Response of a soft-bottom harpacticoid community to stingray (Dasyatis sabina) disturbance

The recolonization by harpacticoid copepods of patches disturbed by stingrays [Dasyatis sabina (LeSeur)] feeding in a subtidal (2–3 m depth) site off the Florida gulf coast (Lat. 29°54.55N, Long. 84°31.45W) was followed. Samples from disturbed patches could no longer be distinguished from control samples in terms of numbers of harpacticoids 29 h after disturbance. No species became significantly disproportionately abundant during the recovery suggesting that small-scale natural disturbances are not an important organizing force in this community.     

Habitat preferences of coral-associated fishes are altered by short-term exposure to elevated CO2

Rising atmospheric carbon dioxide (CO₂) concentrations are causing additional CO₂ to be absorbed by the oceans. Recent studies show that exposure to elevated CO₂ causes olfactory impairment in reef fishes; however, the ecological consequences of this impairment are largely unknown. This study examined the effects of short-term exposure to elevated CO₂ on habitat preferences of coral-dwelling gobies. Adult gobies collected from the reef at Lizard Island (Great Barrier Reef, Australia) were exposed for 4 days to ambient CO₂ (440 μatm) or elevated CO₂ (880 μatm). Habitat preferences were then tested in laboratory and field experiments at ambient conditions. In olfactory preference tests, Paragobiodon xanthosomus displayed a strong preference for odour cues of their sole host coral Seriatopora hystrix; however, this preference was absent in gobies exposed to elevated CO₂. Habitat choice experiments conducted in the field showed that Gobiodon histrio placed on dead coral colonies located preferred live habitat within 24 h; however, gobies exposed to elevated CO₂ associated with both preferred and non-preferred habitats in approximately equal frequency. Preferred habitats are known to confer fitness advantages to coral-dwelling gobies. Consequently, these results suggest that future elevated CO₂ levels might affect the ability of habitat specialist fishes to select favourable habitats.     

水稻土甲烷氧化菌对镉胁迫的响应

重金属污染影响土壤微生物群落结构与活性,间接影响土壤碳（如CO2、CH4）的生物地球化学循环和全球气候变化。甲烷氧化菌氧化消耗CH4,降低大气中CH4含量,在缓解由温室气体导致的全球温暖化方面起着重要作用。本研究通过短期土壤培养实验,比较研究了不同强度重金属镉（Cd）胁迫下,水稻土中甲烷氧化菌的多度、群落组成及其氧化CH4潜势的差异。结果表明,添加Cd含量越大,水稻土氧化CH4潜势越弱,甲烷氧化菌pmoA基因拷贝数显著减少;甲烷氧化菌多度与水稻土氧化CH4潜势之间存在显著正相关关系（P〈0.001）。群落组成分析发现,在相对低含量Cd（1 mg.kg-1）条件下,有新的甲烷氧化菌菌属出现,而添加较高含量Cd（10 mg.kg-1）时甲烷氧化菌种类减少。总之,Cd胁迫降低水稻土中甲烷氧化菌多样性及其氧化CH4潜势,可能导致原位CH4消耗减少,从而增加稻田CH4排放。     

Short- and long-term effects of eutrophication on the secondary production of an intertidal macrobenthic community

Secondary production of a macrobenthic community at an intertidal mudflat was estimated for 33 successive months. Sampling was carried out along a eutrophication gradient, including non-eutrophied Zostera meadows, an intermediate muddy area, and a strongly eutrophied sand-muddy flat, where macroalgal blooms of Enteromorpha spp. usually occur. The Zostera meadows were always the most productive habitat (145–225 g ash-free dry weight m^–2 year^–1). In the short term, the macroalgal bloom benefited the total estuarine production by enhancing the annual production in the eutrophied area. Nevertheless, our results show that this increase was short lived and in no way sufficient to match the production in the Zostera meadows. In the long term, the present study provides evidence that the disappearance of macrophyte beds, as a result of ongoing eutrophication, constitutes a major threat to the sustainability of the estuarine ecosystem.Communicated by S.A. Poulet, Roscoff     

The progressive changes of the copepod community from the eastern Adriatic coast caused by eutrophication

In 1976–1985 period, some changes have been found during long‐term monitoring of physical, chemical and biological parameters in front of the largest harbours of the eastern Adriatic coast. For that reason, the control has been continued in 1985–1988 period.

