Opening statement for Topic 1: " What is the Baltic contribution to the European marine biodiversity? What is the marine biodiversity knowledge in NAS countries?"
by Professor Krzysztof Jazdzewski , University of Lodz, Poland
Because of its young age, low salinity, small depth, harsh thermic regime and pollution, the biological diversity of organisms living in the Baltic is low. It decreases in the direction from south-west to north-east, presenting an interesting gradient of marine species richness. The level of this impoverishment is different in various groups of organisms. For instance the species richness in marine fishes decreases from some 120 species in the North Sea to some 40 species at Polish shores (central Baltic) - here we have a threefold decrease. Much higher decrease is observed in many invertebrate groups; it is estimated as being on the average of the order of magnitude (10-fold). For instance for Amphipoda the recent checklists prepared for North-East Atlantic and for the Baltic Sea gave the following species counts : 741 versus 68, respectively (in the Baltic Sea along Polish coast only some 30 amphipod species were hitherto recorded). Also some highest taxa (phyla, classes) of marine animals are totally or nearly absent in the Baltic Sea (cephalopods, echinoderms). Numerous marine species do enter as adults even in the Bothnian Bay, but due to the low salinity they cannot reproduce there (a case of cod, Gadus morrhua). A crab Carcinus maenas reaches only the Gulf of Gdansk in the Baltic and also here we have to do only with not reproducing, wandering adults. Some species are recorded only as pelagic larvae entering the Baltic in a haphazard way with irregular inflow of saline water masses (for instance Pagurus bernhardus). Low temperature prevailing in northern and eastern parts of the Baltic can also be the reason why some genuine brackishwater species of Lusitanian-boreal or Mediterranean-boreal occurrence range have their distribution limits in the Baltic more or less at the entrance to the Vistula Lagoon (for instance the isopods Cyathura carinata, Sphaeroma rugicauda, S. hookeri or an amphipod Melita palmata).
Marine boreal, euryhaline organisms are the natural main source of the present Baltic flora and fauna. This "core" is supplemented by several (?) glacial/postglacial relicts of Arctic / subarctic origin that have entered this basin probably during the Yoldia Sea period (Myoxocephalus quadricornis, Saduria entomon, Monoporeia affinis, Limnocalanus grimaldii and some others) as well as by numerous freshwater euryhaline taxa, whose contribution decreases from north-east to south-west and which can dominate in the fauna of lagoons (examples of such elements are fishes Esox lucius, Perca fluviatilis, Rutilus rutilus or an isopod Asellus aquaticus). Baltic Sea is probably devoid of endemic species, being a too recent basin to have unique species evolved. On the other hand Baltic Sea, with its peculiar salinity fitting well to the Remane's curve minimum, is especially rich in genuine brackishwater species. As examples one can mention here the polychaetes Alkmaria romijni, Manayunkia aestuarina, amphipods Gammarus duebeni, Apocorophium lacustre or a prawn Palaemonetes varians. This faunistically (and floristically) impoverished basin is recently enriched by several alien taxa of different biogegraphic origin. Ponto-Caspian region appeared to be a very important donor of these aliens, that become locally an important element of fauna (for instance a cladoceran Cercopagis pengoi and a fish Neogobius melanostomus). Also North-American hydrobionts were successful in conquering Baltic waters. One of them - a polychaete Marenzelleria viridis - became a dominant element of zoobenthos in many Baltic areas. Another American invader is the amphipod Gammarus tigrinus quickly extending its range in the Baltic.
It is worth to mention that some alien species have established their rich populations in the Baltic or in its lagoons and estuaries long ago. Examples are a hydrozoan, Cordylophora caspia, a bivalve Dreissena polymorpha (both) of Ponto-Caspian origin), another bivalve Mya arenaria (an especially old immigrant brought probably by Vikings) and a much younger invader - American crayfish Orconectes limosus (in lagoons). Other Ponto-Caspian immigrants already conquered at least three southern Baltic lagoons - Kuronian, Vistula and Szczecin ones; they are amphipods Pontogammarus robustoides and Obesogammarus crassus.
