Biotic Index Values Research Articles

Differences Found in the Macroinvertebrate Community Composition in the Presence or Absence of the Invasive Alien Crayfish, Orconectes hylas.

Introductions of alien species into aquatic ecosystems have been well documented, including invasions of crayfish species; however, little is known about the effects of these introductions on macroinvertebrate communities. The woodland crayfish (Orconectes hylas (Faxon)) has been introduced into the St. Francis River watershed in southeast Missouri and has displaced populations of native crayfish. The effects of O. hylas on macroinvertebrate community composition were investigated in a fourth-order Ozark stream at two locations, one with the presence of O. hylas and one without. Significant differences between sites and across four sampling periods and two habitats were found in five categories of benthic macroinvertebrate metrics: species richness, percent/composition, dominance/diversity, functional feeding groups, and biotic indices. In most seasons and habitat combinations, the invaded site had significantly higher relative abundance of riffle beetles (Coleoptera: Elmidae), and significantly lower Missouri biotic index values, total taxa richness, and both richness and relative abundance of midges (Diptera: Chironomidae). Overall study results indicate that some macroinvertebrate community differences due to the O. hylas invasion were not consistent between seasons and habitats, suggesting that further research on spatial and temporal habitat use and feeding ecology of Ozark crayfish species is needed to improve our understanding of the effects of these invasions on aquatic communities.

Riverine Ecosystem Assessment of Cagayan de Oro River for Sustainable Resource Utilization

Assessment of the environmental health of Cagayan de Oro River was conducted in five different stations namely Uguiaban Bridge in Sitio Balaun, Rafting Site in Barangay Mambauaya, Pelaez Bridge in Taguanao, Poblacion (Ysalina Bridge) and Macajalar Bay Estuary. The environmental health assessment of the river was based on water quality indicators, biological indicators and social indicators. The water quality indicators included flow rate, color, pH, temperature, biological oxygen demand (BOD), dissolved oxygen (DO), nitrate (NO3), nitrite (NO2), phosphate ( PO4 ), pesticide and total coliform. Biological indicators on the other hand included macro invertebrates and riparian vegetation. While social indicators covered the anthropogenic activities and environmental awareness of the barangay residents which was attained by conducting a survey. The research design used qualitative and quantitative methods to analyze data gathered from the foregoing indicators. The findings revealed that water quality testing were well within standards except for total coliform which always showed exceedingly high values. In terms of the total coliform, the water quality is not within Class A standards. The biological assessment through the bio indicators revealed Field Biotic Index (FBI) values interpreted as having the likelihood of substantial organic pollution. This assessment served to supplement the result of the water quality testing. Hence, there is a need to bring back the water quality in terms of total coliform to Class A. The riparian vegetation survey also showed a decline from upstream to downstream. On the aspect of environmental awareness of the barangay residents, the survey indicated only at moderate level and has some policy implications especiallly in areas which are greatly impacted by land-based activities particularly residential, commercial and industrial activities. Keywords: Ecosystem, Cagayan de Oro River, assessment, sustainability.

Ostracoda and foraminifera response to a contaminated environment: the case of the Ex-Military Arsenal of the La Maddalena Harbour (Sardinia, Italy)

Negative responses of biotic communities as trackers of pollutant dispersion has shown that microfaunal distribution can play a useful role in investigating marine coastal ecosystems. A detailed study was carried out on Ostracoda and benthic foraminiferal assemblages from the contaminated environment of the Ex-Military Arsenal of the La Maddalena Harbour, located on the south-eastern coast of La Maddalena Island (Sardinia, Italy), to investigate the responses to pollution of these micro-organisms in this area using integrated multidisciplinary approaches. The area is affected by industrial waste, mainly heavy metals, as well as by seasonally intense maritime traffic. The analysis of surficial sediment shows enrichment in pollutants including As, Hg, Zn, Cu, Pd, Cd and hydrocarbon (chain length C>12). Variability of the assemblages, population density, species diversity and frequency of deformity suggest that these microorganisms are promising monitoring groups for contaminated marine areas. A total of 28 genera and 42 species of ostracods (three species were found alive; 17 species are autochthonous in at least one sampling station, while 28 are always allochthonous), were collected, while only 9 genera and 16 species of living benthic foraminifera were recognized. The biocoenosis is poorly represented, and shows low values of biotic indices. On the other hand, the foraminiferal thanatocoenosis is diverse and rich, but a high percentage of abnormal tests indicates degraded environmental conditions in almost the entire area. Changes in biotic indices, presence of tolerant species and development of abnormal tests constitute the main responses of Foraminifera and Ostracoda to pollution in the examined area.

