High pressure effects on marine invertebrates and fishes

A survey of literature and of new information from the author's laboratory is presented concerning the comparative pressure physiology of marine invertebrates and fishes. Short term experiments on littoral marine animals have revealed that the taxonomic groups exhibiting the greatest resistance to high pressures are those with the greatest vertical distributions in the deep sea, namely, echinoderms, molluscs, amphipods, isopods and polychaetes. Shallow water species which possess high thermal and osmotic resistance also show an exceptionally high degree of pressure resistance. The relative differences in genetic pressure resistance of lower marine invertebrates are the same in whole, intact animals and in isolated, surviving tissue pieces. Adaptation of nonregulating euryoecous invertebrates to higher temperatures, higher osmotic concentrations and higher calcium contents of the tissues results in increased pressure resistance. Under pressure, the optimum cellular pH shifts downward to a lower pH range.Lecture presented on October 23, 1967 at Duke University, Marine Laboratory, Beaufort (USA); on November 6, 1967 at the Instituto di Biologia Marinha of the University of São Paulo (Brasil); and on November 8, 1967 at the Institute of Marine Science of the University of Miami (USA).     

Limited trophodynamics effects of trawling on three Mediterranean fishes

Trawling has a significant effect on the structure of marine communities, yet the ubiquity of trawling impacts makes testing such effects difficult. This study examines trawling impacts on trophodynamics of three fishes among the Gulfs of Castellammare and Termini Imerese (northern Sicily), the first of which has been subject to a trawling ban since 1990 that initially resulted in an eightfold increase in total fish biomass. The Gulf of Termini Imerese remains heavily fished and was treated as a control site. Nitrogen and carbon stable isotope data were used to assess fishing induced changes in trophic levels or source of production supporting three demersal fish species; Mullus barbatus, Merluccius merluccius and Lophius budegassa following a control-impact approach. The exclusion of trawling resulted in only small alteration of δ¹⁵N in two of the three-three species. There were no systematic changes in the δ¹³C of any species sampled. Thus, a large influence of trawling on the trophodynamics of the studied species at sampled size was discounted. Although stable isotopes do not have spatial or temporal resolution to identify detailed shifts in diet composition, their integrative nature highlights that the trophic role these species play is robust to fishing impacts at scales over which the fishery operates. This is despite a significant increase in the abundance of these species and of total fish biomass within the protected area.

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Negative effects of nitrogen deposition on Swiss butterflies

Nitrogen (N) deposition from agriculture and combustion of fossil fuels is a major threat to plant diversity, but its effects on organisms at higher trophic levels are unclear. We investigated how N deposition may affect species richness and abundance (number of individuals per species) in butterflies. We reviewed the peer-reviewed literature on variables used to explain spatial variation in butterfly species richness and found that vegetation variables appeared to be as important as climate and habitat variables in explaining butterfly species richness. It thus seemed likely that increased N deposition could indirectly affect butterfly communities via its influence on plant communities. To test this prediction, we analyzed data from the Swiss biodiversity monitoring program for vascular plants and butterflies in 383 study sites of 1 km² that are evenly distributed throughout Switzerland. The area has a modeled N deposition gradient of 2–44 kg N ha⁻¹ year⁻¹. We used traditional linear models and structural equation models to infer the drivers of the spatial variation in butterfly species richness across Switzerland. High N deposition was consistently linked to low butterfly diversity, suggesting a net loss of butterfly diversity through increased N deposition. We hypothesize that at low elevations, N deposition may contribute to a reduction in butterfly species richness via microclimatic cooling due to increased plant biomass. At higher elevations, negative effects of N deposition on butterfly species richness may also be mediated by reduced plant species richness. In most butterfly species, abundance was negatively related to N deposition, but the strongest negative effects were found for species of conservation concern. We conclude that in addition to factors such as intensified agriculture, habitat fragmentation, and climate change, N deposition is likely to play a key role in negatively affecting butterfly diversity and abundance.     