This paper presents some recent results about copepods‐dominant mesozooplankton group—as they respond very quickly (both by composition and biomass) to the changes of the environment they inhabit. Besides the increased copepod density, further increasing of maximal values of Acartia clausi was found at the whole investigated area in 1987 and 1988, caused by progressive eutrophication of the eastern Adriatic coastal waters.     

Integrating empirical and heuristic knowledge in a KBS to approach stream eutrophication

The nutrient enrichment of rivers and its consequences are among the most severe water quality problems in Europe, causing eutrophication and other problems. The decision-making processes involved in the management of these problems require extensive human expertise from people who deal directly with day-to-day stream problems, as well as empirical knowledge based on scientific research. This means that eutrophication is a complex problem, the optimal management of which requires an integrated and multidisciplinary approach. This approach can be taken using a Knowledge-Based System (KBS) built upon the concepts and methods of human reasoning. Accordingly, a KBS was developed within the STREAMES project. In this KBS most of the knowledge needed for managing eutrophication problems was organised and structured in the form of a decision tree (DT). The methodology specially developed to build this KBS, as well as the internal structure of the eutrophication decision tree, is presented here. The good DT obtained led to consider the KBS a suitable tool to support the management of eutrophication.     

The costs of intersexuality: a crustacean perspective

Increasing concerns over rising intersexuality in the animal kingdom and the ability of certain chemicals to disrupt the endocrine system have demanded a better understanding of the costs associated with such conditions. Whilst intersexuality appears relatively widespread throughout gonochoristic crustaceans, i.e. those crustacean species with two separate sexes, the fitness costs have rarely been reported. Through comparable investigation of normal and intersex specimens of the highly abundant marine/estuarine amphipod Echinogammarus marinus (Leach) these fitness costs were determined. Measurements taken to assess fitness costs included fecundity, fertility and embryonic development, maturation period, and any morphological deformities that might result in reduced pairing success. Results from this study suggest that intersex E. marinus suffer from reduced fecundity and fertility, and mature at a larger size than normal specimens. These fitness costs can also, to a certain extent, be related to the degree of intersexuality. It is suggested that the increased size and morphological abnormalities observed in intersexes may result in reduced pairing success. Investigations into intersex organisms, i.e. those organisms with known dysfunctional endocrine systems, and the costs associated with such conditions, should aid researchers in assessing effects at the population and community level.Communicated by J.P. Thorpe, Port Erin     

Flux of 141Ce through a euphausiid crustacean

The role of the Mediterranean euphausiid Meganyctiphanes norvegica in the cycling of radiocerium (¹⁴¹Ce) was examined. When uptake of ¹⁴¹Ce occurs directly from the water, a dynamic population equilibrium is reached at a concentration factor of about 250. Molting was responsible for up to 99% loss of total body burden at first molt, and about 45% of the remaining activity at second molt, thus denying true longterm equilibrium to individual animals. Fecal pellets did not contain measureable ¹⁴¹Ce activity when the euphausiids accumulated the isotope from water, thus proving that surface adsorption was the key accumulating process from water. When radiocerium was taken in through ingestion of labelled Artemia, about 99% of the body burden was voided as fecal pellets. Excretion by this route was accelerated when euphausiids were fed non-radioactive Artemia during loss phase. Radioactive counts of the pellets confirmed that all ingested ¹⁴¹Ce was lost through defecation. When ¹⁴¹Ce was ingested as labelled phytoplankton, a substantial fraction of the total body burden occurred in the molts, which indicated that the phytoplankton lost ¹⁴¹Ce to the water and the radioactivity was subsequently adsorbed to outer surfaces of the euphausiids. Molts, fecal pellets, and freshly-killed euphausiids lost ¹⁴¹Ce to the water exponentially, the rates being similar to the exponential portions of the loss curves for live, non-molting individuals. It is suggested that M. norvegica, and probably other pelagic zooplankters, can greatly accelerate radiocerium transport to the ocean floor by packaging the isotope as fecal pellets. In coastal areas subject to low-level radioactive waste disposal, ¹⁴¹Ce might be ionic (or at least soluble) to a great extent, in which case euphausiids could take up the isotope rapidly and accelerate its vertical transport via molting.     