Species Composition, Distribution and Habitat Types of Odonata in the iSimangaliso Wetland Park, KwaZulu-Natal, South Africa and the Associated Conservation Implications

Maputaland–Pondoland–Albany, South Africa has been identified as a biodiversity hotspot and centre for endemism. Odonata make good indicators of freshwater ecosystem health. Consequently we compiled a list of Odonata species recorded to date in the iSimangaliso Wetland Park. We then detailed important species in terms of endemism, conservation status, and potential as indicator species. Finally, we compared Odonata assemblages of different sites sampled within the park to illustrate habitat importance. Species identified during two formal surveys and incidental observations made during the study period were combined with an existing database to compile an accurate and up to date species list for the iSimangaliso Wetland Park. Data from this study were then analyzed to determine which water bodies had the most similar species composition. The Dragonfly Biotic Index (DBI) value of each study area was also determined. We recorded 68 odonate species in the iSimangaliso Wetland Park, adding 13 species to the Ezemvelo KwaZulu-Natal Wildlife database for the area. This brings the total number of Odonata species for the iSimangaliso Wetland Park to 86. Eight species are red-listed, 12 are restricted in South Africa to the coastal plains of northern KwaZulu-Natal, and the remainder occurs widely across the southern African savanna. Analyses indicate that species odonate assemblages were most similar in water bodies with comparable habitats. iSimangaliso Wetland Park is identified as an important area for Odonata diversity and endemism, a trend also reflected by the DBI values. Shifts in the existing species assemblages would indicate changes within the ecosystem and thus this species account provides necessary baseline data for the area. Species Conservation efforts should thus target water bodies of varying habitat types to protect greater species diversity.

Benthic invertebrate community in Khur-e-Mussa creeks in northwest of Persian Gulf and the application of the AMBI (AZTI's Marine Biotic Index)

Benthic invertebrates are a well-established target in environmental quality status evaluations. The AMBI (AZTI's Marine Biotic Index) was developed to determine the impacts and the quality status of soft-bottom marine benthic communities. The aim of this study was investigating multivariate pattern of benthic invertebrate community and application of AMBI (AZTI's Marine Biotic Index) for determining quality of health status in Khuzestan coastal waters. Seasonal samplings were collected from eight creeks over one year study by Peterson grab sampler, beginning from October 2005. All creeks are characterized by muddy bottom. According to sensitivity to environmental stress, macrobenthic animals classified into 5 ecological groups. Among 28 identified faunal groups the most abundant groups were polychaets, molluscs, crustaceans and nematodes, respectively. Two way ANOVAs showed only seasonal significant differences in mean abundance (P<0.05) and Margalef richness index values (P<0.05), while all of studied creeks shows similar biological characters based on benthic communities. According to annual mean of AMBI value all creeks were in ecological group III with slightly polluted condition, except for Darvish that was in unpolluted category. In the present study, although the number of species initially increased, but due to appearance of dominant species such as Capitella sp. and nematods (as opportunist species), diversity values reduced. In general, according to AMBI and Biotic index values, the most creeks are classified into unpolluted and slightly polluted categories except for Zangy, Doragh and Patil in summer and also Zangy and Bihad in winter which was in moderate to heavily polluted category. Different types of exploitation, industrial and shipping activities in this area could result in unbalanced to polluted status in benthic animals (as the best indicators in sediment quality assessment) so these results can be acceptable.

Aerobic treatment of dairy wastewater in an industrial three-reactor plant: Effect of aeration regime on performances and on protozoan and bacterial communities

