Observations on ventilatory and net-spinning activities of larvae of the genus Hydropsyche Pictet (Trichoptera, Hydropsychidae) under experimental conditions

Larvae of three species of the genus Hydropsyche with distribution patterns indicating they are associated with increasing ranges of flow rate and temperature in the sequence H. instahilis, H. pelhicidula, H. angustipennis, were selected for study. Experiments on frequency of ventilatory movements indicated that the larvae were increasingly tolerant to dissolved oxygen concentration, flow rate and temperature in the same sequence of species. Experiments on net-spinning indicated a corresponding order of preference for higher temperatures and a general preference for higher flow rates. During experiments on net-spinning the number of larval casualties, ascribed to encounters between individuals, showed marked contrasts between species. The significance ofthe behaviour ofthe larvae under experimental conditions is discussed with reference to their distribution in the field.     

The Trichoptera of Øvre Heimdalsvatn

Trichopteran larvae were sampled on soft substrata at all depths, on stony substrata in the exposed zone, and the adults in emergence traps, placed along the lake shore. Fourteen species were taken as larvae in the lake. On stony substrata and in the exposed zone Polycentropus flavomaculatus (Pictet) was dominant, followed by Limnephilus nigriceps (Zetterstedt) in terms of numbers. In terms of biomass L. nigriceps dominated followed by Potamophylax cingulatus (Stephens).
Species which usually inhabit running water made up for a larger part of the trichopteran fauna of the exposed zone.
The two most numerous species showed different habit preferences. P. flavomaculatus was most common on stable stony bottom, while L. nigriceps was most common on unstable stony bottom. The other species showed no significant preference. On unstable soft bottom at 3 m and below, Mystacides azureus (L.) dominated, accounting for about 90% of the total trichopteran fauna both in terms of weight and numbers.
The major trichopteran species in the lake were either detritus feeders, such as M. azureus, L. nigriceps and Potamophylax spp. or omnivores such as P. flavomaculatus and Molanna albicans (Zetterstedt).     

Predation and the prey community of a headwater stream

SUMMARY 1. Predatory, net-spinning larvae of the caddis Plectrocne-mia conspersa (Curtis) were abundant in the acid headwaters of some southern English streams where fish were absent, but were scarce or absent downstream where brown trout ( Salmo trutta L. ) occurred.
2. Field enclosure experiments showed that both underyearling and older brown trout reduced the density of P. conspersa . However, whereas small trout affected the overall density of caddis, older fish reduced that of large larvae only.
3. Although P. conspersa is itself an important invertebrate predator there was little evidence of an indirect effect of brown trout on the prey of P. conspersa . Perhaps the diets of brown trout and P. conspersa are so similar that fish simply replaced the caddis as top predator.     

Spatial and temporal dispersion patterns of golden perch, Macquaria ambigua, larvae in an artificial floodplain environment

Golden perch larvae were stocked into a pond and inundated floodplain system in south-eastem Australia to determine movement patterns of the larvae onto and off the floodplain area. A total of 428 larvae were caught moving from the floodplain into the pond whereas only 18 were collected moving in the reverse direction. Thirty one larvae were caught at open water sites in the pond and floodplain, but only three were collected from sites on the floodplain which provided shade, timber or water flow. Transect samples from the pond also yielded more larvae than samples from floodplain transects, indicating a distinct spatial dispersion pattern in favour of the pond.
Spatial dispersion patterns of golden perch larvae appear to correspond with gradients in water quality between the pond and floodplain habitats. Stratification occurred in the pond but did not develop on the floodplain. Water on the floodplain was cooler, harder and contained less oxygen than surface water from the pond. Die1 oscillations occurred in water temperature, pH, dissolved oxygen, carbon dioxide and acidity, but there was no significant corresponding pattern in the distribution of larvae.
Dispersion of golden perch larvae between pond and floodplain habitats is not random, and may be actively influenced by local-scale variations in water quality.     