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.     

Spatial patterns of macroalgal abundance in relation to eutrophication

Based on a large monitoring data set from Danish coastal waters we tested the hypotheses: (1) The vertical pattern of algal abundance is regulated by exposure in shallow water and by light limitation towards deeper water, resulting in a bell-shaped abundance curve, with peak abundance located deeper at more exposed sites, (2) in deeper water, total algal abundance and abundance of perennial algae decrease along a eutrophication gradient while (3) abundance and relative abundance of opportunists increase. The vertical pattern of algal abundance showed a peak at intermediate water depths which was located deeper in more exposed areas and thus confirmed our first hypothesis. For algae growing from depths of peak abundance and deeper, the study demonstrated that total algal abundance and abundance of perennials and opportunists at given depths decreased significantly along a eutrophication gradient and the relationships had high explanatory power (R ² = 0.53–0.73). These results confirmed our second hypothesis. By contrast, the relative abundance of opportunists responded solely to salinity and was largest in the most brackish areas, in contradiction to hypothesis three. The lack of coupling between eutrophication and relative abundance of opportunists arises because both opportunists and the entire algal community were light limited and their ratio therefore relatively insensitive to changing water clarity. The analyses indicated that algal abundance initially responded slowly to increasing eutrophication but showed a more marked response at TN concentrations of 35–40 μM. However, the existence of possible threshold nutrient levels demands further analyses.     

Spawning and development of three coral-associated Lithophaga species in the Red Sea

Lithophaga date mussels from three species (L. lessepsiana, L. simplex and L. purpurea) were removed from their stony coral hosts in the Red sea at Eilat, Israel. Spawning, observed in the laboratory on several occasions during 1987–1988, appeared to be closely tied to lunar periods, occurring primarily during the last quarter and the new moon. Embryonic and larval development was typical of that described for other mytilids and, except for pigmentation differences, which could be discerned during embryogenesis, the developmental stages of the three species were indistinguishable. Development to the pediveliger stage took 3 to 4 wk in standard culture conditions, but raising the temperature to 27.5 °C increased the growth rate of larvae of L. lessepsiana by as much as three-fold, so that the pediveliger stage was attained in 16 d. Larvae resulting from spawning by L. simplex adults removed from the coral Astreopora myriophthalma grew significantly faster in culture than larvac from adults removed from the coral Goniastrea pectinata (comparison of slopes, p<0.05). The latter individuals showed a 6-d growth plateau at the early umbone stage. Metamorphically competent larvae were capable of delaying metamorphosis for up to 4mo, which would allow an extended period for dispersion and would increase the chance of finding a suitable substratum in the natural environment.     

黄土高原矿区土壤细菌群落对地表塌陷和土地复垦的响应

中国一半的煤炭生产能力集中于生态脆弱的黄土高原,采矿活动进一步加剧了当地生态环境恶化,尤其是土壤退化.微生物是土壤物质转化的动力,对外界干扰十分敏感,厘清其变化对生态恢复和治理尤为重要.为此,本研究以黄土高原大柳塔煤矿及黑岱沟煤矿为对象,利用高通量测序技术和分子生态网络分析方法,揭示土壤细菌群落多样性及不同活动影响下土壤细菌群落之间的联系与差异.结果表明,不同活动对土壤理化性状影响显著,塌陷区有机质、速效磷、速效钾呈显著性下降(P0.05),复垦区土壤有机质、水分、pH和电导率则显著增加(P0.05),塌陷对土壤理化性状产生了抑制作用,复垦呈现促进作用.不同活动对土壤细菌群落产生不同的影响,塌陷区多样性指数降低了约20%,复垦则多样性指数增加了63%,但塌陷区、复垦区优势菌门保持一致.不同活动对土壤细菌分子生态网络的影响迥异:塌陷后分子生态网络趋于复杂,网络连接数及互作关系明显增强;复垦后则生态网络模块增加,模块内部趋于简单.为应对地表塌陷和土地复垦,土壤细菌往往改变菌种间关系作适应性变化.塌陷更多地促进相互合作以适应养分的贫瘠,复垦则促进模块数增加并趋于合作以获取更多的资源.     

