Isolation and characterization of polymorphic microsatellites for the sardine Sardina pilchardus (Clupeiformes: Clupeidae)

The sardine Sardina pilchardus Walbaum, 1792 is a small pelagic fish species that sustains an economically important fishery in the eastern Atlantic Ocean. Eight perfect microsatellite loci of sardine were characterized from a partial genomic library enriched for CA repeat sequences. All loci revealed high levels of polymorphism, with the number of alleles per locus ranging between 22 and 45, and an average observed heterozygosity of 0.772. The newly described loci can be employed to determine population genetic structure of the sardine, and may aid in fishery management of this species.     

Ontogenetic diet shifts of rough scad Trachurus lathami in the North Patagonian shelf (south-west Atlantic Ocean)

Rough scad Trachurus lathami is a key pelagic fish in the Argentinean continental shelf (ACS, south-west Atlantic Ocean), with recent increases in abundance. It is a main prey of fishes and marine mammals, and shares the environment with commercially relevant pelagic species (Engraulis anchoita and Scomber colias), playing an important role linking lower and upper trophic levels in the ecosystem. This study aims to determine the ontogenetic changes in the diet composition, feeding strategy, trophic niche breadth and trophic level of T. lathami in the North Patagonian Shelf (43°–45°30′S). The stomach contents of adult fish (n = 238) were analysed. The results suggest a clear ontogenetic shift in the diet at a size of ~190 mm. Smaller individuals (160–190 mm) were specialized on misidaceans, and showed the highest trophic level, while larger T. lathami (221–230 mm) consumed decapods (Peisos petrunkevitchi) and teleosts (eggs and larvae). Trophic niche breadth was higher at the medium-sized class (191–220 mm), which mainly preyed on copepods (Calanoides carinatus) and chaetognaths (Sagitta spp.), evidencing a more diverse diet and a rather generalist strategy. Updated information on the trophic ecology of T. lathami evidences its extremely plastic feeding behaviour, being able to adapt its trophic niche to the most readily available food items from the mesopelagic community.     

Trophic niche overlap between round sardinella (Sardinella aurita) and sympatric pelagic fish species in the Western Mediterranean

The northward expansion of round sardinella (Sardinella aurita) in the Mediterranean Sea, together with declines and fluctuations in biomass and landings of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) observed in recent decades, may suggest potential inter‐specific competition in the pelagic domain. The coexistence of sympatric zooplanktivorous fish species might therefore be exposed in part to trophic niche overlap and competition for food. Combining visual diet characterization under the microscope with DNA metabarcoding from stomach contents of fish collected in spring results show that predation on relatively large krill is equally important for sardinella than for the other two niche overlapping species. Furthermore, an important overlap is found in their isotopic niche, especially with anchovy, using nitrogen (δ¹⁵N) and carbon (δ¹³C) stable isotopes in muscle tissue. In fact, the three fish species are able to feed effectively in the whole prey size spectrum available during the sampled season, from the smallest diatoms and copepods to the larger prey (i.e., decapods and euphausiids), including fish larvae. Moreover, effective predation upon other large prey like siphonophores, which is observed only when multi‐proxy analyses in stomach contents are applied, might also be relevant in the diet of sardinella. The overlapping diet composition in spring, together with the effective use of food resource by sardinella, can be of special interest in potential future scenarios with warmer water temperature leading to lower zooplankton and/or higher jellyfish availability, where sardinella may take advantage over other species due to its feeding plasticity.     

A preliminary examination of the diet and feeding of sea sweep Scorpis aequipinnis (Pisces: Scorpididae) from coastal waters of south-western Victoria, Australia

The diet and feeding of sea sweep (Scorpis aequipinnis) was investigated from 230 specimens collected from the south-western Victorian coastline between January and July, 2002. Stomach content analysis indicated that S. aequipinnis are browsing omnivores (55.6% algae, 25.4% animal, by dry weight), with rhodophytes found to be the most important component of their diet (93.5% frequency of occurrence; 42.6% dry weight; 45.5% prey-specific abundance). However, the relative proportions of the major dietary components differed significantly between size classes. The dietary composition of small individuals ( < 150 mm total length) was significantly different to larger individuals, primarily due to a higher degree of carnivory exhibited by the smaller fish. S. aequipinnis were found to be highly flexible feeders exploiting both benthic and pelagic food resources, characterised by irregular periods of selective carnivorous feeding.     