An industrial three-reactor plant treating 45 m3 d−1 of dairy wastewater was monitored to investigate the effect of different aeration regimes on performance efficiency and to find relationships with bacterial and protozoan communities in the activated sludge. During the study, the plant was maintained at six different “on/off” cycles of the blower (45/15, 15/15, 15/45, 30/30, 30/45 and 30/60 min), providing between 30.2 and 90.6 kg O2 d−1, and the main chemical/biochemical parameters (COD, BOD, NH4+, NO2−, NO3−, PO43−, etc.) were determined. When at least 45.4 kg O2 d−1 (30/45) were provided, COD removal efficiencies were always in the range 88–94% but decreased to about 70% under aeration regimes 15/45 and 30/60. Ammonium ion degradation performance was compromised only in the lowest aeration regime (15/45). Total number of protozoa and their species richness, and bacterial viable counts and denaturing gradient gel electrophoresis (DGGE) profiles were used to characterize the microbiota of the activated sludge. Cell abundances and community structures of protozoa and bacteria were very similar in the three aerated reactors but changed with the aeration regimes. In particular, the 15/45 and 30/60 regimes led to low protozoan diversity with prevalence of flagellates of the genus Trepomonas at the expense of the mobile and sessile forms and, thus, to a less efficient activated sludge as indicated by Sludge Biotic Index values (3 and 4.5 for the two regimes, respectively). The structure of the bacterial community strongly changed when the aeration regimes varied, as indicated by the low similarity values between the DGGE profiles. On the contrary, number of viable bacteria and values of the biodiversity index remained stable throughout the whole experimentation. Taken together, the results of the present study clearly indicate that aeration regime variations strongly influence the structure of both protozoan and bacterial communities and, above all, that a high biodiversity among protozoan populations in the activated sludge is prerequisite for high performances in dairy wastewater treatment.

Evaluation of the benthic macroinvertebrate distribution in a stream environment during summer using biotic index

The purpose of this study is to evaluate the benthic macroinvertebrate distribution in the Keşap Stream (in the Eastern Black Sea Region of Turkey) for the summer period using biotic index. The water quality was assessed through the application of the Belgian biotic index. For this purpose, benthic macroinvertebrate sampling was performed in six sites along the Keşap Stream in the summer period, in July 2007. The distribution of dominant genera of the sites was evaluated according to water quality. According to the Belgian biotic index, II, III and IV water quality classes (slightly, moderately and heavily polluted, respectively) were determined in the stream. In addition, diversities of benthic macroinvertebrates in six sites were calculated. The biotic index values are found also consistent with the diversity values. Especially, in areas of the stream after industrial facilities water quality decreased. However, very heavy pollution was not observed accord to the biotic index values. It was found that Ephemeroptera was the dominant major taxon in all sampling sites. As a result of this biological evaluation, Ephemeroptera were concluded to be the most common taxa in the stream and the ephemeropterans, Potamanthus, Baetis and Ephemerella were dominant genera in the conditions of slightly, moderately and heavily polluted.

Seasonal variability in the Macroinvertebrate Community Index: Are seasonal correction factors required?

Freshwater macroinvertebrate data collected from streams in Taranaki, New Zealand (1981–2006) were used to examine seasonality of biological indices including taxon richness, %EPT (Ephemeroptera, Plecoptera, and Trichoptera) richness, and the hard‐ and soft‐bottomed (‐sb) stream versions of the Macroinvertebrate Community Index (MCI). All indices tested showed modest but statistically significant seasonal variation in hard‐bottomed streams. Seasonal means for the MCI were within ±3.0% of the annual mean. The Semi‐Quantitative MCI (SQMCI) (±4.3%), %EPT richness (±7.4%) and taxon richness (±7.7%) showed greater seasonal variability than the MCI. MCI, SQMCI, and %EPT richness were significantly higher in spring and winter compared with autumn and summer. Taxon richness was lower in winter than in other seasons. In soft‐bottomed streams, SQMCI‐sb showed least seasonality (within ±3.6% of the annual mean, nonsignificant), followed by MCI‐sb and taxon richness (±4.7%), and %EPT richness (±11.2%). Spring and winter MCI‐sb and SQMCI‐sb values tended to be significantly higher than those calculated from summer or autumn samples, although most values were within 5% of the annual site means. Examination of seasonal variation in species traits and their relationships to observed seasonal patterns of biotic indices did not support the suggestion that seasonal variations in life histories of aquatic macroinvertebrates affect index values. Rather, seasons with higher biotic index values were associated with a greater frequency of flow disturbance, which is consistent with the view that the character of New Zealand's stream macroinvertebrate communities with their poorly‐synchronised life histories, has been shaped by the unpredictable physical environment. We recommend the MCI and MCI‐sb for State of Environment reporting in New Zealand for cost‐effectiveness and because data requirements and seasonal variation were less than for quantitative alternative indices. We suggest that seasonal variability is unlikely to confound interpretation, and does not need to be considered.

