259 research outputs found
Scientific basis of the chapter "Environmental change: a historical perspective"
No full text<p>Scientific basis of the chapter “Environmental change: a historical perspective” by Diane S. Srivastava, Jenny L. McCune, and Heike K. Lotze in “Reflections of Canada: Illuminating Our Opportunities and Challenges at 150+ Years”. (ed. P. Tortell) 2017. Publ. by the Peter Wall Institute for Advanced Studies, University of British Columbia</p>
Predator decline leads to decreased stability in a coastal fish community
No full textFisheries exploitation has caused widespread declines in marine predators. Theory predicts that predator depletion will destabilise lower trophic levels, making natural communities more vulnerable to environmental perturbations. However, empirical evidence has been limited. Using a community matrix model, we empirically assessed trends in the stability of a multispecies coastal fish community over the course of predator depletion. Three indices of community stability (resistance, resilience and reactivity) revealed significantly decreasing stability concurrent with declining predator abundance. The trophically downgraded community exhibited weaker top-down control, leading to predator-release processes in lower trophic levels and increased susceptibility to perturbation. At the community level, our results suggest that high predator abundance acts as a stabilising force to the naturally stochastic and highly autocorrelated dynamics in low trophic species. These findings have important implications for the conservation and management of predators in marine ecosystems and provide empirical support for the theory of predatory control
Plankton and dissolved nutrient data from 2016 mesocosm experiment manipulating Si:N and copepod grazing on Baltic Sea plankton community
No full textPhytoplankton, microzooplankton, copepod and dissolved nutrient data from a mesocosm experiment, which took place in summer 2016. A range of Si:N ratios and two levels of copepod grazing pressure were manipulated on a natural plankton community in Kiel Bay, Southern Baltic Sea, Germany
Recovery of marine animal populations and ecosystems
No full text11 pages, 3 figures, 2 tablesMany marine populations and ecosystems have experienced strong historical depletions, yet reports of recoveries are increasing. Here, we review the growing research on marine recoveries to reveal how common recovery is, its magnitude, timescale and major drivers. Overall, 10–50% of depleted populations and ecosystems show some recovery, but rarely to former levels of abundance. In addition, recovery can take many decades for long-lived species and complex ecosystems. Major drivers of recovery include the reduction of human impacts, especially exploitation, habitat loss and pollution, combined with favorable life-history and environmental conditions. Awareness, legal protection and enforcement of management plans are also crucial. Learning from historical recovery successes and failures is essential for implementing realistic conservation goals and promising management strategiesFinancial support was provided by the Sloan Foundation’s Census of Marine Life FMAP Program, the Natural Sciences and Engineering Research Council of Canada and Dalhousie University. MC was funded by the European Community Marie-Curie Post-doctoral Fellowship through the International Outgoing Fellowships (IOF; Call: FP7-PEOPLE-2007-4-1-IOF) to ECOFUN and LA by the European Commission through FP7.2009-1, Contract 244104–THESEUSPeer reviewe
Radical changes in the Wadden Sea fauna and flora over the last 2000 years
No full textHumans have interacted with the Wadden Sea since its origin 7,500 years ago. However, exploitation, habitat alteration and pollution have strongly increased since the Middle Ages, affecting abundance and distribution of many marine mammals, birds, fish, invertebrates and plants. Large whales and some large birds disappeared more than 500 years ago. Most small whales, seals, birds, large fish and oysters were severely reduced by the late 19th and early 20th centuries, leading to the collapse of several traditional fisheries. In the 20th century, conservation efforts have enabled some breeding birds and seals to recover. But other species declined further due to continuing exploitation, habitat destruction, pollution and eutrophication. Moreover, complex three-dimensional habitats such as oyster banks, Sabellaria reefs and subtidal eelgrass beds have been lost completely. In contrast, several opportunistic species such as gulls, polychaetes, green algae and exotic invaders increased during the 20th century. Taken together, multiple human impacts have caused dramatic losses of large predators and habitat-building species in the Wadden Sea over the last 500 years. Although still of high natural value and global importance, the Wadden Sea is a fundamentally changed ecosystem. On the other hand, reduced hunting pressure, increased habitat protection and reduced river pollution have enabled the recent recovery of several species and an increase in environmental quality. These successes, together with a historical vision of what was once possible, should guide current and future conservation, restoration and management efforts towards a more sustainable interaction between man and the sea
