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Complex effect of projected sea temperature and wind change on flatfish dispersal
No full textClimate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle‐tracking model coupled to a 3D‐hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability in larval transport over the period 1995–2011. Then, using a subset of representative years (2003–2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panel on Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year‐to‐year variability is explained at a regional scale and that a 9‐year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase response to the reduced temperature (−9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (−58%) and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention −4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management
European silver eel (<i>Anguilla anguilla</i> L.) migration behaviour in a highly regulated shipping canal
Get PDFAmong the many man-made structures that facilitate shipping, navigable canals take an important position. These canals may offer energetically favourable migration routes for diadromous fish, but they may also obstruct fish migration, for instance at shipping locks. Because the use of shipping canals by, and their effects on, migrating fish remain unknown, we assessed whether these canals can play a significant role in the migration of the critically endangered European eel. Only one third of 70 acoustically tagged silver eels completed migration through a shipping canal, and did so at a very low pace (average -1) due to delays at shipping locks and most likely also due to the disruption of water flow. These delays may come at an energetic cost, hampering the chances of successful migration. Knowledge on the impact of shipping canals on diadromous fish is crucial for proper management regulations. For instance, the observation that eels mostly migrated at night and during spring and autumn can support water managers to define adequate measures to improve eel migration in shipping canals
How unknown is the world's biodiversity? Free-living flatworms as an example
Get PDFEven at the start of the 21st century, the actual biodiversity of the world's marine ecosystems is still largely unknown. Not surprisingly, especially the smallest creatures are much understudied. Among the least known taxonomical groups are the microturbellarians, small free-living flatworms that inhabit sandy beaches or live epiphytically on algae. With a rough conservative estimation of about 15.000 species still to be described, an enormous task still lays ahead for classical morphology-based taxonomy. And not only is the relative number of species already described limited, but on top of that most of them are described from a few marine ecoregions only, mostly from the Western and Northern Europe, and the Mediterranean. The major part of the world's coasts and deep sea habitats never were investigated. This lack of knowledge greatly hampers further research regarding biogeography, ecology or even phylogeny. In recent years we have tried to shed light on several questions regarding the evolution and ecology of these animals, including the origin of a symbiotic life style, the history of major habitat shifts and the "Everything small is everywhere"-hypothesis, research that is still ongoing. These studies were only possible because of a big taxonomical effort and trustable databases, and the results will briefly be presented
Selective and context-dependent effects of chemical stress across trophic levels at the basis of marine food webs
No full textHuman activities increasingly impact the functioning of marine food webs, but anthropogenic stressors are seldom included in ecological study designs. Diet quality, as distinct from just diet quantity, has moreover rarely been highlighted in food web studies in a stress context. We measured the effects of metal and pesticide stress (copper and atrazine) on the contribution of a benthic intertidal diatom community to two processes that are key to the functioning of intertidal systems: biomass (diet quantity) and lipid (diet quality) production. We then examined if stressors affected diatom functioning by selectively targeting the species contributing most to functioning (selective stress effects) or by changing the species’ functional contribution (context‐dependent effects). Finally, we tested if stress‐induced changes in diet quality altered the energy flow to the diatoms’ main grazers (harpacticoid copepods). Diatom diet quantity was reduced by metal stress but not by low pesticide levels due to the presence of an atrazine‐tolerant, mixotrophic species. Selective effects of the pesticide reduced diatom diet quality by 60% and 75% at low and high pesticide levels respectively, by shifting diatom community structure from dominance by lipid‐rich species toward dominance by an atrazine‐tolerant, but lipid‐poor, species. Context‐dependent effects did not affect individual diatom lipid content at low levels of both stressors, but caused diatoms to lose 40% of their lipids at high copper stress. Stress‐induced changes in diet quality predicted the energy flow from the diatoms to their copepod consumers, which lost half of their lipids when feeding on diatoms grown under low and high pesticide and high metal stress. Selective pesticide effects were a more important threat for trophic energy transfer than context‐dependent effects of both stressors, with shifts in diatom community structure affecting the energy flow to their copepod grazers at stress levels where no changes in diatom lipid content were detected
Metabarcoding of museum samples stored in formalin: analysing the prey and microbiome composition of Antarctic fish (<i>Trematomus</i> sp.)
Get PDFWe present the first study to assess the prey item and microbiome composition of Antarctic fish that have been stored in formalin for prolonged amounts of time. We applied a technique of treatment of the stomachs/hind guts with an alkaline solution and heat in order to extract DNA. We then amplified a region of the COI mitochondrial gene for stomachs and 16S rRNA nuclear gene for the hindgut samples to assess the prey item and microbiome composition, respectively. We employed extensive quality and contamination controls in order to ensure reliable results. We found that stomach samples were characterized strongly by contamination. In contrast, microbiome composition clustered differently from all our quality control samples. Therefore, we have high confidence in the quality of the microbiome composition data. Furthermore, we found a weak correlation between microbiome composition and standard length (size) of the fish. Due to high dropout rates among samples few were left and therefore the results are lacking statistical confidence. Results will be compared with contemporary samples once these have been further analyzed
