Test of Competitive Interactions for Space Between Two Benthic Fish Species, Burbot Lota lota, and Stone Loach Barbatula barbatula

The substrate preferences, growth rates and foraging efficiency of two small benthic fish species, juvenile burbot, Lota lota, and stone loach, Barbatula barbatula, were compared in combined outdoor mesocosm and indoor laboratory experiments. Both species preferred the same stony substrate when alone, but significant differences in habitat selection were found between the two species under food deprivation and competition conditions. In burbot, preference for the stony habitat was reinforced under food-deprivation conditions and became even stronger when a potential competitor, the stone loach, was present. In contrast, stone loach switched to the gravel substrate when either starving or in the presence of a heterospecific competitor. Growth rates and foraging efficiency of burbot were significantly highest in the stony substrate and decreased with finer substrates. In stone loach, neither growth rates nor foraging efficiency were significantly different among the different substrates. The results provide an example of habitat partitioning by means of different competition styles, with a stenoecious, dominant style of the burbot and an euryoecious, evasive style of stone loach allowing coexistence of two sympatric fish species by graded interactions at an individual level in the littoral zone of a large lake.     

Effects of Predation Risk on Habitat Selection by Water Column Fish, Benthic Fish and Crayfish in Stream Pools

Predation risk can affect habitat selection by water column stream fish and crayfish, but little is known regarding effects of predation risk on habitat selection by benthic fish or assemblages of fish and crayfish. I used comparative studies and manipulative field experiments to determine whether, (1) habitat selection by stream fish and crayfish is affected by predation risk, and (2) benthic fish, water column fish, and crayfish differ in their habitat selection and response to predation risk. Snorkeling was used to observe fish and crayfish in, (1) unmanipulated stream pools with and without large smallmouth bass predators (Micropterus dolomieui >200 mm total length, TL) and (2) manipulated stream pools before and after addition of a single large smallmouth bass, to determine if prey size and presence of large fish predators affected habitat selection. Observations of microhabitat use were compared with microhabitat availability to determine microhabitat selection. Small fish (60–100 mm TL, except darters that were 30–100 mm TL) and crayfish (40–100 mm rostrum to telson length; TL) had significantly reduced densities in pools with large bass, whereas densities of large fish and crayfish (> 100 mm TL) did not differ significantly between pools with and without large bass. Small orangethroat darters (Etheostoma spectabile), northern crayfish (Orconectes virilis), and creek chubs (Semotilus atromaculatus) showed significantly greater densities in pools without large bass. The presence of large smallmouth bass did not significantly affect depths selected by fish and crayfish, except minnows, which were found significantly more often at medium depths when bass were present. Small minnows and large and small crayfish showed the greatest response to additions of bass to stream pools by moving away from bass locations and into shallow water. Small darters and sunfish showed an intermediate response, whereas large minnows showed no significant response to bass additions. Response to predation risk was dependent on prey size and species, with preferred prey, crayfish and small minnows, showing the greatest response. Small benthic fish, such as darters, are intermediate between small water column fish and crayfish and large water column fish in their risk of predation from large smallmouth bass.     

Relationship of Farm Level Pesticide Use and Physical Habitat on Benthic Community Status in a California Agricultural Stream

The objectives of this study were to: (1) evaluate temporal and spatial trends in water quality parameters, physical habitat metrics, and benthic community metrics in the Orestimba Creek from years 2000 to 2005, and (2) assess the relationship of benthic community condition from ten Orestimba Creek stations and both pesticide use at the farm level and physical habitat conditions. Significant year effects were reported for temperature, pH, dissolved oxygen, and turbidity. In general, most of the 17 physical habitat metrics did not show statistical variability over the 6-year period. Most of the benthic metrics were variable over the 6-year period. A total of 41 herbicides, 14 organophosphorus (OP) insecticides, and 5 pyrethroids were applied to 23 sections of land bordering the Orestimba Creek from 2000 to 2004. The OP insecticides showed the strongest relationship to benthic metrics using univariate regression models when all three classes of pesticides were compared; however, these statistical relationships had low R² values. Stepwise regression analysis showed statistically significant relationships between most benthic metrics and habitat metrics. In general, both pesticide applications and physical habitat have a similar but modest statistical association with benthic communities. However, the relationship of both pesticide applications and physical habitat on benthic communities in the Orestimba Creek appear to be insignificant compared to the magnitude of spatiotemporal patterns reported.     

