Edge function in patchy mussel bed habitats: variation across nearby rocky shore sites

Mussels form dense three-dimensional beds that serve as habitat to other species. In rocky shores, these beds are often interspersed by gaps due to patchy dislodgement/mortality caused by the action of waves, predators, and/or extreme temperatures. Although mussel patches and gaps are known to support distinctive invertebrate communities, variations in invertebrate habitat function between the interior and edges of mussel patches and gaps were not yet examined. Here, we evaluated variations in habitat properties and invertebrate composition between the edge and interior of mussel (Brachidontes rodriguezii) patches and gaps at three rocky shore sites in the Southwestern Atlantic. Our results indicate that the interior and edge of mussel patches differ in terms of mussel size and density (i.e., a surrogate of habitat structure) and the amount of sediments they accumulate. However, this does not directly translate into consistent differences on temperature, desiccation, and invertebrate composition across sites. As it concerns to gaps, we generally observed increased limpet (Siphonaria lesonii) densities at their edges, which suggests that they encounter favourable conditions by the perimeter of mussel patches. The lack of consistent edge effects on the invertebrates of mussel patches suggests that their species composition would remain largely unaffected by expected increases in gap and edge habitat formation due to ongoing increases in the frequency and magnitude of storms and heat waves. Yet, if increased availability of edge habitats leads to increased overall density of limpets in these rocky shores, then changes could be expected in algal production, composition, and dynamics.

From Extremely Acidic to Alkaline – Diversity of Aquatic Invertebrates in Forest Mining Lakes Under the Pressure of Acidification

Human activities, including mining industry, have considerably degraded the water habitats worldwide. Acidification has severely affected aquatic environments with acidifying pollutants and constitute threat to freshwater biodiversity. The study area is unique for addressing the effects of mining-related acidification on biodiversity in freshwater ecosystems along a pH gradient (2.4-9.6). Using multivariate ordination techniques, we analysed taxa distribution to determine how variations in invertebrate composition correlated with environmental factors. The results revealed differences in pH of water, salinity indicators, hardness, and content of calcium, nitrites, and iron. The highest iron content, relatively high values of conductivity and chlorides was found in the extremely acidic mining lakes. A clear decreasing tendency was observed for the number of taxa with increasing acidity (Oligochaeta, Chironomidae, Glossiphonidae). The density of Hirudinidae, Lestidae, Libellulidae, Caenidae, Sialidae, Dytiscidae, Helodidae, Hydrophilidae and Polycentropodidae increased along with decreasing pH. Specific communities were found with increasing acidity, therefore a progressive increase in acidity will probably have further influence on biological life and water chemistry. The data yielded offer an opportunity to fill knowledge gaps concerning less-studied aquatic environments and links environmental pollution with communities, which is especially important because forest habitats are especially exposed to different climatic factors and threats.

Factors influencing the structure of macroinvertebrate communities in subarctic lakes affected by wildfires

Fires are a natural phenomenon in the boreal forest, but their frequency is expected to increase over the coming century. Fires may affect water quality and invertebrates in lakes, but there have been few studies in the northern boreal forest to describe these impacts. We collected data on water quality, macrophytes, and invertebrates from 20 lakes in the Sahtú Settlement Area of the Northwest Territories. Nine lakes were affected by fires in their catchments 4-5 years before data collection, while eleven were not. Our results showed that few water quality variables were associated with fires. However, remote sensing and field observations suggested that macrophyte biomass was higher in lakes affected by burns and this variable was a significant predictor of invertebrate composition. Burn history was an important predictor of the richness and abundance of invertebrates, but natural variability in lake properties was more important for explaining differences among lakes. Our results suggest that a better understanding of the effects of wildfires might be gained by examining how post-fire changes in macrophytes affect other trophic levels.

Impact of Land Use and Runoff on Stream Quality

Climate changes, intensive agricultural production, and expanding urban areas make the study of runoff and its possible impact on stream quality increasingly important. In this study, we examined large datasets concerning catchment type, stream quality, and invertebrate composition in a comprehensive geographic information system study. The aim was to examine correlations between land use type and quality of the receiving waters to detect possible differences in anthropogenic impacts. The studied area covered 937 km2, and the dataset included 1672 stretches of streams and data from 468 fauna sampling stations. Runoff from agricultural areas more negatively influenced the stream quality than runoff from urban areas. Considering urban catchments, the areas with separate sewer systems generally influenced the stream quality less than catchments with combined sewer systems. In conclusion, the catchment of any specific stream must contain an area with a minimum of 20–30% without agriculture or urban areas to obtain good ecological status; when focusing only on the riparian zone (10 m on each side of the stream), a minimum of 40–55% is needed to create a good ecological status. Therefore, management focus on the entire catchment is important and separate sewers should be preferred rather than combined sewers.

Antibiotics as chemical warfare across multiple taxonomic domains and trophic levels in brown food webs

Bacteria and fungi secrete antibiotics to suppress and kill other microbes, but can these compounds be agents of competition against macroorganisms? We explore how one competitive tactic, antibiotic production, can structure the composition and function of brown food webs. This aspect of warfare between microbes and invertebrates is particularly important today as antibiotics are introduced into ecosystems via anthropogenic activities, but the ecological implications of these introductions are largely unknown. We hypothesized that antimicrobial compounds act as agents of competition against invertebrate and microbial competitors. Using field-like mesocosms, we tested how antifungal and antibacterial compounds influence microbes, invertebrates, and decomposition in the brown food web. Both antibiotics changed prokaryotic microbial community composition, but only the antibacterial changed invertebrate composition. Antibacterials reduced the abundance of invertebrate detritivores by 34%. However, the addition of antimicrobials did not ramify up the food web as predator abundances were unaffected. Decomposition rates did not change. To test the mechanisms of antibiotic effects, we provided antibiotic-laden water to individual invertebrate detritivores in separate microcosm experiments. We found that the antibiotic compounds can directly harm invertebrate taxa, probably through a disruption of endosymbionts. Combined, our results show that antibiotic compounds could be an effective weapon for microbes to compete against both microbial and invertebrate competitors. In the context of human introductions, the detrimental effects of antibiotics on invertebrate communities indicates that the scope of this anthropogenic disturbance is much greater than previously expected.

