Timothy P. Moulton

Effects of ephemeropterans and shrimps on periphyton and sediments in a coastal stream (Atlantic forest, Rio de Janeiro, Brazil)

Abstract We investigated the importance of shrimps (Atyidae and Palaemonidae) and ephemeropterans (Baetidae) in the removal of periphyton and sediments in a Neotropical stream. The experimental site was open with homogeneous bedrock, shallow depth (8–15 cm), and intermediate water current velocity (0.2–0.3 m/s). We used 2 intensities of electrical current to exclude both shrimps and ephemeropterans (high-intensity treatment) or only shrimps (low-intensity treatment) from fixed areas (180 × 30 cm) of bedrock. When both ephemeropterans and shrimps were excluded in 2 experiments, matter accumulated on the bedrock to 5 and 20× the level in controls; when only shrimps were excluded, no accumulation was observed. Chlorophyll a increased significantly in the high-intensity exclusion, but most of the accumulation was fine organic and inorganic matter. In experiment 1, benthic matter and chlorophyll a decreased by an order of magnitude in areas in which ephemeropterans increased ∼40×. The increase in ephemeropterans was associated with a reduction in shrimp activity. In experiment 2, no increase in ephemeropterans was observed. Palaemonid shrimps (Macrobrachium olfersi) were more common than atyid shrimps (Potimirim glabra) in the study area. Therefore, we assumed that Macrobrachium, rather than Potimirim, interacted negatively with ephemeropterans and that Macrobrachium did not remove periphyton. We concluded that baetid ephemeropterans (particularly Americabaetis sp.) were the most important grazers and removers of benthic matter in this system.

Patterns of periphyton are determined by cascading trophic relationships in two neotropical streams

Indirect foodweb interactions often determine the dynamics of aquatic ecosystems. Predators may reduce the activity of herbivores, which, in turn, may cause basal resources to increase. We studied the patterns of distribution of periphyton (organic and inorganic mass and chlorophyll) on rocks in pools in two Atlantic rainforest coastal streams that varied with respect to the presence or absence of fish. A steep waterfall apparently prevented most fish species from colonising the upper parts of one stream; the other stream was apparently naturally without most species of fish. When fish were present, atyid shrimps and baetid mayflies were less abundant compared with parts of the streams without fish. Concomitant with this, the quantity of periphyton organic and inorganic masses was much greater in the presence of fish. Previous experiments showed that atyid shrimps (Potimirim glabra) and baetid mayflies could reduce the quantity of periphyton by grazing and bioturbation. We deduce that fish inhibit the grazing and bioturbing activities of Potimirim and baetid mayflies, which resulted in larger quantities of inorganic and organic mass of periphyton in parts of streams with fish. Cascading interactions may be common in Atlantic coastal forest streams.

Seasonal and spatial differences in feeding habits of the Neotropical otter Lontra longicaudis (Carnivora: Mustelidae) in a coastal catchment of southeastern Brazil

The diet of the Neotropical otter Lontra longicaudis (Olfers, 1818) is one of the best known aspects of its biology throughout its distribution range. However, most dietary studies have been undertaken during short time periods, making it difficult to identify temporal patterns in the feeding behavior of the species. The present study aimed to describe the diet of L. longicaudis in the lower region of the Mambucaba Catchment, state of Rio de Janeiro, Brazil, during a three year period, based on analyses of spraints (feces). The results show fish as the main prey item (frequency of occurrence, FO = 85.78%), as already described in previous studies. Crustaceans were the second main prey (FO = 70.67%), occurring in the spraints during the whole year, however presenting a higher frequency of occurrence than fish in samples collected during some months. Anurans were the third most important prey item (FO = 9.56%) and mammals, birds and reptiles were preyed upon only rarely (less than 4%). Fish and crustaceans were present in the diet of the species throughout the year and frogs were important mostly from June to August (dry season). This higher rate of predation on amphibians during the drier months was probably related to the decrease of the main prey.

