Analysis of active rotenone concentration during treatment of the Rondegat River,Cape Floristic Region,South Africa

Most endemic freshwater fish species of the Cape Floristic Region are listed as threatened, due mainly to the impacts of invasive alien fish species. The piscicide rotenone has been identified as a potential tool to aid the conservation of indigenous species through the removal of invasive fish. Rotenone was used in the Rondegat River, Cederberg, where smallmouth bass Micropterus dolomieu had extirpated the indigenous fish. An initial rotenone treatment in March 2012 was followed by another in March 2013. Due to concerns following the first treatment about possible build-up of rotenone between treatment stations, the second treatment included monitoring of rotenone concentrations during the treatment. Measured concentrations were consistently below the selected treatment concentration of 37.5 µg l^?1 and dropped to below the tested effective piscicidal concentration of 12.5 µg l^?1 at some sampling points. There was no build-up of rotenone within the treatment zones, but rotenone took longer than expected to clear out of the treatment area. The rotenone was effectively neutralised when the neutralisation station was operational, but was still detectable after neutralisation was terminated.     

Do hotspots fall within protected areas? A Geographic Approach to Planning analysis of regional freshwater biodiversity

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Running on empty? Freshwater feeding by spawning anadromous alewife Alosa pseudoharengus

Anadromous alewife Alosa pseudoharengus (n = 202; mean ± s.d . fork length = 231 ± 14 mm) were captured from 10 May to 27 June 2018 in an upper watershed lake on the Isthmus of Chignecto, Canada (45°57′N, 64°14′W). Thirty individuals (mean ± s.d. fork length = 250 ± 12 mm) were captured in an adjacent estuary downstream of a tide gate on 25 April 2018. Comparing estuarine to freshwater specimens, mean gonad mass and gonadosomatic indices in males and females decreased approximately 40% and 60%, and 31% and 50%, respectively. Individuals were characterized as pre-spawners in the estuary and spawners in the lake. Males maintained similar body condition throughout the spawning run whereas female condition decreased 9.4% between the estuary and lake. Stomach fullness decreased comparing estuarine and freshwater specimens, yet 93% of stomachs examined from individuals captured in the lake contained prey. Most males fed throughout all spawning stages (3%–17% empty stomachs), while all females fed during pre- and post-spawning stages and some fasted during spawning (11% empty stomachs). Cumulative prey curve never reached an asymptote, either weekly or for the entire sampling period, so freshwater diet may not have been completely described. Calanoid copepods (79.3%I_A) were a diet staple, with the secondary prey of mayfly nymphs (O. Ephemeroptera) consumed more by females (13.6%I_A) than males (6.2%I_A). PERMANOVA and PERMDISP analyses revealed significant dietary differences in freshwater were weekly and not due to dispersion effects, thus most likely due to feeding on various development stages of insect species. Our results challenge the long-held paradigm that anadromous A. pseudoharengus fast during the spawning migration.     

Phytoplankton flora in the Warri/Forcados Estuary of southern Nigeria

The phytoplankton flora of the Warri/Forcados estuary varied from typical fresh and brackish water forms to purely distinct marine species. These were made up of members of the Bacillariophyta (about 80 species), Chlorophyta (over 90 species), Cyanophyta (16 species), Dinophyceae (10 species) and the Euglenophyta (8 species). The bulk of the species belonging to the Chlorophyta, Cyanophyta and the Euglenophyta were almost exclusively fresh-water in distribution, being limited to habitats of less than 0.5 salinity. Members of the Bacillariophyta were found in all habitats, occurring freely in freshwater, estuarine, and marine ecosystems. In all cases, no true examples of euryhalinity were recorded. The majority of dinoflagellates encountered, as well as a number of marine diatoms, manifested stenohaline peculiarities as they could not tolerate a wide salinity range.The overall influence of the periodic shift in salinity and some physico-chemical parameters along the stretch of the estuary brought about by strong tidal effects and the variable seasonal volume of water discharge or runoff on the pattern and limit of distribution of phytoplankton species is highlighted.     

Massive upstream migrations by a tropical freshwater neritid snail

While upstream movements of benthic invertebrates have been reported, gregarious upstream migrations of freshwater snails have never been described. We report a possible adaptation to downstream drift by a population of the Neritid (Archeogastropoda) snail,Neritina (Clypeolum) latissima (Broderip, 1833), in the Rio Claro, a small coastal river in Corcovado National Park, Costa Rica. We observed large numbers of these snails in gregarious upstream migration. Snails migrated in narrow lines up to 32 meters long, containing thousands of snails. The migration covered over 1 km of the stream. Larval and juvenile snails are more susceptible to washout by current, and differential mortality of these age classes in the estuarine and ocean environment may provide the selective pressure for the evolution of this behavior.     

