Survival of Diplectrona modesta banks (Trichoptera : Hydropsychidae) during short periods of desiccation

Larvae of the caddisfly, Diplectrona modesta (Hydropsychidae), were found to be permanent inhabitants of a small, intermittent, headwater stream in southern Ontario. They survived desiccation for at least four weeks in summer. A laboratory experiment gave a mean survivorship of 50% after 30 days without water in stream gravel and stones after the larvae had been permitted to construct their shelters. Survivors were those that constructed their tubes deep in the substrate.     

Phosphatase activities of the aquatic moss <Emphasis Type="Italic">Warnstorfia fluitans</Emphasis> (Hedw.) Loeske from an acidic stream in North-East England

A study was made of the aquatic environment, tissue nutrient composition and surface phosphatase activities of the aquatic moss Warnstorfia fluitans in Brandon Pithouse Stream, a small acidic stream in N-E England. The water, which originates from an underground spring, had been pH 2.6 for at least 30 years, but about 3.9 during the present study. The moss was by far the most abundant phototroph during all this period. Seasonal changes in aqueous nitrogen and phosphorus fractions were measured over a 2-year period near the source. Most of the filtrable N and P were at times organic, but the very high N:P ratio (even if organic N is excluded) suggests that only organic phosphate is likely to be important for the moss. There was a high peak in organic phosphate in late spring in both study years. Surface phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities were highly correlated in the field and in axenic culture, though there were some differences in response to environmental factors. Axenic material showed higher PMEase and PDEase activities when grown with organic P than with inorganic P. Although the data suggest that internal P content is an important factor influencing phosphatase activities, PDEase activity was especially marked when the moss was grown with the diester, DNA, as P source, indicating that at least one of its surface phosphatases can also respond directly to the environment. Handling editor: S. M. Thomaz     

Mastophoropsis canaliculata (Harvey in Hooker) gen. et comb. nov. (Corallinaceae,Rhodophyta) in Southern Australia

Mastophoropsis canaliculata (Harvey in Hooker) gen. et comb. nov. (Corallinaceae, Rhodophyta) is restricted to south-eastern Australian waters. It is unique among Corallinaceae in possessing an erect, tenacular, branched, taeniform, non-geniculate thallus which produces multiporate tetrasporangial conceptacles. Based on a detailed morphological and anatomical study, including an examination of the designated lectotype, this taxon is referred to the tribe Phymatolitheae in the subfamily Melobesioideae and its relationships to other non-geniculate Corallinaceae are discussed. A simplified microtechnique procedure involving decalcification with nitric acid, resin embedding and staining serially mounted sections with KMnO₄ also is outlined. X-ray microanalysis of surface tissues indicates that calcification occurs largely as CaCO₃ and that various structures contain substantially differing amounts of Ca.     

Are biological classifications of headwater streams concordant across multiple taxonomic groups?

1. Studies assessing human impacts on freshwater ecosystems are typically based on a single taxonomic group, often macroinvertebrates or fish. Unfortunately, the degree to which such macroinvertebrate or fish‐based surveys can be generalised across other taxonomic groups remains largely unknown. A prerequisite for useful generalisations is that different taxonomic groups exhibit concordant patterns of community structure across sites. 2. We examined the concordance among fish, benthic macroinvertebrates and bryophytes in 32 streams in a boreal catchment in Finland. Our goal was to test how consistently different taxonomic groups classify stream sites; for example, can site groupings based on macroinvertebrates be used as a surrogate for bryophyte or fish assemblage classification? 3. Our results show that community classifications in headwater streams are not concordant across taxonomic groups, at least not at the within‐river system scale. The lack of concordance reflected the fact that all three groups responded to different environmental factors. Macroinvertebrate community structure was mainly correlated with stream size and pH, whereas bryophytes were related to water colour, nutrient content and in‐stream habitat variability. Fish community structure was best described by stream depth, substrate size and water oxygen concentration. 4. Our results suggest that great care should be taken when typologies based on benthic macroinvertebrates, or any other taxonomic group, are extrapolated to other groups in creating typologies of lotic environments.     

Evidence for non-random spatial positioning of migrating smolts (Salmonidae) in a small lowland stream

1. The ontogenetic development of anadromous salmonids includes downstream emigration of immature individuals from freshwater towards the marine environment. Although this migration of juvenile salmonids (smolts) may be associated with severe mortalities, only limited attention has been paid to the spatial positioning of smolts in small streams. 2. Using a novel approach, this study examined the vertical and horizontal positioning of brown trout and Atlantic salmon smolts while performing downstream migration in a small lowland stream. 3. Pre‐smolts of indigenous and hatchery‐reared (F1) brown trout (Salmo trutta), and two different populations of Atlantic salmon (S. salar), were tagged with passive integrated transponder (PIT) tags and subsequently released upstream of an antenna array consisting of five circular swim‐through PIT antennas. Antennas were positioned in order to determine whether the migrating smolts were bottom or surface oriented, and if they were oriented towards the mid‐channel or the stream bank. 4. During the smolt emigration period, data describing both the detection of the migrating fish and the amount of water passing through the antennas were collected. This was accomplished in order to determine if the fish were performing active positioning behaviour independently of the vertical and horizontal discharge distributions in the stream. 5. The results showed that the smolts migrated in a non‐random spatial pattern independently of the stream discharge distributions. Vertically, the indigenous brown trout and the Atlantic salmon demonstrated a preference for the bottom orientated positions. In contrast, the distribution of the F1 brown trout was not different from the discharge distribution. The latter observation suggests random vertical positioning, which may be indicative of inferior migratory performance. Horizontally, all tested smolt populations strongly preferred the mid‐channel positions. 6. The discharge‐corrected preferences for certain spatial positions suggest that smolt emigration is not entirely a matter of passive displacement in lowland streams. 7. Anthropogenically altered channels may inhibit or delay downstream emigration of smolts resulting in increased mortalities. Given that the smolts in this study actively selected spatial positions in the mid‐channel and near the bottom, it is suggested that deep, mid‐channel furrows may be used to help guide migrating smolts past adverse habitats in lowland streams.     