Effects of temperature and dissolved oxygen on heart rate,ventilation rate and oxygen consumption of spangled perch,Leiopotherapon unicolor (Günther 1859), (Percoidei,Teraponidae)

Summary Heart, ventilation and oxygen consumption rates ofLeiopotherapon unicolor were studied at temperatures ranging from 5 to 35°C, and during progressive hypoxia from 100% to 5% oxygen saturation. Biopotentials recorded from the water surrounding the fish corresponded to ventilation movements, and are thought to originate from the ventilatory musculature. Cardio-respiratory responses to temperature and dissolved oxygen follow the typical teleost pattern, with bradycardia, increased ventilation rate and reduced oxygen consumption occurring during hypoxia. However, ventilation rate did not increase at 15°C and below. Ventilation rate showed a slower response to increasing temperature (normoxic Q₁₀=1.39) than heart rate and oxygen consumption (normoxic Q₁₀=2.85 and 2.38).L. unicolor is unable to survive prolonged hypoxia by utilising anaerobic metabolism, but has a large gill surface area which presumably facilitates oxygen uptake in hypoxic environments. Periodic ventilation during normoxia in restingL. unicolor may improve ventilation efficiency by increasing the oxygen diffusion gradient across the gills.Abbreviations EBG electrobranchiogram - ECG electrocardiogram     

Prevalence, intensity, and differential development of Pseudodelphis oligocotti (Nematoda: Dracunculoidea) in sympatric fish hosts of the northeastern Pacific coast

Counter to expectations of coevolved parasite-host relationships, parasites frequently infect hosts that never contribute to their reproduction, making the identification of a parasite's true host-specificity problematic. Pseudodelphis oligocotti (Nematoda: Dracunculoidea) infects several coastal Pacific fishes, but its course of development appears highly variable, suggesting that incidence does not reflect effective host range. To determine the host range of P. oligocotti and describe its relationship to various potential hosts, 24 fish species were examined from several British Columbia localities for prevalence, intensity, and extent and tissue location of parasite development. Pseudodelphis oligocotti infects 9 species of fishes from 5 orders, of which penpoint gunnel, Apodichthys flavidus, showed the highest prevalence and intensity, up to 80% and 19 (+/- 17.1 SD) worms per host, respectively. Although subadult and adult P. oligocotti occurred in all 9 fishes, larvigerous P. oligocotti only occurred in A. flavidus and rarely in the northern clingfish, Gobiesox maeandricus. Infective first-stage larvae were recovered from gill tissue of A. flavidus. Thus, at most only 2 of the 9 host species infected by P. oligocotti actually contribute to its transmission. The occurrence of P. oligocotti in diverse hosts may be accounted for by the parasite's indiscriminant mode of transmission via ingestion of free-living intermediate copepod hosts, where highly exposed or more suitable fishes (or both) are closely related by diet and microhabitat. This study demonstrates how parasite transmission and host ecology can greatly affect observed host range and ultimately its potential for expansion.     

卵形鲳鲹胚胎及早期仔鱼耗氧量的研究

运用SKW-3微量呼吸仪对卵形鲳鲹(Trachinotus ovatus)胚胎和早期仔鱼的耗氧量进行测定,研究温度、盐度及pH的变化对胚胎耗氧量和Cu²⁺、Cd²⁺等重金属离子对早期仔鱼的耗氧量的影响。结果表明:在(25±0.5)℃条件下,卵形鲳鲹胚胎和早期仔鱼的耗氧量均随着发育时间的延长总体上呈上升的趋势,胚胎耗氧量在出膜前达到最大值,其中以原肠期和出膜期耗氧量变化最为显著。胚胎耗氧量随着温度、盐度、pH的增大而逐渐升高,在水温25℃、盐度35和pH为8时耗氧量到达最大值,随后逐渐减小。随着Cu²⁺浓度的升高,早期仔鱼耗氧量呈先增大后减小,在0.01mg·L^-1时耗氧率最大:胚胎耗氧量随着Cd²⁺浓度的升高而逐渐降低。     

