Interactions between seagrasses and burrowing ghost shrimps and their influence on infaunal assemblages

The current study examined the direct interactions between intertidal seagrasses (Zosteraceae) and burrowing ghost shrimps (Callianassidae) and their influence on associated infaunal assemblages. Reciprocal transplant experiments conducted in two temperate regions revealed different interactions between both types of organism. In the U.S.A., seagrass prospered in all treatments, irrespective of the presence of ghost shrimp, whilst ghost shrimp declined in plots containing seagrass. In New Zealand, neither transplanted ghost shrimp nor seagrass became established in experimental plots, at the same time, neither type of organism appeared to be affected by the experimental addition of transplants. The differences in interactions between seagrass and ghost shrimp appeared to be related to seasonal differences in the timing of the transplant experiments and the pairing of particular ghost shrimp and seagrass species in each region. Infaunal assemblages showed distinct differences between seagrass and ghost shrimp treatments and reflected the dominant type of organism present. In treatments where transplanted seagrass or ghost shrimp became established, assemblage composition shifted in accordance with the type of transplanted organism. Differences in assemblage composition were characterised by higher relative abundances of discriminating taxa in treatments dominated by seagrass. The overall patterns of infaunal assemblage composition were correlated with a number of variables including the number of shoots, above-, below-ground seagrass biomass, % fines/sand, % total organic carbon, and sediment chlorophyll a. Findings from this study highlight the functional importance of intertidal seagrasses and burrowing ghost shrimps and reveal some of the ecological repercussions associated with changes in the distribution of these sympatric ecosystem engineers.     

An examination of the spatial and temporal generality of the influence of ecosystem engineers on the composition of associated assemblages

The present study evaluated the generality of ecosystem engineering processes by examining the influence of sympatric burrowing shrimps (Callianassidae) and intertidal seagrasses (Zosteraceae) on benthic assemblage composition in two temperate regions, south-eastern New Zealand and north-western U.S.A. In each region, intertidal macrofauna assemblage composition was determined at sites of different burrowing shrimp/seagrass density and where both species co-occured, in three different size estuaries/tidal inlets, on two occasions. Results from both regions showed that the presence of shrimps and seagrasses consistently influenced the composition of the associated infaunal assemblages at all sites, in both summer and winter. Macrofauna assemblages at shrimp sites were significantly different to those at seagrass-only and mixed sites, whereas the composition of the latter sites was similar. The differences observed between sites were best explained by sediment variables. In New Zealand, % fines and seagrass debris showed the highest correlation to differences in assemblage composition, and in the U.S.A. % fines, % carbon and sediment turnover (by shrimp) appeared to be the most important environmental parameters measured. Four to six taxa exhibited the greatest discriminating significance (including corophiid amphipods, spionid polychaetes and oligochaetes) for dissimilarities in assemblage composition observed at the different sites, with generally lower abundances at shrimp than at seagrass sites. The present study highlights the functional importance of seagrasses and bioturbating shrimps as ecosystem engineers in soft-sediment environments, and reveals the generality of their influence on associated macro-invertebrate assemblages. The findings also allow for further development of a heuristic model for ecosystem engineering by shrimp and seagrass which indicate that numerical models that aim to explore the relationship between ecosystem engineer populations and habitat modification should be expanded to capture the interaction of co-occurring engineers and be both spatially and temporally explicit.     

Edge effects on fauna in fragmented seagrass meadows

Abstract Fragmented habitats are a common occurrence in many marine systems, but remain poorly studied in comparison to their terrestrial counterparts. Here, I show that crustaceans inhabiting fragmented Zostera seagrass meadows show a dramatic response (change in abundance) to patch edges, with 11 out of 12 tests showing greatest abundance at the boundary between sand and seagrass. These patterns occurred on a scale of 0.25–1 m around the patch edge. Changes in seagrass biomass are unlikely to explain this pattern, as seagrass biomass increased smoothly at the patch edge, and did not decline towards patch interiors. In contrast to crustaceans, only a few polychaete taxa responded to the patch edge (9 of 25 tests), and bivalves generally did not show a response (1 of 5 tests). These latter groups are predominantly infaunal, and their lack of response may be partly due to the presence of substantial quantities of seagrass root and rhizome material in the sand habitat, which was defined visually based on the lack of above‐ground seagrass components only.     