The Structure of a Macroinvertebrate Community in a Northern German Lake Outlet (Lake Belau,Schleswig-Holstein) with Special Emphasis on Abundance,Biomass and Secondary Production

The structure of macroinvertebrate communities was studied at I I sampling sites of the outlet of Lake Belau in the lowlands of northern Germany. To describe the structures of macrobenthic animal communities three different units were examined: abundance, biomass, and secondary production. 112 taxa were collected from the entire stream. The numbers of species ranged from 31 (fine sand) to 70 (submerged macrophytes). For the stream, average macroinvertebrate density was 18.400 ind. M⁻¹. Density was highest at the macrophytes amounting to 35,630 individuals per m², and lowest in the pure sand with only 3,900 ind. M⁻². Average biomass (dry mass) was 194 g DM m⁻² varying from 9.8 (peat) to 381 g DM m⁻² (gravel with mollusk shells near the upstream lake). For the stream, average annual production was 129 g DM m⁻² varying from 15 (peat) to 286 g DM m⁻² (macrophytes). The highest values for each unit were found in stream sections with gravel and submerged macrophytes. Lower values occured in sections that contained peat and sand. Usually, a single structure of the macroinvertebrate community was dominated by less than ten taxa, which varied at each sampling site depending on the units observed.     

Effects of Eutrophication on Young-of-the-year Freshwater Fish Communities in Coastal Areas of the Baltic

Abundance, growth, habitat and food choice of young-of-the-year (Y-O-Y) freshwater fishes were investigated in a gradient of eutrophication in a Baltic inlet. Secchi-disc depth decreased from 3 to 0.5m along the gradient with an accompanying reduction in submerged vegetation coverage. There were positive trends in Y-O-Y abundance with increasing turbidity for cyprinids, pikeperch, ruffe and smelt, and a negative trend for perch, leading to a shift from a perch dominated community in the reference area to a cyprinid dominated in the eutrophic area. The species composition of adult fishes resembled the Y-O-Y species community, indicating that community structure was determined already during early juvenile interval. Perch and cyprinid Y-O-Y preferred areas with submerged macrophytes while pikeperch and smelt were found more frequently in open waters. Perch Y-O-Y growth was reduced in eutrophic areas compared to references, especially in the size range where they change from foraging on zooplankton to benthic organisms. The deterioration of visual conditions caused by high turbidity is suggested to be negative for feeding of perch especially in deeper water. There was no evident growth reduction for pikeperch, which may be explained by a visual physiology well adapted to turbid conditions. The combined effects of turbidity and competition for food resources on growth and survival in eutrophic waters are discussed.     

北部湾海域小型底栖动物丰度和生物量

根据2008年10月4日至8日北部湾海域生态环境综合调查资料,对北部湾海域小型底栖动物的类群组成、丰度和生物量分布进行了分析研究,结果表明,研究海域的小型底栖动物平均丰度约为399.09±452.20 had·10cm^-2,平均生物量约为359.56±324.45μg·10cm^-2;按丰度来讲,分选出的14个类群中,自由生活海洋线虫的丰度为最优势,约占总丰度的92.69%,其次为底栖桡足类和多毛类,分别约占总丰度的3.28%和2.47%;线虫、多毛类和桡足类分别约占总生物量的41.16%、38.34%和6.76%。研究海域的钦州、防城港市沿岸海区小型底栖动物平均丰度相对较高,其平均丰度约为614.98±799.63 ind·10cm^-2;涠洲岛周边海区和北海南部近岸海区平均丰度分别约为481.68±240.03 ind·10cm^-2和278.14±126.38 ind·10cm^-2;对照海区的小型底栖动物平均丰度约仅有197.37±116.72 ind·10cm^-2。根据各站位小型底栖生物的种类组成及其丰度进行了多样性分析,各站位丰富度指数介于0.466～1.516之间,均匀度指数介于0.203～1.13之间,Shannon-Weiner指数(H')介于0.141～0.783之间。根据类群组成及其丰度进行组平均法聚类分析,把研究海区各站位分成了3个不同的底栖生物群落。研究海区线虫和桡足类丰度的比率变化范围在5.02～223.83之间。     