Contrasting effects of habitat loss and fragmentation on coral-associated reef fishes

Disturbance can result in the fragmentation and/or loss of suitable habitat, both of which can have important consequences for survival, species interactions, and resulting patterns of local diversity. However, effects of habitat loss and fragmentation are typically confounded during disturbance events, and previous attempts to determine their relative significance have proved ineffective. Here we experimentally manipulated live coral habitats to examine the potential independent and interactive effects of habitat loss and fragmentation on survival, abundance, and species richness of recruitment-stage, coral-associated reef fishes. Loss of 75% of live coral from experimental reefs resulted in low survival of a coral-associated damselfish and low abundance and richness of other recruits 16 weeks after habitat manipulations. In contrast, fragmentation had positive effects on damselfish survival and resulted in greater abundance and species richness of other recruits. We hypothesize that spacing of habitat through fragmentation weakens competition within and among species. Comparison of effect sizes over the course of the study period revealed that, in the first six weeks following habitat manipulations, the positive effects of fragmentation were at least four times stronger than the effects of habitat loss. This initial positive effect of fragmentation attenuated considerably after 16 weeks, whereas the negative effects of habitat loss increased in strength over time. There was little indication that the amount of habitat influenced the magnitude of the habitat fragmentation effect. Numerous studies have reported dramatic declines in coral reef fish abundance and diversity in response to disturbances that cause the loss and fragmentation of coral habitats. Our results suggest that these declines occur as a result of habitat loss, not habitat fragmentation. Positive fragmentation effects may actually buffer against the negative effects of habitat loss and contribute to the resistance of reef fish populations to declines in coral cover.     

Indirect effects of an exploited predator on recruitment of coral-reef fishes

The more ecologists examine the role of trait-mediated indirect interactions (TMIIs), especially in regulating predator-prey interactions, the more we recognize their fundamental role in structuring food webs. However, most empirical evidence for TMIIs comes from studies that are either conducted in laboratory or mesocosm venues or are restricted to simple food webs involving lower trophic-level animals. Here, I quantified the direct and indirect effects of interactions between high-level vertebrate predators on their vertebrate prey using a field experiment. Specifically, I tested how varying densities of a large-bodied, top predator (Nassau grouper; Epinephelus striatus) affected persistence, growth, and behavior of two smaller-bodied, intermediate predators (coney and graysby groupers; Cephalopholis fulva and C. cruentata) on 20 isolated patch reefs in the Bahamas. Large-bodied groupers are capable of consuming their smaller-bodied counterparts, and previous observational studies have indicated that local abundances of these groupers are negatively correlated. I measured the effects of interactions among groupers on lower trophic-level prey by quantifying recruitment of coral-reef fishes to the reefs. The field experiment demonstrated a strong trophic cascade that was entirely mediated by modified behavior of the intermediate predators. These results indicate that indirect, nonlethal interactions in natural systems can have strong cascading effects even at high trophic levels and in high-diversity food webs. Incorporating the complexity of such indirect effects into fisheries management may improve the sustainability of fished populations and strengthen marine conservation efforts; however these results also indicate that the effects of fishing are complex and difficult to predict.     

Negative effects of vertebrate herbivores on invertebrates in a coastal dune community

Although competition has been a major focus in ecology for the past century, most empirical and theoretical studies in this area have emphasized interactions between closely related species. However, there is growing evidence that negative interactions among distantly related taxa also occur and may be far more important than previously thought. In this study, we took advantage of an 11-year-old replicated vertebrate-exclosure experiment in a coastal dune community in northern California, USA, to examine the effects of the two most common vertebrate herbivores (jackrabbits and black-tailed deer) on the abundance of the three most visible invertebrate herbivores (two snail, a moth, and a grasshopper species). Our results indicate that four of the six possible pairwise interactions were significantly negative for the invertebrates. Jackrabbits reduced the abundances of snails by 44-75%, tiger moth caterpillars by 36%, and grasshoppers by 62%. Deer reduced the abundances of snails by 32%, increased the abundances of caterpillars by 31%, and had no measurable effect on grasshopper abundance. Our data also revealed that jackrabbits significantly decreased the volume of forbs and common shrubs and the flowering by grasses in our study plots. We were unable to detect an effect of deer on these measures of vegetation. These results suggest that by changing vegetation, jackrabbits may reduce invertebrate populations that are limited by food, protective structures, or microclimate provided by plants. Of these three mechanisms, only shade was strongly supported as limiting snail numbers in smaller-scale manipulations. In most systems, as in this one, the number of pairs of distantly related herbivores far exceeds the number of pairs of congeners. Since interactions among distantly related herbivores may be common in many cases, these interactions are likely to be important and should receive far more attention from ecologists.     