Responses of Chironomidae (Diptera; Insecta) to the exclusion of shrimps and Ephemeroptera in a coastal forest stream, Rio de Janeiro, Brazil

In a benthic community on a continuous flat granite substrate in a third-order coastal forest stream, the dominant chironomid (Cricotopus) increased in number when shrimps (Macrobrachium olfersi and Potimirim glabra) and baetid ephemeropterans were excluded by electricity. The response appeared to be mediated by an increase in periphyton and sediments, rather than a reduction of direct predation or interference. Chironomids, periphyton and sediments decreased significantly compared to the control when shrimps only were excluded. Baetid ephemeropteran appeared to be the most important determinants of periphyton and sediment mass; the density of chironomids appeared to follow the quantity of periphyton and sediments.

Strong interactions of Paratya australiensis (Decapoda:Atyidae) on periphyton in an Australian subtropical stream

Atyid shrimps are often an abundant component in undisturbed tropical streams. Studies in coastal streams in Puerto Rico and Brazil have demonstrated the importance of this group in removing periphyton and sediment from hard substrates and their effects on the composition and quantity of periphytic algae. We used experimental exclosures to investigate the influence of the small atyid Paratya australiensis on periphyton accrual on hard substrates in a coastal stream in the subtropics of Australia. We measured organic and inorganic matter, chlorophyll and algal biovolume in the presence and absence of shrimps on natural and artificial substrates. We found a 5-fold increase in the amount of organic matter on natural substrate in the absence of P. australiensis and a two to 10-fold increase in total periphyton mass on artificial substrate. The natural substrates did not show differences in biovolume of algae, however, algal biovolume on the artificial substrates was significantly higher in the exclusion treatment and diatoms were most affected. We conclude that P. australiensis can be considered a strongly-interacting element of the stream biota and an important species for monitoring and conservation.

Patterns of periphyton chlorophyll and dry mass in a neotropical stream: a cheap and rapid analysis using a hand-held fluorometer

Periphyton distribution is affected by various physical, chemical and biological factors at different scales. In the present study, a cheap and rapid method of measurement was used to obtain the many samples necessary for spatial analysis of periphyton along an altitudinal gradient in a low-order stream in south-east Brazilian Atlantic rain-forest. Fluorescence and turbidity were measured using a hand-held fluorometer and calibrated to the chlorophyll and dry mass of periphyton. Periphyton on the horizontal and vertical surfaces of different boulders was examined and shading and water current were measured as covariables. The three upstream sites with higher abundances of potentially grazing and bioturbing shrimps and mayflies had significantly less periphyton dry mass than the three downstream sites. Chlorophyll was positively related to water current, but not to shading. Variabilities in the dry mass and chlorophyll among boulders within sites were not associated with the distribution of shrimps and mayflies. The in vivo measurement was cheap, rapid, sensitive and reasonably precise compared with standard methods. The necessary sacrifice of detail of pigments (different chlorophylls and pheophytin) and dry mass (organic and inorganic constituents) and probably precision was compensated for by the insights gained from the ability to obtain a large number of samples in a hierarchical design.

Conservation of catchments: some theoretical considerations and case histories from Rio de Janeiro

Conservation has developed along two lines: protection of species and communities, and preservation of natural resources. Catchments provide the natural unit for conservation since they are the fundamental unit of terrestrial ecosystems and account for most of the flow of materials. Urban streams of the city of Rio de Janeiro are generally well protected in their headwaters by the large urban parks in steep terrain. However, the lower reaches are often very heavily impacted by sewage, channelling, etc. Fauna that require estuarine habitats for part of their life history are excluded from such streams. Ecosystem functioning in urban streams is probably changed through the loss of strongly-interacting shrimp. Leaf decomposition was found to be reduced in urban streams compared to pristine streams in one study. Conservation entities in the state of Rio de Janeiro tend to protect the mountainous areas; piedmont and coastal plain habitats are generally impacted by agriculture and habitation. Many attempts are being made to conserve catchments in the state of Rio de Janeiro; we discuss 4 case histories, which have different constraints and employ different strategies for management and conservation.

