Showing papers in "Hydrobiologia in 2001"

The interaction between water movement, sediment dynamics and submersed macrophytes

Abstract: Water movement in freshwater and marine environments affects submersed macrophytes, which also mediate water movement. The result of this complex interaction also affects sediment dynamics in and around submersed macrophyte beds. This review defines known relationships and identifies areas that need additional research on the complex interactions among submersed macrophytes, water movement, and sediment dynamics. Four areas are addressed: (1) the effects of water movement on macrophytes, (2) the effects of macrophyte stands on water movement, (3) the effects of macrophyte beds on sedimentation within vegetated areas, and (4) the relationship between sediment resuspension and macrophytes. Water movement has a significant effect on macrophyte growth, typically stimulating both abundance and diversity of macrophytes at low to moderate velocities, but reducing growth at higher velocities. In turn, macrophyte beds reduce current velocities both within and adjacent to the beds, resulting in increased sedimentation and reduced turbidity. Reduced turbidity increases light availability to macrophytes, increasing their growth. Additionally, macrophytes affect the distribution, composition and particle size of sediments in both freshwater and marine environments. Therefore, establishment and persistence of macrophytes in both marine and freshwater environments provide important ecosystem services, including: (1) improving water quality; and (2) stabilizing sediments, reducing sediment resuspension, erosion and turbidity.

White-band disease and the changing face of Caribbean coral reefs

Abstract: In recent decades, the cover of fleshy macroalgae has increased and coral cover has decreased on most Caribbean reefs. Coral mortality precipitated this transition, and the accumulation of macroalgal biomass has been enhanced by decreased herbivory and increased nutrient input. Populations of Acropora palmata (elkhorn coral) and A. cervicornis (staghorn coral), two of the most important framework-building species, have died throughout the Caribbean, substantially reducing coral cover and providing substratum for algal growth. Hurricanes have devastated local populations of Acropora spp. over the past 20–25 years, but white-band disease, a putative bacterial syndrome specific to the genus Acropora, has been a more significant source of mortality over large areas of the Caribbean region.

Jellyfish blooms: are populations increasing globally in response to changing ocean conditions?

Abstract: By the pulsed nature of their life cycles, gelatinous zooplankton come and go seasonally, giving rise in even the most undisturbed circumstances to summer blooms. Even holoplanktonic species like ctenophores increase in number in the spring or summer when planktonic food is available in greater abundance. Beyond that basic life cycle-driven seasonal change in numbers, several other kinds of events appear to be increasing the numbers of jellies present in some ecosystems. Over recent decades, man’s expanding influence on the oceans has begun to cause real change and there is reason to think that in some regions, new blooms of jellyfish are occurring in response to some of the cumulative effects of these impacts. The issue is not simple and in most cases there are few data to support our perceptions. Some blooms appear to be long-term increases in native jellyfish populations. A different phenomenon is demonstrated by jellyfish whose populations regularly fluctuate, apparently with climate, causing periodic blooms. Perhaps the most damaging type of jellyfish increase in recent decades has been caused by populations of new, nonindigenous species gradually building-up to ‘bloom’ levels in some regions. Lest one conclude that the next millennium will feature only increases in jellyfish numbers worldwide, examples are also given in which populations are decreasing in heavily impacted coastal areas. Some jellyfish will undoubtedly fall subject to the ongoing species elimination processes that already portend a vast global loss of biodiversity. Knowledge about the ecology of both the medusa and the polyp phases of each life cycle is necessary if we are to understand the true causes of these increases and decreases, but in most cases where changes in medusa populations have been recognized, we know nothing about the field ecology of the polyps.

Interactions of pelagic cnidarians and ctenophores with fish: a review

Abstract: Medusae, siphonophores and ctenophores (here grouped as ‘pelagic coelenterates’) interact with fish in several ways. Some interactions are detrimental to fish populations, such as predation by gelatinous species on pelagic eggs and larvae of fish, the potential competition for prey among pelagic coelenterates and fish larvae and zooplanktivorous fish species, and pelagic coelenterates serving as intermediate hosts for fish parasites. Other interactions are positive for fish, such as predation by fish on gelatinous species and commensal associations among fish and pelagic coelenterates. The interactions range from beneficial for the gelatinous species (food, parasite removal), to negative (predation on them). We review existing information and present new data on these topics. Although such interactions have been documented frequently, the significance to either fish or pelagic coelenterate populations is poorly understood. The effects of pelagic coelenterates on fish populations are of particular interest because of the great importance of fisheries to the global economy. As fishing pressures mount, it becomes increasingly important to understand how they may influence the balance between pelagic coelenterates and fish.