Comparison of Macroinvertebrate‐Derived Stream Quality Metrics Between Snag and Riffle Habitats1

Abstract: We compared benthic macroinvertebrate assemblage structure at snag and riffle habitats in 43 Wisconsin streams across a range of watershed urbanization using a variety of stream quality metrics. Discriminant analysis indicated that dominant taxa at riffles and snags differed; Hydropsychid caddisflies (Hydropsyche betteni and Cheumatopsyche spp.) and elmid beetles (Optioservus spp. and Stenemlis spp.) typified riffles, whereas isopods (Asellus intermedius) and amphipods (Hyalella azteca and Gammarus pseudolimnaeus) predominated in snags. Analysis of covariance indicated that samples from snag and riffle habitats differed significantly in their response to the urbanization gradient for the Hilsenhoff biotic index (BI), Shannon’s diversity index, and percent of filterers, shredders, and pollution intolerant Ephemeroptera, Plecoptera, and Trichoptera (EPT) at each stream site (p ≤ 0.10). These differences suggest that although macroinvertebrate assemblages present in either habitat type are sensitive to detecting the effects of urbanization, metrics derived from different habitats should not be intermixed when assessing stream quality through biomonitoring. This can be a limitation to resource managers who wish to compare water quality among streams where the same habitat type is not available at all stream locations, or where a specific habitat type (i.e., a riffle) is required to determine a metric value (i.e., BI). To account for differences in stream quality at sites lacking riffle habitat, snag‐derived metric values can be adjusted based on those obtained from riffles that have been exposed to the same level of urbanization. Comparison of nonlinear regression equations that related stream quality metric values from the two habitat types to percent watershed urbanization indicated that snag habitats had on average 30.2 fewer percent EPT individuals, a lower diversity index value than riffles, and a BI value of 0.29 greater than riffles.

Louisiana waterthrushes (Seiurus motacilla) and habitat assessments as cost‐effective indicators of instream biotic integrity

Summary1. Benthic stream animals, in particular macroinvertebrates, are good indicators of water quality, but sampling can be laborious to obtain accurate indices of biotic integrity. Thus, tools for bioassessment that include measurements other than macroinvertebrates would be valuable additions to volunteer monitoring protocols.2. We evaluated the usefulness of a stream‐dependent songbird, the Louisiana waterthrush (waterthrush, Seiurus motacilla) and the Environmental Protection Agency Visual Habitat Assessment (EPA VHA) as indicators of the macrobenthos community in headwater streams of the Georgia Piedmont, U.S.A. We sampled macrobenthos, surveyed waterthrushes and measured habitat characteristics along 39 headwater reaches across 17 catchments ranging from forested to heavily urbanised or grazed by cattle.3. Of the indicators considered, waterthrush occupancy was best for predicting relative abundances of macrobenthic taxa, while the EPA VHA was best for predicting Ephemeroptera–Plecoptera–Trichoptera (EPT) richness. Individual components of EPA VHA scores were much less useful as indicators of EPT richness and % EPT when compared with the total score. Waterthrushes were found along streams with higher % EPT, a lower Family Biotic Index (FBI) values and greater macrobenthos biomass.4. While macroinvertebrates remain one of the most direct indicators of stream water quality, stream bird surveys and reach‐scale habitat assessments can serve as cost‐effective indicators of benthic macroinvertebrate communities. Using stream‐dependent birds as an early warning signal for degradation of stream biotic integrity could improve the efficacy of catchment monitoring programmes in detecting and identifying perturbations within the catchment.

Macroinvertebrate assemblages in conditions of low-discharge streams of the Cerová vrchovina highland in Slovakia