About rats and jackfruit trees: modeling the carrying capacity of a Brazilian Atlantic Forest spiny-rat Trinomys dimidiatus (Günther, 1877) – Rodentia, Echimyidae – population with varying jackfruit tree (Artocarpus heterophyllus L.) abundances

We carried out a six-year study aimed at evaluating if and how a Brazilian Atlantic Forest small mammal community responded to the presence of the invasive exotic species Artocarpus heterophyllus, the jackfruit tree. In the surroundings of Vila Dois Rios, Ilha Grande, RJ, 18 grids were established, 10 where the jackfruit tree was present and eight were it was absent. Previous results indicated that the composition and abundance of this small mammal community were altered by the presence and density of A. heterophyllus. One observed effect was the increased population size of the spiny-rat Trinomys dimidiatus within the grids where the jackfruit trees were present. Therefore we decided to create a mathematical model for this species, based on the Verhulst-Pearl logistic equation. Our objectives were i) to calculate the carrying capacity K based on real data of the involved species and the environment; ii) propose and evaluate a mathematical model to estimate the population size of T. dimidiatus based on the monthly seed production of jackfruit tree, Artocarpus heterophyllus and iii) determinate the minimum jackfruit tree seed production to maintain at least two T. dimidiatus individuals in one study grid. Our results indicated that the predicted values by the model for the carrying capacity K were significantly correlated with real data. The best fit was found considering 20~35% energy transfer efficiency between trophic levels. Within the scope of assumed premises, our model showed itself to be an adequate simulator for Trinomys dimidiatus populations where the invasive jackfruit tree is present.

Differentiating the roles of shrimp and aquatic insects in leaf processing in a Neotropical stream

There is interest in the relationships between macroconsumers (e.g. shrimp) and aquatic insects, as well as their role in ecological processes, including leaf breakdown, in tropical freshwater environments. Many studies have shown that shrimp have the capacity to reduce the abundance of aquatic insects (by predation and behavioural inhibition) and promote leaf breakdown as shredders. To discriminate between these effects, we used fresh leaves of Erythroxylum pulchrum and manipulated the presence of shrimp and insects by electric exclusion at high and low intensities of electric field. In the control treatment (no electric exclusion) shrimp (the brushing collector Potimirim brasiliana and the shredding omnivore Macrobrachium olfersii) and aquatic insects (including shredders) were present. The low-intensity electric field excluded only shrimp, whereas the high-intensity electric field excluded both shrimp and medium- and large-sized aquatic insects (>2mm). Leaf processing was approximately twice as fast in the absence of shrimp and in the presence of insects than when both or neither were present. This implied a trophic cascade of shrimp acting as potential predators of insect shredders, but not acting as shredders themselves. We postulate that increased leaf processing was caused by a behavioural response of the putative shredders to the absence of shrimp; abundant leptophlebiid ephemeropterans were the most likely shredders.

Reviewing carbon spiraling approach to understand organic matter movement and transformation in lotic ecosystems

Aim Understanding riverine carbon cycling is a major issue for stream ecologists. Over the past 60 years, important advance in carbon dynamics and ecosystem energy flow have been made mainly through the Budget and Metabolism approaches. However, much less focus has been given to the quantification of longitudinal movement of organic matter. The concept “Organic Carbon Spiraling” (SOC) was formulated in the early 80s, and represented a substantial advance in the understanding of the longitudinal flow of elements in lotic systems. Methods In this review, we summarize the history behind the SOC concept, cover the major advances at the time of its creation, describe the operational variables and the equation for SOC calculation, and discuss future directions and current applications of this approach. Results/Conclusions We emphasize the need for integrating the C spiraling approach in other regions of the globe, given that measurements are almost exclusive of North America. Such comparative studies can elucidate important drivers of C export, storage and oxidation. Advance in dissolved organic carbon characterization, and improvements in heterotrophic respiration measurements are required to improve SOC accuracy, as well as realistic estimates of benthic stock. With the current interest in examining how lotic systems contribute to regional and global C budgets, we argue that SOC is an effective way to achieve this goal and answer classical questions in stream ecology.