Nitrogen retention in wetlands, lakes and rivers

Abstract: As human activities continue to alter the global nitrogen cycle, the ability to predict the impact of increased nitrogen loading to freshwater systems is becoming more and more important Nitrogen retention is of particular interest because it is through its combined processes (denitrification, nitrogen sedimentation and uptake by aquatic plants) that local and downstream nitrogen concentrations are reduced Here, we compare the magnitude of nitrogen retention and its components in wetlands, lakes and rivers We show that wetlands retain the highest proportion of total nitrogen loading, followed by lakes and then rivers The differences in the proportion of N retained among systems is explained almost entirely by differences in water discharge Denitrification is the primary mechanism of nitrogen retention, followed by nitrogen sedimentation and uptake by aquatic plants

A physical context for gelatinous zooplankton aggregations: a review

Abstract: The magnitude and extent of jellyfish blooms are influenced not only by the biology and behavior of the animal, but also by the geographic setting and physical environment. Hydrography alone is often thought to cause or favor gelatinous zooplankton aggregations, however, it is clear that interactions between biology of the animal and physics of the water are very important sources of population variations, especially at local scales. We summarize the role of physical processes and phenomena that promote aggregations of gelatinous zooplankton. We have identified and discussed a suite of physical gradients that can be perceived by gelatinous zooplankton. These include light, gravity, temperature, salinity, pressure and turbulence. A recurring theme is accumulation of jellyfish around physical discontinuities such as fronts (shelf-break, upwelling, tidal and estuarine) and pycnoclines (thermoclines and haloclines). Interestingly, there are few data to suggest that large-scale, quasi-stationary features, such as the largest oceanic fronts, serve to physically aggregate gelatinous animals at a similar scale. Rather, examples of local aggregations appear to dominate the literature. We also discuss various jellyfish behaviors that are theorized to promote aggregation, feeding and reproduction in relation to physical discontinuities.

Reproduction and life history strategies of the common jellyfish, Aurelia aurita, in relation to its ambient environment

Abstract: The scyphozoan Aurelia aurita (Linnaeus) is a cosmopolitan species, having been reported from a variety of coastal and shelf sea environments around the world. It has been extensively studied over the last 100 years or so, and examination of the literature reveals three striking features: (1) the presence of populations in a wide range of environmental conditions; (2) large inter-population differences in abundance and life history patterns over large and small spatial scales; and (3) inter-annual variability in various aspects of its population dynamics. A. aurita is clearly a highly flexible species that can adapt to a wide range of environmental conditions. While various physiological and behavioural characteristics explain how A. aurita populations can take advantage of their surrounding environment, they do not explain what governs the observed temporal and spatial patterns of abundance, and the longevity or lifespan of populations. Understanding these features is necessary to predict how bloom populations might form. In a given habitat, the distribution and abundance of benthic marine invertebrates have been found to be maintained by four factors: larval recruitment (sexual reproduction), migration, mortality and asexual reproduction. The aims of this review are to determine the role of reproduction and life history strategies of the benthic and pelagic phases of A. aurita in governing populations of medusae, with special attention given to the dynamic interaction between A. aurita and its surrounding physical and biological environment.

Growth in Crustacea — twenty years on

Abstract: Developments during the past 20 years are reviewed for four aspects of crustacean growth. These are the hormonal control of moulting, the effects of external factors on growth rate, the patterns of growth and the determination of age. Hormonal control. The nature and structure of Moult Inhibiting Hormone has been determined, though the mechanism by which it inhibits crustecdysone production is still unclear. A role in moult control by Crustacean Hyperglycaemic Hormone has been demonstrated, but needs clarification. Methyl farnesoate, a juvenile hormone like substance, occurs in Crustacea: however, a clear function as a juvenile hormone has yet to be shown. External factors. The effect of increased temperature in reducing moult increments is supported by further data. Reduced food supply causes smaller moult increments and longer intermoult periods: the latter effect is generally proportionately greater. A role for CHH in this process is hypothesised. Patterns of growth. Little advance has occurred in understanding the rationale for the diversity of growth patterns. Computer modelling offers promise, but is constrained by lack of data on natural mortality for validation. Determination of age. The basic methods available remain size frequency analysis and tagging programmes. There have been advances in technology and methods of analysis, but no major breakthrough. Novel methods include radionuclide ratios (expensive, complex and give only duration of current intermoult), lipofuschin pigment assay (promising, but needs further validation), and annular structures in the infra-cerebral organ (still very speculative).

