Fine sediment reduces vertical migrations of Gammarus pulex (Crustacea: Amphipoda) in response to surface water loss

Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances

Mapping of quantitative trait loci for flesh colour and growth traits in Atlantic salmon (Salmo salar)

<p>Abstract</p> <p>Background</p> <p>Flesh colour and growth related traits in salmonids are both commercially important and of great interest from a physiological and evolutionary perspective. The aim of this study was to identify quantitative trait loci (QTL) affecting flesh colour and growth related traits in an F2 population derived from an isolated, landlocked wild population in Norway (Byglands Bleke) and a commercial production population.</p> <p>Methods</p> <p>One hundred and twenty-eight informative microsatellite loci distributed across all 29 linkage groups in Atlantic salmon were genotyped in individuals from four F2 families that were selected from the ends of the flesh colour distribution. Genotyping of 23 additional loci and two additional families was performed on a number of linkage groups harbouring putative QTL. QTL analysis was performed using a line-cross model assuming fixation of alternate QTL alleles and a half-sib model with no assumptions about the number and frequency of QTL alleles in the founder populations.</p> <p>Results</p> <p>A moderate to strong phenotypic correlation was found between colour, length and weight traits. In total, 13 genome-wide significant QTL were detected for all traits using the line-cross model, including three genome-wide significant QTL for flesh colour (Chr 6, Chr 26 and Chr 4). In addition, 32 suggestive QTL were detected (chromosome-wide P < 0.05). Using the half-sib model, six genome-wide significant QTL were detected for all traits, including two for flesh colour (Chr 26 and Chr 4) and 41 suggestive QTL were detected (chromosome-wide P < 0.05). Based on the half-sib analysis, these two genome-wide significant QTL for flesh colour explained 24% of the phenotypic variance for this trait.</p> <p>Conclusions</p> <p>A large number of significant and suggestive QTL for flesh colour and growth traits were found in an F2 population of Atlantic salmon. Chr 26 and Chr 4 presented the strongest evidence for significant QTL affecting flesh colour, while Chr 10, Chr 5, and Chr 4 presented the strongest evidence for significant QTL affecting growth traits (length and weight). These QTL could be strong candidates for use in marker-assisted selection and provide a starting point for further characterisation of the genetic components underlying flesh colour and growth.</p

Survival of eggs of Atlantic salmon (Salmo salar) in a drawdown zone of a regulated river influenced by groundwater

Groundwater may create refuges for Atlantic salmon egg survival during low flows in regulated rivers and thus play an important role for survival during winter. To investigate the links between the survival of salmon embryos and hyporheic hydrological processes during permanent winter drawdown, a 100-m-long and 50-m-wide gravel area in a regulated river, the River Suldalslågen, was used for an experimental study. Surface and subsurface water levels were monitored with 2-min time resolution by means of water pressure sensors placed in pipes. Temperature, conductivity and dissolved oxygen were also measured. Eight cylindrical boxes, each with two compartments (at 10- and 30-cm depth, respectively) containing 50 Atlantic salmon eggs, were placed in the river bed substrate of both the drawdown zone and the permanently wetted area as a reference. They were regularly checked for survival during winter from January to May, coinciding with egg development period for this river. Survival rates in boxes in the dewatered river bed were between 8 and 78% during winter, compared to 80 to 99% in the reference wetted area. The main driver for egg survival in the dewatered area was groundwater with sufficient oxygen levels