Behavioral responses of a larval crustacean to hydrostatic pressure: Rhithropanopeus harrisii (Brachyura: Xanthidae)

Responses of the four zoeal stages of the crab Rhithropanopeus harrisii (Gould) to step and continuous changes in hydrostatic pressure were analyzed with a video system. Crabs were collected from the Neuse River estuary (North Carolina, USA) from June to August, 1987. The lower thresholds for step increases and decreases in pressure were 3 and 8 to 10 mbar, respectively. There was little change in sensitivity with zoeal development. Tests of larval responses in a light field that simulated the underwater angular light distribution indicated positive phototaxis does not occur upon pressure changes. In darkness, rates of pressure increase at and above 0.175 mbar s^-1 induced high barokinesis and negative geotaxis in all but Stage IV zoeae, which had a threshold of 1.19 mbar s^-1. Since larval sinking and descent swimming speeds exceed these threshold rates, larvae can move rapidly enough to produce suprathreshold changes in pressure which evoke behavioral responses. Slow rates of pressure decrease induced passive sinking while rapid rates caused an active ascent. This ascent response upon a pressure decrease is unreported among crustaceans, and is hypothesized to function for avoidance of feeding and respiratory currents of benthic invertebrates. The descent response occurs in all zoeal stages, except IV, at rates of pressure decrease (0.4 to 0.71 mbar s^-1) that are within the range of ascent swimming speeds. These results support Sulkin's negative feedback depth regulation model. The absolute distances moved before corrective vertical responses to threshold rates of pressure change are initated delimit the depth regulatory window. In darkness, the asymmetry of the window would lead to an ascent. It is hypothesized that light is an additional component in depth regulation, and that the limits and symmetry of the depth regulatory window may be controlled by the level of light adaptation.     

Historical eutrophication in a river-estuary complex in mid-coast Maine.

European settlement of New England brought about a novel disturbance regime that impacted rivers and estuaries through overfishing, deforestation, dams, and water pollution. The negative consequences of these activities intensified with industrialization in the 19th and 20th centuries, often resulting in ecosystem degradation. Since environmental legislation was implemented in the 1970s, improvement in water quality has been tangible and widespread; however, ecological recovery can require substantial amounts of time and may never be complete. To document the natural baseline conditions and investigate the recovery of a severely degraded river-estuary complex in mid-coast Maine, we examined diatoms, pollen, total organic carbon, total nitrogen, stable isotopes, total phosphorus, biogenic silica, and trace metals in intertidal sediments and established a chronology with 14C, 210Pb, and indicator pollen horizons. Both climate variability and human effects were evident in the sedimentary record of Merrymeeting Bay, the freshwater tidal portion of the Kennebec estuary. Natural climate variability was apparent in an episode of high sedimentation and altered diatom abundance during the 12th and 13th centuries and in changing pollen abundances between the 16th and 19th centuries, indicative of regional cooling. During the 18th century, colonial land clearance began an era of high sedimentation and eutrophication that strongly intensified with industrialization during the late 19th and 20th centuries. Improvements in water quality over the past 30 years in response to environmental regulation had little effect on ecosystem recovery as represented by the sedimentary record. Diatom composition and productivity and high fluxes of organic C, total P, and biogenic Si in recent sediments indicate that rates of nutrient loading remain high. These environmental proxies imply that aquatic productivity in Merrymeeting Bay was originally nutrient limited and water clarity high, relative to today. Further recovery may require more stringent regulation of nutrient inputs from industrial and municipal point sources. This historical study can contribute to public debate about the environmental management of this unusual river-estuary complex by describing its long-term natural baseline, thereby illustrating the upper limit of its potential for recovery.     