Macroinvertebrate communities at 16 sites in Cerová vrchovina highland were sampled in 2000–2001 to analyze the influence of environmental factors on community structure with emphasis on Ephemeroptera, Plecoptera and Trichoptera (EPT). The extreme hydrological conditions of this area determine the macroinvertebrate community structure. Totally, 16 Ephemeroptera, 8 Plecoptera and 36 Trichoptera taxa were found. Predators of the families Perlidae, Perlodidae and Chloroperlidae (Plecoptera) were absent. The record of Protonemura aestiva is the second one in Slovakia. Ephemeroptera were represented mainly by rheophilous taxa. A rare lowland species Baetis tracheatus was found, known previously just from West Slovakia. Trichoptera were mainly represented by submontane rheophilous taxa. Species preferring low currents or backwaters from the family Limnephilidae were also recorded. Altitude and dissolved oxygen content were found to be the most important environmental variables determining the EPT community structure. Six types of streams were distinguished by the results of multivariate analysis, taxonomic composition and metric values. They belong to two main types: (1) EPT communities of the natural streams and (2) EPT communities of disturbed streams, where two types of stressor were identified–organic pollution and low discharge. A similarity between EPT communities of organically polluted streams and streams with very low flow was discovered. Values of biotic indices decreased in summer. The most diversified communities were found in the spring during higher water levels and better oxygen conditions.

Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics

Benthic macroinvertebrate samples were collected from natural substrates in disturbed and undisturbed South Carolina upper coastal plain streams to determine if taxa richness and other bioassessment metrics were significantly related to stream size as predicted by the River Continuum Concept (RCC). Linear, quadratic, and lognormal regression models indicated that stream width was positively related to total number of taxa; number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa; and total number of organisms. Linear regression showed that the expected number of taxa at undisturbed sites ranged from 35 in 2.0 m wide streams to 64 in 16.0 m streams. Comparable values were 8–20 for EPT and 109–261 for number of organisms. Stream width was inversely related to biotic index values indicating a decrease in average organism tolerance with increasing stream size. ANCOVA showed that the effects of stream size were similar for disturbed and undisturbed sites. Rank correlations and multidimensional scaling (MDS) showed that Lepidoptera and Trichoptera were more abundant in larger streams and Annelida in smaller streams. Stream size related changes in benthic macroinvertebrate community composition are often ignored in bioassessment protocols; however, failure to adjust metrics for stream size can lead to erroneous conclusions. Adjustments are possible by analyzing regression residuals stripped of stream size related variance, dividing the area beneath the maximum taxa richness line into equal size units for metric scoring, or scaling metrics based on predicted reference values.

Seasonal Succession in the Aquatic Insect Community of an Ozark Stream

ABSTRACT We studied the temporal pattern of the aquatic insect assemblage of an Ozark stream by sampling riffle areas every two weeks from early February through late July, 2002. Total richness of the assemblage, for the entire study, was 138 taxa, including 57 from the dipteran family Chironomidae. Richness levels, per sampling period, ranged from the low 40s to the high 50s and were highest in late March through mid-April. Assemblage composition shifted from one dominated by chironomids in the winter and spring to one dominated by mayflies in the late spring and early summer and by caddisflies in summer. EPT richness levels, diversity, biotic index values, and relative abundances of functional feeding groups varied substantially during the study, occasionally even between two-week sampling periods. The data suggested that, for this type of stream, winter and summer are the times of year that the insect assemblage is least dynamic. These periods, despite lower overall community richness, may therefore be more appropriate to compare samples from different locations or years.

Structure et bioévaluation de l'état écologique des communautés benthiques d'un écosystème lagunaire de la côte atlantique marocaine

The Merja Zerga lagoon is a semi-enclosed marine ecosystem in which various types of human activities have been developed. This paper characterizes the biosedimentary units of the lagoon and defines a reference status of the quality and health of the macrozoobenthic communities that can be used as bioindicators of the quality of the global marine environment. Specific and functional diversity were high: 147 taxa were identified; they were distributed within seven main trophic groups. Trophic structure is dominated by the suspension-feeding bivalve Cerastoderma edule and the deposit-feeding bivalve Scrobicularia plana, while micrograzers and macroherbivores remain low. Biotic index values indicated that the site is moderately perturbed and that the benthic communities are unbalanced. Nevertheless, the communities showed a seasonal stability of abundances and a high specific richness all through the year. To cite this article: H. Bazairi et al., C. R. Biologies 328 (2005).