Long-term observations of deepwater renewal in Crater Lake,Oregon

We examine observations of key limnological properties (primarily temperature, salinity, and dissolved oxygen), measured over a 14-year period in Crater Lake, Oregon, and discuss variability in the hypolimnion on time scales of days to a decade. During some years (e.g., 1994–1995), higher-than-average wintertime deep convection and ventilation led to the removal of significant amounts of heat and salt from the hypolimnion, while dissolved oxygen concentrations increase. In other years, such as the winter of 1996–1997, heat and salt concentrations increase throughout the year and dissolved oxygen levels drop, indicating conditions were dominated by the background geothermal inputs and dissolved oxygen consumption by bacteria (i.e., minimal deep convection). Over the entire 14 year period, no statistically significant trend was observed in the annual hypolimnetic heat and salt content. Measurements from several thermistors moored in the hypolimnion provide new insight into the time and space scales of the deep convection events. For some events, cool water intrusions are observed sequentially, from shallower depths to deeper depths, suggesting vertical mixing or advection from above. For other events, the cooling is observed first at the deepest sensors, suggesting a thin, cold water pulse that flows along the bottom and mixes more slowly upwards into the basin. In both cases, the source waters must originate from the epilimnion. Conditions during a strong ventilation year (1994–1995) and a weak ventilation year (1996–1997) were compared. The results suggest the major difference between these 2 years was the evolution of the stratification in the epilimnion during the first few weeks of reverse stratification such that thermobaric instabilities were easier to form during 1995 than␣1997. Thus, the details of surface cooling and wind-driven mixing during the early stages of␣reverse stratification may determine the net␣amount of ventilation possible during a particular year.     

A revised key to larvae of the genus Plectrocnemia (Polycentropodidae: Trichoptera) in Britain, with notes on Plectrocnemia brevis McLachlan

SUMMARY. The key distinguishes the previously unknown larva of Plectrocnemia brevis McLachlan from larvae of the other two British Plectrocnemia species, P. conspersa (Curtis) and P. geniculata McLachlan. Notes are given on the larval habitat, life cycle and identification of the adult of P. brevis.     

The influence of some ecological factors on the metabolism—temperature curve of the larvae of Limnephilus rhombicus (Trichoptera, Limnephilidae)

SUMMARY. The oxygen uptake of Limnephilus rhombicus , a typical inhabitant of lentic waters, was measured in three different experimental situations: in still water with a plastic mesh as a substrate, in stirred water with a plastic mesh and in still water without any substrate. Water flow caused a small increase in oxygen uptake at all temperatures but principally above 15°C. The presence or absence of the plastic substrate had little influence on oxygen uptake; L. rhombicus can be active over the whole range of temperatures studied but its activity is always small. Its metabolism—temperature curve stands out in having a plateau between 5 and 10°C, with a steeper part between 10 and 20°C, the slope of which varies according to the conditions. Maximum oxygen uptake at high temperatures was relatively low (1235 ± 153 μl O₂g dry wt-1h-1 at 25°C).
The results are compared with those obtained previously for the larvae of Microptema testacea which inhabit flowing zones in brooks. L. rhombicus larvae appear both as cold-water animals and as animals from highly variable biotopes. They are in fact very ubiquitous and occupy all lentic biotopes from cold and mountainous districts to temperate lowlands.     

