Description: Dispersal connects patches within metapopulations and is crucial to the persistence of many species, particularly those living in discontinuous habitat. Rock pools are excellent habitats in which to study dispersal in time as well as space, because many of the organisms that live within them make resistant long-lived dormant stages, they are often abundant, and they are easy to sample. The rock pools on Appledore Island, Gulf of Maine, USA, are home to several cladocerans, including Moina macrocopa and Daphnia pulex  ×  pulicaria hybrids. Both taxa exist in extremely high abundances in some pools and make diapausing eggs enclosed in ephippia that are dispersed in time by hatching long after they are produced, and are also known to spatially disperse via pool overflows and by adhering to gulls. I hypothesized that ephippia of both taxa would also be spatially dispersed by wind. I found that while Moina are present in more pools, more abundant in those pools, and produce more ephippia, many more Daphnia ephippia dispersed into traps placed around the island. This may be explained, in part, by differences in the buoyancy of ephippia between the two species. A higher propensity to disperse may result in Daphnia relying more heavily on the spatial context of rock pools than Moina.

Description: The resting stages of freshwater zooplankton constitute a special mechanism for passive dispersal, often displaying a variety of adaptations so as to ease transport. In floodplain systems, macrophytes are one of the most representative biotic groups showing interactions with the zooplankton community. The annual fluctuations in the hydrometric level of the Paraná River favour the displacement of this aquatic vegetation in floodplain environments. This paper hypothesizes that the roots and submerged portions of different macrophytes contain zooplankton resting stages which are able to hatch when environmental conditions are favourable. In turn, this contributes to the dispersal of zooplankton by plants when they are displaced by the flood pulse. Six macrophyte species were sampled ( Eichhornia crassipes , Azolla filiculoides , Limnobium spongia , Pistia stratiotes , Eichhornia azurea and Nymphoides indica) from lakes within the Paraná River floodplain. Roots and submerged portions of vegetation were stored (90 days) at 4 °C then incubated at 25 °C for 90 days. Hatchling emergence was recorded at 2-day intervals during this period. In total, 70 zooplankton taxa were recorded in all macrophyte samples; rotifers were the most representative group (69%) followed by cladocerans (28%) and copepods (3%). The roots and submerged parts of aquatic vegetation house viable zooplankton resting stages. This phenomenon allows the dispersal of resting stages and therefore colonization of new habitats during the displacement of macrophyte species.

Description: Overabundant growth of emergent lacustrine plants can cause biodiversity, ecosystem service and economic loss. The two-basined Wuchang Lake is a typical small shallow lake within the Yangtze River floodplain. Expansion of the emergent macrophyte Zizania latifolia at Wuchang Lower Lake (to 49 km 2 in area, c. 87.0% of Lower Lake) has increasingly denied the local community open water for fishing since the 1980s. To better understand the causes of these changes and potential remediation, we used annual Landsat imagery from 1975 to 2012 to determine the patterns of expansion between years as well as the effects of water levels in different seasons and trophic status on the annual extent of macrophytes in the Lower Lake. These analyses showed that: (1) Z. latifolia progressively covered the Lower Lake, while remaining confined to one inlet in the Upper Lake; (2) despite the generally increasing trend, there were obvious annual variations in area of Z. latifolia ; (3) variation of water level in spring contributed to between-year variation in area and was significantly negatively correlated with expansion in Z. latifolia . Based on these results, to reduce the expansion in Z. latifolia , we recommend maintaining spring Lower Lake water levels above at least at 11.6 m and better at 12 m, cutting shoots in June and July, with subsequent shoot removal in autumn.

Description: Although diatoms are important bioindicators of ecological quality, their ecological traits are still not well understood. A major issue is that of substrate preferences, which may result in differences in production, and assemblage structure and composition, and which should therefore be taken into account for ecological quality assessment studies. Thus, in this work, the periphyton grown on sand and ceramic tiles in indoor controlled channels were compared to understand whether substrate differences lead to differences in: periphyton production (chlorophyll- a ), chlorophyll- b and c concentrations, diatom assemblages (diversity-Shannon-Wiener, cell density, taxonomic composition, trait proportions), and ecological quality assessments (IPS-‘ Indice de Polluosensibilité Spécifique ’). A combined inoculum of periphyton from four Portuguese streams was introduced to the running channels (six sand and six tile) and left to colonize for 35 days. Epilithic (tiles) and epipsammic (sand) assemblages were sampled at days 14 and 35. We verified that there were no differences in chlorophyll- a concentration over time and between substrates. On both sampling occasions, the epipsammic assemblages had higher concentration of chlorophyll- c and diatom density but without significant differences over time in each substrate. The taxonomic composition was different between substrates and over time. However, these differences were not reflected in ecological quality assessment. The diversity was also similar between substrates in both sampling occasions, but it was higher at day 14. Mobile and stalked species were more abundant over the entire study and differed significantly between substrates, with the epipsammic assemblages presenting higher abundances of both traits. We concluded that the colonizing substrate influences diatom assemblages but not the ecological quality assessment.