The ctenophore Mnemiopsis in native and exotic habitats: U.S. estuaries versus the Black Sea basin

Abstract: The native habitats of the ctenophore, Mnemiopsis, are temperate to subtropical estuaries along the Atlantic coast of North and South America, where it is found in an extremely wide range of environmental conditions (winter low and summer high temperatures of 2 and 32 °C, respectively, and salinities of <2–38). In the early 1980s, it was accidentally introduced to the Black Sea, where it flourished and expanded into the Azov, Marmara, Mediterranean and Caspian Seas. We compile data showing that Mnemiopsis has high potentials of growth, reproduction and feeding that enable this species to be a predominant zooplanktivore in a wide variety of habitats; review the population distributions and dynamics of Mnemiopsis in U.S. waters and in the Black Sea region; and examine the effects of temperature and salinity, zooplankton availability and predator abundance on Mnemiopsis population size in both regions, and the effects of Mnemiopsis on zooplankton, ichthyoplankton and fish populations, focusing on Chesapeake Bay and the Black Sea. In both regions, Mnemiopsis populations are restricted by low winter temperatures (<2 °C). In native habitats, predators of Mnemiopsis often limit their populations, and zooplanktivorous fish are abundant and may compete with the ctenophores for food. By contrast, in the Black Sea region, no obvious predators of Mnemiopsis were present during the decade following introduction when the ctenophore populations flourished. Additionally, zooplanktivorous fish populations had been severely reduced by over fishing prior to the ctenophore outbreak. Thus, small populations of potential predators and competitors for food enabled Mnemiopsis populations to swell in the new habitats. In Chesapeake Bay, Mnemiopsis consumes substantial proportions of zooplankton daily, but may only noticeably reduce zooplankton populations when predators of Mnemiopsis are uncommon. Mnemiopsis also is an important predator of fish eggs in both locations. In the Black Sea, reductions in zooplankton, ichthyoplankton and zooplanktivorous fish populations have been attributed to Mnemiopsis. We conclude that the enormous impact of Mnemiopsis on the Black Sea ecosystem occurred because of the shortage of predators and competitors in the late 1980s and early 1990s. The appearance of the ctenophore, Beroe ovata, may promote the recovery of the Black Sea ecosystem from the effects of the Mnemiopsis invasion.

Patterns of spread of coral disease in the Florida Keys

Abstract: Reefs in the Florida Keys are experiencing a dramatic increase in the number of localities and number of species with coral disease. In extensive surveys from Key Largo to Key West in 160 stations at 40 randomly chosen sites, there has been a dramatic increase in (1) the number of locations exhibiting disease (82% of all stations are now affected, a 404% increase over 1996 values), (2) the number of species affected (85% of all species are now affected, a 218% increase over 1996 values), and (3) the rate of coral mortality (the deep fore-reef at Carysfort experienced a 60% reduction of living coral cover during the survey). Two null hypotheses (1) that the incidence of disease has remained constant through time and (2) that the apparent increase in disease is due to a lack of comparable earlier data, are both falsified. Different diseases exhibit different patterns of spread: some diseases (e.g. black band) exhibit low incidence and jump rapidly between sites; other diseases (e.g. white pox) exhibit patchy distributions and increase in frequency at affected sites from one year to the next. The central question of why so many corals are becoming simultaneously susceptible to a host of marine pathogens remains unanswered.

Anthropogenic salinisation of inland waters

Abstract: Many inland waters are becoming more saline from human activities, particularly in semi-arid and arid regions. The causes and distribution of anthropogenic salinisation, the salinisation of freshwater lakes, rivers and streams, and increases in the salinity of large, permanent saline lakes are discussed. The impacts of anthropogenic salinisation are far-reaching, increasing, deleterious and largely irreparable. Environmental, social and environmental costs are high. Attention is drawn to the importance of anthropogenic salinisation and its impacts. The need for better recognition of the costs of salinisation and for more effective management is stressed.

The symbiotic role of marine microbes on living surfaces

Abstract: Every surface immersed in the sea rapidly becomes covered with a biofilm On inanimate surfaces, this is often followed by colonisation by larger organisms, and general macrofouling On the other hand, the majority of marine organisms remain relatively free from macrofouling, although some may be covered in a thin film of epibiotic bacteria The role of these bacteria in maintaining the health of the host has received little attention Here we describe an ecological role for epibiotic bacteria from seaweed surfaces These epibionts may play a protective role, releasing compounds into the surrounding seawater that help prevent extensive fouling of the surface These compounds may also have industrial and medical applications The relative ease of culturing these microbes, compared to other bacteria that produce active compounds suggests seaweed-associated bacteria may be useful in bioprocess applications, such as the production of antimicrobial or antifouling compounds

Pelagic coelenterates and eutrophication: a review

Abstract: Although eutrophication is a widespread problem in marine waters, its effects are often difficult to separate from normal fluctuations of pelagic coelenterate populations and from other anthropogenic changes due to industrial pollution, construction, introductions, global warming and overfishing The least complex situations are in small coastal water bodies such as the Caribbean lagoons and Scandinavian fjords Typically, the diversity of pelagic coelenterates decreases, but the biomass of a small number of species (such as the hydromedusae Aglantha digitale and Rathkea octopunctata and the scyphomedusae Aurelia aurita and Cassiopea spp) may increase Adaptations that may allow these species to survive under eutrophic conditions are discussed

