Composition,distribution and biomass of meiobenthos in the Oosterschelde estuary (SW Netherlands)

Meiofauna composition, abundance, biomass, distribution and diversity were investigated for 31 stations in summer. The sampling covered the whole Oosterschelde and comparisons between the subtidal — intertidal and between the western-central — eastern compartment were made.Meiofauna had a community density ranging between 200 and 17 500 ind 10 cm^–2, corresponding to a dry weight of 0.2 and 8.4 gm^–2. Abundance ranged between 130 and 17 200 ind 10 cm^–2 for nematodes and between 10 and 1600 ind 10 cm^–2 for copepods. Dry weight biomass of these taxa was between 0.5–7.0 gm^–2 and 0.008–0.3 gm^–2 for nematodes and copepods respectively.The meiofauna was strongly dominated by the nematodes (36–99%), who's abundance, biomass and diversity were significantly higher intertidally than subtidally and significantly higher in the eastern part than in the western part. High numbers were positively correlated with the percentage silt and negatively with the median grain size of the sand fraction. The abundance and diversity of the copepods were highest in the subtidal, but their biomass showed an inverse trend being highest on the tidal flats.The taxa diversity of the meiofauna community and species diversity of both the nematodes and the copepods were higher in subtidal stations than on tidal flats. In the subtidal, the meiofauna and copepod diversity decreased from west to east, whereas nematode diversity increased.The vertical profile clearly reflected the sediment characteristics and could be explained by local hydrodynamic conditions.Seasonal variation was pronounced for the different taxa with peak abundance in spring, summer or autumn and minimum abundance in winter.Changes in tidal amplitude and current velocity enhanced by the storm-surge barrier will alter the meiofauna community structure. As a result meiofauna will become more important in terms of density and biomass, mainly due to increasing numbers of nematodes, increasing bioturbation, nutrient mineralisation and sustaining bacterial growth. A general decrease in meiofauna diversity is predicted. The number of copepods is expected to decrease and interstitial species will be replaced by epibenthic species, the latter being more important in terms of biomass and as food for the epibenthic macrofauna and fishes.     

Horizontal and vertical distribution of meiofauna on sandy beaches of the North Sea (The Netherlands, Belgium, France)

Sandy intertidal zones were analysed for the presence of meiofauna. The material was collected on six macro-tidal sandy beaches along the North Sea (The Netherlands, France, Belgium), in order to analyse the vertical and horizontal meiofaunal distribution patterns. Eleven higher meiofauna taxa (one represented by larval stage—Copepoda nauplii) were recorded. The maximum total meiofauna abundance was observed on the Dutch beach (4,295±911 ind. 10 cm⁻²) in the Westerschelde estuary, while the lowest values (361±128 ind. 10 cm⁻²) were recorded in France at the Audresselles beach. Meiofauna of the different localities consisted mainly of nematodes, harpacticoids and turbellarians. Nematodes numerically dominated all sampled stations, comprising more than 45% of the total meiofauna density. Meiofauna was mainly concentrated at the sand surface with about 70% present in the uppermost 5 cm. Meiofauna occurred across the entire intertidal zone. A clear zonation pattern in the distribution of meiofauna taxa across the beaches was observed. The present work suggests that designation of exposed sandy beaches as physically controlled (McLachlan 1988) does not explain their biological variability.     

Distribution,abundance and ecology of the meiofauna in a tropical estuary along the west coast of India

