Do beds of subtidal estuarine seagrass constitute a refuge for macrobenthic biodiversity threatened intertidally?

Biodiversity differentials between macrobenthic assemblages associated with adjacent intertidal and subtidal areas of a single seagrass system were investigated for the first time. Assemblage metrics of conservation relevance—faunal abundance and its patchiness, faunal richness, and beta diversity—were examined at four contrasting dwarf-eelgrass localities in the Knysna estuarine bay, part of South Africa's Garden Route National Park but a system whose intertidal areas are heavily impacted anthropogenically. Faunal assemblages were significantly different across all localities and between subtidal and intertidal levels at each locality although their taxonomic distinctness was effectively constant. Although, as would be expected, there were clear trends for increases in overall numbers of species towards the mouth at all levels, few generalities relating to the relative importance of the subtidal seagrass habitat were evident across the whole system—magnitude and direction of differentials were contingent on locality. Shore-height related differences in assemblage metrics were minor in the estuarine and lagoonal zones but major in the marine compartment, although the much greater subtidal faunal abundance there was largely consequent on the superabundance of a single species (the microgastropod Alaba pinnae), intertidal zones then displaying the greater species diversity due to greater equitability of species densities. Along its axial channel, the Knysna subtidal seagrass does not support richer versions of the intertidal polychaete-dominated assemblages fringing it; instead, it supports different and more patchily dispersed gastropod-dominated ones. At Knysna at least, the subtidal hardly constitutes a reservoir of the seagrass biodiversity present intertidally.

Advances in Understanding Landscape Influences on Freshwater Habitats and Biological Assemblages

<i>Abstract.</i>—Anthropogenic activities including urbanization, agriculture, and dams degrade stream habitats and are a dominant reason for global biodiversity declines in fluvial fish assemblages. Declining diversity trends have been well documented in many regions of the world; however, fishes vary regionally in response to anthropogenic land use, resulting from complex relationships between landscape variables and mechanisms controlling stream fish assemblages. To test for differences in regional fish response to anthropogenic land use, we conducted our study across five freshwater ecoregions in the temperate mesic portion of the United States and evaluated data characterizing stream fish assemblages from 10,522 locations across all study freshwater ecoregions. Fishes were summarized by metrics describing assemblage structure, trophic groupings of species, levels of tolerance to anthropogenic stressors, and life history characteristics, with seven metrics used for analyses. Natural and anthropogenic landscape variables were assessed across freshwater ecoregions, and we tested for regionally specific influences of percent catchment urbanization, percent catchment agriculture, and catchment densities of dams and stream-road crossings on stream fishes. We used cascade multivariate regression trees to quantify variance explained in fish metrics by these landscape variables after controlling for influences of natural landscape variables, including catchment area, catchment lithology, and elevation of study sites. Results indicated differences in dominant influences by freshwater ecoregion, as well as differences in the levels of anthropogenic land use influencing fishes within and across freshwater ecoregions. For example, urban land use was the most influential anthropogenic land use in both Appalachian Piedmont and Chesapeake Bay freshwater ecoregions, with fish assemblage metrics showing responses at 10% and 1% catchment urban land use, respectively. In contrast, dam density in the network catchment was the most influential anthropogenic variable on fish assemblage metrics in both the Laurentian Great Lakes and Middle Missouri freshwater ecoregions. Also, large amounts of agriculture in the catchment was the most influential anthropogenic land use on fish assemblage metrics in the Upper Mississippi freshwater ecoregion. Knowledge of regional differences in the top contributing anthropogenic landscape variables and the levels at which fish assemblages respond to these variables lends insight into mechanisms controlling stream fish assemblages by freshwater ecoregions and can aid in development of region-specific conservation strategies to prevent biodiversity loss from current and future anthropogenic land use.

Ecological assessment of East Hammar marsh, Iraq using a number of ecological guides