Sub-lethal effects of disturbance on a predatory net-spinning caddisfly

1. The sub-lethal effects of hydrologic disturbances on stream invertebrates are poorly understood, but integral to some models of how disturbances influence population and community dynamics. Carnivorous larvae of a net-spinning caddisfly, Plectrocnemia conspersa , have a strong predatory impact in some streams. Their silken nets, however, are vulnerable to high flow disturbance and the consequent destruction of nets could reduce predatory impacts and have life history consequences.
2. In a laboratory experiment, we manipulated the frequency of disturbances that destroyed the nets of P. conspersa , in the presence and absence of potential prey. Animals were housed individually and each trial lasted 8 days. We estimated net size, cumulative mass of silk produced, net allocation (net mass expressed as a proportion of body mass), per capita prey consumption and growth or mass loss of larvae.
3. In the absence of prey, increased disturbance frequency was accompanied by increased loss of body mass, a reduction of net size and an increase in the cumulative mass of silk produced. At the highest disturbance frequency, larvae eventually gave up producing nets. The ratio of net mass to body mass decreased with increasing disturbance, suggesting a trade-off in the allocation of resources, with a decreasing proportion of resources available for foraging. In the presence of prey, increased disturbance frequency was accompanied by a reduction in per capita prey consumption. Although foraging success offset the costs of silk production, growth rate decreased with increasing disturbance and could eventually lead to reduced body size and fecundity of adults.
4. These sub-lethal effects suggest that hydrologic disturbances could impose metabolic costs and reduce foraging efficiency of this predator. Thus, disturbances may reduce predator impact on prey populations and reduce predator population size without any direct mortality or loss of individuals.     

Rapid behavioral responses of an invertebrate larva to dissolved settlement cue

Larvae of the nudibranch Phestilla sibogae were used to study whether a natural dissolved settlement cue (from their prey, Porites compressa, an abundant coral on Hawaiian reefs) induces behavioral responses that can affect larval transport to suitable settlement sites. As cue and larvae are mixed in the turbulent flow over a reef, cue is distributed in fine-scale filaments that the larva experiences as rapid (seconds) on/off encounters. To examine larval responses in this setting, individual larvae were tethered in a small flume with flow simulating water velocity relative to a freely swimming larva, and their responses to realistic temporal patterns of cue encounter were videotaped. Competent larvae quickly ceased swimming in cue filaments and resumed swimming after exiting filaments. The threshold cue concentration eliciting a response was 3%-17% of concentrations within heads of P. compressa in nature. When moving freely in filtered seawater, competent larvae swam along straight paths in all directions at approximately 0.2 cm s(-1), whereas in water conditioned by P. compressa, most ceased swimming and sank at approximately 0.1 cm s(-1). The ability of larvae to rapidly respond (by sinking) to brief encounters with dissolved settlement cues can enhance their rapid transport to the substratum, even in wave-driven turbulent flow.     

溶氧水平对鲫鱼代谢模式的影响

为了探讨水体溶氧水平对鲫幼鱼(Carassius carassius)运动、消化能力及其交互作用的影响,在(25.0±0.5)℃温度条件下,测定了8(饱和溶氧水平)、2和1mg/L溶氧水平下摄食(饱足摄食)和空腹组(空腹2 d)鲫鱼的临界游泳速度(Ucrit)、运动前耗氧率(MO2pre-exercise)、活跃耗氧率(MO2active)和代谢范围(MS)。摄食诱导的耗氧率上升在各溶氧水平下无显著差异。在饱和溶氧水平下,摄食组和空腹组的Ucrit没有显著差异,但在1和2 mg/L条件下,摄食组的Ucrit显著低于空腹组(P<0.05)。在饱和溶氧水平条件下,消化和运动诱导的耗氧率上升在各个游泳水平均能完全叠加,且摄食组鱼类与空腹组鱼类具有相似的MS和Ucrit和更高的MO2active,提示鲫鱼在常氧下为添加代谢模式。随着溶氧水平下降至2和1mg/L,呼吸能力(摄食组的MO2active)对溶氧水平下降较运动耗氧率更为敏感,消化诱导的耗氧率增加只能在较低游泳速度叠加,与空腹组鱼类比较,摄食组鱼类的MS和Ucrit显著下降,MO2active无显著差异,提示低氧下消化和运动对氧气需求竞争的加剧使其代谢模式转化为消化优先。     

Microhabitat selection by the fishfly larva, Parachauliodes japonicus, in relation to its mode of respiration

SUMMARY. 1. Larvae of Parachauliodes japonicus (Megaloptera: Corydalidae) were tracked in streams using miniature radio-transmitters.
2. Larvae usually stayed under stones in shallow water for several days, but occasionally moved about on the stream bed at night.
3. Larvae possess a pair of respiratory tubes on abdominal segment VIII, which can be used as a snorkel to obtain oxygen from the atmosphere. Because respiratory rates decreased as dissolved oxygen decreased, larvae turned to air-breathing under lowered oxygen conditions. When in shallow water, they can alter respiratory mode from aquatic respiration to air breathing instantly by raising their caudal respiratory tubes to the surface of the water.
4. Microhabitat selection and respiratory behaviour are compared with those obtained previously for Protohermes grandis larvae, which belong to the same family and often inhabit the same stream as P. japonicus , but which have gill tufts on abdominal segments I-VII instead of respiratory tubes. The respiratory constraint on microhabitat preference by aquatic insects is discussed.     