Changes in Marine Biodiversity as an Indicator of Climate Change
No full textAmbient temperature is very likely the most important environmental factor determining the distribution and diversity of life in the oceans. Hence, climate change is expected to alter marine biodiversity on a global scale. Here we review observed and predicted effects of climate change on the diversity of marine species. Overall, an increasing number of studies demonstrate that effects of climate change on marine biodiversity are already apparent from local to global scales. So far, long-term fish and plankton monitoring data have provided the most compelling evidence for climate-driven changes in species distribution and diversity, but studies involving other groups such as corals, seaweeds, and mammals are increasing. As a general pattern, tropical regions often experience a loss of species due to elevated heat stress, whereas temperate regions increase in diversity, as species migrate polewards. Net increases in diversity are also expected in the polar regions, but so far there are few observations to support this. Complex patterns of change can emerge where ocean warming is accompanied by the effects of sea level rise, acidification, habitat change, changes in ocean circulation, stratification, and other aspects of global change. From a management perspective, the conservation of biological diversity will provide insurance and resilience in the face of rapid global change. Cumulative impacts of exploitation, habitat destruction and other threats to biodiversity need to be minimized to maintain the adaptive capacity of marine ecosystems in the present and coming centuries. This might be particularly pressing in tropical regions and developing countries, which will face exceptional socio-economic and climate-related pressures, as well as in the polar regions, which are faced with a multitude of emerging pressures
Phänologische und Ökophysiologische Untersuchungen an Grünalgen im Wattenmeer
No full textIn einem Teilgebiet des Königshafens von Sylt (Nordsee) wurden 1993 phänologische und ökophysiologische Untersuchungen an den heterogenen Grünalgenmatten des Wattenmeeres durchgeführt. Im Untersuchungsgebiet traten 12 Arten der Gattung Enteromorpha und 3 Arten der Gattung Ulva auf Enteromorpha radiata war die häufigste Art. Ihr folgten E. prolifera und E.clathrata. In geringeren Mengen waren E. torta, E. flexuosa, E. linza und die drei Ulva-Arten U. lactuca, U. rigida und U. scandinavica zu finden. E. compressa, E. intestinalis, E. linziformis, E. pilifera, E. raljsii und E. simplex zählten zu den seltenen Arten. Im Vergleich zu :früheren Artenlisten aus dem Königshafen konnten E. ahlneriana und E. ramulosa nicht wiederentdeckt werden. Hingegen wurden U. rigida und U. scandinavica neu nachgewiesen. Die Grünalgenmatten waren fleckenhaft verteilt und erreichten im Mai 1993 im Möwenberg-Watt ihre größte Ausdehnung mit einem Bedeckungsgrad von 9,8 ± 11,6%. Dies war mit der durchschnittlichen Bedeckung in den Vorjahren vergleichbar. Die Biomasse war jedoch geringer. Während in den letzten Jahren eine Biomasse von mehr als 50 g TG/m2 vorherrschte, wurden 1993 nur 2,3 ± 1,3 g TG/m2 aufgebaut. In dieser geringen Ausdehnung und Dicke hatten die Grünalgen kaum einen Einfluß auf das Ökosystem. Im Verlauf der Vegetationsperiode fand eine Artensukzession von fädigen zu flächigen Formen statt. Während im Frühjahr E. torta, E. clathrata und E. prolifera das Bild prägten, dominierte E. radiata im Sommer. Neben ihr traten nach und nach E. flexuosa, E. linza und U. lactuca auf Im Herbst wurden die Grünalgen aus dem Gebiet verdriftet. Zu diesem Zeitpunkt waren noch wenige Exemplare von U. lactuca, U. rigida und U. scandinavica zu finden. Ulva- und flächige Enteromorpha-Arten traten im Gebiet nicht als Keimlinge auf Es wird vermutet, daß diese Formen in ihrem Hauptvorkommensbereich, dem unteren Eulitoral, keimten und bei Erreichen einer bestimmten Größe von der Strömung losgerissen und ins obere Eulitoral verdriftet wurden. Fünf Enteromorpha-Arten wurden in Bezug auf ihr Wachstum im Labor getestet. Sie bevorzugten alle Temperaturen um 20°C und Lichtintensitäten von 80 μmol Photonen/m2s und mehr. Ohne Zugabe von Nährmedium war ein Wachstum in dem im Sommer nährstoffarmen