The distribution and abundance of subtidal meiofauna in Mandovi estuary of Goa were studied from June 1983 to June 1984. Monthly faunal abundance ranged from 491 to 2791/10 cm² and dry weight biomass from 0.16 to 2.80 mg 10 cm². Free living nematodes were the dominant group contributing over 75% of the total density and 30 to 42% of the total biomass. Among nematodes the deposit feeders were more abundant in fine muddy substratum while epigrowth feeders dominated in sandy substratum.Harpacticoids were next, comprising 6.9 to 8.7% of the total meiofauna number, followed by turbellaria (3.8–4.5%), polychaeta (2.8–3.2%) and ostracods (1.6–4.5%) The contribution of other groups to faunal density was 4.5–6.2%. In the biomass the ostracods contributed most (29.8–54.7%), followed by nematodes (23.8–34.6%). Over 60% of the fauna occurred in the top 2 cm of the sediment and the faunal density reduced significantly with increasing depth in the sediment. The vertical distribution of meiofauna was positively correlated to the vertical distribution of Eh, chlorophyll a and interstitial water. Seasonality was greatly influenced by the south-west monsoon and the fauna quickly repopulated after the monsoon. Salinity, temperature and food influenced the faunal abundance.     

Foraminifera and meiofauna on an intertidal mudflat,Cornwall, England: Populations; respiration and secondary production; and energy budget

A rich and varied meiofauna inhabits a Cornish mudflat near the mouth of the Tamar River in southwestern England. Population densities range from 117 to 943 individuals · g^–1 (wet) sediment (1.4–11.4 × 10⁶ individuals · m^–2), with foraminifera, harpacticoid copepods and nematodes appearing in nearly equal numbers and comprising most of the meiofauna. Seasonally, meiofaunal numbers rise and fall with solar radiation and vary inversely with river discharge. Two species, the atestate allogromiid A and the calcareous Haynesina germanica (Ehrenberg), far outnumber other foraminifera; their population densities and growth rates reach maxima in spring and summer.Monthly rates of sediment respiration are locally variable, but clearly increase from winter (4.13 ml O₂ · m^–2 · h^–1 in December) to spring (38.87 ml O₂ · m^–2 · h^–1 in April). Experiments and calculations ascribe approximately 30% of this total to the meiofauna (including microfauna and microflora), 50% to bacteria and less than 20% to chemical oxidation. A tentative energy budget for the mudflat suggests that secondary production by meiofauna is small as compared with coastal environments elsewhere, and that meiofaunal production (426 Kcal · m^–2 · y^–1) is nearly twice meiofaunal respiration (252 Kcal · m^–2 · yr^–1).     

Meiofauna communities along a depth transect off Halley Bay (Weddell Sea-Antarctica)

Summary Meiofauna communities from 10 stations along a depth transect from approximately 500 to 2,000 m off the Halley Bay Station (Weddell Sea) are investigated. Representatives of about 30 smallsized taxa of higher category are found, most of them belonging to the meiofauna. Loricifera are recorded for the first time for the Southern Ocean. At one of the stations a maximum of 22 taxa occur, the mean number of taxa ranges from 7 to 16. Nematoda, Harpacticoida, Ostracoda, Polychaeta and Bivalvia are present at all sampling sites. Nematodes are always dominant representing more than 90% of the individuals per sample, followed by harpacticoids (3%) and kinorhynchs (1.2%). Important fractions of the meiofauna (an average of more than 50%) occur in strata below the top 0–1 cm layer. Maximal density is 3,800 individuals (10 cm^–2), the mean abundance per station ranges from 790 to 3,720 individuals (10 cm^–2) and the overall mean is 1,700 individuals (10 cm^–2). Multivariate analysis (TWINSPAN, Cluster analysis, DCA) discriminates between three communities which are correlated with depth and sediment characteristics: the near shelf-ice, the slope and the deep-sea communities.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

The structure of the plankton community of the Öregrundsgrepen (southwest Bothnian Sea)