Biogeographic patterns in major marine realms: function not taxonomy unites fish assemblages in reef,seagrass and mangrove systems

We examine the effects of different biogeographic histories on assemblage composition in three major marine habitats in two biogeographically distinct marine realms. Specifically, we quantify the taxonomic and functional composition of fish assemblages that characterise coral reef, seagrass and mangrove habitats, to explore the potential effects of biogeographic history and environment on assemblage composition. The three habitats were surveyed in the Caribbean and on the Great Barrier Reef using a standardised underwater visual census method to record fish size and abundance data. The taxonomic composition of assemblages followed biogeographic expectations, with realm‐specific family‐level compositions. In marked contrast, the functional composition of assemblages separated habitats regardless of their biogeographic locations. In essence, taxonomy characterises biogeographic realms while functional groups characterise habitats. The Caribbean and Indo‐West Pacific have been separated for approximately 15 million years. The two realms have different taxonomic structures which reflect this extended separation, however, the three dominant shallow‐water marine habitats all retain distinct functional characteristics: seagrass fishes are functionally similar regardless of their taxonomic composition or biogeographic location. Likewise, for coral reefs and mangroves. The results emphasise the advantages and limitations of taxonomic vs. functional metrics in evaluating patterns. Taxonomy primarily reflects biogeographic and evolutionary history while functional characteristics may better reflect ecological constraints.     

Conserving a variety of ancient forest patches maintains historic arthropod diversity

Forests are naturally extensive tracts. However, in South Africa natural fires over many millennia have reduced forested areas into small remnants spread throughout a grassland matrix. Small patches, especially distant patches, are generally considered to be adverse for forest specialists, owing to decreased forest interior and increased edge. Here we test this assumption by determining the impact of forest interpatch distance and patch size on epigaeic arthropod diversity in this globally rare vegetation type. Forty patches were selected: ten large (100–435 m diameter) that are distant (500–645 m) from other patches, ten large that are close to other patches (38–97 m), ten small (30–42 m) that are distant, and ten small-close patches. Each patch had two plots: edge and interior. Arthropods were sampled using pitfall traps, Berlese-Tullgren funnels and active searches. Interiors and edges had similar species richness and composition, excluding spiders, which were richer in interiors. Patch size significantly influenced species richness of predatory beetles and arthropod assemblages, excluding spiders. Effect of the interaction between patch size and interpatch distance on species richness and composition varied among taxa. Furthermore, large patches supported similar assemblages regardless of interpatch distance. Arthropod response, particularly ants to patch size and interpatch distance, was partly shaped by the matrix type. The percentage of surrounding grassland had little effect on arthropod diversity. We can conclude that large and close patches are important for arthropod conservation. Nevertheless, it is also important to conserve a variety of patch sizes at various distances to maximize overall arthropod composition.     

The surface ocean productivity response of deeper water benthic foraminifera in the Atlantic Ocean