Genetic identification of Anisakis larvae in European hake from Atlantic and Mediterranean waters for stock recognition

The occurrence of seven species of the larval parasitic nematode Anisakis , which can be used as a biological tag for hake Merluccius merluccius stocks throughout their geographical range, is reported. Hake were collected from 14 localities in the Mediterranean Sea and the Atlantic Ocean. Anisakis larvae ( n  = 1950), which were recovered, were identified to species by means of genetic markers (allozymes). Within Anisakis type I, the larvae of A. pegreffii , A. simplex s.s ., A. typica and A. ziphidarum were detected, while within Anisakis type II, A. physeteris , A. brevispiculata and Anisakis sp. were identified. There were significant differences in the relative proportions of the various Anisakis species identified in hake samples from the Mediterranean Sea and Atlantic Ocean, suggesting the existence of different stocks of M. merluccius in European waters.     

Determination of feeding mode in fishes: the importance of using structural and functional feeding studies in conjunction with gut analysis in a selective zooplanktivore Chirostoma estor estor Jordan 1880

Anatomical and histological studies of the endangered atherinid Chirostoma estor estor reveal that the species is ideally adapted to feeding on zooplankton. It has a superior protractile mouth with short unicuspid mandibular teeth. The buccal cavity is a highly adapted branchial sieve with branchial spines which develop in complexity with age to form a continuous flexible interdigitated mat. The filter bed has many of the characteristics of a cross-flow filter, which is ideal for a continuously feeding and filtering animal as the filter bed will not readily become occluded. The aggregates from the cross-flow filter pass to the rear of the buccal cavity where they are triturated by well-developed pharyngeal teeth. The species has a short intestine (<0·3 × body length) with no histological evidence of stomach-like structures, no pyloric caecae and with trypsin-like enzymes operating at high pH. Feeding trials with natural plankton showed a sequence of particle size selection as the animals grow, with older animals taking cladocerans up to 700 μm in diameter. Although some adults occasionally take small fish prey, cumulatively, the present studies indicate that the fish is a zooplankton feeder throughout all its life stages.     

The diet of native and invasive fish species along the eastern Mediterranean coast (Osteichthyes)

The opening of the Suez Canal in 1869 enabled the invasion of more than 100 alien fish species into the Mediterranean. The aim of the present study was to compare the diet of native and alien fish species and to identify possibly shared food resources. We examined the diet composition of 13 of the most abundant fish species (6 alien, 7 native) on shallow soft bottom off southern Israel. All 13 species are omnivorous/carnivorous. The native fish exhibited a wider diversity of food types than the aliens. Alien fish prey upon and are preyed by native species as well as by other alien fish. A high level of diet overlap was found among some species, the aliens Saurida lessepsianus and Scomberomorus commerson overlapped with the native Synodus saurus; and the alien Nemipterus randalli with the native species Pagrus caeruleostictus, Lithognathus mormyrus and Pagellus erythrinus. The identified diet overlap is discussed, and the possibility of competitive interactions between these species is considered.     

Atlantic bluefin tuna Thunnus thynnus feeding ecology in the northern Gulf of Mexico: a preliminary description of diet from the western Atlantic spawning grounds

A combination of stomach contents, nitrogen stable‐isotope and tissue C:N values are presented to demonstrate feeding activity of Atlantic bluefin tuna Thunnus thynnus on the Gulf of Mexico (GOMEX) spawning grounds. Diets include teleosts, cephalopods, crustaceans and a pelagic tunicate (Pyrosoma atlanticum). Results reveal the need to classify the GOMEX as a T. thynnus feeding ground.     

Observations on the biology and seasonal variation in feeding of the east coast round herring Etrumeus wongratanai (Clupeiformes), off Scottburgh,KwaZulu-Natal,South Africa

The basic biology and ecology of the South African east coast round herring Etrumeus wongratanai was investigated from samples of fish collected between 2013 and 2016. This species is short-lived and reaches a maximum of 3 years of age, with rapid growth in its first year of life. It reproduces from June to December (austral summer) and condition factor was lowest in May through to August and increased from September, probably reflecting the physiological strain before and during spawning. Fish larvae were the most important food items consumed during summer, whereas eucalanid copepods were the most important prey at other times of the year. Stable-isotope data suggest that there are gradual changes in the trophic level with increasing fish size, δ¹⁵N and δ¹³C values also differed between seasons. The results obtained here are compared with those of other Etrumeus species, regionally and globally.     