Description: To restore deteriorated lake ecosystems, it is important to identify environmental factors that influence submerged macrophyte communities. While sediment is a critical environmental factor for submerged macrophytes and many studies have examined effects of sediment type on the growth of individual submerged macrophytes, very few have tested how sediment type affects the growth and species composition of submerged macrophyte communities. We constructed submerged macrophyte communities containing four co-occurring submerged macrophytes ( Hydrilla verticillata , Myriophyllum spicatum , Ceratophyllum demersum and Chara fragilis ) and subjected them to three sediment treatments, i.e., clay, a mixture of clay and quartz sand at a volume ratio of 1:1 and a mixture at a volume ratio of 1:4. Compared to the clay, the 1:1 mixture treatment greatly increased overall biomass, number of shoot nodes and shoot length of the community, but decreased its diversity. This was because it substantially promoted the growth of H. verticillata within the community, making it the most abundant species in the mixture sediment, but decreased that of M. spicatum and C. demersum . The sediment type had no significant effects on the growth of C. fragilis . As a primary nutrient source for plant growth, sediment type can have differential effects on various submerged macrophyte species and 1:1 mixture treatment could enhance the performance of the communities, increasing the overall biomass, number of shoot nodes and shoot length by 39.03%, 150.13% and 9.94%, respectively, compared to the clay treatment. Thus, measures should be taken to mediate the sediment condition to restore submerged macrophyte communities with different dominant species.

Description: Vegetated habitats provide numerous benefits to nekton, including structural refuge from predators and food sources. However, the sensory mechanisms by which fishes locate these habitats remain unclear for many species, especially when environmental conditions (such as increased turbidity) are unfavorable for visual identification of habitats. Here, a series of laboratory experiments test whether three species of adult fish (golden topminnow Fundulus chrysotus Günther 1866, sailfin molly Poecilia latipinna Lesueur 1821, and western mosquitofish Gambusia affinis Baird and Girard 1853) use plant chemical cues to orient to one of two habitats [hydrilla Hydrilla verticillata (L.f.) Royle or water hyacinth Eichhornia crassipes (Mart.) Solms]. First, experiments in aquaria were conducted offering fish a choice of the two habitats to determine preference patterns. Next, a two-channel flume, with each side containing flow originating in one of the two habitats, was used to determine whether preferences were still exhibited when fish could only detect habitats through olfactory means. While patterns among the three fish species tested here were variable, results did indicate consistent habitat preferences despite the lack of cues other than olfactory, suggesting that these organisms are capable of discriminating habitats via chemical exudates from plants. As such, olfactory mechanisms likely provide vital information about the surrounding environment and future work should be directed at determining how anthropogenic inputs such as eutrophication and sediment runoff affect the physiology of these sensory capabilities.

Description: The Frasassi cave system in central Italy hosts one of the few known examples of a groundwater metazoan community that is supported by sulfur-based lithoautotrophic microbes. Despite the challenging conditions represented by high concentrations of H 2 S and low concentrations of O 2 , this cave system is home to many invertebrate species. Here, we analyzed the copepods inhabiting sulfidic lakes and non-sulfidic dripping pools in order to investigate how environmental conditions in sulfidic waters regulate the spatial distribution of the cave microcrustacean community over time. We also sampled copepod assemblages of sulfidic lakes under conditions of both high and low H 2 S concentration. Cluster analysis and canonical correspondence analysis separated the copepod assemblages inhabiting dripping pools from those of sulfidic lakes. H 2 S concentration, pH and O 2 concentration were identified as the main factors regulating community structure. These results indicate that the distribution of groundwater copepods within the cave system is ecologically and spatially structured. Sulfidic lakes showed lower Simpson dominance, higher Shannon diversity and higher Pielou equitability at higher H 2 S concentrations. The complex community structure of the copepods of the Frasassi cave system suggests that a chemosynthetically produced food source facilitated the colonization of stygobionts in sulfidic groundwater due to their tolerance to the environmental conditions.

Description: The toxicity of a harmful algal bloom is strongly determined by the relative abundance of non-toxic and toxic genotypes and might therefore be regulated by competition for growth-limiting resources. Here, we studied how the toxic Microcystis aeruginosa strain PCC 7806 and a non-toxic mutant compete for nitrogen and phosphorus under constant and pulsed nutrient supply. Our monoculture and competition experiments show that these closely related genotypes have distinct nutrient physiologies and that they differ in their ability to compete for nitrogen and phosphorus. The toxic wild type won the competition under nitrogen limitation, while the non-toxic mutant dominated under phosphorus limitation. Pulses of both nitrogen and phosphorus increased the dominance of the toxic genotype, which lead to an even faster competitive exclusion of the non-toxic genotype under nitrogen pulses and to coexistence of both genotypes under phosphorus pulses. Our findings indicate that the genotype level dynamics driven by resource competition can be an important factor in determining cyanobacterial bloom toxicity.

Description: Principal response curves analysis (PRC) is widely applied to experimental multivariate longitudinal data for the study of time-dependent treatment effects on the multiple outcomes or response variables (RVs). Often, not all of the RVs included in such a study are affected by the treatment and RV-selection can be used to identify those RVs and so give a better estimate of the principal response. We propose four backward selection approaches, based on permutation testing, that differ in whether coefficient size is used or not in ranking the RVs. These methods are expected to give a more robust result than the use of a straightforward cut-off value for coefficient size. Performance of all methods is demonstrated in a simulation study using realistic data. The permutation testing approach that uses information on coefficient size of RVs speeds up the algorithm without affecting its performance. This most successful permutation testing approach removes roughly 95 % of the RVs that are unaffected by the treatment irrespective of the characteristics of the data set and, in the simulations, correctly identifies up to 97 % of RVs affected by the treatment.