The Influence of Physical Habitat,Pyrethroids, and Metals on Benthic Community Condition in an Urban and Residential Stream in California

This study was designed to characterize benthic communities and physical habitat in both an urban (Kirker Creek) and residential (Pleasant Grove Creek) stream in California in late spring of 2006 and 2007. Concurrent water quality evaluations, physical sediment parameters, pyrethroids, bulk metals, and SEM/AVS ratios were also measured during both years of this study. The relationship of various benthic metrics to physical habitat metrics, pyrethroids, and metals was evaluated for each stream using stepwise multiple linear regressions with both years combined for each stream, as well as both years and both streams combined, to increase the statistical power for determining significant relationships. Physical habitat was determined to be poor in each stream during both years of sampling. More than 100 benthic taxa were reported annually for both streams based on 2006 and 2007 sampling. A significant result from the stepwise regression analysis combining data for 2 years across both streams is that when habitat metrics and to a lesser degree metals are considered in the statistical models pyrethroids do not display any significant relationships to the benthic metrics. In summary, it is apparent from this analysis that the health of benthic communities in both streams is primarily affected by habitat metrics.     

Effects of Nutrient Addition on Community Productivity and Structure of Serpentine Vegetation

Abstract: The effects of a nutrient addition experiment on the plant biomass of garigue vegetation on ultramafic (serpentine) soils in Tuscany, Italy, were investigated. Although community composition was not significantly changed, fertilization had a significant positive influence on biomass production. The most affected species groups were woody species (chamaephytes and phanerophytes), annual grasses and annual forbs; the bio mass increase of the perennial grasses and perennial forbs was statistically not significant. Soil extractable elements differed for calcium and potassium in the plots where they were added; sodium and nickel extractabilities were reduced by calcium ad dition due to the increased soil pH. Biomass production was linked more to major nutrient addition than to reduced nickel extractability, confirming that serpentine vegetation of Tuscany is mainly affected by nutritional stress rather than soil heavy metal content. The addition of calcium had a low effect on pri mary production of these ultramafic soils.     

Spatial Patterns of Benthic Macroinvertebrates in Intertidal Areas of a Southern European Estuary: The Tagus, Portugal

This study characterizes the composition and spatial distribution patterns of the benthic macrofauna in the intertidal mudflats of the Tagus estuary, western Portugal. A total of 68 species, more than 226,000 specimens with a total wet weight biomass of approximately 1170 g were identified in 380 sites. The species Streblospio shrubsolii, Cyathura carinata, Tharyx sp., Hydrobia ulvae and Tubificids were the most common and abundant. Scrobicularia plana strongly dominated the biomass. The invertebrate macrofauna of the Tagus estuary shows similarities to what is known from other temperate mudflats. The diversity of species, their overall abundance and the ratio of Molluscs plus Crustaceans to Polychaete species corroborate the distinctiveness between temperate and tropical mudflats and sandflats. The spatial distribution of the fauna reflects the sediment characteristics but the relationship between the environmental and the biological data is not as strong as obtained for sublittoral areas. This relationship diminishes from the sublittoral shelf to sublittoral estuarine areas, showing minimum values in this study, suggesting that such a relationship is less straightforward as natural disturbance increases. Nevertheless, a mixture of grain-size, elevation (inundation time) and particular habitats (relic oyster beds) form the best explanatory factors for the spatial distribution patterns of the intertidal benthic macrofauna of the Tagus estuary.     

