Marine invertebrates and noise

Within the set of risk factors that compromise the conservation of marine biodiversity, one of the least understood concerns is the noise produced by human operations at sea and from land. Many aspects of how noise and other forms of energy may impact the natural balance of the oceans are still unstudied. Substantial attention has been devoted in the last decades to determine the sensitivity to noise of marine mammals—especially cetaceans and pinnipeds—and fish because they are known to possess hearing organs. Recent studies have revealed that a wide diversity of invertebrates are also sensitive to sounds, especially via sensory organs whose original function is to allow maintaining equilibrium in the water column and to sense gravity. Marine invertebrates not only represent the largest proportion of marine biomass and are indicators of ocean health but many species also have important socio-economic values. This review presents the current scientific knowledge on invertebrate bioacoustics (sound production, reception, sensitivity), as well as on how marine invertebrates are affected by anthropogenic noises. It also critically revisits the literature to identify gaps that will frame future research investigating the tolerance to noise of marine ecosystems

Asymmetric dispersal structures a riverine metapopulation of the freshwater pearl mussel Margaritifera laevis

Unidirectional water flow results in the downstream-biased, asymmetric dispersal of many riverine organisms. However, little is known of how asymmetric dispersal influences riverine population structure and dynamics, limiting our ability to properly manage riverine organisms. A metapopulation of the freshwater pearl mussel Margaritifera laevis may be sensitive to river currents because mussels are repeatedly exposed to downstream drift during floods-a parasitic life stage is the only, limited period (similar to 40 days) during which larvae (glochidia) can move upstream with the aid of host fish. We hypothesized that water-mediated dispersal would overwhelm upstream dispersal via host fish, and therefore, that upstream subpopulations play a critical role as immigrant sources. To test this hypothesis, we examined the effects of both up-and downstream immigrant sources on the size of target subpopulations in the Shubuto River system, Hokkaido, Japan. We found that target subpopulation size was dependent on the upstream distribution range of reproductive subpopulations and the number of upstream tributaries, which are proxies for the number of potential immigrants moving downstream. In contrast, little influence was observed of downstream immigrant sources (proximity to downstream reproductive subpopulations). These results were consistent even after accounting for local environments and stream size. Our finding suggests that upstream subpopulations can be disproportionately important as immigrant sources when dispersal is strongly asymmetric

Biological characteristics of silver-phase Japanese eels, Anguilla japonica, collected from Hamana Lake, Japan

The biological characteristics of 259 silver-phase Japanese eels, Anguilla japonica, were investigated in Hamana Lake, Japan from 2003 to 2007, to obtain basic data for this species at the downstream migration. Their silvering stage, condition factor, three internal (gonad-somatic index: GSI, hepato-somatic index and gut index) and two morphometric (fin index and eye index) indices were calculated. The overall sex ratio tended to be female (61%), but the sex ratio differed among years and months. Silver eels of S1 stage (early silver) were predominant than S2 (late silver) for both sexes (female: 67%, male: 77%). Female eels attained to larger size (mean: 659.3 mm) and older age (9.9 years) than males (527.7 mm and 8.3 years). The GSI increased from October to December whereas gut index decreased with months, but significant change in morphometric indices were not found within silver-phase. The results of this study suggest that silver-phase Japanese eels have a wide range of the biological characteristics, but significant differences can occur in sex ratio and the proportion of silvering stages among years, and in internal indices within silver-phase during their downstream migration season

Data from: Asymmetric dispersal structures a riverine metapopulation of the freshwater pearl mussel Margaritifera laevis

Unidirectional water flow results in the downstream-biased, asymmetric dispersal of many riverine organisms. However, little is known of how asymmetric dispersal influences riverine population structure and dynamics, limiting our ability to properly manage riverine organisms. A metapopulation of the freshwater pearl mussel Margaritifera laevis may be sensitive to river currents because mussels are repeatedly exposed to downstream drift during floods—a parasitic life stage is the only, limited period (~40 days) during which larvae (glochidia) can move upstream with the aid of host fish. We hypothesized that water-mediated dispersal would overwhelm upstream dispersal via host fish, and therefore, that upstream subpopulations play a critical role as immigrant sources. To test this hypothesis, we examined the effects of both up- and downstream immigrant sources on the size of target subpopulations in the Shubuto River system, Hokkaido, Japan. We found that target subpopulation size was dependent on the upstream distribution range of reproductive subpopulations and the number of upstream tributaries, which are proxies for the number of potential immigrants moving downstream. In contrast, little influence was observed of downstream immigrant sources (proximity to downstream reproductive subpopulations). These results were consistent even after accounting for local environments and stream size. Our finding suggests that upstream subpopulations can be disproportionately important as immigrant sources when dispersal is strongly asymmetric