Biological Assessment of Cannon Creek, Missouri by Use of Emerging Chironomidae (Insecta: Diptera)

A biological assessment was done to determine the impact of heavy metal discharge from the Schuykill Metals Recycling Plant (SMCP) on Cannon Creek, Missouri, its receiving stream. The relationship between sediment chemistry and chironomid emergence was examined. Twenty-four heavy metals and nutrients from the SMCP discharge effluent were examined in Cannon Creek from above the effluent, at the effluent, and below the effluent. Five heavy metals (barium, cadmium, lead, manganese, and zinc) and sodium varied significantly between sites. Changes in community composition, mean abundance of emerging chironomids, and Kansas Biotic Index Values were used to detect impairment by heavy metals and nutrients in Cannon Creek. Concentrations of lead and zinc in Cannon Creek were at levels potentially lethal to chironomids, yet mean abundance of emerging chironomids actually increased with the increase of heavy metals and nutrients and showed a strong and positive correlation with barium and sodium, and a weaker correlation with increases in lead and cadmium. Chironomid diversity patterns did not correlate with the concentrations of heavy metals in Cannon Creek. Community similarity between sites was greatest between the reference site and the site at the SMCP discharge effluent. Low similarity between sites was attributed to gross changes in stream morphology rather than to any effects from the SMCP effluent. Finally, the KBI tolerance values to heavy metals for chironomids in Cannon Creek were above those encountered in the reference condition for the Western Cornbelt Plains Ecoregion, indicating minimal impairment.

Longitudinal changes in macroinvertebrate assemblages in the Meuse River: anthropogenic effects versus natural change

AbstractA collaborative study among three nations (France, Belgium, Netherlands) along the Meuse River developed a consistent approach for collecting and interpreting macroinvertebrate data. Specific mesohabitats were sampled in 16 locations along an 800‐km stretch of this lowland regulated river. The objective was to assess the ‘river health’ using macroinvertebrate communities as indicators of biological and ecological variation in space. The main changes in assemblages were investigated using multimetric and multivariate approaches. The authors examined relationships between faunal variations and both physico‐chemical gradients and man‐made disturbances. We related species traits to faunal changes and habitat characteristics.Both a gradual shift from a macroinvertebrate assemblage dominated by insects to a community dominated by crustaceans and molluscs and a drastic decrease in biotic index values were observed along the longitudinal gradient. Taxa were distributed according to oxygen, nitrate and ammonium concentrations, pH, conductivity and summer hydraulic conditions. But major faunal differences among sites could not be explained simply by physico‐chemical variables. The trait analysis underlined the role of temporary habitats in structuring the summer macroinvertebrate community of sites of the uppermost French sector, which supported the most diverse community in terms of trait combination. Downstream the macroinvertebrate community exhibited a more simple and less stable functional organization.We concluded that the Meuse River exhibited both a high biodiversity and a ‘reasonably good’ water quality in the upper reaches. Two transition zones highlighted the influence of a high degree of human impact on stream integrity. Regulation for navigation, ship traffic and heavily polluted effluent discharges influenced instream conditions via multiple processes determining a decline of both habitat stability and diversity. However, the rare occurrence of habitat‐sensitive species in the lower reaches indicated that a partial recovery of communities may be predicted if restoration and protection of disturbed (especially riparian) habitats are fulfilled. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Bird communities and extended biotic index (EBI) in some tributaries of the Tiber river

1. Riparian birds and macroinvertebrates were studied in five reaches of four tributaries of the Tiber river (Italy). The first aim was to check if stream quality, assessed by extended biotic index (EBI) values, could represent change in the riparian zone, assessed through the bird community. The second was to consider whether stream quality affects the presence of riverine bird species. 2. Stream quality and richness of the riparian bird community were related. In streams with more disturbed macroinvertebrate communities, but also in agricultural areas, the relative frequency of granivorous species increased in the riparian zone. 3. Dippers Cinclus cinclus occurred exclusively in reaches with the best stream quality, but the relationship between grey wagtails Motacilla cinerea and stream quality was less clear. 4. These results support the judicious use of riverine and riparian birds as biological indicators. Copyright © 1999 John Wiley & Sons, Ltd.