Taxonomic composition and variations in density and biomass of the plankton community in the Öregrundsgrepen, a shallow coastal area, were investigated from June 1972 to November 1973. The phytoplankton biomass was large in spring but small during the rest of the year. The spring bloom was dominated by diatoms and dinoflagellates, especially byThalassiosira spp. which were also important during other seasons. Small forms, such asCryptomonas spp.,Rhodomonas spp. and monads, dominated during summer. Blue-green algae were never of any major importance. During the summer, the trophogenic layer exceeded 10 m in thickness. The metazoan fauna was of lower diversity than the plankton flora. The dominating species, the copepodsAcartia bifilosa andEurytemora affinis, constituted on the average 83% of the standing crop. The low salinities, 5–6 S, were regarded as the principal pertinent limiting factor. The metazoan fauna reached large biomass values from July to October. The protozoan fauna (in the case of ciliates), obtained biomass maxima during the spring bloom. It is suggested that the Öregrundsgrepen represents an area of elevated productivity within a region of low overall production, presumably due to local upwelling. From June 1972 to May 1973, the average biomasses were: phytoplankton 0.464 g C m^–2, ciliates 0.040 g C m^–2, copepod nauplii 0.010 g C m^–2, micro-rotifers 0.004 g C m^–2, and mesozooplankton (larger than 0.2 mm) 0.312 g C m^–2. It is estimated that about than 60% of the phytoplankton production is consumed by the microzooplankton (<0.2 mm).     

Abundance and composition of the sea-ice meiofauna in off-shore pack ice of the Beaufort Gyre in summer 2002 and 2003

We studied the abundance, biomass and potential ingestion rates of meiofauna in multi-year sea ice (MYI) of the Beaufort Gyre during two icebreaker expeditions in summers 2002 and 2003. Ice cores were taken at a total of ten stations and analyzed for ice temperature, salinity, chlorophyll a (Chl a), and ice meiofauna abundances. In 2002, ice was free of snow and covered with melt ponds. In 2003, snow still covered the ice and a slush-layer was found in the ice-water interface. The vertical distribution of Chl a mostly followed C-shaped curves with elevated concentrations at the bottom and top of the ice. Ice meiofauna was mainly restricted to the bottom 10 cm of the ice and was dominated by turbellarians, harpacticoid copepods and nematodes. The meiofauna abundances (range: 8–3,000 individuals m^–2) and Chl a concentration (range: 0.1–1.7 mg Chl a m^–2) were similar to estimates for MYI of the Transpolar Drift, but about 2 orders of magnitude below coastal fast first-year ice estimates. Calculated potential meiofaunal ingestion rate, based on allometric equations and volume estimates from the literature, was about 1% of published daily algal production rates and was thus unlikely to constrain algal biomass accumulation.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.     

Meiobenthos in mangrove areas in eastern Africa with emphasis on assemblage structure of free-living marine nematodes

A survey was conducted to examine spatial variations in the population density of major meiofaunal taxa and the assemblage structure of free-living marine nematodes within 5 mangrove areas on the west and east coast of Zanzibar. Meiofauna densities in surface sediments (0–5 cm) ranged from 205 to 5263 ind. 10 cm², being on average 1493 ind. 10 cm². Of the 17 major taxa recorded, nematodes dominated (64–99%) in all samples while harpacticoid copepods were usually second most abundant. Within all areas the numbers of meiofauna were very variable and significant differences among areas were only detected for oligochaetes and turbellarians. Densities of nematodes, harpacticoids, polychaetes and turbellarians were, however, significantly (P<0.001) higher at low water stations compared with mid and high water stations. Harpacticoids were negatively correlated with the numbers of fiddler crab (Uca spp.) burrows. Other correlations between environmental factors (grain size, temperature, salinity, oxygen tension, prop root density, fiddler crab burrows) and major meiofaunal taxa were non-significant. A total of 94 nematode genera were recorded from four mangrove areas. The most abundant and frequent genera were Microlaimus and Spirinia, followed by Desmodora and Metachromadora. Representatives of the genera most common in current study are found all over the globe. There was a high variation in nematode assemblage structure within and between sampling areas indicating the absence of a well defined nematode assemblage confined to mangrove areas. In a hypersaline area diversity was much reduced and where salinity was over 100%. the fauna was restricted to 3 nematode genera, Microlaimus, Theristus and Bathylaimus. Multidimensional scaling ordination (MDS) of the nematode genera separated samples taken from low water stations from other stations, the assemblage structure being significantly different at the low water stations. Numbers of selective deposit feeders were negatively correlated with average grain size and positively correlated with silt content.     