Positive indirect effects of reef fishes on kelp performance: the importance of mesograzers

It has been suggested that microcarnivorous reef fishes may play an important role in giant kelp forest communities by preventing infestations of mesograzers that could severely impact or potentially destroy recovering kelp forests after extreme disturbance events. However, these trophic linkages, specifically the direct and indirect effects of fishes on the biomass of mesograzers, grazing intensity, and the performance of giant kelp, have not been sufficiently quantified and evaluated as to their importance and in the absence of such disturbance events. We examined experimentally the effects of mesograzers on the growth and performance of giant kelp in the presence and absence of their fish predators near Santa Catalina Island, California (U.S.A.). Mesograzer biomass and grazing intensity were significantly higher when fishes were excluded from giant kelp, which in turn, lowered kelp performance. This pattern was consistent both on experimental plots of kelp as habitat isolates, and on a continuous reef. Moreover, the abundance of mesograzers was inversely related to the abundance of kelp perch among several kelp-forested reefs, suggesting that these effects can occur at larger spatial scales. Because of differences in the diet and behavior of two microcarnivorous fishes, the kelp perch and se?orita, we conducted an experiment manipulating each species and its density independently to determine their separate effects on mesograzers and kelp performance. Concurrently we examined the growth and mortality of juvenile kelp. Grazing intensity decreased, estimates of kelp performance increased, and the growth of juvenile kelp increased with increasing densities of fish but with no detectable effects between fishes. Our results demonstrate that these microcarnivorous fishes have positive indirect effects on kelp performance by reducing mesograzer biomass and grazing intensity, and the early life stages of other fishes also may be important. More specifically, these fishes have a positive effect on the density of fronds of giant kelp that can result in greater recruitment success and the abundance of kelp-associated invertebrates and fishes. Indeed, this study suggests that mesograzers have the potential to be one of the most important herbivores in kelp forest ecosystems.     

Selenium deficiency in Yugoslavia and possible effects on health

New data on Se-deficiency in Yugoslavia are presented. The results include Se contents of soils, cereal crops and garlic grown in the investigated soils, and human serum and scalp hair from several towns and regions in this country. All data indicate a serious Se-deficiency. Analyses of human tissues show a very low Se-status of the Yugoslav population. In some regions, Se contents of garlic, grains and human serum and hair are approaching those in the low-selenium zone in China. It is assumed that the very low Se-status of the human population could be a risk factor for the endemic nephropathy and the urinary tract tumours in endemic areas.Originally presented at the 8th Meeting of the Society for Environmental Geochemistry and Health, University of Reading, England (April 1990) (Volume 13, No.2 (1991) of this journal) and subsequently submitted as a volunteered paper.     

Growth maximization in early sardine larvae: a metabolic approach

Sardine larvae are forced to grow as fast as possible to reduce larval mortality. Thus, changes in biochemical composition during the first steps of sardine larval growth are intended to maximize larval growth rate efficiency and survival. Protein and RNA weight-specific growth rates were the highest and their corresponding doubling times the shortest among all the biomolecules, reflecting the importance of fast growth during early stages of larval development. The protein percentage increased and the carbohydrate and lipid percentages decreased during early growth until they reached, respectively, a percentage of 73.7, 3.1 and 18.0%. These percentages would represent the optimal proportion of biochemical components in sardine early larvae and they are the result of the trade-off between, in the short term, the protein proportion necessary to optimize larval movement and growth and, in the long term, the minimum lipid percentage necessary to guarantee energy reserves to fuel metamorphosis. RNA/DNA ratio increases during larval growth up to an asymptotic optimal value of ≈3.5 in postflexion larvae. Nutritional condition of sardine larvae was good and was influenced by the parental effect through the egg biochemical composition and by the growth trajectory determined by the actual environmental conditions.     

