Form function of sulcus acusticus of the sagittal otolith in seven Sciaenidae (Acanthuriformes) species using geometric morphometrics (southwestern Atlantic).

The morphology of otoliths determines the function they perform, and it is influenced by genetic and environmental factors. Knowing those relationships is necessary to understand the role of hearing in fish. The objectives of this work were: exploring the shape of the sulcus of the sagittal otolith in seven species of Sciaenidae, in relation to sound production, and analyzing whether the shape and size of the sulcus can be used as a phylogenetic character. For this purpose, geometric morphometry analysis was carried out using landmarks data. It was found that there is an influence of size on the shape of the sulcus, and significant differences were found between the shapes of the sulcus (permutational multivariate analysis of variance). Three general shapes of the sulcus were identified (using principal component analysis, canonical variate analysis, and clustering): (1) in species that produce sounds at dominant frequencies <350 Hz, the deformation of the sulcus showed a tendency towards circularity of the ostium; (2) in those species that produce sounds at frequencies >350 Hz, the ostium showed a flattened ovoid shape, and the cauda increased its length; (3) the species that do not produce sounds, did not show any modifications, relative to the form of consensus. Despite finding sister species that presented similar sulcus shapes in the phylogeny, the results did not confirm that this can be used as a phylogenetic character. This work discusses whether the combined effects of phylogenetic legacy and natural functional selection have led to convergent evolution for the sulcus form. The differences presented by the sulcus of species that occupy the same clade, could indicate that there is a displacement of characters. The sagittal otolith and the sensory macula associated with the sulcus acusticus are highly plastic structures that are subject to strong evolutionary pressure in relation to environmental and behavioral factors, resulting in great variability in shapes that can be associated with a specific character. The variation in the shape of the sulcus would allow the analysed species to coexist in the same coastal soundscapes, without losing their particular hearing needs, even in case of overlapping their spatial and temporal distribution areas.

Stranding of Mesopelagic Fishes in the Canary Islands.

Most mesopelagic fishes perform large diel vertical migrations from the deep-sea zone to the surface. Although there is a trade-off between a higher food availability at the upper layers and an energy cost and predation risk, incursion towards the surface also implies a transport by currents, where the fish are exposed to a stranding risk on the coast. Here, we reported the first documented stranding of mesopelagic fishes along the southeast shore of Gran Canaria Island. Our study hypothesized that (1) the influence of the Canary Current, (2) the dominant incidence of the Trade Winds during summer, and (3) the presence of an upwelling filament coupled with an anticyclonic eddy south of Gran Canaria Island were the causative mechanisms of the strandings. Diaphus dumerilii (Myctophidae family) was the main species found as observed from an external morphological analysis using traditional taxonomy. The otolith contour analysis suggested the presence of other Diaphus spp. and Lobianchia dofleini. Nevertheless, the otolith morphological features described in the literature suggested that all the specimens were actually D. dumerelii. Errors in the identification were mainly due to the high intraspecific variability found in the otolith morphology. Even so, two patterns of oval and elliptic shapes were described with significant differences in its morphometry.

Interannual trophic behaviour of a pelagic fish predator in the western Mediterranean Sea.

The exploitation of forage fish species can modify the functioning of marine ecosystems potentially impacting the population status of predators. This may be the case for the western Mediterranean Sea, where a reduction in the biomass of two key pelagic forage fish (European anchovy Engraulis encrasicolus and European sardine Sardina pilchardus) could produce a change in the diet composition of their main predators, which would consume alternative preys or change the size of the prey consumed. Here, we aimed to investigate the potential effect of biomass reduction of sardine and anchovy in the western Mediterranean Sea on the trophic preferences of the little tunny (Euthynnus alletteratus), a medium-sized predator that present a high consumption of these forage fish. We compared its interannual trophic ecology by combining the analysis of stomach contents and stable isotopes. Specifically, we examined if the diet of little tunny changed in its main trophic habits (diet composition, prey size, and trophic niche) during a 6-year period. We found that small pelagic fish, especially clupeiformes, were the most important prey group for the little tunny during the study period. However, we found changes in the body size of anchovy and the relative importance of sardine in recent years, probably reflecting the reported reduction in the biomass and body size of these two forage fish in the study area. In addition to these changes, we found an increase in some demersal and benthopelagic species in the diet of little tunny, which could act as an alternative diet resource.