The ecological status of the East Hammar marsh was evaluated by using a number of ecological guides: water quality index (WQI), Carlson trophic state index (TSI) and fish integrated biological index (F-IBI) during the period from November 2012 to October 2013. The results revealed that the annual value of WQI varied from 51.1 (marginal) for historical data before desiccation to 67.8 (fair) for data after inundation. The marsh was evaluated to be mesotrophic (TSI= 42.0). IBI scores were calculated from 16 separate assemblage metrics based on the fish species richness, species composition and trophic guilds. The ecological status of the marsh was found to be fair (F-IBI= 47.7) and was slightly better than the status of the marsh after 2-4 years of restoration activities. The rather low improvement in the situation of the marsh indicates that the environment is still fragile and requires the allocation of water share from the Tigris and Euphrates rivers to restore marsh normality.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—At broad scales, the types and intensities of human disturbances to ecosystems vary along natural gradients. Biological assemblages also vary with natural and human disturbance gradients. We defined least-disturbed conditions for a set of water chemistry, catchment, and site-scale indicators of disturbance, for 835 Environmental Monitoring and Assessment Program sites in the Mountains, Xeric, and Plains regions of 12 conterminous western United States. For each disturbance indicator, the definition of least-disturbed was adjusted by the sites’ locations on the primary natural gradients. For example, the least-disturbed condition for phosphorus in eastern Plains streams allowed up to 100 µg/L total phosphorus, while in western Plains streams, less than 30 µg/L total phosphorus was required. Sites were scored by the number of times they met the least-disturbed condition for all disturbance indicators. We also applied this process to score for most-disturbed condition. The importance of disturbance types varied regionally and along natural gradients. For example, catchment-scale disturbance measures did not distinguish between least- and most-disturbed sites for small streams at higher elevations, but were important for larger streams and at lower elevations. We examined regional-scale patterns in aquatic vertebrate species and assemblage metrics, and macrobenthos assemblage metrics at least- and most-disturbed sites. Most-disturbed sites in the Mountains and Xeric regions had higher proportions of nonnative and tolerant vertebrates and noninsect macrobenthos, and lower proportions of Ephemeroptera, Plecoptera, and Trichoptera individuals and taxa than did the least-disturbed sites. The Plains region has been extensively used by humans and showed less contrast between disturbance classes for most of these measures.

Landscape Influences on Stream Habitats and Biological Assemblages

<em>Abstract.</em>—We analyzed data from 38 sites on 31 large rivers in Wisconsin to characterize the influence of environmental variables at the basin, reach, and site scales on fish assemblages. Electrofishing and site habitat data were collected for a distance of 1.6 km per site. Environmental variables included conductivity, substrate, and fish cover at the site scale; distance to impoundments, dams, and length of riverine habitat at the reach scale; and land cover, climate, and geology at the basin scale. Of the 77 fish species found, 39 occurred in more than 10% of the sites and were retained for analyses of fish abundance and biomass. Redundancy analysis (RDA) was used to relate species abundance, biomass, and 16 assemblage metrics to environmental variables at the three spatial scales. The site and basin scales defined fishes along a gradient from high conductivity, fine substrate, and agricultural land cover to low conductivity, rocky substrate, and forested land cover. For abundance and biomass, the strongest assemblage pattern contrasted northern hog sucker <em>Hypentelium nigricans</em>, blackside darter <em>Percina maculata</em>, and logperch <em>P. caprodes </em>with common carp <em>Cyprinus carpio</em>, channel catfish <em>Ictalurus punctatus</em>, and sauger <em>Sander canadensis</em>. The <em>H. nigricans </em>group, along with high values of index of biotic integrity and some assemblage metrics (percent lithophilic spawners, percent round-bodied suckers), corresponded with the forested end of the ecological gradient, whereas the <em>C. carpio </em>group and percent anomalies corresponded with the agricultural end. Natural environmental conditions, including bedrock geology type, bedrock depth, surficial geology texture, basin area, and precipitation, also influenced the fish assemblage. Partial RDA procedures partitioned the explained variation among spatial scales and their interactions. We found that widespread land cover alterations at the basin scale were most strongly related to fish assemblages across our study area. Understanding the influence of environmental variables among multiple spatial scales on fish assemblages can improve our ability to assess the ecological condition of large river systems and subsequently target the appropriate scale for management or restoration efforts.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—Data collected as part of two studies to examine the influences of landscape modification on the ecology of three coastal Southern California river systems—the Calleguas Creek, Malibu Creek, and Santa Clara River watersheds—provided the opportunity to examine relations between urbanization and fish assemblages in Southern California coastal streams. Fish were collected at 63 sites from 1999 to 2001. Watershed land use was determined and classified into three land use types: agriculture, developed, and open space. Seven fish assemblage metrics were examined, including species richness, number of native and alien species, total fish abundance, percent abundance of native and alien species, and percent abundance of arroyo chub <em>Gila orcuttii</em>. Ten fish species were collected, and arroyo chub was the only species collected in all three watersheds. Native species included arroyo chub, threespine stickleback <em>Gasterosteus aculeatus</em>, steelhead <em>Oncorhynchus mykiss</em>, and Pacific staghorn sculpin <em>Leptocottus armatus</em>. There were no significant differences in fish assemblage metrics among the three land-use types. Both wetted stream width and depth were significantly related to native fish abundance. Results from this study suggest that the relatively species poor fish assemblages of Southern California may not be sensitive to watershed land use disturbance, but may be sensitive to local hydrologic conditions.