We test the relationship of deep sea benthic foraminiferal assemblage composition to the surface ocean productivity gradient in the low latitude Atlantic Ocean using 81 surface sediment samples from a water depth range between 2800 and 3500 m. The samples are selected so that the surface ocean productivity gradient, controlling the flux of organic carbon to the seabed, will be the most important environmental variable. The first two principal components of the assemblage data account for 73% of data variance and are clearly linked to the productivity gradient across the Atlantic. These components show that under higher productivity the assemblages contain a higher abundance of Uvigerina peregrina, Melonis barleeanum, Globobulimina spp. and other taxa with probable infaunal microhabitats. Alabaminella weddellensis, a species linked to episodic phytoplankton debris falls, is also important in these assemblages. As productivity decreases there is a regular shift in assemblage composition so that low productivity assemblages are dominated by Globocassidulina subglobosa and several Cassidulina species along with Epistominella exigua. We hypothesize that these taxa are epifaunal to very shallow infaunal since nearly all organic carbon oxidation occurs near the sediment-water interface in low productivity settings. Discriminant function analysis of the foraminiferal assemblages, with groups selected on the basis of surface ocean productivity, shows clear separation among five productivity levels we used. This analysis demonstrates that productivity variations have a strong influence on assemblage composition. Finally, we used two groups of samples from the Rio-Grande Rise representing water depths from 2007 to 2340 m and 2739 to 3454 m to test for effects produced by changing water depth. All these samples are from a low productivity region and represent nearly identical environmental conditions. Although the low productivity nature of all the Rio-Grande Rise samples is obvious, there are assemblage differences between our depth groups. We cannot account for the assemblage differences with changes in organic carbon flux, dissolution effects or other physical/chemical properties of the ocean. Thus there are as yet unidentified factors related to water depth which cause some assemblage variation in the low productivity setting we investigated.     

Inter-annual patterns in macroinvertebrate communities of wilderness streams in Idaho, U.S.A.

This study examined the inter-annual variation in macroinvertebrate assemblages in six wilderness streams in central Idaho over a 6-year period (1990–1995). Benthic macroinvertebrates and associated environmental correlates were sampled during baseflow each summer. Little environmental change, as assessed using coefficients of variation (CVs) for substrate size and embeddedness, width, depth and periphyton standing crops, occurred in the streams over the period of study. There was also little temporal change in macroinvertebrate assemblages based on the relative abundance of the 10 most abundant taxa, all shredder taxa and all plecopteran taxa. CVs for individual taxa were substantially greater than those of most community measures, with rare taxa contributing 30–50% of the variation for any one stream. Frequency distributions for taxa CVs excluding rare taxa were more normally distributed. Differences in assemblage structure among streams were attributed to stream size (shift in shredder assemblages) and temperature (shift in plecopteran taxa). These data indicate a long-term (multi-year) persistence in the macroinvertebrate composition of these pristine streams, thus supporting the premise that such streams are excellent references for use in long-term biomonitoring programs.     

Influence of setting,sieve size,and sediment depth on multivariate and univariate assemblage attributes of coral reef-associated mollusc death assemblages from the Gulf of Aqaba

Measures of diversity and ecology of marine invertebrate assemblages depend on a variety of factors including environmental conditions and methodological decisions. In this study, the influence of such factors on multi- and univariate assemblage parameters of molluscan death assemblages from the Gulf of Aqaba (Red Sea, Jordan) was evaluated. Sediment samples were collected at two coral reef types, a patch reef at 13 m of water depth characterized by fine-grained sediments and a Millepora-fringing reef with coarse-grained sediments at 5 m of water depth. The upper and lower 10 cm of the sediment column were separately removed and sieved with mesh sizes of 1 and 2 mm. A large dataset of 6400 bivalve and gastropod shells was compiled to evaluate how setting, sediment depth, and sieve size influenced taxonomic composition and species richness, species-abundance patterns and the Shannon–Wiener index, the number of drilled shells per species and drilling frequency (DF) of the assemblage. Setting had the strongest impact on all aspects, followed by sieve size, but sediment depth was insignificant, probably due to complete homogenization of the sediments by reworking and bioturbation. Multivariate assemblage parameters distinguished much better between categories (setting, sieve size) than univariate measures. Sieve size-related disagreements recognized between the two higher taxa are mostly due to the underlying difference in body-size distribution of bivalve and gastropod assemblages. We conclude that species richness and other ecological characteristics of molluscan death assemblages in coral reef-associated sediments will most strongly reflect habitat complexity of the sites chosen, are significantly influenced by methodological decisions (i.e., sieve size), will only poorly preserve temporal patterns, and the results will differ between bivalves and gastropods.     

