Emergence patterns and microhabitat preference of aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) on a longitudinal gradient of barrage lake system

Aquatic dance flies (Empididae; Clinocerinae and Hemerodromiinae) are important components of freshwater assemblages, especially in running waters. They are predators as larvae and adults and thus essential for understanding aquatic food webs. This study was conducted in Plitvice lakes National Park (Croatia) representing a wide variety of freshwater habitats (springs, streams, lakes and tufa barriers). Adults were collected monthly from March 2007 until March 2009 using pyramid-type emergence traps at 13 locations. A total of 3865 specimens comprising 18 species were collected. The dominant genus was Chelifera, while the most abundant species was Hemerodromia unilineata. All species were univoltine except Chelifera precabunda, Chelifera pyrenaica and Chelifera stigmatica that were bivoltine. Considerable differences in composition and structure of aquatic dance flies assemblages were recorded along a longitudinal gradient of studied sites, primarily related to differences in physical and chemical parameters of water. Water temperature was the main factor influencing the timing of emergence. Hemerodromia species preferred variable water temperature throughout the year while the majority of the Chelifera species preferred stable water temperature characteristic of spring sites. Furthermore, discharge affected assemblage composition of aquatic dance flies. The highest abundance of aquatic dance flies was recorded in lotic habitats with fast water current over substrates of moss, gravel and particulate tufa with detritus. These results give a new insight on microhabitat preference and their distribution on unique karstic habitats.     

The impact of dredge-fill on Posidonia oceanica seagrass meadows: regression and patterns of recovery

Posidonia oceanica meadows can be severely damaged by dredge-fill operations. We report on the construction of gas pipelines that occurred between 1981 and 1993 in SW Sicily, Italy. A large portion of the meadow was mechanically removed, and the excavated trench was filled with a mosaic of substrates, ranging from sand to consolidated rock debris. Meadow loss and recovery were quantified over 7 years after the end of operations. We recorded an overall loss of 81.20 ha of meadow. Substrate strongly affected recovery as the percent cover by P. oceanica consistently increased on calcareous rubble, reaching values of 44.37 ± 3.05% in shallow sites after 7 years, whereas no significant increase occurred on other substrates. As in the Mediterranean Sea exploitation of coastal areas continues to grow with consequent impacts on P. oceanica meadows, this case study illustrates how artificial rubble-like materials could be employed to support the restoration of damaged meadows.     

Long-time emergence patterns of Limnophora species (Diptera,Muscidae) in specific karst habitats: tufa barriers

The hunter-fly genus Limnophora (Muscidae: Coenosiinae) is an important component of running water assemblages. Both adults and larvae are predators, the adults mostly feeding on blackflies (Simuliidae) and other small aquatic insects. This study was conducted at two tufa barriers in Plitvice Lakes National Park (NP) (tufa barrier Labudovac and tufa barrier Kozjak-Milanovac) and at two tufa barriers in Krka National Park (NP) (tufa barrier Roški slap and tufa barrier Skradinski buk). Adults were collected monthly from February 2007 until December 2013 at Plitvice Lakes NP and from September 2013 to October 2014 at Krka NP, using pyramid-type emergence traps. Over the 7-year study period at the Plitvice Lakes tufa barriers, a total of 193 specimens belonging to 6 species were collected, while during the 1-year study period at the Krka tufa barriers a total of 848 specimens belonging to 4 species were collected. Abundance of Limnophora specimens at the Krka NP sites was up to 30 times higher than at the Plitvice Lakes NP sites, which could be attributed to higher levels of potential food and higher water temperatures. The dominant species at the Plitvice Lakes sites were Limnophora pulchriceps and Limnophora riparia. At the Krka tufa barriers, the dominant species at site Roški slap was Limnophora croatica and at site Skradinski buk Limnophora riparia. The highest numbers of emerging specimens at all sites were present in the summer months. At the Plitvice Lakes sites most species were univoltine or bivoltine, while at the Krka sites most species were multivoltine. Water temperature was the main factor influencing the timing of emergence and the duration of the flight period. The highest abundance of Limnophora species was recorded over moss substrate. A significant positive correlation emerged between the numbers of emerging prey and the numbers of emerging specimens of Limnophora. These results give a new insight into the microhabitat preferences and prey-predator relationships of Limnophora.     

