Hydrobiologia

Bellingan, Terence; Hugo, Sanet; Woodford, Darragh; Gouws, Jeanne; Villet, Martin; Weyl, Olaf

doi: 10.1007/s10750-019-3885-zpmid: N/A

South Africa’s Cape Fold Ecoregion supports a unique freshwater fish assemblage with many endemics. To mitigate impacts of alien invasive fishes on this unique assemblage, nature conservation authority CapeNature used rotenone to remove smallmouth bass (Micropterus dolomieu) from the Rondegat River. We investigated whether the rotenone treatments had an adverse impact on the aquatic macroinvertebrate community over the long-term, the first study of its kind in Africa. We monitored macroinvertebrates within treated and untreated (control) sites on multiple sampling events for 2 years before and 2 years after two rotenone treatments. We analysed the difference in invertebrate abundance between treatment and control sites before and after treatment, using generalised linear mixed models with sampling event as a random factor to partition out natural fluctuations in abundances over time. Populations fluctuated widely in control and treatment sites over the study period, and we found no effect that could be clearly attributed to rotenone. We conclude that macroinvertebrates recovered rapidly after treatment, probably through drift from untreated areas upstream, with no long-term adverse effects. We recommend that the presence of uninvaded upstream refuges that may provide demographic rescue be used as a key discriminating factor for future conservation purposed rotenone deployments.

Simpson, L.; Stein, C.; Osborne, T.; Feller, I.

doi: 10.1007/s10750-019-3905-zpmid: N/A

In North America, the dynamic ecotonal boundary between mangrove and salt marsh is currently fluctuating in response to freeze-free winters, which can cause rapid alterations in a number of wetland processes and attributes. Permanent plots were established in pure salt marsh habitat along the Atlantic coast of Florida in 2015, and by 2018, mangrove saplings had encroached into plots. In this study, above- and belowground biomass measurements and soil C in the top 10-cm soil profile were quantified in 2018 and compared to 2015 data to better understand the effects of mangrove encroachment on C storage in salt marsh habitat. Plant and soil fractions were tested for δ13C stable isotopic signatures to elucidate soil C sources. In 3 years, mangrove biomass increased dramatically and soil C doubled in pure salt marsh plots, consequently increasing total C in the system. Soil organic matter increased, while there was no change in soil C:N. δ13C values suggest that soil C was derived mainly from salt marsh soil organic matter, especially that of belowground, rather than aboveground biomass. These results provide real-time, quantitative data on the encroachment of mangroves into salt marshes over a relatively short period of time.

Musetta-Lambert, Jordan; Kreutzweiser, David; Sibley, Paul

doi: 10.1007/s10750-019-3907-xpmid: N/A

Forested headwater streams are strongly connected to their surrounding riparian areas via the transfer of energy subsidies that underpin instream food webs and, therefore, are highly sensitive to riparian disturbances that influence allochthonous inputs. We compared terrestrial and aquatic invertebrates found in drift across headwater streams in boreal forested catchments with wildfire, harvest with minimum 30-m riparian buffers, and reference catchment histories. Fire-disturbed streams contained significantly greater aquatic invertebrate abundance and biomass compared to reference and harvested streams, but no significant trends were seen for terrestrial invertebrate abundance or biomass. Furthermore, fire-disturbed streams supported distinct drifting invertebrate communities compared to reference and harvested sites, driven by high abundances of the mayfly Baetis and caddisfly Dolophilodes. Aquatic invertebrate drift communities were compositionally dissimilar between fire and harvested sites, but not reference sites and no trends were found for terrestrial invertebrate drift samples. Subtle but detectable differences in drifting invertebrate community metrics, structure, and biomass suggest that the effects of wildfire persist well beyond a decade post-fire in boreal headwater streams. Forest management that emulates natural fire disturbance, including streamside disturbance, may be important for promoting the observed patterns detected in our fire-disturbed catchments.