From spring sources to springbrook: Changes in environmental characteristics and benthic fauna

Spatial patterns in macroinvertebrate communities and some abiotic factors were examined in three rheocrene springs and their springbrooks (Kraków-Cz?stochowa Upland, southern Poland). The mean discharge of particular springs ranged from 5 to 11 L s^?1, and its annual fluctuations were small. Water temperature was very stable at all sampling sites. In the eucrenon the number of benthic taxa was the smallest (9–14 determined to the family level), but the densities were the highest (approx. 14000 ind. m^?2). The biggest changes in macroinvertebrate composition were observed in the modified hypocrenon, which is an artificial pond. The lowest number of taxa were found in a natural, short springbrook with a nondiversified bottom substrate. The density of crenophilic taxa (Drusus trifidus, Dugesia gonocephala, Elmidae) diminished along the springbrooks, while the opposite trend was observed for ubiquitous taxa (some Oligochaeta, Asellus aquaticus and Chironomidae). Even in a very short natural springbrook (30 m), Drusus trifidus, the only species of Trichoptera found in the springs discussed here, goes through the entire development cycle. The strongest influence of a big river was observed at the outflow of one of the natural springbrooks, where the highest number of riverine oligochaete species were found. The benthic fauna of the springs studied here differed from that found in other springs in this area — the absence of the typical crenophilic species Bithynella austriaca (Gastropoda) and the presence of Gianus aquedulcis (Oligochaeta) may indicate the autonomy of the spring fauna in the Mstów area, possibly resulting from the postglacial geomorphological formation of this region or differences in habitat conditions.     

Comparison of solutes, nutrients, and bacteria inputs from two types of groundwater to the Rhône river during an artificial drought

Solute, nutrient and bacterial inputs to the River Rhône from the interstitial habitat of a gravel bar and the floodplain aquifer were investigated during an artificial drought. Eight springs were investigated: four groundwater-fed springs in the floodplain, located at the bottom of the bank; and four interstitial-fed springs located at the downstream end of a gravel bar. During this period, the inflows of groundwater to the river represented an average input of 0.77 mg l^–1 of nitrogen (of which 93.3% were nitrates), 0.0187 mg l^–1 of total phosphorus (of which 42.2% was orthophosphate), 3.56 mg l^–1 of silica, 2.315 ± 0.703 mg l^–1 of dissolved organic carbon (DOC, of which 47% was biodegradable) and 7.3 × 10⁴ ± 3.7 × 10⁴ bacteria per ml (of which 8.8% were active). Silica, DOC, biodegradable DOC, and bacteria concentrations displayed temporal variations during the study, which seem to be linked to the biological activity of the groundwater biofilm. There was a strong heterogeneity between the two types of groundwater that flow to the river: concentrations of calcium and alkalinity were higher in bank springs than in gravel bars springs. In these latters, sulfate, sodium, nitrogen, phosphorus were significantly higher.     

The meiobenthos of five mangrove vegetation types in Gazi Bay,Kenya

The vertical distribution of meiofauna in the sediments ofAvicennia marina,Bruguiera gymnorrhiza,Ceriops tagal,Rhizophora mucronata andSonneratia alba at Gazi Bay (Kenya), is described. Seventeen taxa were observed, with highest densities in the sediments ofBruguiera (6707 ind. 10 cm^–2), followed byRhizophora (3998 ind. 10 cm^–2),Avicennia (3442 ind. 10 cm^–2),Sonneratia (2889 ind. 10 cm^–2) andCeriops (1976 ind. 10 cm^–2). Nematodes accounted for up to 95% of total densities; other common taxa were copepods, turbellarians, oligochaetes, polychaetes, ostracods and rotifers. High densities occurred to about 20 cm depth in the sediment. EspeciallyCeriops sediments show still high densities of nematodes (342 ind. 10 cm^–2) and copepods (11 ind. 10 cm^–2) in the deepest layer (15–22 cm). Particle size and oxygen conditions were major factors influencing meiobenthic distribution;Uca burrows had a major impact on distribution and abundance of meiofauna.     

