Henn Ojaveer

Ecological Impact of Ponto-Caspian Invaders in the Baltic Sea, European Inland Waters and the Great Lakes: An Inter-Ecosystem Comparison

We review the ecological impacts of Ponto-Caspian invaders in the Baltic Sea, selected lakes and rivers in inland Europe, and the North American Great Lakes. Each of these regions has been invaded multiple times in recent decades by Ponto-Caspian invertebrates and fishes. In attempt to identify predictable patterns, we compared the magnitude and direction of the impacts of these invaders on ecosystem components (phytoplankton, zooplankton, benthos and fish) and processes within each region. Most introductions appear to have increased local species richness rather than replace native species. Their impact on functional (rather than taxonomic) diversity, however, is of ecological importance. Ponto-Caspian organisms have become dominant members of various trophic levels (herbivores, detritivores and consumers) in benthic and pelagic food webs. They have apparently caused large-scale ecosystem impacts in the Great Lakes, whereas their role in Baltic Sea ecosystem is less pronounced, more spatially limited and, in part, camouflaged by other long-term ecological changes such as eutrophication. In all three regions, Ponto-Caspian invaders have altered multiple abiotic and biotic components and energy flow of ecosystems. Owing to the paucity of studies using pre- and post-invasion datasets, we cannot yet produce robust predictions for most of these invaders.

Distribution and Population Characteristics of Cercopagis pengoi in Lake Ontario

The spatial and vertical distribution of a recent exotic species, the predatory cladoceran Cercopagis pengoi, was studied in Lake Ontario in September 1999. Only typical forms of the species C. pengoi, characterized by a relatively long tail with an S-bend and claws with straight or backwardly bent tips, were found. Structure of the Cercopagis population was rather uniform over the lake, consisting mainly (over 90%) of parthenogenetic females. Median epilimnetic abundance and biomass was 295/m3 (max. = 2,544/m3) and 13.4 mg DW/m3 (max. = 113.3 mg DW/m3), respectively. Cercopagis contributed a median of 15.8%, and at maximum 73.8%, of the total crustacean zooplanktonic biomass (exclusive of nauplii). Abundances showed a significant positive relationship with distance from shore (r2 = 0.34, p < 0.01), but distribution was independent of the depth and temperature of the epilimnion. Cercopagis did not exhibit any diurnal vertical migration patterns: over 90% of the individuals stayed either in the epilimnion or within the metalimnion during the day and night. The proportion of individuals, both live specimens and carcasses of dead individuals, in cooler layers was negligible (< 3%). The following weight (W) – body length (L) relationship was developed during the study: ln(W) = 2.98*ln(L) - 6.42 (r2 = 0.85, p < 0.001).

The future of the oceans past: Towards a global marine historical research initiative

Historical research is playing an increasingly important role in marine sciences. Historical data are also used in policy making and marine resource management, and have helped to address the issue of shifting baselines for numerous species and ecosystems. Although many important research questions still remain unanswered, tremendous developments in conceptual and methodological approaches are expected to contribute to a comprehensive understanding of the global history of human interactions with life in the seas. Based on our experiences and knowledge from the “History of Marine Animal Populations” project, this paper identifies the emerging research topics for future historical marine research. It elaborates on concepts and tools which are expected to play a major role in answering these questions, and identifies geographical regions which deserve future attention from marine environmental historians and historical ecologists.

Exploitation of biological resources of the Baltic Sea by estonia in 1928–1995

Abstract The main exploitable biological resources in the Estonian zone of the Baltic Sea are fish stocks. Fishes of marine origin constitute the main bulk (on the average 91%) of catches. Some freshwater and migratory fishes, having usually only marginal role in the total weight of fish landings, are of special importance for local fishermen in certain regions. Other living resources — red algae and seals-have been exploited in rather small amounts. The main factors having controlled changes in the condition of fish stocks and catches are natural conditions, marine pollution, eutrophication and exploitation rate.

Report on the nature and types of driver interactions including their potential future

The Baltic Sea is a dynamic environment responding to various drivers operating at different temporal and spatial scales. In response to climate change, the Baltic Sea is warming and the frequency of extreme climatic events is increasing (Lima & Wethey 2012, BACC 2008, Poloczanska et al. 2007). Coastal development, human population growth and globalization intensify stressors associated with human activities, such as nutrient loading, fisheries and proliferation of invasive and bloom-forming species. Such abrupt changes have unforeseen consequences for the biodiversity and the function of food webs and may result in loss of ecological key species, alteration and fragmentation of habitats. To mitigate undesired effects on the Baltic ecosystem, an efficient marine management will depend on the understanding of historical and current drivers, i.e. physical and chemical environmental conditions and human activities that precipitate pressures on the natural environment. nThis task examined a set of key interactions of selected natural and anthropogenic drivers in space and time, identified in Task 3.1 as well as WP1 and WP2 (e.g. physico-chemical features vs climate forcing; eutrophication vs oxygen deficiency vs bio-invasions; fisheries vs climate change impacts) by using overlay-mapping and sensitivity analyses. The benthic ecosystem models developed under Task 2.1 were used to investigate interactions between sea temperature and eutrophication for various depth strata in coastal (P9) and offshore areas (P1) of the Baltic Sea. This also included investigation on how the frequency and magnitude of deep-water inflow events determines volume and variance of salinity and temperature under the halocline, deep-water oxygen levels and sediment fluxes of nutrients, using observations and model results from 1850 to present (P1, P2, P6, P9, P12). The resulting synthesis on the nature and magnitude of different driver interactions will feed into all other tasks of this WP3 and WP2/WP4. Moreover, the results presented in this report nimprove the process-based and mechanistic understanding of environmental change in the Baltic Sea ecosystem, thereby fostering the implementation of the Marine Strategy Framework Directive.