Across-reach consistency in macroinvertebrate distributions among litter patch types in Japanese headwater streams

Different types of litter patches with contrasting macroinvertebrate assemblages have been observed within a stream reach. This study examined whether distributions of macroinvertebrates among three litter patch types (riffle, middle, edge) were consistent between reaches with different channel characteristics in headwater streams in central Japan. Mass of leaves per unit area was significantly higher in riffle and edge patches than in middle patches, which was consistent between reaches, while no consistent pattern was evident between reaches for mass of either woody material or small litter fragments. Distribution among the patch types was consistent between reaches for 11 out of 13 dominant macroinvertebrate taxa; density was highest in riffle patches for 5 taxa and in middle patches for 5 taxa. Although we previously related densities of some taxa to mass of woody material or small litter fragments, hydraulic characteristics (water depth, current velocity), which were consistent between reaches, may be more important determinants of macroinvertebrate distributions among the patch types, even within pools (i.e. middle and edge patches) where current is uniformly low. The results of this study indicate that a reach-scale macroinvertebrate community structure associated with litter is likely to vary according to litter patch type composition, which would be affected by channel characteristics of the reaches.     

Linking taphonomy to community-level abundance: Insights into compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps)

Although actualistic live/dead comparisons lead to robust estimates of fidelity of modern death assemblages, quantitative evaluation of fidelity of fossil assemblage remains uncertain. In this paper, effects of storm reworking on compositional fidelity of the Upper Triassic shell concentrations (Eastern Alps, Austria) are evaluated. An exploratory approach is based on comparison of reworked and non-reworked assemblages in ordination analyses. Non-reworked assemblages of one or more communities provide a baseline for evaluation of fidelity of reworked assemblages. In siliciclastic-rich intervals of the Kössen Formation, shell concentrations are represented by (1) packstones with small, shallow infaunal bivalves, (2) floatstones and pavements with large semi-infaunal bivalves, and (3) bioclastic marlstones. In carbonate-rich intervals, bioclastic floatstones with bivalves and brachiopods occur. Analyzing all shell concentrations, eight sample groups sharing similar species composition are discriminated. Limited effect of storm reworking on composition of shell concentrations is indicated by (1) a general persistence of six sample groups when only non-reworked assemblages are analyzed, (2) similarity in composition between reworked and non-reworked assemblages within sample groups, and (3) compositional segregation between non-reworked assemblages of distinctive sample groups, mostly without any reworked assemblages of intermediate composition.Depth-related variations in dead-shell production, shell destruction and body size governed preservation and distribution of the shell concentrations along onshore-offshore gradient in the Kössen Basin. First, at times when environmental conditions were unfavorable for shell producers, coupled with high background shell destruction rates, limestone beds formed during storm events were shell-poor. Second, less common shell concentrations in upper than in lower parts of siliciclastic intervals can be related to higher environmental stress in shallower habitats. Third, the difference between shell concentrations dominated by small and large bivalves is driven by between-habitat differences in body size and is not due to a differential sorting of small and large shells. Combining community analysis based on species abundances with taphonomic analysis can thus be helpful in tracking fidelity of fossil assemblages.     

Identifying the scales of variability in stream macroinvertebrate abundance, functional composition and assemblage structure