Characterization of Aspergillus sydowii (Thom et Church), a fungal pathogen of Caribbean sea fan corals

Abstract: In the Caribbean, the fungus Aspergillus sydowii is currently causing an epizootic among sea fan corals (Gorgonia spp.). To elucidate potential factors that may have facilitated the emergence of this disease, we characterized and compared temperature requirements, susceptibility to coral crude extracts, and metabolic profiles of pathogenic (marine) and non-pathogenic (terrestrial) strains of A. sydowii Growth of all A. sydowii strains were observed at all temperatures tested (22–36°C) with an optimum of approximately 30°C. Sea fan crude extracts inhibited growth of A. sydowii but were less effective at higher temperatures. Thus, temperature is likely to have a strong influence on the dynamics of the Gorgonia-Aspergillus interaction by promoting the growth of the pathogen while reducing the efficacy of host resistance. Metabolically, marine A. sydowii strains pathogenic to sea fans were distinct from non-pathogenic terrestrial strains.

Jellyfish as food.

Abstract: Jellyfish have been exploited commercially by Chinese as an important food for more than a thousand years. Semidried jellyfish represent a multi-million dollar seafood business in Asia. Traditional processing methods involve a multi-phase processing procedure using a mixture of salt (NaC1) and alum (A1K[SO4]2 · 12 H2O) to reduce the water content, decrease the pH, and firm the texture. Processed jellyfish have a special crunchy and crispy texture. They are then desalted in water before preparing for consumption. Interest in utilizing Stomolophus meleagris L. Agassiz, cannonball jellyfish, from the U. S. as food has increased recently because of high consumer demand in Asia. Desalted ready-to-use (RTU) cannonball jellyfish consists of approximately 95% water and 4–5% protein, which provides a very low caloric value. Cannonball jellyfish collagen has shown a suppressing effect on antigeninduced arthritis in laboratory rats. With the great abundance of cannonball jellyfish in the U. S. coastal waters, turning this jellyfish into value-added products could have tremendous environmental and economicbenefits.

Enteroviruses detected by reverse transcriptase polymerase chain reaction from the coastal waters of Santa Monica Bay, California: low correlation to bacterial indicator levels.

Abstract: Microbiological water quality at beaches is typically measured only by indicator bacteria, even though viruses are also a concern, because classical culture-based virus assays are not suitable. In this study, molecular-based assays for the detection of enteroviruses by reverse transcriptase polymerase chain reaction (RT-PCR) were performed on 50 coastal seawater samples taken from Santa Monica Bay, CA, over a six-year period, and compared with indicator bacteria. Sample sites were near freshwater outlets in the Bay and popular sandy beaches. RT-PCR is a primer-based molecular biology technique, used to detect the genomes of specific groups or types of viruses based upon conserved sequences. Results of the 50 analyses showed our ultrafiltration concentration methods and RT-PCR protocol could be used consistently to detect enteroviruses from 20 l samples of coastal seawater. Of the 50 samples, 16 (32%) were positive for enteroviruses, 27 (54%) were negative and 7 (14%) were inconclusive. There was no significant correlation between the presence of enteroviruses and individual standard microbiological indicators of fecal contamination, specifically total coliforms, fecal coliforms, or enterococci (r=0.14, r=0.28 and r=0.34, respectively, p>0.05). However, there was a significant correlation (r=0.71) to a combined set of bacterial water quality standards, involving all three indicators, recently adopted in California. There was no significant correlation between the RT-PCR results and levels of rainfall (a large source of runoff), but our analyses demonstrated that positive results for enteroviruses were significantly more likely during the winter `wet' season than during the summer `dry' season. Our results demonstrate that RT-PCR is an effective method for the detection of enteroviruses in coastal seawater, and they suggest that bacterial indicators are not necessarily good predictors of the presence of such viruses. Enteroviruses are known to be important etiological agents of disease from recreational water contact, so analysis for their presence might be advisable at certain locations (e.g. high-use sandy beaches) or during certain seasons of the year.