Phytoplankton Community Structure in the Drainage Network of a Mediterranean River System (Aliakmon,Greece)

Phytoplankton structure was studied in Aliakmon river basin in April (highflow) and September (lowflow) 1995 in 29 sampling sites. Abundance and biomass were generally low and ranged considerably between sites. Benthic diatoms contributed greatly to the suspended algal assemblages whereas trends of potamoplankton development were observed downstream. Limnoplankton and especially chlorophytes developed in the areas where lentic conditions prevailed. The nature of changes in phytoplankton seemed to be both longitudinal and temporal. Multivariate techniques revealed that areas with distinctive morphology, hydrology and anthropogenic inputs tended to have similar phytoplankton composition although no simple relation with physico-chemical factors can be shown. Human impact was more obvious on phytoplankton at the lowflow period. Generally, discharge played a significant role to the structure of phytoplankton communities.     

The Impact of the Extreme Floods in July 1997 on the Ichthyocenosis of the Oder Catchment Area (Czech Republic)

Changes in the ichthyocenosis of five smaller streams of 2nd to 4th order existing in the spring section of the River Odra (Oder) catchment area, in the territory of the Czech Republic, were observed before and after the catastrophic floods of July 1997. Quantitative catches using electro-fishing were performed in June, August, and September 1997, i.e. a month before and 2 months after the floods. The maximum flow of water in the examined sites usually reached or exceeded the limit of the so-called ȁ8once in a century high waterȁ9. Extreme floods did not influence statistically the proven average readings of species diversity of ichthyocenosis in the examined sites (p = 0.5625), species variety (p = 0.7316), abundance per hectare (p = 0.3125), and biomass per hectare (p = 0.4375). A distinctive decline in abundance and also in the biomass of the ichthyocenosis took place in geomorphic reaches. Significant incisions and alterations in the routes of the streams were also observed. Statistical data of catches of key reophilous fish species from the River Oder catchment basin, all of which were affected by the floods, in the periods 1995–1996, 1997, and 1998–1999, were evaluated. Catches of the species of Salmo trutta and Thymallus thymallus in 1997 considerably increased. Only Thymallus thymallus experienced a more pronounced decrease in the years after the floods, when compared with the average readings made in the period 1995–1996. The readings of the adult abundance of Barbus barbus and Chondrostoma nasus did not prove a negative impact of the floods on the adult population of both species in the assessed years. Our findings suggest that the original fish communities may be naturally well adapted to culmination flows.     

Impact of temperature on food intake and growth in juvenile burbot

The effect of temperature on food consumption, food conversion and somatic growth was investigated with juvenile burbot Lota lota (age 0 years). Juvenile burbot showed a significant dome shaped relationship between relative daily food consumption ( C _R) and temperature ( T ) with C _R = − 0·00044 T ² + 0·01583 T  − 0·06010; ( n  = 90, r ² = 0·61). Maximum C _R was at 17·9° C (95% CL 17·2–18·6° C). The temperature related instantaneous growth rate ( G ) also followed a dome shaped function with G  = − 0·000063 T ² + 0·002010 T  − 0·007462; ( n  = 95, r ² = 0·57), with maximum growth rate at 16·0° C (95% CL 15·3–16·6° C). A significant linear relationship was found between the water temperature and the conversion coefficient ( C _C) with C _C = − 1·63 T  + 59·04; ( n  = 80, r ² = 0·74). The results indicate that juvenile burbot in large lakes benefit from higher water temperatures in the littoral zone, by increased food uptake and growth, especially during the warm summer months. Because profundal water temperatures do not reflect the optimal temperature for food consumption in large burbot, temperature is unlikely to be the main proximate factor for the obligate littoral‐profundal migration of juvenile burbot observed in many lake populations.     