1. Many natural ecosystems are heterogeneous at scales ranging from microhabitats to landscapes. Running waters are no exception in this regard, and their environmental heterogeneity is reflected in the distribution and abundance of stream organisms across multiple spatial scales. 2. We studied patchiness in benthic macroinvertebrate abundance and functional feeding group (FFG) composition at three spatial scales in a boreal river system. Our sampling design incorporated a set of fully nested scales, with three tributaries, two stream sections (orders) within each tributary, three riffles within each section and ten benthic samples in each riffle. 3. According to nested anova s, most of the variation in total macroinvertebrate abundance, abundances of FFGs, and number of taxa was accounted for by the among‐riffle and among‐sample scales. Such small‐scale variability reflected similar patterns of variation in in‐stream variables (moss cover, particle size, current velocity and depth). Scraper abundance, however, varied most at the scale of stream sections, probably mirroring variation in canopy cover. 4. Tributaries and stream sections within tributaries differed significantly in the structure and FFG composition of the macroinvertebrate assemblages. Furthermore, riffles in headwater (second order) sections were more variable than those in higher order (third order) sections. 5. Stream biomonitoring programs should consider this kind of scale‐dependent variability in assemblage characteristics because: (i) small‐scale variability in abundance suggests that a few replicate samples are not enough to capture macroinvertebrate assemblage variability present at a site, and (ii) riffles from the same stream may support widely differing benthic assemblages.     

The contribution of small individuals to density–body size relationships

The relationship between density and body size is central to our understanding of species assemblages. The greatest challenge in sampling complete assemblages is obtaining reliable estimates of all taxa regardless of body size. We therefore examined the density-body size relationship in a coral reef fish assemblage using a novel sampling method which permits reliable quantification of the small/cryptic reef fish fauna. We found a negative linear relationship between density and adult body size. This is in marked contrast to the polygonal relationship previously described for other local scale assemblage studies. Our linear relationship may be a consequence of the larger differences in body size among taxa. Spanning over five orders of magnitude, the range of body sizes appears to be an important factor in shaping density-body size relationships.     

Response of fauna in seagrass to habitat edges,patch attributes and hydrodynamics

This study has investigated the taxon‐specific responses of fauna to patch edges, and how these relate to patch attributes (patch size, seagrass biomass and water depth), and hydrodynamics in the seagrass habitat. Faunal abundances were sampled at the edge, 2 m in from the edge, and in the middle of 10 seagrass patches of variable size in Port Phillip Bay, Australia. Five of nine taxa showed edge effects. There were higher abundances at the edge compared with the middle for porcellid harpacticoids, and an increase in abundance from the edge to the middle of the patches for tanaids and isopods. For caprellid and gammarid amphipods, the edge effect varied across patches. Changes in current within the patch and patch size were related to the variability in the edge effect pattern of caprellids. None of the measured environmental variables (seagrass biomass, current and water depth) or patch size had a role in the variable edge effect pattern of gammarid amphipods. At the patch level, the distribution of six of nine taxa in this study, namely isopods, polychaetes, ‘other harpacticoids’, porcellid harpacticoids, cumaceans and gammarid amphipods, was related to differences in average water depth, average seagrass biomass and patch size. Our study indicates that the faunal response to edges cannot be generalized across seagrass habitat, and the implications of habitat area loss will vary depending on the taxon under consideration.     

Seagrass habitat complexity and macroinvertebrate abundance in Lakshadweep coral reef lagoons,Arabian Sea

Macrofauna of seagrass community in the five Lakshadweep atolls were studied and compared. The associated epifaunal and infaunal taxa comprising nine major taxonomic groups, showed significant differences in the total number of individuals (1041–8411 m^–2) among sites and habitats. The density of macrofauna was directly related to mean macrophytic biomass (405–895 g wet wt. m^–2). The fauna was dominated by epifaunal polychaetes, amphipods and isopods in the vegetated areas. When compared with the density of nearby unvegetated areas , seagrass meadows harbour a denser and richer macroinvertebrate assemblage .     

Environmental factors accounting for benthic macroinvertebrate assemblage structure at the sample scale in streams subjected to a gradient of cattle grazing