Winter anoxic layer in Lake Hibara

The concentration of dissolved oxygen in waters 0.5–0.6 m above the bottom of Lake Hibara, a dimictic lake, was zero in early spring of 1994 and 1997. The concentrations in early spring of 1992, 1993, 1995, 1996, and 1998 ranged from 3.75 to 10.1 mg l⁻¹. The depth profiles of water temperature suggest that water had not circulated prior to the sample collections of 1994 and 1997, but it had done so in the cases of the other years, suggesting that winter conditions were well preserved in the former years. On the other hand, the dissolved oxygen in the same strata decreased severely in summer. However, more or less titratable amounts of dissolved oxygen still remained (0.01–0.73 mg l⁻¹) at the final stages of summer stratification from 1992 to 1998. These facts show that a completely anoxic condition is not formed in this lake in summer but is sometimes formed in winter. It is interesting to note that in spite of unfavorable winter conditions for oxygen consumption, i.e., shorter duration and lower water temperature, oxygen is exhausted. These facts suggest that ventilation to the depths is much greater in summer than in winter. Received: March 5, 1999 / Accepted: October 18, 1999     

MASS MORTALITIES OF FISH IN SOUTH AFRICAN ESTUARIES

Summary

Changes to the physico-chemical environment have been identified as the cause of fish mass mortalities in South African estuaries. Most published accounts have linked these mortalities to a single dominant factor such as low salinity, low or high temperature, low concentration of dissolved oxygen, and high sediment loads. A review of the evidence suggests that, although single factor induced mortalities do occur, the role of supplementary factors in triggering fish kills may be more important than previously acknowledged. The most frequently interacting factors in a southern African context appear to be salinity and water temperature, dissolved oxygen and water temperature, and suspensoids and dissolved oxygen. In some cases all the above factors may be operational in creating an environment which is unsuitable for the survival of certain estuarine-associated fish species.     

水体溶氧影响陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)对完全水淹的耐受力

溶氧是水环境中一个重要的环境因子,为了探讨水中的溶氧含量水平是否会对陆生植物的耐淹能力造成影响,研究了陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)在遭受不同溶氧含量水体完全淹没后的生长表现、存活情况和非结构碳水化合物的变化。实验结果表明:(1)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的存活。受高溶氧水体完全水淹的喜旱莲子草和牛鞭草主茎的完好程度和存活叶的数量均显著高于遭受低溶氧水体完全水淹的喜旱莲子草和牛鞭草,喜旱莲子草和牛鞭草在高溶氧水体完全水淹后的生物量比低溶氧水体完全水淹后要高;(2)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的生长,受高溶氧水体完全水淹的喜旱莲子草主茎伸长生长和不定根生长显著强于受低溶氧水体完全水淹的喜旱莲子草,在不定根的生长上牛鞭草也具有同样的表现。(3)高溶氧水环境有利于减小被完全淹没的喜旱莲子草和牛鞭草的碳水化合物消耗,两种植物在受高溶氧完全水淹后体内具有的非结构性碳水化合物含量均比受低溶氧完全水淹后高。(4)喜旱莲子草比牛鞭草能更好地耐受完全水淹,当处于低溶氧完全水淹时表现得更为明显,本研究表明入侵物种喜旱莲子草比本地物种牛鞭草具有更强的环境适应能力和水淹耐受能力。     

Water balance in the sugarbeet root maggot Tetanops myopaeformis,during long‐term low‐temperature storage and after freezing