Benthic meiofauna responses to five forest harvest methods

Benthic meiofauna were collected from the pools of minute (0 order) streams in the Ouachita National Forest, Arkansas during March 21–23, 1996 to see if benthic communities responded to forest harvest methods in a similar manner as plankton communities collected two years prior. The study streams and their watersheds (2–6 ha) were located in 14–16 ha forest stands that were selected for comparability of stands. Five treatment stands were paired with adjacent undisturbed reference stands (10 total). Treatment stands were subjected to one of five harvest methods listed in order of decreasing severity of harvest disturbance to the stands: (1) clearcut; (2) pine seed-tree; (3) pine shelterwood; (4) pine-hardwood group selection; and (5) pine single-tree selection. The mean number of taxa per site was 14 with a range of 9–20 taxa including rotifers, copepods, nematodes, dipterans, ostracods and `other' meiofauna. Densities of total meiofauna (mean=2449 No. l ^–1) were significantly higher (p= 0.002) in treated sites. Highest densities occurred in single-tree and clearcut treatments. Rotifers were significantly more numerous at the single-tree treatments (p=0.03) and nematodes were significantly greater at the clearcut treatments (p=0.03). We conclude that benthic meiofauna in these headwater streams are sensitive to silviculture practices and that the impact of forest harvest persists for at least 2.5 years.     

The gulf of Bothnia: The northernmost part of the Baltic Sea

Summary The Baltic Sea, one of the largest brackish water areas in the world, can be characterized as a young, cold sea containing an impoverished ecosystem due to salinity stress. The present Baltic Sea was formed as late as 2000 to 2500 years ago when the Danish sounds became more narrow and shallow. The inflow of freshwater from the surrounding land areas caused the Baltic to gradually attain its brackish character. Today the Baltic covers an area of some 366,000 km² as a series of basins separated by shallower areas and filled with about 22,000 km³ of brackish water. These basins are, from north to south, the Gulf of Bothnia, the Gulf of Finland, the Gotland Sea and the Bornholm Sea. The climate gradient ranges from almost arctic conditions in the extreme north to a more maritime climate in the southern parts. The North Sea salt water is connected to the Baltic through the shallow Kattegat and the sills in the Danish sounds. The inflow of salt water occurs in two different ways,viz. as a continuous flow along the bottom due to the salinity gradient and as pulses of salt water generated by the distribution of air pressure and the direction of the wind. The freshwater input (500 km³) from mainly the large rivers equals roughly the net outflow and stresses the south-bound current along the Swedish coast that also compensates for the salt water inflow. Tidal movements can be seen in the southern Baltic, but are of minor importance for the system. The residence time of the total water mass is 25 years and the hydrographical conditions within the different basins are stable and dominated by a permanent halocline, and a thermocline developing every spring. The salinity ranges from about 1–2 per mille in the innermost part of the Gulf of Bothnia to 10–15 per mille in the Bornholm Sea. Total vertical mixing takes place during winter in at least the northern parts of the sea. Due to the climate-gradient, the ice condition differs from about four months of total ice-cover in the inner parts of the Gulf of Bothnia to one month or less of coastal ice in the southern part of the Baltic. Thus, the seasonal effect is more pronounced in the northern parts.The living systems of the Baltic are reduced and adapted to these varying conditions. When comparing the deeper soft bottoms of the Gulf of Bothnia to the rest of the Baltic, the following pattern can be seen. The pelagic primary productivity increases by a factor 6 from north to south. The southern parts of the sea show a pronounced spring peak, while in the north the spring development is delayed or replaced by a summer maximum. The total increase of the macrofauna biomass is striking, from about 1 g.m^–2 (w.wt) in the north to 100 g.m^–2 (w.wt) or more in the south. The meiofauna and the zooplankton biomasses show less variability. The meiofauna increases by a factor of 2–4, giving a biomass of about twice that of the macrofauna in the northernmost part. The extremely low salinity of this area causes the exclusion of bivalves (filter-feeders) from the fauna. Available data, pooled with the high metabolic rate of the meiofauna, roughly follow the changes in primary productivity within the Baltic Sea. The changing ratio of macro- to meiofauna, as well as results from intensive studies of the macrobenthic amphipodPontoporeia affinis (Lindström), suggest that the macrofauna is regulated mainly by food limitation and that the benthic and pelagic systems are closely coupled.     