Macroinvertebrate assemblages were related to environmental factors that were quantified at the sample scale in streams subjected to a gradient of cattle grazing. Environmental factors and macroinvertebrates were concurrently collected so assemblage structure could be directly related to environmental factors and the relative importance of stressors associated with cattle grazing in structuring assemblages could be assessed. Based on multivariate and inferential statistics, measures of physical habitat (% fines and substrate homogeneity) had the strongest relationships with macroinvertebrate assemblage structure. Detrital food variables (coarse benthic and fine benthic organic matter) were also associated with assemblage structure, but the relationships were never as strong as those with physical habitat measures, while autochthonous food variables (chlorophyll a and epilithic biomass) appeared to have no association with assemblage structure. The amount of variation explained in taxa composition and macroinvertebrate metrics is within values reported from studies that have examined macroinvertebrate metric–sediment relationships. The % Coleoptera and % crawlers had consistent relationships with % fines during this study, which suggests they may be useful metrics when sediment is a suspected stressor to macroinvertebrate assemblages in Blue Ridge streams. Findings from this study also demonstrate the importance of quantitative sampling through time when research goals are to identify relationships between macroinvertebrates and environmental factors.     

Factors influencing macroinvertebrate assemblages in artificial subtropical ponds of Taiwan

Macroinvertebrate assemblages and its association with environmental factors at the 11 artificial subtropical ponds of Taiwan were examined using the multivariate analysis software STATICO. The aims of the study were to determine whether spatial and seasonal variation of macroinvertebrate assemblages changed seasonally, to examine which environmental factors determined the spatial and temporal structure of maroinvertebrate assemblages, and to compare between-pond variations in the taxon composition of macroinvertebrates. Macroinvertebrates were collected seasonally by a corer and a sweep net in 2007, and 13 physical and chemical factors were measured at the same time. A total of 31 macroinvertebrate taxa were collected during the sampling period, and the most dominant taxa were Chironomidae (31.7% of total animal abundance) and Tubificidae (22.4%). STATICO identified pond size, pond depth, sediment depth, and altitude as the major abiotic factors and Bufo melanostictus (Amphibia) as the major biotic factor to influence macroinvertebrate assemblages at these ponds. These factors changed with seasonality. For example, the abundance of B. melanostictus was the most important factor during the spring but became much less important in other seasons. According to the spatial distribution patterns of macroinvertebrate assemblages, macroinvertebrates could be split into two groups based on their dispersal. The active dispersers, such as insect taxa, were strongly associated with pond size and the passive dispersers, such as non-insect taxa, were strongly associated with the pond depth and/or sediment depth. The results of this study suggested that pond size might influence macroinvertebrate assemblages through their dispersal mechanisms and that the environmental factors which influenced the macroinvertebrate assemblages most changed with seasons in this study area.     

Space–time interactions and invertebrate assemblage change in stream networks

Streams form hierarchical, dendritic physical networks, but relatively little is known about how this spatial structure affects community assembly. We investigated interactions between changes over time in macroinvertebrate assemblages and their distribution in space (the space–time interaction) in stream networks. Assemblages were sampled from every tributary, and every reach between tributaries, to determine effects of network position on assemblage composition, in four West Coast, South Island, New Zealand, headwater networks. Using canonical redundancy analysis, we found that macroinvertebrate assemblages were significantly spatially structured and species assemblages changed significantly between two sampling periods. The most important environmental variables (averaged over all AIC models) explaining change in assemblage composition were related to disturbance, local habitat/resources and habitat size. The lack of a significant interaction between space and time, however, indicated the spatial pattern of assemblages remained the same over time, regardless of changes in assemblage composition. Consistent spatial structuring could be the result of unchanging processes such as those arising from the universal nature of stream topology and hydrology acting both on habitat‐ and dispersal‐ related community processes. Thus, we conclude that although community assemblages changed over time, the spatial arrangement of communities could potentially be predicted from stream network topology and hydrology.     

