Mögliche Ursachen des geringen Heringsnachwuchses in der Nordsee

Though the stocks of North Sea herring seemed to have recovered from small numbers since the mid-1990s we do recently observe a new decline in the spawning stock biomass. This is mainly caused by four consecutive years of small reproduction. Whilst the adults produce enough eggs and larvae only few survive until mature stages. The reasons for the bad recruitment are not clear. In this paper we investigate the influence of climate conditions, in particular the North Atlantic Oscillation (NAO) that obviously triggers the interaction between the size of the spawning stock and the abundance of larvae. We show that approximately 60 % of the recruitment variance can be explained by specific constellations of spawning stock size and climatic conditions. Beside physical factors we also discuss several working hypotheses shedding light on the influence of biological variables on the fluctuation of herring offspring.

Morphometric, meristics and comparative studies of Chrysichthys nigrodigititus (Lacepede) from Lagos Lekki and Badagry Lagoons, Lagos State, south west Nigeria

Morphometric measurements, meristic counts and comparative studies of Chrysicthys nigrodigitatus samples from Lagos, Lekki, and Badagry Lagoons was carried out to determine the amount of variation among the species from the different locations using seven meristic and two morphometric characters. Significant differences were observed only between the headlength (F==14.02; P<00.05), number of anal rays (F=19.9; P<0.05) and of gill raker counts (F=142.0, 160.94; P<0.05). The differences observed in the meristic characters could be attributed to environmental and climatic differences of the three isolated sites and therefore phenotypic rather than genetic. This study is valuable for the selection of quality strains of fish species for aquaculture production

"Global Change" und das Meer als Nahrungsquelle

The potential importance of marine produetion as a protein ressource for a growing human population can hardly be overestimated. Climatic changes in the marine environment may affect marine production in a significant way. Increasing levels of UV-B may decrease primary production and thus diminish the food base for harvestable marine ressources. Direct effects on early stages of fishes may occur. Temperature changes can lead to additional mortality in the early phase of life histories of fishes. In spite of the potentially negative scenario, actual effects of global change on the ressources have not been detected so far. The marine organisms dispose of a significant level of pre-adaptation to changes of environmental factors both on a seasonal and an interannual scale. Effects on marine life may therefore be less dramatic than those on terrestrial systems, which are more directly linked with the exponentially growing human population.

Ist die gegenwärtig verstärkte Einwanderung südlicher Fischarten in die Nordsee schon eine Folge des Treibhauseffektes

Due to the greenhouse effect,a long term warming of the atmosphere is expected. For most people the last relative mild winters and the previous two hot summers are clear signals for such a climatic change. Changes in species compositions and the sudden arrival of southern species in the North Sea are explained as consequences of the greenhouse effect. Comparing the situation in the last decades an attempt is made in this article to show the natural variability in the occurrence and to give an answer to the above question.

The importance of periodic droughts for maintaining diversity in the freshwater environment

Whereas some species may rely on periodic drought conditions for part of their life histories, or have life strategies suited to exploiting the habitat or changed environmental conditions that are created by drought, for other organisms it is a time of stress. Periodic drought conditions therefore generate a series of waves of colonization and extinctions. Studies on lowland wet grassland, in winterbournes and in the toiche zone of both ponds and rivers, also demonstrate that different organisms are competitively favoured with changing hydrological conditions, and that this process prevents any one species from overwhelming its competitors. Competitive impacts may be inter- and intraspecific. It is therefore apparent that the death of organisms such as adult fish during severe drought conditions, though traumatic for human onlookers and commercial interests, may be merely a regular occurrence to which the ecosystem is adapted. The variability of climatic conditions thereby provides a direct influence on the maintenance of biological diversity, and it is this very biodiversity that provides the ecosystem with the resilience to respond to environmental changes in both the short and the longer term.

Rapid changes in the vegetation of a shallow pond in Epping Forest, related to recent droughts

Over much of Britain, 1995 and 1996 have been perceived as drought years. To evaluate the impact that local climatic conditions are having upon successional changes in higher vegetation (macrophytes), Speakmans Pond in Epping Forest was surveyed and mapped in 1996. The results are related to previous vegetation surveys carried out in 1989 and 1991. In 1989 the dominant marginal vegetation was floating sweet-grass Glyceria fluitans, which also covered a major part of the main body of the pond. Other abundant species included soft rush Juncus effusus, reed mace Typha latifolia and yellow flag Iris pseudocorus. A small (central) area of open water contained bladderwort Utricularia vulgaris and white water-lily Nymphaea alba. A similar plant coverage was found in 1991, with a dominance of floating sweet-grass along the shallow eastern edge. A marked change in the pond was found during the 1996 survey of vegetation in July, when the pool was dry. The major plant cover now consisted of creeping bent Agrostis stolonifera, with isolated clumps of Yorkshire fog Holcus lanatus around the edges; both are terrestrial grasses found on land surrounding the pond. Rushes (Juncus) had increased their distribution round the margins of the pond, and the patch of yellow flag noted in 1989 and 1991 was not found in 1996. The deeper trenches were also dry, but a small patch of white water-lily remained adjacent to one of the trenches.

