km than other populations separated by thousands of kilometres. The study of hybrids formed by crossing both in nature and in the laboratory between Fucus serratus and F. evanescens is of considerable interest to the scientific community. Interestingly an asymmetry exists in nature in the hybrid development as only F. evanescens eggs can be fertilized by F. serratus sperms Will the offspring develop into an independent species? Will sterility barriers develop? Do the hybrids develop because the involved species are in closer physical contact in a non-tidal area compared to a tidal area? In Enteromorpha intestinalis six microsatellites loci were found and five were used
The most interesting biogeographical aspects of the Baltic are its salinity gradient, which extends from the Atlantic with oceanic salinity down to near fresh water in the inner parts of the Baltic estuary, and its young age, being only about 7.000 years old as a brackish water basin. These characteristics have led to strong selection pressure among the organisms in the Baltic Sea, and therefore the area is especially tractable for testing evolutionary diversification and adaptation. Ecophysiological comparisons between the Atlantic and Baltic sea algae show that morphological and physiological (measured as photosynthetic performance, growth rate and salinity tolerance) variation is widespred among the species. Also genetic differentiation has been found along the salinity gradient with no apparent hybridization along the contact zones. Our aim is to find out, how common the morphological, physiological and genetic adaptation is in the Baltic Sea algae, whether these are linked together, and what is the history behind the adaptive strategies. This will be done by the study of three integrated levels of the benthic algal populations along the salinity gradient. The central objectives will be to establish a comprehensive reference culture collection from the Baltic Sea across the Skagerrak/Kattegat salinity gradient (task 1), to assess the growth, survival and dispersal performance of salinity ecotypes and phylogeny of biogeographic populations (task 2), and finally to explore the genetic diversity in Baltic Sea populations (task 3).

Task 1 The baseline culture collections will be established and maintained in the Scandinavian Culture Collection for Algae and Protozoans, University of Copenhagen, and they will include all important species of red, brown and green algae.
Task 2. The salinity ecotypes occurring over a range of salinity will be assessed using classical gradient tables.
Task 2 and 3. DNA sequencing will be used for assessing cryptic level species and subspecies diversity. Phylogenetic history and distributional patterns will be studies in selected species of Enteromorpha, Ceramium and Fucus, which provides the link between the palaeoclimatic events and the dominant role they have in their present habitats. Information from task 2 and 3 will be used for correlation analyses between ecotypes and population differentiation. The project will be coordinated from University of Copenhagen (Denmark), and partners are University of Groningen (the Netherlands), University of Kiel (Germany), University of Oslo (Norway) and University of Helsinki (Finland).
Keywords: Reference culture collection, autecology, adaptation, dispersal, phylogentic history, DNA sequences.

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Københavns Universitet
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2D,Oester Farimagsgade
1353 København K

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