Lorenz, Stefan; Wolter, Christian

doi: 10.1007/s10750-019-3908-9pmid: N/A

The most widespread pressure impacting river ecological status is the degradation of key hydromorphologic elements, such as sediment type and flow rate. However, almost nothing is known about the quantitative relationship between benthic invertebrate abundance and these elements. This synthesis compiles quantitative data on physical requirements and thresholds for invertebrates relative to two hydromorphologic factors: substrate size and hydraulic energy (measured as shear stress). Both factors are commonly a focus of river rehabilitation. However, we found only limited literature data that we could use to identify invertebrate preferences (189 taxa). Preferred substrate sizes of all stream epifauna we examined varied between 0.05 and 400 mm and they prefer shear stresses from 0.13 to 3.67 N m−2. There was no difference in variation of preferred conditions between the examined taxonomic levels. We suspect that taxa preferring hydraulic environments with shear stresses < 0.64 N m−2 are affected more by environmental factors than solely being constrained by substrate or hydraulic energy preferences. Such taxa might be useful as sensitive indicator species for evaluating stream integrity. Hence, to optimize restoration success for riverine biota, hydromorphological forces should be mitigated by manipulating habitat complexity in a way that it enhances intact ecological processes.

Dainez-Filho, Mário; Michelan, Thaísa; Louback-Franco, Nayara; Souza, Douglas; Cafofo, Emanuel; Thomaz, Sidinei

doi: 10.1007/s10750-019-3909-8pmid: N/A

The deposition of plant detritus changes sediment features, but little is known about how the accumulation of detritus affects the colonization of invasive and native submerged macrophytes. We tested the predictions that (i) submerged macrophyte occurrences correlate positively with the presence of detritus over sediment; (ii) the colonization of submerged macrophytes increases in the presence of detritus; (iii) the invasive macrophyte Hydrilla verticillata grows faster than the native macrophyte Egeria najas independent of the presence of detritus and (iv) E. najas is affected by competition with H. verticillata, and competition is mediated by the presence of detritus. We evaluated the co-occurrences of submerged macrophytes and detritus in situ and experimentally tested the effects of detritus on submerged macrophyte growth with and without competition. The presence of submerged macrophytes and detritus was negatively correlated in situ. Our experiments indicate that the detritus of emergent macrophytes, including invasive macrophytes, enhances nutrients after reflooding and increases the early growth of submerged macrophytes but does not influence the outcome of competition. Thus, the facilitation of invasive success at the beginning of detritus decomposition (indicated by our experiments) may be counteracted by negative effects after a long decomposition period (indicated by our field data).

Ferreira-Rodríguez, Noé

doi: 10.1007/s10750-019-3910-2pmid: N/A

Freshwater mussels are considered sedentary organisms. However, their foot provides the organ of locomotion, which enables an active behaviour. Their behaviour includes righting, horizontal movements and burrowing into the substrate. The objective of this study was to analyse the influence of non-native (Corbicula fluminea) competitors on the pedal activity of native (Unio delphinus) freshwater mussels in a climate change context. The pedal activity was scored and compared among different species compositions, population density and exposure to heat wave progression. The results showed a significant effect of species composition and heat wave progression. In addition, a significant effect of species composition × population density was found. Mussels at low density conditions exposed to dense aggregations of C. fluminea showed lower pedal activity than individuals in intraspecific treatments, or individuals at high density conditions exposed to low densities of C. fluminea. Maximum pedal activity was recorded at the thermal peak. After that, pedal activity was reduced when high temperature was maintained over time. Altogether, present results suggest that lower pedal activity at high C. fluminea densities may expose mussels to more intense interspecific competition. In addition, heat waves may compromise mussels’ ability to locate refuge areas in front of receding waters.

Tuya, Fernando; Asensio, Maite; Bosch, Néstor; García, Alvaro; Navarro, Alberto

doi: 10.1007/s10750-019-3911-1pmid: N/A

The conservation of coastal seascapes requires a better understanding of how different dimensions of biodiversity are represented between juxtaposed habitats. We explored patterns of taxonomic, functional, and phylogenetic diversity of fishes between four habitats (sandy bottoms, rocky reefs of high and low relief, and mixed bottoms) within a semi-lagoon seascape (Las Canteras beach) in Gran Canaria Island. Data on fish presence in each habitat were provided by weekly snorkeling tours, at day and night, from August 2015 to August 2018. Indices that measured ‘how much’ biodiversity, i.e., ‘how many species’ (species richness), ‘how much functional dissimilarity’, and ‘how much evolutionary history’ were larger on rocky bottoms. However, indices that measured phylogenetic differentiation, i.e., ‘how different’, via the taxonomic distinctiveness and the Mean Pairwise Distance index were particularly high on sandy bottoms, because of the presence of elasmobranchs, which were absent from rocky bottoms. The ‘phylogenetic signal’, whether phylogenetically related species are functionally similar, was significant on rocky bottoms, but non-significant on sandy bottoms, reflecting phylogenetic ‘overdispersion’ on sandy bottoms and phylogenetic ‘clustering’ on hard bottoms. From a conservation perspective, sandy bottoms cannot be underrated, particularly in the context of maximizing indices that measure ‘how phylogenetically different’ biodiversity is.