Limnology in Sicily: A history of fresh waters surrounded by the sea

The aim of this short article is to trace the history of limnology in Sicily, from the end of the last century up to the present, and pay a little homage to a scientist to whom limnology is deeply indebted: G.E. Hutchinson. Due to its insular and climatic conditions, Sicily is characterised by a drainage network formed by numerous short, torrent-like rivers, and by a few small, natural lakes. The geological characteristics of the island strongly condition the quality of these small waterbodies which generally have surface areas of less than 0.2 km super(2). The earliest observations on Sicilian lentic waters go back more than a century; in particular, at the end of the 19th century, some of the issues regarding the natural lakes had already been brought into focus. Subsequent studies on natural waterbodies concentrated on the geomorphology of landslide lakes or lakes created by the dissolution of the gypsum tableland. However, many of the waterbodies no longer exist because of land reclamation which took place up to the first half of the 1950s. During the last 35 years, there has been a notable increase in limnological publications. In addition, these studies show a more careful and integrated approach to the limnological aspects of waterbodies, compared with the early studies.

Application of diatom analysis for the study of the history of the lakes of north-west USSR. [Translation from: Istoriya Ozer; Trudy Vses.Simp.Vilnius p1-7. Vilnius, 1970.]

During late - and post-glacial times lakes played a leading role in the development of the landscape of the North-west European part of USSR. A variety of geographic circumstances created great variegation of natural conditions in lakes and determined the composition of their diatoms. The basic stages of the development of the diatom flora of lakes are linked with general climatic changes. The deepwater regions of large periglacial lakes of the North-west USSR are inhabited by plankton diatoms of the genera Melosira and Cyclotella. Diatom analysis is further applied for the study of the history of the lakes of north-west USSR.

Changes in the phytoplankton

An article discussing changes observed in phytoplankton of the Lake District. An overview is given of previous phytoplankton studies undertaken in the area, detailing some changes found in various waterbodies. Water quality changes in Lake Windermere are mentioned, including the gradual increase of dissolved organic matter (DOM), believed to be caused by the increase of sewage to the lake. The lakes in the Alps are given as an example of a similar anthropogenic pollution scenario. The treatment of a Lake District tarn with bone meal is described. The article goes on to discuss the composition of plankton throughout the year under a variety of climatic conditions. A figure shows seasonal variation in the consistuents of phytoplankton in Windermere (north basin).

Design for Survival: Sustainability for Planet and Structure

Buildings in Port Aransas encounter drastic environmental challenges: the potential catastrophic storm surge and high winds from a hurricane, and daily conditions hostile to buildings, vehicles, and even most vegetation. Its location a few hundred feet from the Gulf of Mexico and near-tropical latitude expose buildings to continuous high humidity, winds laden with scouring sand and corrosive salt, and extremes of temperature and ultraviolet light. Building construction methods are able to address each of these, but doing so in a sustainable way creates significant challenges. The new research building at the Marine Science Institute has been designed and is being constructed to meet the demand for both survivability and sustainability. It is tracking towards formal certification as a LEED Gold structure while being robust and resistant to the harsh coastal environment. The effects of a hurricane are mitigated by elevating buildings and providing a windproof envelope. Ground-level enclosures are designed to be sacrificial and non-structural so they can wash or blow away without imposing damage on the upper portions of the building, and only non-critical functions and equipment will be supported within them. Design features that integrate survivability with sustainability include: orientation of building axis; integral shading from direct summer sunlight; light wells; photovoltaic arrays; collection of rainwater and air conditioning condensate for use in landscape irrigation; reduced impervious cover; xeriscaping and indigenous plants; recycling of waste heat from air conditioning systems; roofing system that reflects light and heat; long life, low maintenance stainless steel, high-tensile vinyl, hard-anodized aluminum and hot-dipped galvanized mountings throughout; chloride-resistant concrete; reduced visual impact; recycling of construction materials.