The bioenergetic basis for the decrease in metabolic diversity at increasing salt concentrations: implications for the functioning of salt lake ecosystems

Abstract: Examination of the microbial diversity in hypersaline lakes of increasing salt concentrations shows that certain types of dissimilatory metabolism do not occur at the highest salinities. Examples are methanogenesis from hydrogen and carbon dioxide or from acetate, dissimilatory sulfate reduction with oxidation of acetate, and autotrophic nitrification. The observations can be explained on the basis of the energetic cost of haloadaptation used by the different metabolic groups and the free-energy change associated with the dissimilatory reactions. All halophilic microorganisms spend large amounts of energy to maintain steep gradients of Na+ and K+ concentrations across their cytoplasmic membrane. Most Bacteria and also the methanogenic Archaea produce high intracellular concentrations of organic osmotic solutes at a high energetic cost. The halophilic aerobic Archaea (order Halobacteriales) and the halophilic fermentative Bacteria (order Halanaerobiales) use KCl as the main intracellular solute. This strategy, while requiring far-reaching adaptations of the intracellular machinery, is energetically more favorable than production of organic compatible solutes. By combining information on the amount of energy available to each physiological group and the strategy used to cope with salt stress, a coherent model emerges that provides explanations for the upper salinity limit at which the different microbial conversions occur in hypersaline lakes.

The impact of water hyacinth, Eichhornia crassipes (Mart) Solms on the abundance and diversity of aquatic macroinvertebrates along the shores of northern Lake Victoria, Uganda

Abstract: This study examined the impacts of the alien waterweed, water hyacinth, on the abundance and diversity of aquatic macroinvertebrates in the littoral areas of northern Lake Victoria in Uganda. The weed had undergone explosive growth on the lake causing serious disruption to people, the economy and the ecosystem. This study was confined to impact of the weed in the littoral zone, not to the large floating mats of vegetation which float across the lake and clog large areas of shoreline. The littoral area studied comprised of fringing mats of Eichhornia crassipes (Mart) Solms (water hyacinth) to the lakeward of Cyperus papyrus; water hyacinth mats undergoing colonisation by Vossia cuspidata (Roxb.) Griff.; and a typical Cyperus papyrus L shore with no outer floating mat of water hyacinth. Numerical abundance (Nos. m−2) and diversity (No. of taxa) of macroinvertebrates recovered from pure Eichhornia crassipes and the Eichhornia-Vossia succession increased from the fringe of the Cyperus papyrus towards the open water. In the typical Cyperus papyrus fringe, in the absence of water hyacinth, abundance was highest at the papyrus/open water interface and dropped off sharply towards open water. The Shannon–Weaver diversity index (H′) of macroinvertebrates decreased progressively from pure Eichhornia crassipes stands, to Vossia/Eichhornia beds and Cyperus papyrus stands (H′=0.56, 0.54 and 0.34, respectively) but were not significantly different. Dissolved oxygen decreased from open water into vegetation where it approached anoxia. Water hyacinth appeared to enhance the abundance and diversity of aquatic macroinvertebrates at the interface with the open water. The impoverished abundance and diversity of the macroinvertebrates deeper into the vegetation mats suggested negative environmental impacts of the water hyacinth when the fringe is too wide. Further research is recommended to establish the optimum width of the fringe of stationery water hyacinth that promotes maximum abundance and diversity of aquatic macroinvertebrates and, possibly, of other aquatic life. Since this study in 1997, there has been a dramatic decrease in Eichhornia infestations and by June 2000 it appeared largely to exist only as fringing vegetation in bays and inlets.

Demographic, landscape, and meteorological factors controlling the microbial pollution of coastal waters

Abstract: Coastal areas in the United States and many other countries are considered to be desirable regions to live and recreate. However, as human use of coastal land and water increases, so does the incidence of aquatic-borne disease from contact with contaminated water and eating contaminated shellfish. Movement of humans into coastal areas both greatly increases the number of sources of microbial pathogens and radically alters the landscape through increased construction activity and paving of former natural areas. On a regional scale, increases in human population over a 14-year period in coastal North Carolina were strongly correlated with increases in shellfish bed closures due to high fecal coliform bacterial counts. On a watershed scale, an analysis of several tidal creeks found strong correlations between mean estuarine fecal coliform bacterial counts and watershed population, percent developed area and especially with percent impervious surface coverage. Conversion of natural landscapes to impervious surfaces (roads, drives, sidewalks, parking lots and roofs) removes the land’s natural filtration capability, allows for increased concentration of pollutants at the land’s surface and provides a means of rapid conveyance of pollutants to downstream waterways. An analysis of rural watersheds in the Coastal Plain found that stream fecal coliform counts and turbidity were both strongly correlated with rainfall in the previous 24 h in watersheds containing extensive industrial swine and poultry operations, as well as watersheds containing more traditional agriculture and cattle husbandry. In contrast, in watersheds rich in swamp wetlands these relationships were not significant, even in watersheds containing extensive animal production. Based on these findings, we suggest that waterborne microbial pathogen abundance can be minimized in urbanizing coastal areas through reduced use of impervious surfaces and maximal use of natural or constructed wetlands for passive stormwater runoff treatment. In animal husbandry areas, retention of natural wetlands and management practices designed to minimize sediment runoff can likely reduce inputs of pathogenic microbes into streams.

