The natural flow regime of many rivers in the USA has been impacted by anthropogenic structures. This loss of connectivity plays a role in shaping river ecosystems by altering physical habitat characteristics and shaping fish assemblages. Although the impacts of large dams on river systems are well documented, studies on the effects of low‐head dams using a functional guild approach have been fewer. We assessed river habitat quality and fish community structure at 12 sites on two rivers; the study sites included two sites below each dam, two sites in the pool above each dam and two sites upstream of the pool extent. Fish communities were sampled from 2012 to 2015 using a multi‐gear approach in spring and fall seasons. We aggregated fishes into habitat and reproductive guilds in order to ascertain dams' effects on groups of fishes that respond similarly to environmental variation. We found that habitat quality was significantly poorer in the artificial pools created above the dams than all other sampling sites. Fast riffle specialist taxa were most abundant in high‐quality riffle habitats farthest from the dams, while fast generalists and pelagophils were largely restricted to areas below the downstream‐most impoundment. Overall, these dams play a substantial role in shaping habitat, which impacts fish community composition on a functional level. Utilizing this functional approach enables us to mechanistically link the effects of impoundments to the structure of fish communities and form generalizations that can be applied to other systems. Copyright © 2017 John Wiley & Sons, Ltd.

Summary Knowledge of the effects of environment and genotype on behavior during early ontogenetic stages of many fish species including lake sturgeon (Acipenser fulvescens) is generally lacking. Understanding these effects is particularly important at a time when human activities are fundamentally altering habitats and seasonal and diel physical and biotic stream features. Artificial stream channels were used in a controlled experiment to quantify lake sturgeon yolk‐sac larvae dispersal distance and stream substrate preference from different females (N = 2) whose eggs were incubated at different temperatures (10 and 18°C) that simulated stream conditions during early and late spawning and incubation periods in the Black River, Michigan. Data revealed that yolk‐sac larvae exhibited considerable variability in dispersal distance as a function of family (genotype), temperature experienced during previous (embryonic) ontogenetic stages, and environmental ‘grain’. Yolk‐sac larvae dispersal distance varied as a function of the juxtaposition of substrate to location of egg hatch. Lake sturgeon yolk‐sac larvae dispersed from mesh screens attached to bricks and settled exclusively in gravel substrate. Dispersal distance also varied as a function of family and egg incubation temperatures, reflecting differences in offspring body size and levels of endogenous yolk reserves (yolk sac area) at hatch. Expression of plasticity in dispersal behavior may be particularly important to individual survival and population levels of recruitment contingent upon the location, size, and degree of fragmentation of suitable (gravel) habitats between adult spawning and yolk‐sac larvae rearing areas.

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Impoundments are common features of many rivers that often impact abiotic conditions and the organisms that inhabit impacted reaches. As dams alter both local environmental conditions and the ability of organisms to move throughout the habitat, it is difficult to know which factors are driving changes in assemblage composition. To separate these effects, we employed a metacommunity approach to evaluate drivers of assemblage composition in fish and macroinvertebrate communities across two impoundments slated for removal in Danville, Illinois. Based on movement ability, we would expect dams to represent barriers to fish populations, whereas macroinvertebrates, with their motile adult phases, should be easily able to move across impoundments. Therefore, we would expect the assemblage structure of these two groups to be driven by different processes. We sampled habitat quality (measures) and both fish and macroinvertebrate communities in a replicated series of sites across two low‐head dams. As expected, the presence of dams resulted in reduced habitat quality as well as changes in fish and macroinvertebrate quality indices. However, fish and macroinvertebrate assemblages were driven by different metacommunity processes. Fish communities showed strong environmental filtering, responding to local environmental conditions, with no effect of distance between habitats. In marked contrast, macroinvertebrate communities were only related to physical distance between sites, with no indication of environmental filtering. These results suggest that when these dams are removed, fish assemblages should change with the removal of dam‐generated habitats. In contrast, dam removal may not alter macroinvertebrate composition, as it did not vary with habitat but appears driven by local dispersal.Received November 17, 2015; accepted July 17, 2016 Published online October 28, 2016

Blue Carbon ecosystems such as mangroves, saltmarshes and seagrasses have been shown to sequester large amounts of carbon, and subsequently are receiving renewed interest from policy experts in light of climate change. Globally, seagrasses remain the most understudied of these ecosystems, with their total geographic extent largely unknown due to challenges in mapping dynamic coastal environments. As such, species distribution models (SDMs) have been used to identify areas of high suitability, in order to inform our understanding of where unmapped meadows may be located or to identify suitable sites for restoration and/or enhancement efforts. However, many SDMs parameterized to project seagrass distributions focus on physical and not anthropogenic variables (i.e., dredging, aquaculture), which can have negative impacts on seagrass meadows. Here we used verified datasets to identify the potential distribution of Zostera marina and Zostera noltei at a national level for the Republic of Ireland, using 19 environmental variables including both physical and anthropogenic. Using the Maximum Entropy method for developing the SDM, we estimated approximately 95 km2 of suitable habitat for Z. marina and 70 km2 for Z. noltei nationally with high accuracy metrics, including Area Under the Curve (AUC) values of 0.939 and 0.931, respectively for the two species. We found that bathymetry, maximum sea-surface temperature (SST) and minimum salinity were the most important environmental variables that explained the distribution of Z. marina and that high standard deviation of SST, mean SST and maximum salinity were the most important variables in explaining the distribution of Z. noltei. At a national level, we noted that it was primarily physical variables that determined the geographic distribution of seagrass, not anthropogenic variables. We unexpectedly modelled areas of high suitability in locations of anthropogenic disturbance (i.e., dredging, high pollution risk), although this may be due to the binary nature of SDMs capturing presence-absence and not the size and condition of the meadows, suggesting a need for future research to explore the finer scale impacts of anthropogenic activity. Subsequently, this research should foster discussion for researchers and practitioners working on sustainability projects related to Blue Carbon.