Differential survival of coral transplants on various substrates under elevated water temperatures

Closely related scleractinian coral species that exhibited similar survival patterns under relatively normal field conditions responded very differently to the occurrence of an environmental disturbance. The two species studied were Porites cylindrica and Porites rus which occur in the same reef zones in shallow reef flats. Transplants of both species were evenly distributed and attached to three different types of substrate: live coral colonies of P. cylindrica, dead coral colonies (also of P. cylindrica), and epoxy coated metal grids that were raised above the sandy substrate. With the onset of above-normal water temperatures due to the El Ni?o episode of 1998, P. cylindrica transplants immediately showed signs of bleaching stress and tissue necrosis, followed by algal overgrowth and mortality soon afterwards. In contrast, transplants of P. rus bleached more slowly and suffered less mortality, with a few actually showing signs of recovery at the end of the experimental period which covered a total of 14 weeks. These differences in responses could be attributed to properties of the symbiotic zooxanthellae, of the host coral tissue itself, or both. Over-all, survival was good on the metal grids (average of 35%), and on the live coral (average of 22%). It was poor on the dead coral (average of 6%). The metal grids as well as live coral tissue apparently provided a favorable substrate for the attached coral fragments, even for those of a different species. Under the conditions of this particular study, attachment of live coral fragments on already dead colonies for the purpose of increasing live coral cover on the reef did not yield favorable results. This is an area that requires further investigation.     

Plant Species Mediate Rhizosphere Microbial Activity and Biodegradation Dynamics in a Riparian Soil Treated with Bensulfuron‐methyl

A pot experiment was conducted to investigate microbial characteristics and the biodegradation process of bensulfuron‐methyl (BSM) in a rhizosphere soils planted with different riparian plants. The results showed that microbial population decreased with BSM addition in the rhizosphere, especially for bacteria and fungi. The activities of the dehydrogenase (DHase) were stimulated firstly, due to BSM addition, but then were inhibited, and recovered to the initial level, while the activities of the phosphatase and urease showed obviously decreasing trend throughout the whole experiment. Rhizosphere soil substrate‐induced respiration (SIR) was depressed by BSM, especially at the initial 14 days of incubation. Compared to Zizania aquatica and Phragmites australis, Acorus calamus showed a significantly (p < 0.05) higher DHase activity and larger SIR in the rhizosphere soils treated with BSM, which means that A. calamus can effectively alleviate inhibitory effect of the sulfonylurea herbicide addition on microbial activity. There were significant (p < 0.05) differences in microbial degradation dynamics of BSM in the rhizosphere soils among three kinds of riparian plants. A. calamus displayed a significantly (p < 0.05) higher degradation efficiency of BSM in the rhizosphere soils, followed by Z. aquatica and P. australis. The residual BSM concentration in A. calamus rhizosphere soil was 23.1 and 32.2% lower than that in Z. aquatica and P. australis rhizosphere soils, respectively, indicating a greater improvement effect on biodegradation of BSM in A. calamus rhizosphere soils.     

Determining useful benchmarks for the bioassessment of highly disturbed areas based on diatoms

Modern ecological assessments of running waters are based on the a priori definition of ecological benchmarks, given by reference-quality sites. Such benchmarks are established at the level of ecoregions, typologies, or site. Yet, in highly disturbed regions, such as coastal areas of European countries, the assessment of streams’ water quality based on the reference condition concept is very difficult, due to the lack of undisturbed sites. Among others, the reduced number of reference sites may have as a consequence the definition of imprecise ecological benchmarks. Here we tested the hypotheses that (1) the increase in the number of potential reference sites (2) the definition of more precise abiotic thresholds using the least disturbed condition approach (LDC), and (3) the use of diatom assemblages, as the most ubiquitous element in lowland areas, would result in refinement and eventual sub-division of existing river types of a highly disturbed area, such as the Portuguese centre-western region. For this purpose, abiotic data characterising natural conditions of 55 sites from a littoral highly disturbed region were used in a hierarchical classification analysis that revealed the existence of three different sub-groups. In addition, a three-step approach was used to define thresholds for the pressure variables in LDC. Based on these new thresholds, sites in LDC were selected. A hierarchical classification performed to the LDC diatom spring assemblages revealed the existence of two sub-groups, concordant with two of the abiotic sub-groups. Several species contributed to the dissimilarity between the two sub-groups (e.g., Achnanthidium minutissimum and Karayevia oblongella). Differences between the sub-groups were also found in the trait proportions of stalked species. New benchmark values for these two sub-groups, based on the scores of the official diatom index, the Indice de Polluosensibilité Spécifique (IPS), were different from the previous reference value used. Yet, no biological benchmark values were established for one of the groups due to the absence of sites in the LDC. Our study suggests that streambed substrate is an important characterisation variable in the river type definition and highlights that, in spite of the potential refinement in reference conditions and typology obtained, an alternative approach that does not require the use of reference sites should be explored in the future.     