Structure and Dynamics of a Benthic Invertebrate Community in an Intertidal Area of the Tagus Estuary, Western Portugal: A Six Year Data Series

A predictive model, incorporating macroinvertebrate and environmental data, similar to that developed for Australian rivers (AUSRIVAS) and British rivers (RIVPACS) was constructed using a dataset collected from 23 reference (least altered) wetlands on the Swan Coastal Plain, Western Australia, sampled in summer and spring, 1989 and spring, 1990. Four main groups of reference wetlands were identified by UPGMA classification (using the Bray–Curtis dissimilarity measure). Distinguishing environmental variables identified by Stepwise Multiple Discriminant Function Analysis were: calcium, colour (gilvin), latitude, longitude, sodium and organic carbon. Observed to expected ratios of taxa with a >50% chance of occurrence (OE50) derived from the model for a suite of 23 test wetlands sampled in spring, 1997, were significantly correlated with pH and the depth of the sampling sites. Greater discrimination between the test wetlands was provided by the OE50 ratios than either raw richness (number of families) or a biotic index (SWAMPS). Results obtained for a subset of 11 test wetlands sampled with both a rapid bioassessment protocol (incorporating field picking of 200 invertebrates collected in 2 min sweeps from selected habitats) and a semi-quantitative protocol (incorporating laboratory picking of all invertebrates collected in sweeps along 10 m transects at randomly allocated sites) were not significantly different, indicating that the former could be used to reduce the time and costs associated with macroinvertebrate-based wetland monitoring programs. In addition to providing an objective method of assessing wetland condition, predictive modelling provides a list of taxa expected to occur under reference conditions, which can be used as a target in wetland restoration programs. The probable impediment to widespread adoption of predictive modelling for wetland bioassessment is the need to produce models tailored to specific geographic regions and specific climatic conditions. This may incur significant costs in countries, such as Australia, which span a wide range of climatic zones.     

The Impact of Cyclone Fanele on a Tropical Dry Forest in Madagascar

Cyclones, which change tree communities and alter forest structure, are thought to have had a significant selective pressure on the flora and fauna of Madagascar. Very little information, however, is available on the actual impact of cyclones on Malagasy ecosystems. On 21 January 2009, Cyclone Fanele made landfall on the western coast of Madagascar with sustained winds of 185 km/h. We examined the immediate effects of the cyclone on tropical dry forest structure in the Kirindy Mitea National Park. In July and August 2009, we measured the height, diameter at breast height (dbh), and damage for 1361 trees in nine 25 × 25 m plots. We found that: (1) over 95 percent of trees experienced some sort of damage, including 8.8 percent mortality; (2) understory and emergent trees experienced significantly higher mortality than canopy trees; and (3) stem density was reduced 9.2±4.5 percent and biomass was reduced 13.4±8.1 percent after the cyclone. Dbh was the best predictor of trunk damage and mortality. This extensive alteration of forest structure will have a substantial short‐ and long‐term impact on the biotic communities of western Madagascar.     

海南清澜港红树林滩涂大型底栖动物初步研究

对海南清澜港红树林滩涂大型底栖动物进行了定性及定量调查,记录到大型底栖动物４５种,隶属于４个门,２６个科。其中软体动物３１种,占记录到物种数的６８９％;甲壳动物１０种,占记录到物种数的２２２％。优势种是珠带拟蟹手螺（ＣｅｒｉｔｈｉｄｅａｃｉｎｇｕｌａｔａＧｍｅｌｉｎ）、古氏滩栖螺（ＢａｔｉｌａｒｉａｃｕｍｉｎｇｉＣｒｏｓｅ）、中国紫蛤（ＨｉａｔｕｌａｃｈｉｎｅｎｓｉｓＭｏｒｃｈ）及奥莱彩螺（ＣｌｉｔｈｏｎｏｕａｌａｎｉｅｎｓｉｓＬｅｓｏｎ）。大型底栖动物的生物量平均１９８５ｇ／ｍ２、栖息密度３５２４个／ｍ２。软体动物的生物量占到９９％,这可能与取样设在中、低潮区有关。     

The effect of plant density on epiphytic macroinvertebrates associated with a submerged macrophyte,Lagarosiphon ilicifolius Obermeyer,in Lake Kariba,Zimbabwe