Predator biomass,prey density,and species composition effects on group size in recruit coral reef fishes

Group incidence and size are described for recruit parrotfishes, wrasses, and damselfishes on Hawaiian reefs over 3 years (2006–2008) at sites spanning the archipelago (20–28°N, 155–177°W). Coral-poor and coral-rich areas were surveyed at sites with both low (Hawaii Island) and high (Midway Atoll) predator densities, facilitating examination of relations among predator and recruit densities, habitat, and group metrics. Predator and recruit densities varied spatially and temporally, with a sixfold range in total recruit densities among years. Group (≥2 recruits) metrics varied with time and tracked predator and recruit densities and the proportion of schooling species. Groups often included heterospecifics whose proportion increased with group size. A non-saturating relationship between group size and recruit density suggests that the anti-predator benefits of aggregation exceeded competitive costs. Grouping behavior may have overarching importance for recruit survival–even at high recruit densities–and merits further study on Hawaiian reefs and elsewhere.     

Protective effects of Flacourtia indica on doxorubicin-induced cardiotoxicity in rats

This study examined the cardioprotective activity of an ethanolic extract of Flacourtia indica (FI) against doxorubicin (DOX)-induced myocardial infarction (MI) in rats. Different phytoconstituents were identified by gas chromatography-mass spectroscopy. DOX is a chemotherapeutic agent which produces free oxygen radicals that result in serious dose-limiting cardiotoxicity. A DOX dose of 20?mg?kg^?1 body weight is used to bring significant changes in biochemical parameters, endogenous antioxidants, and moderate necrosis in the heart. The pretreatment with FI at two doses (250 and 500?mg?kg^?1) to DOX-treated rats significantly prevented the altered biochemical parameters such as serum marker enzymes serum glutamate-pyruvate transaminase, serum glutamate oxaloacetate transaminase, creatine phosphokinase, and lactate dehydrogenase, lipid profile such as low-density lipoprotein, very low-density lipoprotein, triglycerides, high-density lipoprotein, total cholesterol, and antioxidant parameters such as superoxide dismutase, glutathione, catalase, glutathione peroxidase, and malondialdehyde to near normal level. Serum urea, uric acid, and alkaline phosphate which are increased on DOX administration registered near normal values on pretreatment with FI. In conclusion, these data suggest that the ethanol extract of FI can prevent heart damage by DOX-induced MI in rats and this is likely mediated through its antioxidant activities.     

Variation in secondary metabolite and aragonite concentrations in the tropical green seaweed Neomeris annulata: effects on herbivory by fishes

The tropical alga Neomeris annulata (Dickie) (Dasycladaceae: Chlorophyta) produces brominated sesquiterpenes and deposits aragonite throughout the thallus. This study, conducted throughout 1990–1991, showed that the fleshy, apical portions of the thalli (tips) were high in secondary metabolite concentrations (1.5%, mean combined secondary metabolites based on dry mass) and relatively low in calcium carbonate (aragonite form) (65.2% ash). The basal portions were lower in combined secondary metabolites (0.2% dry mass), and higher in aragonite (90.0% ash). The crude organic extract of the alga deterred fish feeding in the field at concentrations of 5, 10 and 15% dry mass, but not at a lower concentration of 1.5%. Natural concentrations of crude organic extract ranged from 1.5 to 15.3% in whole individuals and averaged 5.1% based on dry mass. Two brominated sesquiterpenes were isolated as major metabolites from the crude extract, but only one deterred feeding at natural concentrations. Ash concentrations in N. annulata were 60% dry mass in both the tips and bases. Aragonite strongly deterred feeding at concentrations of 65 and 90% dry mass. When a naturally occurring combination of organic extract and aragonite in the tips (10% crude extract and 65% aragonite) was compared with that of the bases (0.8% crude extract and 90% aragonite), no significant difference in grazing was observed. Combinations of secondary metabolites and aragonite were also tested against one or the other single defense. The combination of defenses proved a more effective deterrent than either secondary metabolites or aragonite alone.     