Salinity tolerance of Colorado Squawfish,Ptychocheilus lucius (Pisces: Cyprinidae)

Colorado squawfish (Ptychocheilus lucius), were subjected to dilutions of saline water from natural springs near Glenwood Springs, Colorado, to determine salinity tolerance and aquaculture potential of squawfish in this water. Lethal salinity to 50 percent of the fish (96 h LC₅₀) was 13.1 g l^–1, indicating that squawfish survival in higher salinity spring water was not possible.     

Abundance, body composition and reproductive output of Gammarus minus (Crustacea: Amphipoda) in ten cold springs differing in pH and ionic content

1. A survey of thirty-two rheocrene springs in central Pennsylvania revealed that, Like Gammarus in lakes and streams, Gammarus minus is absent from springs with pH <6.0 and conductivity <25μS cm^?1 (total range in pH = 4.6–7.7, and in conductivity = 14–411 μS cm^?1). 2. In ten springs G. minus density was positively correlated with Ca²⁺ and Mg²⁺ hardness, but not with pH, unless three springs with either an exceptionally high velocity or extremely high densities of the potentially competing snail Fontigens nickliniana were omitted. 3. Adults were larger in the springs with few or no large predators than in those with more predators. In all ten springs, adult dry mass was unrelated to spring pH and ionic content, but brooding female dry mass covaried positively with Ca²⁺ and Mg²⁺ hardness in the five predator-poor springs. 4. Body water, Na and Ca contents and body mass/length ratios varied independently of spring pH and ionic content. Water content was inversely correlated with fat content, but even when expressed as a percentage of fat-free wet mass, it was unrelated to water chemistry. 5. In juveniles, males and non-brooding females, fat content varied independently of spring pH and ionic content, but in brooding females it was correlated with alkalinity and Ca²⁺ and Mg²⁺ hardness. The cost of reproduction in brooding females may have been a factor here; they had significantly lower per cent fat than did non-brooding females. Juvenile fat content did not differ significantly among spring populations, whereas adult fat content did. The per cent fat of brooding females covaried positively with body size among springs, and this was marginally true for non-brooding females, as well. The residuals of brooding female per cent fat against dry mass were not related to water chemistry. 6. Brood size (number of embryos in a brood) and brood mass varied significantly among populations, but independently of spring pH and ionic content. Both covaried positively with maternal body size among springs. The residuals of these relationships were unrelated to water chemistry, as was the percentage of females brooding. 7. G. minus from a pH 6 spring survived better and lost less body mass in acidic soft water than did those from a pH 7.6 spring. However, although G. minus has apparently been able to adapt (or acclimate) to pH 6 water it has failed to adapt to more acidic waters. A physiological or structural constraint may be involved because this species has probably had ample opportunity to evolve resistance to dilute acidic water. This hypothesis is consistent with the threshold effect observed: above pH 6 G. minus shows very little evidence of osmotic or metabolic stress, but beiow pH 6 viable populations apparently cannot survive at all. However, the gradual linear decrease in population density of G. minus with decreasing alkalinity and Ca²⁺ and Mg²⁺ hardness suggests that other factors may also be involved (e.g. a decrease in food quality).     

Effect of domestic sewage on sand beach meiofauna at Goa,India

Meiofauna of a sewage-polluted sandy beach, where sand alone constituted > 90%, was surveyed. Nematodes dominated the fauna numerically at all stations, followed by harpacticoid copepods. Most of the animals were confined to the top 5 cm of the sediment. A seasonal pattern was observed in the distribution of the fauna. There were significant spatial and temporal variations in mean meiofauna density, attributed to organic discharge via sewage and prevailing environmental conditions in the study area.     