Formation of Humic-like Substances in Mixed and Pure Cultures of Aquatic Microorganisms

A natural decay of plant and animal biomass in aquatic environments results in the release of different simple structured organic substances into water. In our laboratory experiments we investigated whether some of them, e.g., starch or peptone, and also a complex yeast biomass can be transformed into humic-like substances by natural assemblages and some pure cultures of aquatic microorganisms. After a 6 months incubation most of the cultural media enriched with those natural organic substrates turned dark in color and humic-like substances (HS) could be isolated. However, the original substrate organic carbon was mainly mineralized in microbial cultures, and only about 3 % C was converted into HS. Total yields of HS differed in dependence of the individual substrate used (peptone > yeast > starch), the origin of inoculum (river > lake > groundwater), and the incubation temperature (20°C > 10°C). According to their elemental composition, and their spectroscopical and electrophoretic characteristics the microbially formed HS resembled natural aquatic humic matter, but were higher in aliphatic constituents (carbohydrates, peptides) and lower in aromatic structures. HS-like substances were also obtained from pure cultures of a bacterium Bacillus sphaericus and a fungus Cladosporium cladosporioides. The ¹³C and ¹⁵N isotopic contents of the microbially produced HS differed in dependence on the microbial inoculum and the type of organic substrates used, but in general they indicated anabolic processes to be mainly responsible for the humification of the simple organic substrates used in our experiments.     

Morphology, niche segregation, and escape tactics in a sand dune lizard community

We examined patterns of co-existence for three species of scincid lizards (Sphenops sepsoides, Scincus scincus, and Chalcides ocellatus) in the simple sand dune habitat of North Sinai, Egypt. We first examined the morphological differences among the three species and compared their niche use and escape tactics in the context of their morphologies. Our results suggests that natural selection has favored two different phenotypes, Scincus scincus's long limbs with toe fringes and Sphenops sepspoides's extremely reduced limbs for sand locomotion. These two sand specialists, Sphenops sepsoides and Scincus scincus, shared microhabitats such as soft substrate and occurred further away from vegetation but showed strong separation in the surface temperatures at which they were active. The generalist species, C. ocellatus which lacked toe fringes and had relatively short limbs that were not reduced enough for fossorial movement, was found closer to vegetation and on harder substrates where such traits may be beneficial. Escape tactics may further strengthen habitat partitioning between desert generalists and sand specialists as C. ocellatus sprint to vegetation to escape predators whereas both sand specialists dive into the sand. Our results suggest that traditional ideas about predation risk may not apply to sand diving lizards as they may be able to venture far from vegetation refuges without increased vulnerability to predation.     

Effects of substrate differences on water availability for Arctic lichens during the snow-free summers in the High Arctic glacier foreland

We used observational and experimental analyses to investigate the photosynthetic activity and water relationships of five lichen species attached to different substrates in a glacier foreland in the High Arctic, Ny-Ålesund, Svalbard (79°N) during the snow-free season in 2009 and 2010. After the rains ceased, lichens and their attached substrates quickly dried, whereas photosynthetic activity in the lichens decreased gradually. The in situ photosynthetic activity was estimated based on the relative electron transportation rate (rETR) in four fruticose lichens: Cetrariella delisei, Flavocetraria nivalis, Cladonia arbuscula ssp. mitis, and Cladonia pleurota. The rETR approached zero around noon, although the crustose lichen Ochrolechia frigida grown on biological soil crust (BSC) could acquire water from the BSC and retain its WC to perform positive photosynthesis. The light-rETR relationship curves of the five well-watered lichens were characterized into two types: shade-adapted with photoinhibition for the fruticose lichens, and light-adapted with no photoinhibition for O. frigida. The maximum rETR was expected to occur when they could acquire water from the surrounding air or from substrates during the desiccation period. Our results suggest that different species of Arctic lichens have different water availabilities due to their substrates and/or morphological characteristics, which affect their photosynthetic active periods during the summer.