Internal eutrophication: How it works and what to do about it—a review

In the 1980s and 1990s, it became increasingly clear that changes in external nutrient loads alone could not entirely explain the severe eutrophication of surface waters in the Netherlands. Nowadays, 'internal eutrophication' has become a widely accepted term in Dutch water management practice to describe the eutrophication of an ecosystem without additional external input of nutrients (N, P, K). This review surveys the principal mechanisms involved in this process. It also discusses possible remedies to combat internal eutrophication.     

Response of a Reptile Guild to Forest Harvesting

Abstract:  Despite the growing concern over reptile population declines, the effects of modern industrial silviculture on reptiles have been understudied, particularly for diminutive and often overlooked species such as small-bodied snakes. We created 4 replicated forest-management landscapes to determine the response of small snakes to forest harvesting in the Coastal Plain of the southeastern United States. We divided the replicated landscapes into 4 treatments that represented a range of disturbed habitats: clearcut with coarse woody debris removed; clearcut with coarse woody debris retained; thinned pine stand; and control (unharvested second-growth planted pines). Canopy cover and ground litter were significantly reduced in clearcuts, intermediate in thinned forests, and highest in unharvested controls. Bare soil, maximum air temperatures, and understory vegetation all increased with increasing habitat disturbance. Concomitantly, we observed significantly reduced relative abundance of all 6 study species (scarletsnake [Cemophora coccinea] , ring-neck snake [Diadophis punctatus] , scarlet kingsnake [Lampropeltis triangulum] , red-bellied snake [Storeria occipitomaculata] , southeastern crowned snake [Tantilla coronata] , and smooth earthsnake [Virginia valeriae] ) in clearcuts compared with unharvested or thinned pine stands. In contrast, the greatest relative snake abundance occurred in thinned forest stands. Our results demonstrate that at least one form of forest harvesting is compatible with maintaining snake populations. Our results also highlight the importance of open-canopy structure and ground litter to small snakes in southeastern forests and the negative consequences of forest clearcutting for small snakes.     

Comparative study of crustacean larval photoresponses

Ovigerous females of four brachyuran (Cancer gracilis, Lophopanopeus bellus bellus, Hemigrapsus oregonensis and Scyra acutiforns) and two anomuran (Pagurus beringanus and P. granosimanus) species, which live as adults in coastal areas, were collected near Friday Harbor, Washington, USA, in 1985, and spectral sensitivity and phototactic pattern of their larvae were measured. Responses were compared with previous measurements on estuarine species to determine whether responsiveness varies with adult habitat. Estuarine and coastal species have similar photoresponses. Spectral sensitivity of the test brachyran species had two maxima, one near 400 to 420 nm and another around 500 nm. The anomuran species were similar, but had an additional peak in the region of 580 to 620 nm. This sensitivity is adapted to daytime light conditions in the adult environment, and available spectra at the time of larval movement during diel vertical migration. Upon light adaptation and stimulation with a narrow light field, all six species showed positive phototaxis to high light intensities and a pronounced negative response to low intensities. Only the negative response will occur in natural underwater light conditions, and it is part of a predator-avoidance shadow-response which operates in areas of higher light intensity. The same phototactic pattern is observed in all species when darkadapted except H. oregonensis. If nocturnal vertical migration occurs, this negative response may be responsible for the descent at sunrise and depth maintenance during the day.     

Effects of eutrophication on reef-building corals

Fourteen environmental variables were monitored at seven locations along the west coast of Barbados on a weekly basis over a one-year period, 1981 to 1982. The physicochemical and biological data indicate that an environmental gradient exists as a result of increased eutrophication of coastal waters. Growth rates (linear extension) of Montastrea annularis (Ellis and Solander), measured along the environmental gradient, exhibit high correlation with a number of water quality variables. Concentration of suspended particulate matter is the best univariate estimator of M. annularis skeletal extension rates (r ²=0.79, P<0.0001). The results suggest that suspended particulate matter may be an energy source for reef corals, increasing growth up to a certain maximum concentration. After this, reduction of growth occurs due to smothering, reduced light levels and reduced zooxanthellae photosynthesis.