Recognising mollusc shell contours with enlarged spines: Wavelet vs Elliptic Fourier analyses.

Gastropod shells may present large spines and sharp shapes that vary according to environmental, taxonomic, and evolutionary factors. In these cases, classic morphometric methods used to study shell contour might not provide a clear representation of morphological shell based on angular decomposition of contour. The present study analyzed and compared for the first time the robustness of the contour analysis using wavelet transformed and Elliptic Fourier descriptors for gastropod shells including enlarged spines. For that, we analyzed two geographical and ecological separated populations of Bolinus brandaris from the NW Mediterranean Sea. Results showed that contour analysis of gastropod shells with enlarged spines can be analyzed using both methodologies, but the wavelet analysis provided a better local discrimination. From an ecological perspective, shells with spines of different sizes were observed in both localities suggesting a wide plasticity of the species.

Optimal fishing samplers to reveal the morphological structure of a fish assemblage in a subtropical tidal flat

Morphological characters of species are essential for assessing the functional structure of a fish assemblage, since differences between them, for example in body shape, are related to many functional and ecological traits (e.g., swimming, search for food, striking and capturing prey, evading predators, spawning). Globally, tidal flats are relevant to fish assemblages by offering feeding, refuge, and reproduction grounds. To analyze the morphofunctional structure of the fish assemblage from a tidal flat on the Brazilian coast, we conducted standardized sampling using nine different fishing gears. The geometric morphometric method was applied to describe the fish shapes and verify the morphological structure of the assemblage. Here, we present the influence/susceptibility of each gear type on the morphological diversity of the fish assemblage. The results indicated that beach seine, otter trawl, marginal encircling gillnet, and fish traps, together, were the most effective gears to represent the maximum morphological variability of fish inhabiting that tidal flat. Moreover, the assemblage showed high morphological redundancy considered as a resistance of the ecosystem for avoiding functional diversity loss, emphasizing the importance of complementary gear use when determining fish assemblages in a conservation context.(AU)

Os caracteres morfológicos das espécies são essenciais para avaliar a estrutura funcional de uma assembleia de peixes, uma vez que as diferenças entre elas são indicativas de distintas características ecológicas. De forma geral, as planícies de maré são importantes para assembleias de peixes por oferecerem áreas para alimentação, refúgio e reprodução. Para analisar a estrutura morfofuncional da assembleia de peixes de uma planície de maré na costa brasileira, realizamos amostragens utilizando nove diferentes artes de pesca. Para descrever as formas dos peixes e verificar a diversidade morfológica da assembleia foi aplicado o método de morfometria geométrica. Aqui, apresentamos a influência/suscetibilidade de cada arte de pesca na composição morfológica da assembleia de peixes, uma vez que a forma do corpo está relacionada a diversos aspectos funcionais e ecológicos (como por exemplo nadar, procurar ativamente por comida, atacar e capturar presas, evadir de predadores, se reproduzir). Os resultados indicaram que o arrasto de praia, o arrasto de fundo, a rede de emalhar marginal e as armadilhas, em conjunto, foram os apetrechos mais efetivos para representar a máxima diversidade morfológica dos peixes que habitam esta planície de maré. Além disso, a assembleia apresentou elevada redundância morfológica, fato que indica resistência deste ecossistema para evitar a perda de diversidade funcional.(AU)

Otolith patterns of rockfishes from the northeastern Pacific.