Multivariate analysis of heavy metal and nutrient concentrations in sediments of Taihu Lake, China*

Abstract: Taihu Lake is one of the largest freshwater lakes in China. The Lake is very shallow with a mean depth of 1.9 m and an area of 2428 km2. Nutrient concentrations (Org-C, Tot-N and Tot-P) and heavy metal concentrations (Ag, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sr, Zn, etc.) in the lake's surface sediments were sampled at 13 locations. This was done to determine if industrialized areas along the lake's coastline were impacting the nutrient and heavy metal distribution of the lake's surface sediments. Principal Component Analysis (PCA) was used to assess the degree of contamination and spatial distribution of heavy metals and nutrients in different areas of Taihu Lake.

Phosphate release from anoxic sediments or `What did Mortimer really write?'

Abstract: The release of phosphate from anoxic sediments is still not precisely understood The proposal by Einsele (1936), later adapted by Mortimer (1941, 1942), that this release is caused by the reduction of a FeOOH-phosphate complex, is generally accepted as the reaction mechanism, although there is no experimental evidence for it Golterman (1995a) and De Groot (1991) have shown that this P-release may indeed be brought about by H2S, but only if a large excess of H2S is available In lakes, however, the reducing capacity is relatively small as most of the organic carbon produced by primary production is used for other reduction processes The solubilization of apatite is a likely alternative, as anoxic conditions are automatically concomitant with a pH decrease, and in hard waters the formation of apatite is well demonstrated This mechanism is not active in soft waters, such as those studied by Mortimer Another proposed process is the release of polyphosphate by sediment bacteria Experimental evidence for this mechanism is, however, weak The fourth possibility is the need for bacteria to mineralize a larger part of the sediment organic matter under anoxic conditions in order to obtain the same amount of energy, as some energy will be retained in the fermentation products There is circumstantial evidence for this hypothesis, but laboratory experiments are needed before real evidence will be available

Macroinvertebrate assemblages in Andean Patagonian rivers and streams: environmental relationships

Abstract: Macroinvertebrate communities from 29 streams and rivers of the mountain and the Andean Patagonian Plateau were analyzed. Samples were collected from six river basins, which were part of four different biozones of the Patagonian Ecoregion. Samples from mountain streams were dominated by Plecoptera, Ephemeroptera, Trichoptera and Diptera, while plateau rivers where mainly Diptera, Oligochaeta and Mollusca. Total invertebrate abundance ranged from 7 to 12 249 ind.m−2. Elmidae, Paratrichocladius, Chironomus, Smicridea annulicornis, Parasericostoma ovale and Meridialaris laminata were the most abundant insect taxa, while Nais communis and Hyalella curvispina were the most abundant non-insect taxa. Species-environmental relationships were examined using Canonical Correspondence Analysis. Current speed, conductivity, substrate size and abundance of aquatic plants, were identified as the major variables structuring faunal assemblages. Regression analyses revealed that species richness was negatively correlated with latitude, and positively correlated with water temperature and altitude. Macroivertebrate abundance increased with conductivity, altitude and water temperature. These results suggest that habitat heterogeneity was the strongest predictor of macroinvertebrate assemblages, but species richness could be predicted at a landscape scale using topographical and climatic features.

Impact of Tapes philippinarum farming on nutrient dynamics and benthic respiration in the Sacca di Goro

Abstract: The introduction of the short-necked clam Tapes philippinarum into the Sacca di Goro has over a short period made this coastal environment one of the top European clam production sites. In recent years, this activity has been seriously impacted due to the appearance in the lagoon of large macroalgal beds and the occurrence of dystrophic events causing anoxia and massive deaths of molluscs in the cultivated areas.

Jellyfish fisheries in southeast Asia

Abstract: A few large jellyfish species in the order Rhizostomeae constitute an important food in Chinese cooking. For more than 1700 years, they have been exploited along the coasts of China. Such jellyfish became an important fishery commodity of Southeast Asian countries in the 1970s with increasing demand from the Japanese market. Recently, Japan has imported 5400–10000 tons of jellyfish products per year, valued at about 25.5 million US dollars, annually from the Philippines, Vietnam, Thailand, Malaysia, Indonesia, Singapore and Myanmar. Judging from the type names at market and the external appearance of the semi-dried products, the edible jellyfish harvest in Southeast Asia is composed of more than 8 species. They are caught by various kinds of fishing gear including setnets, drift-nets, hand-nets, scoop-nets, beach-seines and hooks. The fishery is characterized by large fluctuations of the annual catch and a short fishing season that is restricted from two to four months. The average annual catch of jellyfish between 1988 and 1999 in Southeast Asia is estimated to be about 169000 metric tons in wet weight and the worldwide catch is approximately 321 000 metric tons. Needs for future study on the biology of rhizostome jellyfish are discussed as they relate to understanding population fluctuations.