氟与健康的环境流行病学研究

氟是与机体健康密切相关的微量生命元素,原生环境中氟过量或缺乏均会导致机体产生疾病。氟对人类健康的影响已成为全球性的环境健康问题。综合国内外近年来的相关资料,作者概述了环境生态系物质中氟的含量、分布及化学行为,阐述了氟对机体的健康效应,分析了我国地氟病的现状,并指出了今后在氟与健康研究领域中应关注的问题。     

Negative selection effects suppress relationships between bacterial diversity and ecosystem functioning

I assembled bacterial communities to explore the effects of bacterial diversity on multiple ecosystem functions, including bacterial community biovolume, decomposition of particulate organic matter, and biomass transfer to the next trophic level. The experiment used a two-way factorial design with four levels of bacterial diversity (one to four species) and the absence/presence of a bacterivorous ciliated protist Tetrahymena pyriformis as two main factors, and all possible combinations of the four bacterial taxa nested within each diversity level. Bacterial community biovolume increased as bacterial diversity increased, a result due largely to positive selection effects. Decomposition and consumer abundance, however, were unaffected by bacterial diversity, though both varied among bacterial composition treatments. Negative selection effects, the dominance of species that do not contribute significantly to ecosystem functioning, accounted for the lack of diversity effects on decomposition and consumer abundance. The presence of Tetrahymena reduced bacterial community biovolume but increased decomposition, without altering the diversity-functioning relationships. Decomposition was strongly linked with consumer abundance such that communities supporting larger consumer biomass exhibited higher decomposition rates. This study suggests that if the negative selection effect is common, as it might be when examining ecosystem variables other than biomass (due to the presence of keystone species that can contribute disproportionably to ecosystem functioning relative to their abundances), basic bacteria-mediated ecosystem processes, such as decomposition and energy transfer to the next trophic level, may not increase with bacterial diversity.     

Negative effects of stress-resistant drift algae and high temperature on a small ephemeral seagrass species

Seagrasses are threatened by multiple anthropogenic stressors, such as accumulating drift algae and increasing temperatures (associated with eutrophication and global warming, respectively). However, few seagrass experiments have examined whether exposure to multiple stressors causes antagonistic, additive, or synergistic effects, and this has limited our ability to predict the future health status of seagrass beds. We conducted a laboratory experiment to test whether abundance of Gracilaria comosa (3 levels; 0, 1.2, and 3.4 kg WW m⁻²), an algae that is resistant to wide environmental fluctuations (e.g. light, temperature, salinity, and oxygen levels), has negative effects on the small ephemeral seagrass, Halophila ovalis and whether the effects are exacerbated by high temperature (3 levels; 20, 25, and 30°C). We found an additive negative effect of the two stressors when tested simultaneously on 14 seagrass performance measures, with most data variability explained by the drift algae. For the individual plant performance measures (above- and below-ground growth and mortality, leaf area, internode distance, and root length and root volume), we found 5 additive effects, 4 synergistic effects, and 5 effects that were significant only for drift algae. We also documented a significant additive effect of drift algae and temperature on dissolved porewater sulphide (DS). A follow-up correlation analysis between DS and the 14 plant performance measures revealed significant or near-significant linear correlations on 9 of these responses (above- and below-ground growth, leaf area and weight, leaf mortality, and internode distance). In summary, we showed (a) that a stress-resistant drift algae can have strong negative effects on a small ephemeral seagrass, (b) this negative effect can increase both additively and synergistically with increasing temperature depending on performance measure, and (c) the negative effects may be mediated by a build-up of porewater DS. An implication of our findings is that resource managers aiming to preserve healthy seagrass beds in an almost certain future warmer world should increase efforts to keep drift algae populations low.     