Physical and chemical differences in karst springs of Cantabria, northern Spain: do invertebrate communities correspond?

Benthic macroinvertebrate communities were studied and environmental variables were measured in six rheocrene springs in Cantabria, northern Spain. Principal component analysis revealed two different spring types according to their physical and chemical characteristics. Springs from group A (GA) had higher temperature and conductivity, while springs in group B (GB) had higher values of pH, altitude, mean water velocity, percentage of boulders and coarse particulate organic matter. Total number of invertebrate taxa and individuals were not different between GA and GB springs. However, Shannon diversity index was significantly higher for GB springs. Analysis of similarities (ANOSIM) and non-metric multidimensional scaling (NMDS) analysis indicated that invertebrate assemblages from GA and GB springs were different. The snails Theodoxus fluviatilis and Bythinella sp., and the amphipod Echinogammarus spp. had higher densities in GA springs, whereas ephemeropterans, plecopterans, trichopterans and chironomids were more important in GB springs. Higher water velocities in GB springs interacting with predation by Echinogammarus tarraconensis may be responsible for the observed patterns on invertebrate community structure and composition. The taxonomic resolution limited our ability to detect crenobiontic taxa. Sampling aquatic, semi-aquatic and semi-terrestrial habitats are needed to account for the biodiversity patterns of spring habitats.     

Effects of floods on epilithon and benthic macroinvertebrate populations in an unstable New Zealand river

Temporal changes in epilithon biomass and benthic macroinvertebrate density were investigated in the Ashley River, a flood-prone river with an unpredictable discharge regime. Biomass, primary production and respiration of the epilithic community were highest in spring when filamentous algae were present and lowest following two large floods that occurred in close succession. Sixty invertebrate species were taken in benthic samples including 24 species of Trichoptera, 15 Diptera and 4 Ephemeroptera. Larvae of the mayfly Deleatidium (Leptophlebiidae) were numerically dominant and comprised up to 83 % of the fauna in any one month. Mean benthic invertebrate density was highest (9170–18 580 m^{–2) following long periods of low stable flow (< 30 m–3} s^–1) and lowest (230 m^–2) after a major flood (454 m^–3 s^–1). Reductions in benthic density occurred when flow exceeded about 30 m^–3 s^–1, the minimum discharge at which small cobbles are moved. Refuge seeking behaviours, flexible life histories and effective recolonization mechanisms enable the benthos of the Ashley River to persist and recover from frequent, temporally unpredictable disturbances.     

The Chironomid Communities of Woodland Springs and Spring Brooks, Severely Endangered and Impacted Ecosystems in a Lowland Region of Eastern Germany (Diptera: Chironomidae)

The distribution of chironomid species from four springs and twelve spring brooks in a region heavily affected by industrial activity in eastern Germany was studied. The aims were (1) to document the chironomid taxa communities at the species level, as far as possible, and the most important environmental factors of representative springs and spring brooks of the region, (2) to analyse the distribution of the ecological groups within these small ecosystems and (3) to emphasize the importance of the protection of spring areas and spring brooks in this woodland area shown by the chironomid fauna. There was high degree of abiotic variation among the water bodies, with pH ranging from 2.79 to 6.89. While diversity did not correlate with pH nor with conductivity, significant differences existed between the spring mouth and the reaches some metres downstream with respect to several abiotic parameters and the distribution of the chironomids: oxygen concentrations and taxonomic diversities were higher in spring brooks (2.18–8.98mgO₂/l; 5–28 taxa) than in the spring areas (0.13–2.95mgO₂/l; 0–7 taxa). A total of 74 chironomid taxa were recorded. The chironomid communities are characterized by the presence of rheophilic, cold-stenothermic, crenophilic and sometimes tyrphophilic elements in each site. The data show that each of the spring–spring brook systems surveyed is unique both in biotic and abiotic respects. As the spring system is sensitive to changes in landscape functions (e.g. groundwater levels), the fauna can serve as an indicator of landscape health. Therefore, these small ecosystems should be conserved as a reference.