Abundance, distribution, reproduction and diet of notacanthid fishes from the north-east Atlantic

Notacanthid fishes were among the 10 most abundant species sampled in research surveys using fine meshed trawls fished to depths of 3000 m in the Rockall Trough and 4500 m in the Porcupine Seabight between 1975 and 1992. Two species, Noctacanthus bonapartei and Polyacanthonotus rissoanus , were dominant but their population structure and certain aspects of morphometric and reproductive biology differed between the two sampling areas. In general, sex ratios were skewed in favour of females, size increased with depth and male and immature individuals were restricted to shallower depth zones. Fecundity was highly correlated with total weight and showed a positive relationship with species' size. Ovaries contained two batches of eggs and the spawning season was protracted, occurring mostly over winter months. Dietary studies showed a dependence on benthic macro fauna though the two dominant species have different dentition and exploit different trophic niches. In the Rockall Trough, peak abundances for N. bonapartei and P. rissoanus occurred in the 750 m and 1250 m zones, respectively, lying within the depth range currently exploited by commercial deep-water trawls (600–1400 m). The probable impacts of commercial operations on notacanthid fishes are discussed.     

Community structure and diet of roving herbivorous reef fishes in the Abrolhos Archipelago, south-western Atlantic

Community structure and diet of roving herbivorous reef fishes were analysed in 13 study sites around the five islands of the Abrolhos Archipelago, north-eastern Brazil (17°58' S; 38°42' W). This area has been part of the Abrolhos Marine National Park since 1983. Abundances and diets of fishes within the families Scaridae, Acanthuridae and Kyphosidae were compared among groups of sites differing in benthic community structure and exposure regime. The abundance of roving herbivorous fishes was higher in shallower sites than in deeper sites. At all study sites, observations of total herbivorous reef fish community structure revealed that 64% of fishes were acanthurids, 33% were scarids and only 4% were kyphosids. This pattern was predominant in all study sites. The majority of fishes examined in this study had the bulk of their diet based on both algae (35–90%) and detritus (35–65%). Among groups of algae, filamentous algae were the most commonly consumed as the majority of roving herbivorous fishes in Abrolhos feed as scrapers and excavators. The exceptions were the kyphosids, which had a diet consisting primarily of macroalgae (mainly Phaeophyta), and Acanthurus coeruleus that consumed mainly turf algae and very little detritus. The data collected indicate that roving herbivorous fishes in the Abrolhos Archipelago are more abundant at calm sites where detritus and delicate algae, their major food resources, are more abundant. The results presented here, along with underwater observations, suggest that the abundance and diet of these three fish families are associated with substratum cover.     

First global approach: morphological and biological variability in a genetically homogeneous population of the European pilchard, Sardina pilchardus (Walbaum, 1792) in the North Atlantic coast

The European pilchard Sardina pilchardus represents the most commercially relevant fisheries resource in many countries bordering north Atlantic coasts and the Mediterranean Sea, being especially significant along the coast of Morocco. The continuous exploitation of this pelagic species for several decades places Morocco as the leader in sardine production. However, the conditions of exploitation of this resource underwent a great change during the last recent years. In order to identify the populations of the European pilchard sardine (Sardina pilchardus, Walbaum, 1792) in the Atlantic coast of Morocco and Spain, we have combined the truss network data to conduct multivariate analysis with biologic parameters and genetic analysis based on Microsatellite and mitochondrial control region data. Sardine morphometrics data truss variables from 10 samples spanning the Atlantic coast of Morocco were analysed by multivariate analysis. Thirteen morphometric measurements and some biological parameters such as the sex and the age of fishes were made for each individual. Discriminant analysis on size-corrected truss variables and cluster analysis of mean fishes shape using landmark data indicate, that the shape of north Moroccan sardines is distinct from the shape of sardines from south Morocco. However the analysis of the mitochondrial region and four microsatellites loci (Sp2, Sp7, Sp8 and SpI5) demonstrated an homogeneity population in the Moroccan Atlantic coast, with a low but significant genetic differentiation, which followed an isolation-by-distance pattern according to Mantel test.     