Relations Between River Plant Richness in the Portuguese Floodplains and the Widespread Water Knotgrass <Emphasis Type="Italic">(Paspalum Paspalodes</Emphasis>)

We examined the variability of macroinvertebrate assemblage structure, species identities, and functional feeding group composition in relation to stream size, tributary position, and in-stream factors in a boreal watershed in Finland. Our study included three riffle sites in each of three stream sections in each of three stream size classes. Multi-response permutation procedure, indicator value method, and canonical correspondence analysis revealed clear differences in assemblage structure among the stream size classes, with a gradual increase of species richness as the stream size increased. Significant differences in assemblage structure were also found among the tributary river systems. The functional feeding group composition broadly followed the river continuum concept, i.e., headwaters were dominated by shredders, gatherers, or filterers, whereas scrapers increased in relative abundance with stream size. There was, however, considerable variation in the functional feeding group composition both among and within the headwater stream sections. Our findings refer to a strong influence of stream size on macroinvertebrate assemblages, but also factors prevailing at the scale of individual riffles should be considered in biodiversity conservation of lotic ecosystems.     

Short-term responses of phytoplankton to nutrient enrichment and planktivorous fish predation in a temperate South American mesotrophic reservoir

The benthic macroinvertebrate community is an important component of stream diversity, because its members are fundamental connectors among the different trophic levels of running waters. In this study, we assessed alpha and beta diversities of benthic macroinvertebrates in three stream sites and four microhabitats: (i) moss in the air-water interface; (ii) submerged roots of terrestrial plants; (iii) leaf litter deposited in pools; (iv) stones in riffles. We constructed rarefaction curves and compared species richness among microhabitats for each stream site. Additionally, we evaluated which factor, stream site, or microhabitat, was most important in determining variation in assemblage structure, i.e., beta diversity. There was no significant difference among microhabitats in terms of taxa richness evaluated by rarefaction curves. Using partial Constrained Correspondence Analysis (pCCA), we found that microhabitat was most important in determining community composition, accounting for 42.02% of the total variation. Stream sites accounted for 22.27%. In accordance with the pCCA, exploratory multivariate methods (ordination and classification) revealed four distinct groups, corresponding to the four microhabitats, independent of stream sites. Our results indicated that differences among environmental conditions are much more important in the determination of stream assemblage structure than are differences in spatial location. Accordingly, adjacent microhabitats in a single stream site harbor macroinvertebrate assemblages more dissimilar than those found in a single microhabitat at different stream sites. Handling editor: D. Dudgeon     

Relationships between deforestation, riparian forest buffers and benthic macroinvertebrates in neotropical headwater streams

1. Few studies have evaluated the effectiveness of riparian buffers in the tropics, despite their potential to reduce the impacts of deforestation on stream communities. We examined macroinvertebrate assemblages and stream habitat characteristics in small lowland streams in southeastern Costa Rica to assess the impacts of deforestation on benthic communities and the influence of riparian forest buffers on these effects. Three different stream reach types were compared in the study: (i) forested reference reaches, (ii) stream reaches adjacent to pasture with a riparian forest buffer at least 15 m in width on both banks and (iii) stream reaches adjacent to pasture without a riparian forest buffer. 2. Comparisons between forest and pasture reaches suggest that deforestation, even at a very local scale, can alter the taxonomic composition of benthic macroinvertebrate assemblages, reduce macroinvertebrate diversity and eliminate the most sensitive taxa. The presence of a riparian forest buffer appeared to significantly reduce the effects of deforestation on benthic communities, as macroinvertebrate diversity and assemblage structure in forest buffer reaches were generally very similar to those in forested reference reaches. One forest buffer reach was clearly an exception to this pattern, despite the presence of a wide riparian buffer. 3. The taxonomic structure of macroinvertebrate assemblages differed between pool and riffle habitats, but contrasts among the three reach types in our study were consistent across the two habitats. Differences among reach types also persisted across three sampling periods during our 15‐month study. 4. Among the environmental variables we measured, only stream water temperature varied significantly among reach types, but trends in periphyton abundance and stream sedimentation may have contributed to observed differences in macroinvertebrate assemblage structure. 5. Forest cover was high in all of our study catchments, and more research is needed to determine whether riparian forest buffers will sustain similar functions in more extensively deforested landscapes. Nevertheless, our results provide support for Costa Rican regulations protecting riparian forests and suggest that proper riparian management could significantly reduce the impacts of deforestation on benthic communities in tropical streams.