The effect of variations in the density of a submerged macrophyte, Lagarosiphon ilicifolius, on epiphytic macroinvertebrate community structure in the shallow waters of a sheltered bay of Lake Kariba were investigated. The body size class distributions of a mayfly, Cloeon (Ephemeroptera: Baetidae), and the damselfly family, Coenagrionidae, were also assessed with respect to variation in vegetation density. Macroinvertebrates were sampled from low-, moderate- and high-density beds of L. ilicifolius. There were no significant differences in individual taxon and total macroinvertebrate abundances, macroinvertebrate richness and diversity with respect to vegetation density. In all three density categories the functional feeding group (FFG) composition was dominated by collector-gatherers and collector-filterers. The abundance of the two FFGs did not change significantly within each, as well as among, the three vegetation-density categories (ANOVA, p > 0.05). The largest size class of Cloeon occurred only in high-density beds, whereas the largest coenagrionid individuals were obtained from low- and moderate-density beds and were absent from high-density beds. The results suggest that variation in the density of Lagarosiphon does not affect epiphytic macroinvertebrate community structure, but does affect body-size distributions of macroinvertebrate taxa, probably by affecting predator-prey interactions.     

The Impact of Hydrological Restoration on Benthic Aquatic Invertebrate Communities in a New Zealand Wetland

Drainage is a major disturbance affecting wetlands, as drains lower water tables and convert lentic habitats to lotic ones. Consequently, invertebrate communities in drained wetlands are likely to differ from those in unimpacted wetlands. This study investigated the effect of hydrological restoration on invertebrate communities in small drains in a New Zealand fen. Invertebrates were collected over 4 summers from 10 drains within the wetland, one of which was blocked as part of a restoration program. The sampling protocol thus represented a Before‐After Control‐Impact experiment. Invertebrate community composition varied over the 4 years, but variability was greatest in the manipulated drain before and after it was blocked. Relative abundance of the amphipod Paraleptamphopus decreased after blockage, whereas those of the midges Chironomus zelandicus and Tanypodinae increased. Relative abundances of these taxa in control sites were unchanged. Hydraulic restoration thus had a demonstrable impact on the invertebrate communities. The invertebrate community of the blocked drain was compared to that of natural wetlands in undisturbed catchments. Similarity was very low prior to drain blockage, but increased following drain blockage. Invertebrate communities in the restored drain were more similar to those of low pH wetlands than high pH wetlands. Given the goal of restoring the communities to those similar to natural conditions, this was a beneficial result. These results, coupled with studies that showed a decline in the cover of alien pasture grasses around the blocked drain, suggest that drain blockage represents a cost‐effective way of restoring wetland plant and aquatic invertebrate communities, especially where connectivity allows for the natural recruitment of these organisms into restored areas.     

The Effects of Soil Bacterial Community Structure on Decomposition in a Tropical Rain Forest

Soil microorganisms are key drivers of terrestrial biogeochemical cycles, yet it is still unclear how variations in soil microbial community composition influence many ecosystem processes. We investigated how shifts in bacterial community composition and diversity resulting from differences in carbon (C) availability affect organic matter decomposition by conducting an in situ litter manipulation experiment in a tropical rain forest in Costa Rica. We used bar-coded pyrosequencing to characterize soil bacterial community composition in litter manipulation plots and performed a series of laboratory incubations to test the potential functional significance of community shifts on organic matter decomposition. Despite clear effects of the litter manipulation on soil bacterial community composition, the treatments had mixed effects on microbial community function. Distinct communities varied in their ability to decompose a wide range of C compounds, and functional differences were related to both the relative abundance of the two most abundant bacterial sub-phyla (Acidobacteria and Alphaproteobacteria) and to variations in bacterial alpha-diversity. However, distinct communities did not differ in their ability to decompose native dissolved organic matter (DOM) substrates that varied in quality and quantity. Our results show that although resource-driven shifts in soil bacterial community composition have the potential to influence decomposition of specific C substrates, those differences may not translate to differences in DOM decomposition rates in situ. Taken together, our results suggest that soil bacterial communities may be either functionally dissimilar or equivalent during decomposition depending on the nature of the organic matter being decomposed.