'The highly nervous system of the English Lakes': aquatic ecosystem sensitivity to external changes, as demonstrated by diatoms.

The author reviews the stratigraphic diatom profile of Cumbrian lakes since the last glaciation. Knowledge of both present and previous interglacials suggests that a natural cycle of change is imposed on all lakes. The nature of inwashed material is dependant on climatic and natural soilcycles and this affects the water quality and sensitive aquatic biota. Anthropogenic effects are superimposed upon this with forest clearance and pollution. Whilst some Cumbrian diatom profiles extend over the entire post glacial, others cover only detailed sections relating to particular problems. Causes and effect of recent changes in lakes can be studied using indicator species but palaeocology contributes greatly to understanding of long term changes.

Marine biology of the Sierra Leone River Estuary. 1. The physical environment

The Sierra Leone River Estuary is a relatively young drowned river valley, it is shallow except for a deep channel which passes close to the Freetown shoreline. The upper reaches merge into a network of creeks and channels fringed by large areas of mangrove swamps. It is a tidal estuary of the semi-mixed type with the saline oceanic water entering it on a diurnal cycle. The climate of Sierra Leone is marked by a very distinct change between a very wet rainy season and a dry season. The tidal range of the Estuary (spring 3.03m; neap 2.28m) does not impede normal use of the harbour. The tidal variations can be felt as far as 42 miles inland along the water courses of the Sierra Leone River and its tributaries. The volume of fresh water entering the Estuary is large during the rainy season and greatly reduced during the dry season. Consequently there is a marked fall in salinity during the rainy season and higher salinities due to the marine influence prevailing during the dry season. The nature of the shores and bottom, the hydrography and chemistry of the estuarine system have been outlined in relation to the prevailing climatic conditions.

Die Entwicklung des Aufwandes in der deutschen Garnelenfischerei und der Versuch einer Standardisierung der jährlichen Einheitsanlandungen (LPUE) zwischen 1976 und 2010

Brown shrimp is a fastgrowing, shortlived species, and all attempts to use stock assessment methodologies typically applied to other fisheries are usually unsuccessful. Here landings per unit effort data (LPUE) for the German fleet based on a number of effort metrics are used as indices of stock size. Their utility in relation to describing stock development and fisheries management is discussed. LPUE estimates indicate that stock sizes between 1976 and 1989 were relatively stable. In 1990, the lowest reported landings of brown shrimps in Germany coincided with severe economic problems for the shrimp fisheries. From 1990 to 2010 standardised annual indices show that both landings and LPUE estimates have increased at variable rates suggesting large stocks of brown shrimps in recent years. This is discussed in relation to the positive effects of reduced predator abundance and favourable climatic factors.

Effects of the 1997-1998 El Niño on population size and diet of the Galápagos sea lion (Zalophus wollebaeki)

The multi-annual climatic event, El Niño Southern Oscillation (ENSO) is an important factor in the population dynamics of coastal marine species in the Galápagos. The Galápagos sea lion, Zalophus wollebaeki, suffered an apparent population decline of about 50%, considering both mortality and movements away from study sites during the 1997-98 El Niño. This change was in part due to changes in the availability of sardines of the Family Clupeidae, its main prey. These declines resulted partly from elevated mortality (35%) in sea lion colonies, particularly among pups, juveniles (< 1 year old), and dominant males and as a result of movements of adults elsewhere (15%), presumably where there were alternative prey and better environmental conditions.

The structure and margins of the Lake Chilwa fisheries in Malawi: a value chain analysis

Small freshwater pelagic fisheries in closed lakes are very important to millions of people in sub-Saharan Africa providing livelihoods and nutritional security. However, returns from these fisheries have been shown to �uctuate in response to climatic variability. In order to understand the impact of these fluctuations on the livelihoods of people dependant on these fisheries, there is a need for information on how the fish value chain is organized and how it functions in response to variation in supplies. The results will feed into strategies that build resilience in fishing households against the uncertainties arising from unstable ecosystems. The Lake Chilwa fishery value chain is composed of fishers, processors, traders, fish transporters, boat owners, owners of fish processing shades, fisheries associations, gear owners, gear makers, firewood sellers, and traders of fishing gear and equipment. The value chain employs many people and local authorities can consider using this information in the design of rural development strategies for employment generation in small-scale fishing communities. The findings from this study have a number of implications for the improvement of the livelihood of fishers and enhancing their capacity to mitigate against the effects of climate change.