Disturbance history influences the distribution of stream invertebrates by altering microhabitat parameters: a field experiment

1. We investigated the effects of local disturbance history and several biotic and abiotic habitat parameters on the microdistribution of benthic invertebrates after an experimental disturbance in a flood‐prone German stream. 2. Bed movement patterns during a moderate flood were simulated by scouring and filling stream bed patches (area 0.49 m²) to a depth of 15–20 cm. Invertebrates were investigated using ceramic tiles as standardized substrata. After 1, 8, 22, 29, 36 and 50 days, we sampled one tile from each of 16 replicates of three bed stability treatments (scour, fill and stable controls). For each tile, we also determined water depth, near‐bed current velocity, the grain size of the substratum beneath the tile, epilithic algal biomass and standing stock of particulate organic matter (POM). 3. Shortly after disturbance, total invertebrate density, taxon richness and density of the common taxa Baetis spp. and Chironomidae were highest in stable patches. Several weeks after disturbance, by contrast, Baetis spp. and Hydropsychidae were most common in fill and Leuctra spp. in scour patches. The black fly Simulium spp. was most abundant in fill patches from the first day onwards. Community evenness was highest in scour patches during the entire study. 4. Local disturbance history also influenced algal biomass and POM standing stock at the beginning of the experiment, and water depth, current velocity and substratum grain size throughout the experiment. Scouring mainly exposed finer substrata and caused local depressions in the stream bed characterized by slower near‐bed current velocity. Algal biomass was higher in stable and scour patches and POM was highest in scour patches. In turn, all five common invertebrate taxa were frequently correlated with one or two of these habitat parameters. 5. Our results suggest that several ‘direct’ initial effects of local disturbance history on the invertebrates were subsequently replaced by ‘indirect’ effects of disturbance history (via disturbance‐induced changes in habitat parameters such as current velocity or food).     

Substrate selection and seasonal variation in densities of invertebrates in stream pools of a tropical river

Spatial distribution and seasonal variation in densities of the invertebrates were investigated for a year in three stream pools of a South Indian river. The effects of season, substrate type and water depth on the distribution were analyzed. Substrate type and season influenced the invertebrate distribution the most. Leaf packs harboured most of the organisms followed by macro-algal substrate and sand. The lowest densities were observed on rocky substrates and in the water column. Rocky substrates in shallow water supported higher densities of total invertebrates than deeper areas. Chironomid larvae dominated all benthic substrates throughout the year. Of the 19 invertebrate taxa studied, 6 showed no seasonality in densities, and most of the rest showed their highest densities in the pre-monsoon period and lowest in the SW monsoon or post-monsoon periods. However, in two of the three pools, the densities of total invertebrates were highest during the post-monsoon period with secondary peaks in the pre-monsoon period.     

Effect of inorganic sediment on whole-stream productivity

Sediment from agricultural, logging, and mining activities impairs more miles of rivers and streams in the United States than any other type of pollutant, including bacteria, nutrients, oxygen-depleting substances, and metals. However, specific impacts of sediment to streams have not been well studied or understood. To study the effect of inorganic sediment on plant and animal communities in stream ecosystems, we added clay to outdoor experimental streams 520 m long and 3.5 m wide at the Monticello Ecological Research Station (MERS). The streams take water from the Mississippi River and are designed to represent higher order streams in the upper midwestern United States. The sediment loading rates were 300, 200, 100, and 50 mg l^–1. Our first dosing period (mid-August to November 1994) began at the start of a fall bloom in autotroph productivity, and the second (May to August 1995) began before the summer communities were established. During both treatment seasons, the addition of clay significantly increased turbidity and sedimentation, and decreased light penetration in treated streams corresponding roughly to 30–35, 25–30, 15–20, and 5–10 NTU, respectively. In general, the macrophyte and periphyton communities responded quickly after only a few weeks exposure to the sediment additions. Whole-stream respiration was significantly lower in treated streams, decreasing as the amount of sediment added increased. Periphyton biomass (chl a) on tiles and percent cover of macrophytes was significantly lower in treatment streams than in controls. In contrast to expectations and previous findings in two sets of field streams, total whole-stream productivity in the MERS streams was not significantly lower in streams receiving sediment loads than in control streams because the overall photosynthetic efficiency by the plant community compensated for the loss in irradiance.