Rossi, Anna; Colangelo, Paolo; Berline, Léo; Angiulli, Elisa; Ardizzone, Giandomenico; Fassatoui, Chiheb; Sola, Luciana

doi: 10.1007/s10750-019-3914-ypmid: N/A

Many marine organisms have complex genetic patterns that cannot be easily resolved by data analysis on spatial distribution of variability usually applied in population genetic studies. We propose an analytical framework to evaluate the role of dispersal during early life stages that considers the actual hydrodynamic connectivity in the Mediterranean Sea, as a factor shaping the population structure of demersal fishes. To this purpose, and to test different scenarios of gene flow, genotypes of individuals of Pagellus erythrinus sampled at 12 sites in the central Mediterranean Sea were analyzed at ten microsatellite loci. The results show the lack of genetic structure in western Mediterranean basin and a pattern of gene flow that deviates from an isolation by distance model. The observed gene flow estimates appear to be scale-dependent. At local scale, it is likely the result of multifactorial components, whereas at a larger scale it is mainly driven by the sea currents, directly influencing dispersal of larvae between sites not reachable by adult movements. Our results stress the importance of a quantitative analysis of potential early life stage dispersal in any study focusing on the population structure of fishes with a long larval stage.

MacNeil, Calum

doi: 10.1007/s10750-019-3916-9pmid: N/A

It has been hypothesised that freshwater pollution may favour the establishment of tolerant invaders at the expense of less-tolerant residents. To test this, this study capitalises on the aftermath of a farm pollution incident, a slurry discharge to a small British stream, which eliminated the resident macroinvertebrate assemblage. Stream transplant bioassay experiments at the discharge site revealed a higher pollution tolerance of the invasive amphipod Crangonyx pseudogracilis and the isopod Asellus aquaticus than that of the native amphipod Gammarus duebeni celticus and the invasive Gammarus pulex. A. aquaticus recolonised the stream up to the discharge point within days, followed by C. pseudogracilis, then G. pulex, with G. duebeni celticus undetected after a month. Values of a macroinvertebrate-derived biotic index of organic water quality, the Average Score Per Taxon (ASPT), gradually increased up to the discharge point in the 30 days following the incident. In a larger-scale survey (72 river and 12 pond sites), inclusion/exclusion of Gammarus spp. had no effect on ASPT values, while inclusion of C. pseudogracilis increased values, despite an assumed equivalence of these amphipods in the index. Pollution could facilitate the establishment of tolerant invaders, and this has implications for biomonitoring.

Turner, R.; Swenson, Erick; Milan, Charles; Lee, James

doi: 10.1007/s10750-019-3918-7pmid: N/A

Intense sampling of an estuary can reveal relative spatial changes that are significant irrespective of whether or not the estuary is eutrophic, micro- or meso-tidal, disturbed, or restored. This ‘waterscape’ perspective is analogous to a landscape perspective. We collected monthly water samples in the Barataria Basin watershed from 1994 to 2016 at 37 stations along a 129 km transect from 1 km offshore to a freshwater stream. The average Chlorophyll a (Chl) concentration from 267 trips was supported from both nitrogen-fixing cyanobacteria in a freshwater lake and partially from nutrients in seaward sources. Estuarine salinity was correlated with the discharge of the nearby Mississippi River. The main form of N was as organic nitrogen, not inorganic forms that recycle quickly, making changes in inorganic nitrogen concentration an unreliable indicator of net denitrification or uptake. The total nitrogen (TN) and total phosphorus (TP) concentrations declined with dilution towards the coast, but not because of denitrification. The phytoplankton standing biomass reflected the TN:TP ratio in the water column and there was a significant rise in the variability of Chl concentration at 2–6 psu, which was otherwise unremarkably constant. These waterscape patterns and cautionary interpretations may be common to other estuaries.