Characterizing benthic macroinvertebrate and algal biological condition gradient models for California wadeable Streams, USA

The Biological Condition Gradient (BCG) is a conceptual model that describes changes in aquatic communities under increasing levels of anthropogenic stress. The BCG helps decision-makers connect narrative water quality goals (e.g., maintenance of natural structure and function) to quantitative measures of ecological condition by linking index thresholds based on statistical distributions (e.g., percentiles of reference distributions) to expert descriptions of changes in biological condition along disturbance gradients. As a result, the BCG may be more meaningful to managers and the public than indices alone. To develop a BCG model, biological response to stress is divided into 6 levels of condition, represented as changes in biological structure (abundance and diversity of pollution sensitive versus tolerant taxa) and function. We developed benthic macroinvertebrate (BMI) and algal BCG models for California perennial wadeable streams to support interpretation of percentiles of reference-based thresholds for bioassessment indices (i.e., the California Stream Condition Index [CSCI] for BMI and the Algal Stream Condition Index [ASCI] for diatoms and soft-bodied algae). Two panels (one of BMI ecologists and the other of algal ecologists) each calibrated a general BCG model to California wadeable streams by first assigning taxa to specific tolerance and sensitivity attributes, and then independently assigning test samples (264 BMI and 248 algae samples) to BCG Levels 1–6. Consensus on the assignments was developed within each assemblage panel using a modified Delphi method. Panels then developed detailed narratives of changes in BMI and algal taxa that correspond to the 6 BCG levels. Consensus among experts was high, with 81% and 82% expert agreement within 0.5 units of assigned BCG level for BMIs and algae, respectively. According to both BCG models, the 10th percentiles index scores at reference sites corresponded to a BCG Level 3, suggesting that this type of threshold would protect against moderate changes in structure and function while allowing loss of some sensitive taxa. The BCG provides a framework to interpret changes in aquatic biological condition along a gradient of stress. The resulting relationship between index scores and BCG levels and narratives can help decision-makers select thresholds and communicate how these values protect aquatic life use goals

Morphological variation of the Caloneis schumanniana species complex (bacillariophyceae) from different environmental conditions in North American streams

Morphological variations of the Caloneis schumanniana (Grunow) Cleve species complex were studied using multivariate analysis. Populations of three species, synonymized in the literature, i.e., C. schumanniana, Caloneis limosa (Kützing) Patrick and Caloneis lewisii Patrick, were analyzed. Their morphological and ecological characteristics were evaluated and outlined for the sampled streams by US EPA\u27s Western Environmental Monitoring and Assessment Program. Geographic separation among the three taxa was not resolved. This study showed that C. schumanniana has wider ecological tolerance than C. limosa and C. lewisii. Despite the ecological overlap, specific ecological preferences of C. limosa and C. lewisii were described

The potential indicator value of rare taxa richness in diatom-based stream bioassessment

Despite their recognized contribution to species richness, the importance of rare taxa richness in bioassessment is unclear. This study aimed to characterize the environmental factors affecting the number of rare diatom taxa in western U.S. streams and rivers, and to evaluate whether this number can be used to differentiate streams with contrasting human disturbance. Three different categories of rare taxa were used: satellite (taxa with low occurrence and low abundance), rural (taxa with high occurrence and low abundance), and urban (taxa with low occurrence and high abundance). Common taxa were included as a separate category of core taxa (taxa with high occurrence and high abundance). We analyzed 987 diatom samples collected over the period of 5years (2000-2004) for the U.S. Environmental Protection Agency\u27s (EPA) Western Environmental Monitoring and Assessment Program (WEMAP). The results showed that rural taxa richness (number of rural taxa per site) increased along a longitudinal gradient from mountainous, fast-flowing oligotrophic streams with fewer fine substrates to large, slow-moving, nutrient-rich rivers with abundance of fine substrates. Rural taxa richness was the only rarity metric that distinguished least disturbed (reference) sites from the most disturbed (impacted) sites, but it was significantly different only in the mountains ecoregion. Core taxa richness distinguished reference from impacted sites in the West and in each one of the three ecoregions (mountains, plains, and xeric). Our findings revealed that rural taxa richness can be used as an indicator of human disturbance in streams/rivers, especially in the mountains ecoregion, and that rarity definition is important in bioassessment

Revealing hidden diversity in the sheathia arcuata morphospecies (Batrachospermales, rhodophyta) including four new species