Coral bleaching and disease: contributors to 1998 mass mortality in Briareum asbestinum (Octocorallia, Gorgonacea)

Abstract: High sea surface temperature associated with the recent El Nino was responsible for widespread coral bleaching and mortality around the globe in 1998. In addition to mortality caused by temperature and bleaching associated stresses, some of the coral mortality could be due to the outbreak of diseases among already weakened hosts. One possible example of this is the October 1998 epizootic affecting Briareum asbestinum in the Florida Keys, USA. At Carysfort, Sand Key and Western Dry Rocks, between 75 and 90% of B. asbestinum colonies were bleached with prevalence of necroses on bleached colonies ranging from 18 to 70%. Between October 1998 and January 1999, 18 to 91% of colonies on seven 25 × 2 m transects died (mean=68%). In addition, at Carysfort Reef, 65% of necrotic colonies that were tagged in October 1998 were dead by January of the following year. A grafting experiment revealed that lesion-causing infections were transmissible: lesions occurred on 50% of recipient colonies treated with diseased grafts whereas none of the grafts with healthy tissue resulted in disease. Preliminary work to isolate a causative agent yielded a cyanobacterium Scytonema sp., although work to confirm its role in the mass mortality is still on-going. By January 1999, when surviving colonies had regained their color and many lesions had healed, the cause of the Briareum asbestinum mass mortality or even whether a mass mortality had occurred, would have been difficult to ascertain. By any measure, this was a significant epizootic that would have gone undetected or been attributed to bleaching stress in the absence of our evaluation of the role of an infectious disease.

Modeling underwater light climate in relation to sedimentation, resuspension, water quality and autotrophic growth

Abstract: The underwater light climate ultimately determines the depth distribution, abundance and primary production of autotrophs suspended within and rooted beneath the water column This paper addresses the underwater light climate, with reference to effects of suspended solids and growth responses of autotrophs with emphasis on phytoplankton Effects of the most important factors contributing to the absorption and scattering of light in surface waters were described A comparison between spectral and scalar approaches to underwater light climate modeling was made and examples of linear approximations to light attenuation equations were presented It was demonstrated that spectral and scalar photosynthesis models may converge to similar values in spectral-flat, high photon flux environments, but that scalar PAR models may overestimate biomass-specific production by 70% Such differences can lead to serious overestimates of habitat suitability for the growth and survival of submersed macrophytes, particularly in relatively turbid, coastal waters Relationships between physical and optical properties of suspended sediments were described theoretically, and illustrated with modeling examples and measurements It was found that the slowly settling particulate fraction contributed substantially to the suspended solids concentration, and greatly to light attenuation within the water column It was concluded that distinguishing particles by fall velocity and concomitant light attenuation properties in the modeling of underwater light conditions allowed the establishment of useful, although not simply linear, relationships In eutrophic, shallow lakes, the largest contribution to light attenuation often originates from phytoplankton on a seasonal basis (months–years), but from suspended solids behavior on a shorter time scale (days–weeks), particularly when water bodies are wind-exposed Temporal and spatial variabilities in wave height, suspended solids concentrations, and light attenuation within the water column, and their importance for autotrophic growth were described, and illustrated with a case study pertaining to Markermeer, The Netherlands The influence of underwater light conditions on phytoplankton succession was briefly discussed and illustrated with a case study pertaining to Lake Veluwe, The Netherlands It was concluded that modeling the underwater light climate in a water body on a few sites only can indicate how important various components are for the attenuation of light, but based on the current state of the art, it can not be expected that this will provide accurate predictions of the underwater light climate, and of phytoplankton and submersed macrophyte growth

Distribution of macroinvertebrates in relation to physical and biological variables in the littoral zone of nine New Zealand lakes

