Periphytic Structure Research Articles

The Mass Ratio of the Epiphytic Periphyton of the Nyéki-Holt-Duna

The knowledge of the periphytic structure is important for the fact that the composition of epiphytic periphyton indicates the ecologically different habitats, the biological state of water-quality and its changes. Plants like reed, great bulrush, saligot, pondweed, and water-rose separately were collected from the different sampling sites for the epiphytic periphyton examination. We performed the comparability of the monitoring systems based on the periphyton category (mass), the group (ash%), the type (chl-a%), and the character (AI), and we used the biological indicators to determine the ecological state. Taking into consideration the examined years and the results of the analysis of the mass and the chemical composition of the periphyton, by means of the NTPI, the overweight of the good ecological state is characteristic of the Nyéki-Holt-Danube.

Current-mediated periphytic structure modifies grazer interactions and algal removal

By shaping the architecture and taxonomic composition of periphyton, stream current may create periphytic mats on which some grazers can feed and forage more effectively than others. Current-mediated periphytic structure also has the potential to foster positive interactions among grazers if one grazer’s foraging facilitates another’s access to algal food. To examine the extent to which these indirect effects of current influenced periphytic removal and grazer interactions, we conducted a mesocosm experiment with two common grazers, the caddisfly (Trichoptera) Glossosoma verdona and the mayfly (Ephemeroptera) Drunella grandis. Periphyton was allowed to colonize ungrazed tiles for 30 d and assume its natural growth form under three ranges of near-bed current, “slow” (1–5 cm s−1), “medium” (15–20 cm s−1), and “fast” (30–40 cm s−1). Tiles were then exposed to the two grazer species at five densities. A streambed survey quantified Glossosoma and Drunella distributions in relation to near-bed current and periphytic structure (i.e., diatom films vs. filamentous mats) in the Colorado River. After 22 days of grazing, periphytic removal by Glossosoma was influenced by near-bed current and attendant periphytic structure. In slow current, where senescent Ulothrix filaments were abundant, increased Glossosoma density was correlated with an increase in periphyton biomass. Larvae became entangled and immobilized by the diffuse and senescent Ulothrix mat that characterized slow velocity, and Glossosoma mortality and weight loss was greatest in this treatment. By contrast, Drunella reduced periphyton across all density and current treatments. Drunella density correlated with increased Glossosoma survivorship and weight gain in slow current. The driving mechanism for this facilitation appeared to be removal of entangling overstory filaments by Drunella. The streambed survey showed that Glossosoma were negatively associated with filamentous mats, lending support to the hypothesis that clearing action by Drunella in the slow current/senescent Ulothrix treatment facilitated Glossosoma growth and survival. Our study helps underscore the importance of evaluating species interactions over ranges of abiotic conditions and consumer pressure to understand the patterns and processes shaping benthic communities.

Herbivory and irradiance shape periphytic architecture in a Swiss alpine stream

The effects of herbivory and light on epilithic periphyton from Minor Creek (2,200 m above sea level), a Swiss alpine stream, were examined by manipulating light intensity and the densities of two abundant grazers in stream‐side channels. We hypothesized that the high light intensities in Minor Creek (exceeding 2,000 μmol m−2 s−1 on the stream bed) would cause photoinhibiton and thus regulate algal composition and biomass accrual. After 18 d, full sunlight had negative effects on all measures of periphytic abundance in streamside channels. A five‐level light gradient experiment in Minor Creek corroborated these findings: full sunlight suppressed periphytic accumulation.To test the interactive effects of grazing and light, we used two herbivorous insects with distinctly different feeding structures. Ecdyonurus sp. (Heptageniidae) possesses brushing mouthparts; Drusus lateralis (Limnephilidae) has scraping mandibles. In accordance with a conceptual model that predicts algal physiognomy and herbivore feeding mode regulate algal susceptibility to grazing, we hypothesized that Ecdyonurus would primarily reduce physiognomies composing the periphytic overstory (e.g., stalked and filamentous algae), whereas Drusus would have greater access to understory physiognomies (e.g., prostrate forms). In addition, we hypothesized that tall physiognomies would be less abundant under full sunlight due to the exposure of the periphytic mat to photoinhibiting irradiance. Thus, we expected Ecdyonurus to have a smaller effect on periphyton at high light intensities.Light in channels did not directly modify grazing effects; however, the data suggest light intensity altered periphytic susceptibility to grazing. Channels receiving full sunlight had less periphyton, yet grazer weights did not differ between light treatments despite the fact that weight gain for each grazer was negatively correlated with conspecific biomass, implicating competition for limited periphytic food. Algal responses were most pronounced under grazing by Ecdyonurus, which was associated with decreases in the abundance of six of the seven algal physiognomies. Contrary to model predictions, Ecdyonurus reduced low‐lying as well as overstory physiognomies. Drusus, by contrast, was associated with reductions in only four physiognomies. Results from this study suggest that understanding periphytic community responses to grazing will require more sophisticated models of periphytic structure.