Genetic studies in marine fishes

Nine polymorphic loci were found among 42 presumptive protein-coding gene loci surveyed among 474 red drum (Sciaenops ocellatus) sampled in 1987 from 13 nearshore and 1 offshore localities from the Atlantic coast of the southeastern USA and the northern Gulf of Mexico. The mean number of alleles over the polymorphic loci was 3.8, and the average heterozygosity over all loci examined was estimated as 0.047. These data indicate that red drum have normal levels of genetic variability. Wright'sF1 _ST values (the standardized variance of allele frequencies between samples) over all polymorphic loci ranged from 0.009 to 0.027 (meanF1 _ST =0.019), and estimates of the effective number of migrants (N _e m) per generation using Wright's island model ranged from 9.0 to 27.5. High levels of gene flow among the red drum samples were also indicated by Slatkin's qualitative analysis using conditional average allele frequencies. Nei's estimates of genetic distance between pairs of samples ranged from 0.000 to 0.009, indicating a high degree of nuclear gene similarity among all samples. Highly significant heterogeneity in allele frequencies at the locus for adenosine deaminase was detected between red drum sampled from the Atlantic and those sampled from the Gulf and among red drum sampled from the Gulf.     

Factors affecting the spawning period of sardine in two highly oligotrophic Seas

Ovarian histology and weight dynamics of reproductive and somatic tissues were used to investigate seasonality of spawning and factors affecting reproductive period in two E Mediterranean sardine, Sardina pilchardus, populations (central Aegean and Ionian Seas), between September 1999 and May 2001. Despite similarities in the general spawning pattern of the two populations, i.e. protracted spawning season during the colder months of the year, reproductive period in the Ionian was shorter and lagged behind the Aegean by 2–3 months. In both Seas, reproductive period was influenced by body size as smaller females tended to have both shorter and delayed spawning season. Whereas hepatosomatic index (HSI) was consistently higher in reproductively active females during the whole spawning period, seasonality of spawning did not match variations of HSI. In both Seas fluctuations of HSI matched the spring burst of primary productivity and were followed by fluctuations in somatic condition and mesenteric fat by a 2 months’ lag. Somatic condition and reproductive activity displayed inverse seasonal patterns, implying that egg production in sardine basically relies on visceral and muscular fat deposits, accumulated during the summer growing season. Reliance of egg production on past energetic reserves suggests that sardine is a capital breeder, which is a rather efficient strategy in such oligotrophic habitats as the E Mediterranean, where winter spawning is accompanied by a particular decline in adult preying fields.     

Time-dependent effects of chlordane on thyroid histological structure and function in rats

In order to study the time-dependent effects of chlordane on thyroid hormone levels and histological structure in rats, 120 healthy 4-week-old SD rats were divided randomly into 12 groups. Rats in treatment groups were treated orally by gavage with chlordane at a dose of 15 mg kg^?1 for 5, 10, 15, 20, 30, or 40 days, while rats in control group received an equal volume of corn oil. Serum levels of thyroxine (FT4), triiodothyronine (FT3), and thyroid stimulating hormone (TSH) were measured by radioimmunoassay. Sections of thyroids were dyed with hematoxylin–eosin to detect any pathological alterations. In chlordane treated groups, on day 5, changes in serum levels of FT4, FT3, and TSH were not found. On days 10 and 15, serum levels of FT4 and FT3 decreased, accompanied by increased levels of TSH. On days 20, 30 and 40, serum levels of these hormones returned to control values. As for alterations in histology, on day 10–15, follicular epithelium of the thyroid were found to proliferate into two layers in chlordane treated rats. On day 20, in focal areas the two-layer afollicular epithelia were observed to continuously proliferate into 3–4 layers of follicular epithelium, termed hyperplasia plaques. On days 30 and 40, solid buds and secondary follicles to solid buds were detected. The earliest alteration of thyroid hormones in treated SD rats occurred between 5 and 10 days with corresponding histopathologic changes. As the exposure time increased, the serum levels of hormones and histopathology altered in a time-dependent manner.