The sugarbeet root maggot Tetanops myopaeformis Röder (Diptera: Ulidiidae) can be stored in moist sand at 4–6 °C for up to 5 years and is freeze‐tolerant. The majority of stored larvae survive in a state of post‐diapause quiescence and the remainder are in a multi‐year diapause. The present study aims to determine larval water content and water loss rates in diapausing and low‐temperature stored larvae. Body water content ranges from 57% to 70.1%. Two distinct groupings of larvae are revealed based on dry weights. The first group consists of the diapausing larvae and larvae stored for 1 year. This group has significantly higher dry weights than the second grouping, which consists of the larvae stored for 2 and 3 years. There are no significant differences within each group. Larval water losses follow a first‐order kinetic relationship with time. Larvae stored for 2 years lose water at a significantly higher rate than diapausing larvae. Larvae exhibit no active water uptake at storage temperatures. A freezing event does not induce a significant decrease in wet weights, nor does it increase larval water loss rates. These results indicate that metabolic water and the microclimate during storage are key factors enabling the long‐term survival of T. myopaeformis larvae during low‐temperature storage, and may provide insights for maintaining other insect species under similar conditions.     

Temperature and Dissolved Oxygen Determine Submersion Time in Aquatic Beetle <Emphasis Type="Italic">Peltodytes callosus</Emphasis> (Coleoptera: Haliplidae)

Global climate change affects aquatic habitats in a number of ways that pose challenges for aquatic insect populations. Increasing water temperature and corresponding decreases in dissolved oxygen can impact respiratory behaviors, even in air-breathing aquatic taxa. Crawling water beetles (Coleoptera: Haliplidae) exhibit a combined respiratory strategy that employs an air store that is periodically replenished at the water surface. The frequency at which beetles surface to replenish the bubble is determined both by oxygen demand and by the capacity of the air store to uptake oxygen from the surrounding water via diffusion. However, little is known of how changes in water temperature and dissolved oxygen will affect submersion time. We investigated this question in Peltodytes callosus, a species of crawling water beetle that is widely distributed across the American West. We manipulated temperature and dissolved oxygen to mimic changes associated with global climate change and recorded the time between surfacing events. We found that beetles stayed submerged for shorter durations in response to both increasing water temperature and decreasing dissolved oxygen. Our results suggest that beetles may be able to modify their surfacing behavior to respond to climate-induced changes in water quality.     

DEVELOPMENTAL MODE AND SPECIES GEOGRAPHIC RANGE IN REGULAR SEA URCHINS (ECHINODERMATA: ECHINOIDEA)

Among marine benthic organisms, the ability to disperse, primarily during the larval stage, is widely thought to influence the extent of species geographic range. Because related species often differ in their modes of larval development (pelagic, feeding larvae; pelagic, nonfeeding larvae; or brooded development), and these can have dramatically different planktonic intervals, the mode of development may influence geographic range. A global survey of 215 regular echinoids shows that species with pelagic, feeding larvae have significantly larger ranges than those with pelagic, nonfeeding larvae, but there is no difference in ranges between species with pelagic, nonfeeding larvae and those with brooded development. These patterns are maintained within the Cidaroida and the Temnopleuroida, which account for the great majority of species with pelagic, nonfeeding development and brooded development. This limited effect of developmental mode on geographic range is found among species occurring predominantly in waters shallower than 100 m. For species occurring deeper than 100 m, there is no significant difference in geographic range related to type of development. The relationship between developmental mode and species range was examined more closely for circa 30 species for which the developmental period was known from laboratory observations. Adjusting the developmental times to a common temperature, 20°C, using realistic values for Q₁₀ from 2.0 to 3.6, showed a highly significant, negative correlation between egg volume and developmental time, indicating the potential for developmental mode to influence the planktonic interval. However, there was no relationship between time in the plankton, estimated from unadjusted developmental times, and extent of species geographic range. These results suggest that developmental mode may influence extent of species geographic ranges indirectly through the consequences of dispersal for gene flow or recovery from disturbance.