Responses of Aquatic Invertebrates to Declining Oxygen Conditions

Several models for the analysis of data relating the rate ofoxygen uptake to environmental oxygen level have been evaluated.We conclude that the quadratic (or second-degree) polynomial,though hardly perfect, is the best. Data from 31 species ofaquatic invertebrates are described by constants of the quadratic(or second-degree) polynomial equation. The results suggesta phylogenetic trend of increasing regulation of aerobic metabolismin response to declining environmental levels as animals acquirestructures that effectively insulate their respiring tissuefrom the habitat. Many of these species apparently cease withdrawingoxygen from their external environment long before they haveexhausted its supply. Presumably, those species with long lastinginternal oxygen reservoirs, such as gas bubbles or pools ofhigh oxygen affinity hemoglobin, continue to operate aerobicpathways, but those without substantial oxygen storage devicesmust switch over to anaerobic pathways, despite the availabilityof small residual volumes of external oxygen.     

Parasites of Aquatic Exotic Invertebrates: Identification of Potential Risks Posed to the Great Lakes

Exotic species typically lose most of their associated parasites during long-distance spread. However, the few parasites that are co-introduced may have considerable adverse impacts on their novel hosts, including mass mortalities. We present a comprehensive inventory of parasites known to infect 38 species of exotic invertebrates established in the Great Lakes, as well as 16 invertebrate species predicted to arrive in the near future, all of them crustaceans. Based on a literature analysis, we identified a total of 277 parasite taxa associated with the examined invertebrates in their native ranges and/or invaded areas. Of these parasites, 56 species have been documented to cause various pathologies in their intermediate or final hosts, with humans and fishes being the most frequently affected host categories. Potentially harmful parasites were identified in 61% of the invaders for which published information was retrieved (in their ranges outside of the Great Lakes), with molluscs and crustaceans hosting the highest numbers of such parasites. The results of our study provide a baseline for further assessment and management of the parasitological risks posed by exotic species to the Great Lakes.     

Denitrification in Aquatic Environments: A Cross-system Analysis

A meta-analysis was conducted on 136 data sets of denitrification rates (DR) recorded both during the period of highest water temperature and monthly in five types of aquatic ecosystems: oceans, coastal environments, estuaries, lakes and rivers. There was a gradual increase of DR from the ocean to rivers and lakes at both scales, with the rivers showing the highest DR variability. Denitrification peaked during summertime and showed highest seasonal variability in lakes and rivers. High concentrations of nitrate and interstitially-dissolved organic carbon as well as low oxygen concentration in the overlying water enhanced DR both during summer and at a seasonal scale whereas total phosphorus did at the seasonal scale only. There was a positive linear relationship between overlying nitrate and DR over the range of 1–970 μmol NO₃ (r ² = 0.86, P = 0.001). DR in lakes and rivers might reach values doubling those in the more denitrifying terrestrial ecosystems (e.g. agrosystems). Discrepancies in DR and its controlling factors between site-specific studies and this meta-analysis may arise from environmental variability at two, often confounded, scales of observation: the habitat and the ecosystem level. Future studies on denitrification in aquatic environments should address the topic of spatial heterogeneity more thoroughly.     

Development and Macroevolution: Introduction to the Symposium

Despite the historical relationship between embryology and evolutionarybiology, during most of the 20th century developmental biologyand evolutionary biology have existed as two separate subdisciplinesof biology. Recently a reunion of these subdisciplines beganto take place. This reunion involves the formulation of evolutionaryexplanations of developmental phenomena and the applicationof developmental processes as mechanisms of evolutionary change.The symposium speakers have considered both aspects of the reunionas well as some of the theoretical and methodological issuesthat are emerging from it.     

Introduction to the Nigel Barlow Symposium

Dr Nigel Barlow died on 4 June 2003 aged 53 in Christchurch, New Zealand. Nigel completed his PhD at the University of East Anglia in 1977 and emigrated to New Zealand in 1979 where he worked initially at Palmerston North and for the last 12 years for AgResearch at Lincoln. Nigel made an enormous contribution to New Zealand ecological science through the use of mathematically based models. In particular, he worked on insect pests such as grass grubs and vertebrate pests such as possums and rabbits, producing over 130 papers. Nigel’s models of bovine tuberculosis underpinned the current strategies and expenditure of over $50 million each year on the control of wildlife vectors on this disease. Nigel’s capabilities as a scientist were not only in the applied field but also reflected in his ability to win funds with his student John Kean from the prestigious Marsden Fund for basic research on the causes of rarity. He was Editor of the New Zealand Journal of Ecology from 1985 to 1990 and of the Journal of Applied Ecology. Nigel was awarded the New Zealand Ecological Society Award for his outstanding contribution to applied ecology in 1996 and posthumously in 2003 the Caughley Medal for lifetime contributions to wildlife management and ecology by the Australasian Wildlife Management Society. Nigel was a true polymath and enthusiast about all natural history. He had an interest in bird-winged butterflies and regularly vanished into the jungles of Indonesia and Papua New Guinea to study them. He was fascinated by crocodilians and anacondas, mountain climbing, landscape painting, and malt whisky. At work he was resistant to bureaucratic interference but happy to pass on his abilities and insights to his students and numerous colleagues.     