© 2020 The Korean Society of Phycology. The freshwater red algal genus Sheathia contains species with heterocortication (both bulbous and cylindrical cells covering the main axis) and homocortication (only cylindrical cells). When the genus was proposed, the species with heterocortication were revised, but all specimens with homocortication were assigned to Sheathia arcuata with the caveat that it may represent a species complex. Recent studies have described new species with homocortication and S. arcuata has been rendered paraphyletic. In the current study, new sequences of the rbcL and 5′ region of the cytochrome c oxidase subunit I markers were combined with previously published data to construct a robust phylogeny and circum-scribe new species. Four new species, S. abscondita, S. californica, S. plantuloides, and S. transpacifica are proposed. Examination of morphological characters among homocorticate species show no diagnostic characters to distinguish among species, whereas S. plantuloides is only known from sporophytes (chantransia) so it lacks the typical morphological characters derived from the gametophytes for comparison. Although DNA sequence data would be needed to make a positive species identification, geography could be employed to narrow the identification to one or two species. The genus is geographically widespread having been recorded from oceanic islands and five continents, whereas the individual species typically occur on a single continent. With this study, the number of species recognized in Sheathia is raised to 17; seven heterocorticate and 10 homocorticate, making this genus one of the most species rich in the Ba-trachospermales. As well, the resulting phylogeny provides insights into the evolution of heterocortication in Sheathia

Characterizing Benthic Macroinvertebrate and Algal Biological Condition Gradient Models for California Wadeable Streams, USA

The Biological Condition Gradient (BCG) is a conceptual model that describes changes in aquatic communities under increasing levels of anthropogenic stress. The BCG helps decision-makers connect narrative water quality goals (e.g., maintenance of natural structure and function) to quantitative measures of ecological condition by linking index thresholds based on statistical distributions (e.g., percentiles of reference distributions) to expert descriptions of changes in biological condition along disturbance gradients. As a result, the BCG may be more meaningful to managers and the public than indices alone. To develop a BCG model, biological response to stress is divided into 6 levels of condition, represented as changes in biological structure (abundance and diversity of pollution sensitive versus tolerant taxa) and function. We developed benthic macroinvertebrate (BMI) and algal BCG models for California perennial wadeable streams to support interpretation of percentiles of reference-based thresholds for bioassessment indices (i.e., the California Stream Condition Index [CSCI] for BMI and the Algal Stream Condition Index [ASCI] for diatoms and soft-bodied algae). Two panels (one of BMI ecologists and the other of algal ecologists) each calibrated a general BCG model to California wadeable streams by first assigning taxa to specific tolerance and sensitivity attributes, and then independently assigning test samples (264 BMI and 248 algae samples) to BCG Levels 1–6. Consensus on the assignments was developed within each assemblage panel using a modified Delphi method. Panels then developed detailed narratives of changes in BMI and algal taxa that correspond to the 6 BCG levels. Consensus among experts was high, with 81% and 82% expert agreement within 0.5 units of assigned BCG level for BMIs and algae, respectively. According to both BCG models, the 10th percentiles index scores at reference sites corresponded to a BCG Level 3, suggesting that this type of threshold would protect against moderate changes in structure and function while allowing loss of some sensitive taxa. The BCG provides a framework to interpret changes in aquatic biological condition along a gradient of stress. The resulting relationship between index scores and BCG levels and narratives can help decision-makers select thresholds and communicate how these values protect aquatic life use goals

Overlooked and widespread pennate diatom-diazotroph symbioses in the sea.

Persistent nitrogen depletion in sunlit open ocean waters provides a favorable ecological niche for nitrogen-fixing (diazotrophic) cyanobacteria, some of which associate symbiotically with eukaryotic algae. All known marine examples of these symbioses have involved either centric diatom or haptophyte hosts. We report here the discovery and characterization of two distinct marine pennate diatom-diazotroph symbioses, which until now had only been observed in freshwater environments. Rhopalodiaceae diatoms Epithemia pelagica sp. nov. and Epithemia catenata sp. nov. were isolated repeatedly from the subtropical North Pacific Ocean, and analysis of sequence libraries reveals a global distribution. These symbioses likely escaped attention because the endosymbionts lack fluorescent photopigments, have nifH gene sequences similar to those of free-living unicellular cyanobacteria, and are lost in nitrogen-replete medium. Marine Rhopalodiaceae-diazotroph symbioses are a previously overlooked but widespread source of bioavailable nitrogen in marine habitats and provide new, easily cultured model organisms for the study of organelle evolution