Abstract: Macroinvertebrates play a key role in the littoral zone of lakes. Macroinvertebrate community composition is closely linked to habitat conditions. To date, there have been few attempts to relate macroinvertebrates to habitat factors in lakes. In this study, nine mainly oligotrophic lakes from throughout New Zealand were surveyed for macroinvertebrates. The lakes were selected to represent a range of suspended sediment loading and lake level regimes. Within each lake, several sites were selected to provide a range of exposure to wave action. A multiple regression approach was taken to relate macroinvertebrate community composition and habitat characteristics. The results of the analysis suggest that the littoral zone of the lakes we studied could be divided into four general habitats. The first is the wave wash zone characterised by coarse substrates and macroinvertebrate taxa usually associated with lotic environments, such as Ephemeroptera and Plecoptera. The second habitat is associated with macrophytes and is limited at the top by wave action and at depth by light attenuation. In this zone, the snail Potamopyrgus antipodarum is dominant, along with Trichoptera and Odonata. At the base of the macrophytes is the detrital habitat characterised by fine, organic rich sediments and dominated by chironomids, oligochaetes and Trichoptera. At depths below the macrophyte zone, fine sediments are found, and bivalves such as the freshwater mussel Hyridella menziesi are common. While macroinvertebrate abundance can be highly variable, some general predictions of community structure can be made based on a few key environmental factors. Abundance of snails Odonata and Trichoptera was positively related to macrophyte biomass. Some macroinvertebrate groups such as oligochaetes, chironomids, snails and bivalves were more common in fine substrates, while Ephemeroptera were characteristic of coarse substrates. Detrital biomass was important for most of the macroinvertebrate groups studied showing a positive relationship for oligochaetes and Trichoptera and a negative relationship for Ephemeroptera and Plecoptera.

Gradients of salinity stress, environmental stability and water chemistry as a templet for defining habitat types and physiological strategies in inland salt waters

Abstract: The search for pattern in the geographic occurrence of salt lake flora and fauna often reveals strong associations of specific taxa with certain types of water chemistry. Solute composition, along with salinity and habitat stability, may provide a templet shaping the distribution of many organisms inhabiting saline lakes. A review of studies demonstrating habitat associations, specific solute tolerance, and ionic and osmotic adaptations provide evidence of fidelity to particular conditions of environmental chemistry across a wide taxonomic spectrum. Under low salinity conditions, some species show osmoregulatory adaptability to varied solute composition but the capacity for such flexibility is reduced with increased salinity and only certain taxa are found in hypersaline waters dominated by a particular solute. Anionic ratios of chloride, bicarbonate–carbonate, and sulfate appear to be especially important determinants of distribution. Specific solute tolerance presents an alternative explanation to disrupted hydrographic connections in describing how biogeographic distributions may be restricted to certain aquatic habitats in arid regions. Physiological adaptations to chemistry, exemplified in the brine fly genus Ephydra, may be an integral part of the evolution, ecology and diversification of saline water organisms.

Numerical increases and distributional shifts of Chrysaora quinquecirrha (Desor) and Aurelia aurita (Linné) (Cnidaria: Scyphozoa) in the northern Gulf of Mexico

Abstract: Fisheries resource trawl survey data from the National Marine Fisheries Service from a 11–13-year period to 1997 were examined to quantify numerical and distributional changes of two species of northern Gulf of Mexico scyphomedusae: the Atlantic sea nettle, Chrysaora quinquecirrha (Desor), and the moon jelly, Aurelia aurita (Linne). Trawl surveys were grouped into 10 statistical regions from Mobile Bay, Alabama to the southern extent of Texas, and extended seaward to the shelf break. Records of summertime C. quinquecirrha medusa populations show both an overall numerical increase and a distributional expansion away from shore in the down-stream productivity field of two major river system outflows: Mobile Bay and the Mississippi-Atchafalaya Rivers. In addition, there is a significant overlap between summer C. quinquecirrha and lower water column hypoxia on the Louisiana shelf. In trawl surveys from the fall, A. aurita medusae showed significant trends of numerical increase in over half of the regions analyzed. For both species, there were statistical regions of no significant change, but there were no regions that showed significant decrease in number or distribution. The relationships between natural and human-induced (e.g. coastal eutrophication, fishing activity and hard substrate supplementation) ecosystem modifications are very complex in the Gulf of Mexico, and the potential impact of increased jellyfish populations in one of North America's most valuable fishing grounds is a most critical issue. Several hypotheses are developed and discussed to guide future research efforts in the Gulf of Mexico.

Dormancy patterns in rotifers

Abstract: Dormancy is common among rotifers: monogononts produce resting eggs (diapause) commonly after switching to mictic phase, and bdelloids enter anhydrobiosis (quiescence) at any time during their life cycle. Monogononts are short-lived and inhabit coarse-grained environments; their dormancy is a long-lasting diapause, commonly initiated by indirect remote cues. Bdelloids live 3 times as long, live in fine-grained environments and enter short-lasting quiescence as a direct response to changing environment. The two dormancy forms of the rotifers can be related to the temporal variation of their environments and seem to represent diverse responses to disturbance occurring at different rates. The two strategies are alternative and mutually exclusive, as no single rotifer species seems capable of both diapause and quiescence. Dormancy has great ecological significance: it can carry the population through stressful conditions, promote species coexistence and serve as a biodiversity bank providing reliable colonization source.