At the moment these aliens increase the species richness of the Baltic, however we can expect that some of them really may be a threat to the native fauna - some species can be exterminated by competition with successful invaders. For instance the negative influence of Marenzelleria viridis on Corophium volutator has been already observed, whereas in the shallowest part of the Gulf of Gdansk - in the Bay of Puck - the Ponto-Caspian fish Neogobius melanostomus in very short time overdominated the local fish fauna and American Gammarus tigrinus outcompetes six native Gammarus species. Some invaders can be a pest for human activity - a case of Cercopagis pengoi clogging the nets.
Despite the relative poverty of the Baltic Sea when studying its biodiverity one should bear in mind that proper recognition of plants and animals is a primordial, but also time-consuming task. To identify species one should check sometimes tiny morphological details with due patience ("Sitzfleisch"!) ; simply one should become a specialist in a particular group(s). Such a specialist should also know the species variability related to age and season, sexual dimorphism etc. At the same time we are facing a true "extinction" of taxonomists. Their efforts are neglected, their papers are held cheap and application for grants are pushed down - the winners are often biologists practicising something that can be called "applied approximatology". Let me recall that some 50 years ago, before the fundamental papers by Otto Kinne and Sven Segerstrale Gammarus collected in the Baltic Sea was usually
named simply Gammarus locusta and now we know that in the Baltic there are 6 species in question, each of different life cycle, ecological requirements, sensivity to pollution etc. And before scientific effort of Bror Forsman and Charles Bocquet all Jaera was named Jaera marina (= Jaera albifrons) - now we know that this is a complex of 5(6?) species, 3 of them occurring in the Baltic. Of course we need modern taxonomists who understand molecular methods to verify taxa when necessary (the case of Mysis relicta-group), and who can show the differences in ethology and autecology of species. It was really promising to learn from the program of MARBEF (Marine Biodiversity and Ecosystem Functioning) that one of its scientific objectives will be: "To understand how marine biodiversity varies across spatial and temporal scales ..." and then to read in this project that : "Taxonomy is essential in biodiversity studies and species inventories are basic tools ....", and then : "Accurate identification and recognition of species remains a fundamental underpinning of biodiversity research, both basic and applied."
Baltic Sea with its history, physico-chemical parameters and a special mixture of organisms (marine, brackishwater and freshwater) is an ideal "laboratory" to study the ecosystem functioning, the patterns of energy flow and quickly occurring serious changes of this ecosystem. And answering to the original question that would be the Baltic contribution to the European marine biodiversity.
The second question suggested for discussion - what is the marine biodiversity knowledge in NAS countries - is a somewhat provocative one. Yes, we , the scientists from these countries, have been cut by the iron-curtain for a long time, having difficult access to the "western" scientific literature. However we have not stopped studies on the Baltic Sea; sometimes, knowing both Russian and English (or other congress language) we were even more aware what is published in different languages and alphabets. Contemporary with such Baltic knowledge luminaries as Adolf Remane, Sven Segerstrale or Erik Dahl, Baltic Sea was studied here by Kazimierz Demel, Arvi Jarvekulg or Wladyslaw Mankowski, among others. Their numerous successors were or are working in such well known institutions as Sea Fisheries Institute in Gdynia (82 years of activity !), Institute of Oceanography of Gdansk University, Institute of Oceanology PAS in Sopot, Agriculture Academy and University in Szczecin, Laboratory of Polar Biology and Oceanobiology-University of Lodz, Estonian Marine Institute, Coastal Research and Planning Institute-University of Klajpeda (name others, please !). That the papers by NAS scientists are (were) overlooked or neglected - yes , that was first of all the effect of publishing the results mostly in native languages, not in English. The second reason was evidently the very difficult contacts (till 1989) between scientists of two political "blocks", hindering the participation in international symposia. These obstacles were both political and financial ones. But even after breaking that barrier the NAS scientific production is comparatively poorly noticed - we need time to recover. (By the way - it is a good fortune of the NAS scientists to often be the first in recording these recent Ponto-Caspian invaders in the Baltic Sea and its lagoons - simply these species appear first in south-eastern Baltic area).
Krzysztof Jazdzewski |