The legacy of a vanished sea: a high level of diversification within a European freshwater amphipod species complex driven by 15 My of Paratethys regression

The formation of continental Europe in the Neogene was due to the regression of the Tethys Ocean and of the Paratethys Sea. The dynamic geology of the area and repetitious transitions between marine and freshwater conditions presented opportunities for the colonization of newly emerging hydrological networks and diversification of aquatic biota. Implementing mitochondrial and nuclear markers in conjunction with a large‐scale sampling strategy, we investigated the impact of this spatiotemporal framework on the evolutionary history of a freshwater crustacean morphospecies. The Gammarus balcanicus species complex is widely distributed in the area previously occupied by the Paratethys Sea. Our results revealed its high diversification and polyphyly in relation to a number of other morphospecies. The distribution of the studied amphipod is generally characterized by very high local endemism and divergence. The Bayesian time‐calibrated reconstruction of phylogeny and geographical distribution of ancestral nodes indicates that this species complex started to diversify in the Early Miocene in the central Balkans, partially in the shallow epicontinental sea. It is possible that there were several episodes of inland water colonization by local brackish water lineages. Subsequent diversification within clades and spread to new areas could have been induced by Alpine orogeny in the Miocene/Pliocene and, finally, by Pleistocene glaciations. The present distribution of clades, in many cases, still reflects Miocene palaeogeography of the area. Our results point out that investigations of the historical aspect of cryptic diversity in other taxa may help in a general understanding of the origins of freshwater invertebrate fauna of Europe.     

Maintaining Biodiversity in Freshwater Ecosystems on Oceanic Islands of the Tropical Pacific

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Seasonal change in the spatial utilization of host mussels in relation to ovipositor length by female rosy bitterling Rhodeus ocellatus kurumeus

The seasonal changes in ovipositor length and utilization patterns of mussels for oviposition in the rosy bitterling Rhodeus ocellatus kurumeus (Cyprinidae) were investigated in a field experiment and field surveys during the breeding period (April to August). The mean length of ovipositors at oviposition was short at the start (early April) and end (July) of the breeding period. Females with long ovipositor at oviposition were collected between mid‐April and June. Mark‐and‐recapture data showed that ovipositor length at oviposition changed rhythmically throughout the breeding period, shortening and lengthening as the female entered the spawning and resting phase. The density of rosy bitterling embryos in mussels increased between April and June, peaking in May, but decreasing in July. The position of eggs on mussel gills varied from close to the exhalant siphon to deeper inside the gill during April, and periodically thereafter. There was a positive correlation between ovipositor length at oviposition and the distance from exhalant siphon of mussels to eggs deposited by females, suggesting that ovipositor length at oviposition determined the position of eggs deposited on a mussel gill. Because dissolved oxygen in mussel gills decreased with the density of bitterling embryos, suitable positions for embryo survival in gills changed with embryo density. By changing ovipositor length at oviposition, females might be able to spawn their eggs in a position that maximizes embryo survival. Thus, plasticity in ovipositor length at oviposition may play an important role as an adaptation of rosy bitterling in utilizing mussels when their quality as a spawning substratum fluctuates seasonally.     

Spatio-Temporal Distribution of Freshwater Snail Species in Relation to Migration and Environmental Factors in an Irrigated Area from Morocco

Nine sites were sampled 19 times over 2 years in an irrigation system in Morocco in order to study species abundance in a snail community in relation to environmental parameters (including human activities) and migration (geographic distance) among sites. Each site was made of a sink and the first meters of the downstream canal. The snail community included four species (Bulinus truncatus, Lymnaea truncatula, Mercuria similis and Physa acuta). Strong spatial variation in species occurrence and abundance was detected which might be partly due to variation in water availability. However abundance in sinks and canals in which water availability differs were correlated. There was, as predicted, limited evidence in favor of isolation by distance which might be due to fast water current. Dispersal might therefore be an important factor structuring this community. On the other hand, the temporal variation was much more limited. This is consistent with the analysis of individual size distributions in B. truncatus, since no clear-cut cohorts were detected. The environmental parameters recorded (e.g. temperature, occurrence of macrophytes or cleaning of sinks) were extremely variable in time and space, except temperature. Analyzing their association with species through multidimensional methods indicated that P. acuta is ubiquitous and B. truncatus positively associated with macrophytes. These two species were associated in sinks. Less clear trends were detected for the two other species. Annual cleaning of sinks affected all species, but population recovery was fast in B. truncatus and P. acuta.