Meerwasser nicht möglich. Der Jahresgang der Grünalgen ist von den abiotischen Bedingungen abhängig. Im Frühjahr limitiert die Temperatur das Wachstum, im Sommer die sinkenden Nährstoffkonzentrationen. Im Herbst wird das Wachstum durch sinkende Temperaturen und abnehmende Lichtintensitäten gehemmt. Eine Erhöhung der Nährstoffkonzentrationen in der Wassersäule hat bei einer sommerlichen Nährstoffiimitierung des Wachstums große Auswirkungen. Das Massenauftreten der Grünalgen im Wattenmeer seit Beginn der 80er Jahre geht mit einer Zunahme der Nährstoffkonzentrationen in der Deutschen Bucht einher und kann somit als Eutrophierungsfolge angesehen werden. Die einzelnen Arten wiesen unterschiedliche Wachstumsansprüche und -raten auf, die teilweise das jahreszeitlich verschobene Auftreten und die verschieden hohen Biomassen erklären. Die Dominanz von E. radiata war hieraus jedoch nicht abzuleiten und muß andere Ursachen haben. Über den Sommer fand eine permanente Reproduktion der Enteromorpha-Arten statt. Es waren mehr fertile Sporophyten als Gametophyten zu finden. Die einzelnen Enteromorpha-Arten wiesen Unterschiede in ihrer Reproduktivität auf, wobei E. prolifera mit durchschnittlich 20% fertiler Thalli am häufigsten fertil gefunden wurde. Eine Lunarperiodizität in der Reproduktion wurde nicht nachgewiesen. Trotz permanenter Reproduktion zeigten die Keimlinge der Enteromorpha-Arten jahreszeitliche Unterschiede in ihrem Auftreten. Dies wird von Temperatur-, Licht- und den Nährstoflbedingungen beeinflußt. Im Frühjahr waren maximale Zahlen zu finden, die im Sommer aufgrund Nährstoffinangels auf ein Minimum zurückgingen. Mehr als 99% der über den Sommer festgesetzten Zoiden keimten nicht aus, konnten aber in diesem Zustand überwintern. Unter Winterverhältnissen war ein Auskeimen nicht möglich. Im nächsten Frühjahr kann ein riesiges Potential an auskeimfähigen Zoiden zur Verfügung stehen. In der laufenden Vegetationsperiode hat die Reproduktion und somit der Keimlingsnachschub keine Bedeutung für die Grünalgenmatten. Die Keimlinge stellen jedoch im Frühjahr das Nadelöhr für die Entstehung der Grünalgenmatten dar. Die abiotischen Bedingungen im Frühjahr bestimmen Auskeimung und Wachstum der Keimlinge und sind von entscheidender Bedeutung für die Ausbildung und Entwicklung der Grünalgenmatten
Two centuries of multiple human impacts and successive changes in a North Atlantic food web
No full textEuropean colonization of North America severely altered terrestrial and aquatic ecosystems alike. Here, we integrate archaeological, historical, and recent data to derive the ecological history of the Quoddy Region, Bay of Fundy, Canada, an upwelling region rich in marine diversity and productivity. We document successive changes on all trophic levels from primary producers to top predators over the last centuries. Our objectives were to (1) construct a baseline of "what was natural in the coastal ocean," and (2) analyze the sequence and potential interaction of multiple human impacts. Archaeological records highlight the abundance and diversity of marine species used by indigenous people over the last 2000-3000 years. Europeans colonized the area in the late 1700s and rapidly transformed the environment by multiple "top-down" (exploitation), "bottom-up" (nutrient loading), and "side-in" (habitat destruction, pollution) impacts. Most large vertebrates were severely overexploited by 1900, leading .to the extinction of three mammal and six bird species. Diadromous fish dramatically declined after river dam- ming in the early 1800s, and recovery was prevented by subsequent river pollution. Over- fishing of groundfish stocks started in the late 1800s, gradually leading to a final collapse in the 1970s. In the 20th century, decline of traditional fisheries induced a shift to low trophic level harvesting and aquaculture, which increased exponentially over the past 20 years. Eutrophication caused shifts in seaweed and phytoplankton communities: Some long- lived rockweeds were replaced by annual bloom-forming algae, and diatoms were replaced by dinoflagellates. Today, the once unique Quoddy Region shows the most common signs of degradation found in highly impacted coastal areas worldwide. Multiple human influences have altered abundance and composition of every trophic level in the food web and reduced upper trophic levels by at least one order of magnitude. We highlight cumulative and indirect effects that impair the ability to predict and manage highly impacted coastal ecosystems. On the other hand, simple protection and restoration measures in the 20th century led to the recovery of some species. It is these successes that provide guidance for a more sus- tainable interaction of humans with their marine environment
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