Mesozooplankton size structure in the Canary Current System.

Changes in plankton composition influences the dynamics of marine food webs and carbon sinking rates. Understanding the core structure and function of the plankton distribution is of paramount importance to know their role in trophic transfer and efficiency. Here, we studied the zooplankton distribution, abundance, composition, and size spectra for the characterization of the community under different oceanographic conditions in the Canaries-African Transition Zone (C-ATZ). This region is a transition zone between the coastal upwelling and the open ocean showing a high variability because of the physical, chemical, and biological changes between eutrophic and oligotrophic conditions through the annual cycle. During the late winter bloom (LWB), chlorophyll a and primary production were higher compared to that of the stratified season (SS), especially in the upwelling influenced area. Abundance distribution analysis clustered stations into two main groups according to the season (productive versus stratified season), and one group sampled in the upwelling influenced area. Size-spectra analysis showed steeper slopes during daytime in the SS, suggesting a less structured community and a higher trophic efficiency during the LWB due to the favorable oceanographic conditions. We also observed a significant difference between day and nighttime size spectra due to community change during diel vertical migration. Cladocera were the key taxa differentiating an Upwelling-group, from a LWB- and SS-group. These two latter groups were differentiated by Salpidae and Appendicularia mainly. Data obtained in this study suggested that abundance composition might be useful when describing community taxonomic changes, while size-spectra gives an idea of the ecosystem structure, predatory interactions with higher trophic levels and shifts in size structure.

Energetic Implications of Morphological Changes between Fish Larval and Juvenile Stages Using Geometric Morphometrics of Body Shape.

The fish body shape is a key factor that influences multiple traits such as swimming, foraging, mating, migrations, and predator avoidance. The present study describes the body morphological changes and the growth trajectories during the transformation from 24 to 54 days post-hatching in the golden grey mullet, Chelon auratus, using geometric morphometric analysis (GMA). The results revealed a decrease in morphological variability (i.e., morphological disparity) with the somatic growth. The main changes affected head size, elongation, and widening of the body. Given that this variability could affect the metabolism, some individuals with different morphologies and in different ontogenetic developmental stages were selected to estimate their potential respiration rate using the Electron Transport System (ETS) analysis. Differences were detected depending on the developmental stage, and being significantly smaller after 54 days post-hatching. Finally, a multivariate linear regression indicated that the specific ETS activity was partially related to the fish length and body shape. Thus, our findings emphasized the relevance of larval morphological variability for understanding the physiological processes that occur during the development.

Energy density of mesopelagic fishes from the Atlantic Ocean.

Mesopelagic fishes play a central role in marine food webs linking primary consumers to top predators. In this study, measures of direct calorimetry were used to analyse the energy density (ED) of 34 mesopelagic species collected at 12 stations in the equatorial and tropical Atlantic. Mean ED ranged from 2.7 kJ g-1 wet weight (WW) for the lanterfish Lampanyctus nobilis to 8.7 kJ g-1 WW for the lanterfish Benthosema glaciale. This study includes species of the orders Myctophiformes and Stomiiformes and represents migrants, non-migrants and partial-migrants species. The majority of the species were grouped into the medium-energy quality category (ED from 4 to 6 kJ g-1 ); Myctophiformes showed higher energetic values than the Stomiiformes. For the different species, the ED values were discussed in relation to spawning period and energy allocation strategies for reproduction and growth and feeding and migratory behaviour, as well as the ecoregion of study. These values will be useful for future assessment of energetic transfer between trophic levels and energetic modelling of Atlantic ecosystems.

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.

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.

Length-weight relationships of mesopelagic fishes from the equatorial and tropical Atlantic waters: influence of environment and body shape.

Length-weight relationships (LWRs) were estimated for 36 mesopelagic fish species collected from the equatorial and tropical Atlantic encompassing several oceanographic regions: oligotrophic, equatorial, Cape Blanc, Cape Verde and the Canary Islands. The sample was composed of myctophids (25 species), gonostomatids (5), sternoptychids (3), stomiids (2) and phosichthyids (1). The species were clustered according to body shape: "short-deep" (sternoptychids), "elongate" (gonostomatids, stomiids and some phosichthyids) and "fusiform" (myctophids and some phosichthyids). Three types of weight and LWRs were considered: wet weight (WW), eviscerated wet weight (eWW) and eviscerated dry weight (eDW). The study demonstrated that most species present a positive allometric growth, independent of the weight used. However, the allometric value varied in 40-50% of species depending on the type of weight considered. Significant variations linked to fish morphology were found in the relationship between the slope and intercept of the LWR equation. Significant differences were also noted in the water content linked to fish body shape. Based on the distributions of several species we compare their fitness between oceanographic regions using the relative condition factor (Krel ). Except for Diaphus brachycephalus (oligotrophic vs. equatorial waters) and Lampanyctus alatus (equatorial, Cape Blanc, Cape Verde and the Canary Islands), no regional significant differences were observed in the species analysed.

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)

Observations on the occurrence of Spraguea lophii in Mediterranean lophiids.

In the Mediterranean Sea, anglerfish Lophius budegassa and Lophius piscatorius support an important fishery, and landings have increased in recent years. These species are infected by the microsporean Spraguea lophii, a parasite that infects their nervous system giving rise to multiple cysts. Due to the high value of these fish and conspicuous nature of the infection, we determined the apparent prevalence of this parasite in both Lophius spp. Specimens were obtained from commercial catches along the NW Mediterranean Sea during 2013. The parasite was observed in the nerves from the peripheral nervous system of the individuals and was detected at the prevalence of 69.2% (202/292) and 100% (58/58) in L. budegassa and L. piscatorius, respectively. Non-significant differences were noted between sexes of L. budegassa (χ(2) = 0.683; p = 0.409), although a positive correlation was noted between host size and prevalence (χ(2) = 6.134; p = 0.013). During the sampling, two specimens of L. budegassa with atypical morphological characteristics, pigment anomalies and blindness and infected with S. lophii xenomas were described.

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.