ECOLOGY AND DISTRIBUTION OF OSTRACODS ASSOCIATED WITH FLOWING WATERS IN THE EASTERN IBERIAN PENINSULA

ABSTRACT The ostracod fauna of the three main rivers of the central Mediterranean slope of the Iberian Peninsula was studied, with special attention being paid to ecology and distribution. Forty-six stations were sampled in spring and autumn 1995 and thirty ostracod species were collected, two of these (Trujancypris serrata and Heterocypris reptans) new to the Iberian fauna. The most common species were Ilyocypris bradyi, Herpetocypris brevicaudata, Cypridopsis vidua, and Limnocythere inopinata. Cluster analysis showed that these species, together with Ilyocypris inermis and Sarscypridopsisspp. form the most widespread ostracod assemblage in the area, although its widespread distribution is not related to any of the environmental variables monitored. However, factors such as altitude, mean January air temperature, distance from source, flow discharge, water quality, and degree of organic pollution play an important role in explaining the occurrence of less common species. One species group was linked to high elevations and BMWP' biotic index values and low winter temperatures. Candona neglecta best characterizes this assemblage. In the opposite part of this environmental gradient, Ilyocypris gibba, associated with lower altitudes, epitomizes the third species group. Heterocypris salina and Heterocypris incongruens were the species that were most tolerant of organic pollution. Our results are compared with those reported in studies from different habitats (e.g., springs) and latitudes. The implications of our findings for paleoenvironmental reconstruction and water resources management are discussed.

Macrobenthic monitoring in the Lower St. Johns River, Florida

The macrobenthos in the oligohaline 132 km reach of the Lower St. Johns River, Florida, is an unusual blend of freshwater and marine organisms within the annelid, mollusk, aquatic insect, and crustacean groups. During 1993–1994, the community composition was freshwater-oriented in the 47 km (seg I) and estuarine-dominated in the lower 85 km (seg II). Of the total 146 taxa collected, 89% were euryecious 'eutrophic' and 'pollution-tolerant' organisms. Densities ranged between 5000 and 20 000 individuals/m2 ann av and maximum densities (85 000 individuals/m2) occurred in the muck substrate at the confluence of major tributaries and embayments. Throughout the lake-like seg II, benthic hypoxia existed during much of summer through fall. Biotic index values for grab, artificial substrate, and sled trawl samples reflected greatest stresses to the macrobenthos then. Both low taxonomic diversity and densities of organisms at the most downriver stations nearest the port of Jacksonville indicated that toxic substances also adversely affected the macrobenthos. Maintenance of the narrow band of littoral submerged aquatic vegetation (SAV) and adjacent shoreline riparian vegetation is important to sustain macrobenthic communities and other kinds of aquatic life in the river.

A survey of benthic invertebrates in the Suwannee River, Florida

Benthic invertebrate communities were surveyed in a 233 km reach of the middle and lower Suwannee River in Northwestern Florida in the winter 1987 and early summer 1988 to determine their abundance and distribution as potential foods of the Gulf sturgeon, Acipenser oxyrhynchus desotoi, and to determine the effects of possible natural and human-induced disturbances to the communities. In substrates of the tidal oligohaline to mesohaline lower reach of the East Pass site I (km 2) and site II West Pass (km 5) near the Gulf of Mexico, densities of tube dwelling and free swimming amphipods, polychaetes, oligochaetes, and dipterans in the PONAR grabs were moderate (100-999 {iex} individuals/m(2)) to abundant (1000-9999 {iex} individuals m(-2)). Also, at sites I and II, low (10-99 {iex} individuals m(-2)) to moderate densities of dipteran Chironomidae and olive nerite snail were collected in hardboard multiplate artificial substrate samplers. Diversities of benthic invertebrates in both grabs and hardboard multiplates were relatively low. Baetid mayflies were moderately abundant in the dip net samples. Upriver from sites I and II, the transition of an oligohaline tolerant benthic community to a freshwater one was abrupt due to strong freshwater flow. At sites III (km 48) and IV (km 89), benthic invertebrate populations were low to moderate in hardboard multiplate and dip net samples. In the middle reach (km 101 to km 233), aquatic insects were predominant and included; chironomids, mayflies, and beetles, and also, freshwater gammarid amphipods, gastropods, and the Asian clam. In winter, the bottom substrates at sites VII (km 153) and VIII (km 205) contained diverse and dense populations of Chironomidae (5932 m(-2)), the greatest density for a major taxonomic group recorded in this survey. Crayfish were collected in low densities only in artificial substrate samplers from sites IV to IX. Leeches were widespread in the study area. Empirical Biotic Index values that reflect impacts of organic wastes on benthic invertebrate communities were within a narrow range, 3.16 to 6.38, and indicated 'slightly enriched' to 'enriched' water. Of the total 186 benthic invertebrate taxa, 82% had quality values 0 to 5 that indicate overall 'clean water' conditions. The predominant benthic invertebrates in the Suwannee River were detritivorous and the communities reflected oligotrophic to mesotrophic waters.