Comparison of size-structured and species-level trophic networks reveals antagonistic effects of temperature on vertical trophic diversity at the population and species level

It is predicted that warmer conditions should lead to a loss of trophic levels, as larger bodied consumers, which occupy higher trophic levels, experience higher metabolic costs at high temperature. Yet, it is unclear whether this prediction is consistent with the effect of warming on the trophic structure of natural systems. Furthermore, effects of temperature at the species level, which arise through a change in species composition, may differ from those at the population level, which arise through a change in population structure. We investigate this by building species-level trophic networks, and size-structured trophic networks, as a proxy for population structure, for 18 648 stream fish communities, from 4 145 234 individual fish samples, across 7024 stream locations in France from 1980 to 2008. We estimated effects of temperature on total trophic diversity (total number of nodes), vertical trophic diversity (mean and maximum trophic level) and distribution of biomass across trophic level (correlation between trophic level and biomass) in these networks. We found a positive effect of temperature on total trophic diversity in both species- and size-structured trophic networks. We found that maximum trophic level and biomass distribution decreased in species-level and size-structured trophic networks, but the mean trophic level decreased only in size-structured trophic networks. These results show that warmer temperatures associate with a lower vertical trophic diversity in size-structured networks, and a higher one in species-level networks. This suggests that vertical trophic diversity is shaped by antagonistic effects of temperature on population structure and on species composition. Our results hence demonstrate that effects of temperature do not only differ across trophic levels, but also across levels of biological organisation, from population to species level, implying complex changes in network structure and functioning with warming.     

Comparison of two indices based on macrophyte assemblages to assess the ecological status of coastal waters in the transition between the Atlantic and Mediterranean eco-regions

Several indices based on the composition and abundance of aquatic flora have been developed to assess the ecological status of coastal waters along the European coasts in the context of the Water Framework Directive. This directive pointed out the intercalibration of indices based on the same biological element within an eco-region to ensure the consistency and comparability among them. For a better management of coastal areas in the transition zone between two eco-regions, the comparison of indices developed for each eco-region may also be necessary. The aim of this work was to compare two indices based on macrophytes that have been proposed for two different and adjoining eco-regions: the RSL (Reduced Species List) in the Atlantic eco-region and the CARLIT (Cartography of littoral and upper sublittoral communities) in the Mediterranean. These indices were applied in 14 sites in the transition between the Atlantic Ocean and the Mediterranean Sea, where a wide range of anthropogenic pressures can be found, from high (Algeciras Bay) to almost negligible ("El Estrecho" Natural Park). Overall, both indices were sensitive to anthropogenic pressures and suitable to assess the ecological status. The comparison between indices suggested a bias in the assessment of the ecological status between good and high classes due to a different definition of high ecological status class between RSL and CARLIT. In addition, the most important disagreements between indices were found in the most degraded localities. The results showed, however, a high comparability between RSL and CARLIT despite their marked conceptual and methodological differences.     

Phenotypic plasticity and the possible role of genetic assimilation: Hypoxia-induced trade-offs in the morphological traits of an African cichlid

In this study we investigate the possible role of phenotypic plasticity and genetic assimilation in the process of adaptation and evolutionary change in the cichlid Pseudocrenilabrus multicolor victoriae . In the field we compared a population of a stable hypoxic habitat with one of a stable well-oxygenated habitat. In the laboratory, we compared individuals from the same mother raised under hypoxic or well-oxygenated conditions to examine phenotypic plasticity. Morphological parameters of three categories were measured: (a) the gill apparatus, (b) the surrounding structural elements, and (c) the outer shape of the fish. Swamp-dwelling fish had a 29% greater total gill surface area than fish from the well-oxygenated habitat due to their larger gill filament length and greater lamellar area. In the plasticity experiment, total gill surface area was 18% greater in the hypoxia group due to a larger number of longer filaments. Surrounding elements and outer shape also differed between the field populations and between fish grown under hypoxic and well-oxygenated conditions, but there was disparity between the field results and the plasticity experiment. The disparity between field and experimental fish may be due to: (a) differences in selection pressures between populations, (b) different constraints for genetic and plasticity changes, or (c) selection against plastic responses to hypoxia. Our results suggest that both (a) and (c) are involved.     

Considerations on the diet composition and feeding rate of dermersal sharks in 15 European public aquaria