Ecology of Vibrio mimicus in Aquatic Environments

[This corrects the article on p. 2077 in vol. 55.].     

Rate of Bacterial Mortality in Aquatic Environments

A method is proposed which provides a minimum estimate of the rate of bacterial mortality in growing natural populations of planktonic bacteria. This estimate is given by the rate of decrease of radioactivity from the DNA of a [³H]thymidine-labeled natural assemblage of bacteria after all added thymidine has been exhausted from the medium. Results obtained from river water, estuarine water, and seawater show overall bacterial mortality rates in the range 0.010 to 0.030 h⁻¹, in good agreement with the range of growth rates measured in the same environments. Use of selective filtration through Nuclepore filters (pore size, 2 μm) allowed us to determine the contribution of microzooplankton grazing to overall bacterial mortality. Grazing rates estimated by this method ranged from 0 to 0.02 h⁻¹.     

Detection of the Antiviral Drug Oseltamivir in Aquatic Environments

Oseltamivir (Tamiflu®) is the most important antiviral drug available and a cornerstone in the defence against a future influenza pandemic. Recent publications have shown that the active metabolite, oseltamivir carboxylate (OC), is not degraded in sewage treatment plants and is also persistent in aquatic environments. This implies that OC will be present in aquatic environments in areas where oseltamivir is prescribed to patients for therapeutic use. The country where oseltamivir is used most is Japan, where it is used to treat seasonal flu. We measured the levels of OC in water samples from the Yodo River system in the Kyoto and Osaka prefectures, Japan, taken before and during the flu-season 2007/8. No OC was detected before the flu-season but 2–58 ng L⁻¹ was detected in the samples taken during the flu season. This study shows, for the first time, that low levels of oseltamivir can be found in the aquatic environment. Therefore the natural reservoir of influenza virus, dabbling ducks, is exposed to oseltamivir, which could promote the evolution of viral resistance.     

Convergent Evolution of Mechanically Optimal Locomotion in Aquatic Invertebrates and Vertebrates

Examples of animals evolving similar traits despite the absence of that trait in the last common ancestor, such as the wing and camera-type lens eye in vertebrates and invertebrates, are called cases of convergent evolution. Instances of convergent evolution of locomotory patterns that quantitatively agree with the mechanically optimal solution are very rare. Here, we show that, with respect to a very diverse group of aquatic animals, a mechanically optimal method of swimming with elongated fins has evolved independently at least eight times in both vertebrate and invertebrate swimmers across three different phyla. Specifically, if we take the length of an undulation along an animal’s fin during swimming and divide it by the mean amplitude of undulations along the fin length, the result is consistently around twenty. We call this value the optimal specific wavelength (OSW). We show that the OSW maximizes the force generated by the body, which also maximizes swimming speed. We hypothesize a mechanical basis for this optimality and suggest reasons for its repeated emergence through evolution.     

Diatoms: A Novel Source for the Neurotoxin BMAA in Aquatic Environments

Amyotrophic lateral sclerosis (ALS) or Lou Gehrig’s disease is a neurological disorder linked to environmental exposure to a non-protein amino acid, β-N-methylamino-L-alanine (BMAA). The only organisms reported to be BMAA-producing, are cyanobacteria – prokaryotic organisms. In this study, we demonstrate that diatoms – eukaryotic organisms – also produce BMAA. Ultra-high-performance liquid chromatography coupled with tandem mass spectrometry revealed the occurrence of BMAA in six investigated axenic diatom cultures. BMAA was also detected in planktonic field samples collected on the Swedish west coast that display an overrepresentation of diatoms relative to cyanobacteria. Given the ubiquity of diatoms in aquatic environments and their central role as primary producers and the main food items of zooplankton, the use of filter and suspension feeders as livestock fodder dramatically increases the risk of human exposure to BMAA-contaminated food.     

Introduction to the Symposium: What is Computational Neurobiology?

SYNOPSIS. Current advances in computational biology are derivedfrom two sets of ideas established in the work of Santiago Ramóny Cajal. One is the neuron doctrine, which holds that neuronsare the functional units of the nervous system, and has ledto detailed models of neuronal properties based on increasinginformation on the physical and chemical properties of neurons.The second is the idea of networks of neurons with specificpatterns of interconnections that has led to a variety of mathematicalmethods of analyzing such networks. Future work in computationalneurobiology promises to be a blend of these two modeling approaches.     

Stress: a Factor to be Considered in Heterotrophic Microorganism Enumeration from Aquatic Environments

Heterotrophic microorganisms in water samples are susceptible to the transient stress of warmed agar used in the standard methods pour plate procedure, causing significantly decreased recoveries in comparison with a spread plate technique. Microbial starvation can increase susceptibility to a transient warming stress. The standard plate count procedure, as presently described, should not be considered for quantitation of microorganisms from aquatic environments.     

A simple system for the Collection of Leaf-Derived Faecal Pellets of Aquatic Invertebrates

Animals and food (leaves) are confined at a desired temperature in a feeding chamber in the upper portion of the water column of a collector system. Egested material collects in water at 0°C also eliminates coprophagy and physical damage to the pellets.