Geology is a significant indicator of algal cover and invertebrate species composition on intertidal reefs of Ngari Capes Marine Park, south-western Australia

Effective management of rocky intertidal reefs requires an understanding of spatial variation in species composition and abundance, and the identification of high biodiversity areas. This study identified patterns of invertebrate biodiversity on intertidal reefs of differing underlying structure within Ngari Capes Marine Park, south-west Western Australia. Intertidal reef surveys were conducted at 12 limestone and 9 granite sites throughout the park. Geology was a significant indicator of variation in percentage cover of substrate and invertebrate composition, which covaried with rugosity and complexity. Limestone reefs were characterised by a combination of high and low branching algae and a sand–turf matrix, whereas granite reefs consisted of bare rock. A total of 15772 individual invertebrates representing 10 phyla, 16 classes, 60 families and 121 species was recorded. A high abundance of dove (Family Columbellidae) and jewel top snails (Family Trochidae) characterised limestone reefs, whereas an assortment of limpets and chitons characterised granite reefs. Granite reefs contained more species (92v. 63) and a higher mean (±s.d.) number of individuals (119±58v. 42±79m–2) than did limestone reefs. These findings emphasise the effect of underlying geology on the distribution of intertidal invertebrates and the need for management programs to accommodate different habitat types to effectively conserve biodiversity.

Variation in stream metabolism and benthic invertebrate composition along longitudinal profiles of two contrasting river systems

Our study aimed to determine drivers of longitudinal variation in stream metabolism and benthic macroinvertebrate (BMI) composition and assess concordance of these ecological measures for two Canadian rivers (Rat River and Tobacco Creek). Gross primary production was associated with longitudinal position in both rivers but also with the percentage of the watershed used for agriculture and hydrogeomorphic zone. However, within- and among-zone differences in stream metabolism indicated that longitudinal variation followed a staircase pattern rather than a clinal pattern. BMI composition was associated with network position in both rivers, but hydrogeomorphic zones were only important in Tobacco Creek. Among-zone differences in BMI communities in Tobacco Creek depended on season. Concordance between stream metabolism and BMI composition was not observed within either river despite metabolism and BMI composition being associated with longitudinal position. For these rivers, segment-scale hydrogeomorphic conditions appear to be important modifiers of longitudinal patterns observed at the whole river scale. The lack of concordance between stream metabolism and BMI composition suggests reach-scale processes are driving ecological differences within sampling sites.

Phytophilous Fauna of a Small and Artificial Urban Lake

Phytophilous community on Myriophyllum spicatum was studied in a small artificial urban lake in the city of Osijek (eastern Croatia), during the spring and summer season in 2010. In the eutrophic conditions, macrophyte stands were well developed and in the formed periphyton representatives of the following invertebrate taxa were found: Hydrozoa, Nematoda, Gastropoda, Cladocera, Copepoda, Insecta larvae - including families Chironomidae and Coleoptera. They displayed differences in temporal abundance patterns. Two separate phases in macrophyte colonization with differences in invertebrate composition and abundance were recorded. Insect larvae, particularly Chironomidae, were most abundant in the first phase, through the spring period, and Hydra oligactis (brown hydra) was most abundant in the second phase, i.e. summer period. Concurrently, microcrustacean abundance declined towards the end of the summer. Results of the analyses indicated that water temperature and perihyton biomass were the variables exerting the main influence on the invertebrate assemblage, while interestingly, macrophyte size and biomass were negatively correlated with most of the fauna abundance. On the other hand, brown hydra was negatively correlated with all other invertebrate taxa, except gastropods. Larger surface of submersed macrophytes is the main parameter supporting the increase of invertebrate abundance due to providing protection from predators and growth for periphyton, an important food source for these phytophilous organisms. Macrophyte length was positively correlated with Hydra abundance, while Chironomids were more influenced by periphyton biomass. These organisms can indicate water quality conditions and a potential increase in primary and secondary production.

COMPOSICIÓN Y ESTRUCTURA TRÓFICA DE LOS MACROINVERTEBRADOS TERRESTRES DE LA ISLA MALPELO, PACÍFICO COLOMBIANO

Oceanic islands have special ecosystem dynamics due to their isolation and weather conditions influenced by the sea. This is also the case for Malpelo Island, located at the Colombian Pacific, where previous studies showed an invertebrate composition strongly dominated by predatory species. With the aim of contributing to the knowledge of these organisms on the island, 22 sample plots were surveyed, covering three types of microhabitat, classified according to the type of soil, shadow, and vegetation. Sampling took place between May and June 2006, by direct catches. A total of 1294 specimens from seven classes and 25 orders were obtained. Diversity was determined by microhabitat structure complexity, being more diverse the one that presented the greatest degree of heterogeneity. The order Araneae presented the highest number of species, Coleoptera the highest abundance and Staphylinidae the highest relative abundance. Predators showed the highest richness (45.3 %) and abundance (40.6 %) among all trophic guilds. These findings lent support to the idea that the terrestrial system of Malpelo depends on the sea.