To get an overview of the feeding practices applied to dermersal sharks in captivity, a questionnaire was sent to 15 European public aquaria. The most common dermersal shark species kept in the participating aquaria are Carcharhinus plumbeus (n=9), Carcharias taurus (n=7), and C. melanopterus (n=6). Body weight (BW) was calculated using captive estimated body length (BL) and actual weight data obtained from commercial fisheries. The estimated BW for C. plumbeus in all participating aquaria is higher than the calculated BW. The feeding rate (FR) for adult C. plumbeus varied widely within participating aquaria (2.3–11.5% BW_cal/week or 32–112 kcal/kg BW_cal/week). The FR for adult C. plumbeus was lower (1.2–7.9% BW_est/week or 17–99 kcal/kg BW_est/week) using the estimated BW. Adult Carcharias taurus were fed at 1.3–5.0% BW_cal/week or 70–170 kcal/kg BW_cal/week. Negaprion brevirostris was fed at 5.0% BW_est/week or 57 kcal/BW_est/week. The relationship between FR and estimated BW is expressed as FR=54.5 e^?0.033BW. In this study, the feeding frequency for C. plumbeus varied between 1–7 times a week, with an average of 3.3 times a week. Diet in all aquaria consisted of both lean and fatty fish, and sometimes squid or crustaceans. Supplementation of vitamins is common practice in 80% of the surveyed aquaria, although a wide variety of quantity and quality was observed. Ten aquaria (66%) add iodine, as potassium iodide (0.4–12.5 mg KI/kg BW/week) or calcium‐iodate (322–1,500 mg/kg food/week), to their food. Zoo Biol 22:203–226, 2003. © 2003 Wiley‐Liss, Inc.     

The CARLIT method for the assessment of the ecological quality of European Mediterranean waters: Relevance,robustness and possible improvements

The application of the European Union (EU) Water Framework Directive (WFD) requires the assessment of the ecological status (ES) of coastal waters in order to detect environmental changes and implement management plans to prevent their further deterioration. The ES of a water body (WB) has to be assessed on the basis of the status of several biological indicators, referred to as biological quality elements (BQE), such as phytoplankton, macroalgae, seagrasses, macroinvertebrates and fish. We present the most extensive assessment ever undertaken of the ES of Mediterranean waters, by means of the CARLIT index, the most widely used index for the Mediterranean Sea. This index is based on the Ecological Quality Ratio (EQR) between a measured value of Ecological Quality (EQ) and a value corresponding to a reference site. This assessment is based on an extensive field study, covering the whole of the Mediterranean French coasts (including Corsica), 40 WBs and ∼2 970 kilometres of shore (at a 1/2 500 scale). The original Ballesteros CARLIT method is compared to the Nikolić modified method, and we have undertaken the challenge of developing an alternative new simplified CARLIT method. This simplified method, which requires less expert judgement, is easier to implement by local authorities, and provides results similar overall to those of the original method. Previous attempts, if any, to correlate EQRs with anthropogenic stressors (through pressure indices) were mainly based upon land uses or on comprehensive lists of stressors, some spatially very sporadic, temporally highly variable, non-representative of the WB and with the impact poorly established on species and communities. To date, the LUSI (Land Uses Simplified Index) and the MA-LUSI-WB have been the most widely used pressure indices. Here, we propose a new pressure index (HAPI) taking into consideration the possible shortcomings of previous indices. It takes into account the actual pressures at community levels considered by the CARLIT method. It accounts well for the EQR values of the study area, as evidenced by the high correlation coefficient between EQRs and HAPI, better than that of the other pressure indices. The present study provides a comprehensive view of the ES of the French Mediterranean coasts. Surprisingly, the picture is far less cause for concern than expected, although this could result from an artefact due to the focus on superficial waters and habitats inherent to the CARLIT method. Where two successive assessments were performed (23 WBs, 2007–2010 vs 2012–2015), the results were similar, which stresses the robustness of the method and/or the relative stability over time of the overall ES of the WBs, and suggests that the successive assessments could be carried out at low frequency.     

Millennial-scale paleoenvironmental changes in the central Mediterranean during the last interglacial: Comparison with European and North Atlantic records

The environment of the central Mediterranean Sea is investigated on the basis of high-resolution planktonic foraminifera and calcareous nannofossil data (mean sampling resolutions of about 80 and 160 yr, respectively). MIS 5 is characterized by warm, oligotrophic and stratified waters, while coccolithophore communities developed a vertical zonation that, in today's oceans, is typical of the low-latitude gyres. The temperate-subtropical configuration of planktonic foraminifera and calcareous nannofossil assemblages is repeatedly transformed into a temperate-subpolar one during the suborbital cooling episodes C25-C18. A comparison with European pollen sequences and North Atlantic cores over the interval between about 128 and 110 kyr BP is carried out. Records from this broad geographical area show a series of environmental changes that occurred at comparable times. However, the first cooling episodes were more severe at high-latitude (approximately north of 50°N), where an anticipated end of interglacial conditions can be ascribed. Variations in the rate of the Atlantic meridional overturning circulation and the strength of atmospheric circulation in the Northern Hemisphere are discussed as likely climatic forcing mechanisms.