Sagitta otolith shape was analysed in twenty sympatric rockfishes off the southern California coast (Northeastern Pacific). The variation in shape was quantified using canonical variate analysis based on fifth wavelet function decomposition of otolith contour. We selected wavelets because this representation allow the identifications of zones or single morphological points along the contour. The entire otoliths along with four subsections (anterior, ventral, posterodorsal, and anterodorsal) with morphological meaning were examined. Multivariate analyses (MANOVA) showed significant differences in the contours of whole otolith morphology and corresponding subsection among rockfishes. Four patterns were found: fusiform, oblong, and two types of elliptic. A redundancy analysis indicated that anterior and anterodorsal subsections contribute most to define the entire otolith shape. Complementarily, the eco-morphological study indicated that the depth distribution and strategies for capture prey were correlated to otolith shape, especially with the anterodorsal zone.

External morphology explains the success of biological invasions.

Biological invasions have become major players in the current biodiversity crisis, but realistic tools to predict which species will establish successful populations are still unavailable. Here we present a novel approach that requires only a morphometric characterisation of the species. Using fish invasions of the Mediterranean, we show that the abundance of non-indigenous fishes correlates with the location and relative size of occupied morphological space within the receiving pool of species. Those invaders that established abundant populations tended to be added outside or at the margins of the receiving morphospace, whereas non-indigenous species morphologically similar to resident ones failed to develop large populations or even to establish themselves, probably because the available ecological niches were already occupied. Accepting that morphology is a proxy for a species' ecological position in a community, our findings are consistent with ideas advanced since Darwin's naturalisation hypothesis and provide a new warning signal to identify invaders and to recognise vulnerable communities.

Ultrastructural damage of Loligo vulgaris and Illex coindetii statocysts after low frequency sound exposure.

There is a considerable lack of information concerning marine invertebrate sensitivity to sound exposure. However, recent findings on cuttlefish and octopi showed that exposure to artificial noise had a direct consequence on the functionality and physiology of the statocysts, sensory organs, which are responsible for their equilibrium and movements in the water column. Owing to a lack of available data on deep diving cephalopod species, we conducted a noise exposure comparative experiment on one Mediterranean squid, Illex coindetii, and on the European squid Loligo vulgaris. Scanning electron microscopy (SEM) revealed similar injuries in the inner structure of the statocysts, as those found in cuttlefish and octopi. In addition to the ultrastructural description of the lesions, we publish here the first images of the crista-cupula system and inner statocyst cavity of I. coindetii.

Morphology and ultrastructure of saccular otoliths from five species of the genus Coelorinchus (Gadiformes: Macrouridae) from the Southeast Atlantic.

The morphology of the saccular otolith (sagitta) of five species of the genus Coelorinchus (grenadiers) from the southeastern Atlantic (C. coelorinchus, C. fasciatus, C. occa, C. braueri, and C. acanthiger) was analyzed macro- and ultrastructurally by digital image processing and scanning electron microscopy (SEM). Interspecies variations have been noted in the morphology and ultrastructure of the sulcus acusticus and are linked to differences in form of the entire otolith. This relationship may indicate a genetic regulation in the growth of the sulcus. Standard canonical analysis of biometric measurements of the otolith and acoustic sulcus has proved to be a good way to distinguish otoliths of the five species of Coelorinchus. © 1995 Wiley-Liss, Inc.

Differences in morphological features of the sacculus of the inner ear of two hakes (Merluccius capensis and M. paradoxus, gadiformes) inhabits from different depth of sea.

The morphology of the sensory epithelia of the sacculus in two species of hake, Merluccius capensis and M. paradoxus, was analyzed by scanning electron microscopy (SEM). The sensory epithelia have two morphological features that are very different from other gadiform species. These include the presence of two large areas which are only linked by a narrow neck, and the larger proportion of hair cells oriented in the rostrocaudal axis than in other species. The deeper-dwelling species, M. paradoxus, has a larger proportion of hair cell with short ciliary bundles than does the shallower-dwelling species, M. capensis. These morphological specializations could improve the acoustic diserimination and localization capabilities of these species, possibly related to an increase in sensitivity to higher frequency sounds in the deeper-dwelling species. © 1992 Wiley-Liss, Inc.