Joan Navarro

Two novel Anemia enrichment diets containing polar lipid

Abstract Two novel Anemia enrichment diets were tested against control diets of Super Selco (SS) (Artemia Systems, INVE, Ghent) and bakers yeast. The first experimental diet consisted of tuna orbital oil emulsified with 12% herring roe polar lipid (P-T). The second test diet comprised liposomes incorporating the phosphatidylcholine (PC) fraction of herring roe. Enrichment efficiency was measured in terms of lipid class and fatty acid composition of enriched nauplii, with particular attention being paid to PC content, docosahexaenoic acid (DHA) levels and DHA:eicosapentaenoic acid (EPA) ratios. The P-T emulsion yielded Artemia nauplii with 14% DHA (% total fatty acids) and a DHA:EPA ratio of 1.8, significantly higher than in nauplii fed the other three diets. Polar lipid levels in both P-T and SS enriched nauplii were similar (32.4 mg g−1 and 34.7 mg g−1 dry body weight (DBW) of nauplii, respectively). Lower %DHA and DHA:EPA ratios were obtained in liposome-fed nauplii (2% and 0.3, respectively) However, they yielded significantly higher levels of naupliar polar lipid (40.1 mg g−1 DBW) than those fed the two oil emulsion treatments. The significance of these findings is discussed.

Experimental increase of flying costs in a pelagic seabird: effects on foraging strategies, nutritional state and chick condition

A central point in life history theory is that parental investment in current reproduction should be balanced by the costs in terms of residual reproductive value. Long-lived seabirds are considered fixed investors, that is, parents fix a specific level of investment in their current reproduction independent to the breeding requirements. We tested this hypothesis analysing the consequences of an experimental increase in flying costs on the foraging ecology, body condition and chick condition in Cory’s shearwaters Calonectris diomedea. We treated 28 pairs by reducing the wing surface in one partner and compared them with 14 control pairs. We monitored mass changes and incubation shifts and tracked 19 foraging trips per group using geolocators. Furthermore, we took blood samples at laying, hatching and chick-rearing to analyse the nutritional condition, haematology, muscle damage and stable isotopes. Eighty-day-old chicks were measured, blood sampled and challenged with PHA immune assay. In addition, we analysed the effects of handicap on the adults at the subsequent breeding season. During incubation, handicapped birds showed a greater foraging effort than control birds, as indicated by greater foraging distances and longer periods of foraging, covering larger areas. Eighty-day-old chicks reared by treated pairs were smaller and lighter and showed a lower immunity than those reared by control pairs. However, oxygen demands, nutritional condition and stable isotopes did not differ between control and handicapped birds. Although handicapped birds had to increase their foraging effort, they maintained physical condition by reducing parental investment and transferred the experimentally increased costs to their partners and the chick. This result supports the fixed investment hypothesis and is consistent with life history theory.

Ecological Segregation in Space, Time and Trophic Niche of Sympatric Planktivorous Petrels

The principle of competitive exclusion postulates that ecologically-similar species are expected to partition their use of resources, leading to niche divergence. The most likely mechanisms allowing such coexistence are considered to be segregation in a horizontal, vertical or temporal dimension, or, where these overlap, a difference in trophic niche. Here, by combining information obtained from tracking devices (geolocator-immersion and time depth recorders), stable isotope analyses of blood, and conventional morphometry, we provide a detailed investigation of the ecological mechanisms that explain the coexistence of four species of abundant, zooplanktivorous seabirds in Southern Ocean ecosystems (blue petrel Halobaena caerulea, Antarctic prion Pachyptila desolata, common diving petrel Pelecanoides urinatrix and South Georgian diving petrel P. georgicus). The results revealed a combination of horizontal, vertical and temporal foraging segregation during the breeding season. The stable isotope and morphological analyses reinforced this conclusion, indicating that each species occupied a distinct trophic space, and that this appears to reflect adaptations in terms of flight performance. In conclusion, the present study indicated that although there was a degree of overlap in some measures of foraging behaviour, overall the four taxa operated in very different ecological space despite breeding in close proximity. We therefore provide important insight into the mechanisms allowing these very large populations of ecologically-similar predators to coexist.

Foraging segregation between two closely related shearwaters breeding in sympatry

Trophic segregation has been proposed as a major mechanism explaining the coexistence of closely related animal taxa. However, how such segregation varies throughout the annual cycle is poorly understood. Here, we examined the feeding ecology of the two subspecies of Corys shearwater, Calonectris diomedea diomedea and Calonectris diomedea borealis, breeding in sympatry in a Mediterranean colony. To study trophic segregation at different stages, we combined the analysis of isotope values (δ 15N, δ 13C) in blood obtained during incubation and in feathers moulted during chick-rearing and wintering periods with satellite-tracking data during the chick-rearing period. Satellite-tracking and stable isotope data of the first primary feather revealed that C. d. borealis foraged mainly in the Atlantic whereas C. d. diomedea foraged exclusively in the Mediterranean. This spatial segregation could reflect the foraging behaviour of the C. d. borealis individuals before they arrived at the Mediterranean colony. Alternatively, greater wing loading of C. d. borealis individuals may confer the ability to fly across the strong winds occurring at the at the Gibraltar strait. Isotope values of the eighth secondary feather also support segregation in wintering areas between the two forms: C. d. diomedea wintered mainly in association with the Canary current, whereas C. d. borealis wintered in the South African coast. Overall, our results show that spatial segregation in foraging areas can display substantial variation throughout the annual cycle and is probably a major mechanism facilitating coexistence between closely related taxa.

Feather corticosterone of a nestling seabird reveals consequences of sex-specific parental investment

Offspring of long-lived species should face costs of parental trade-offs that vary with overall energetic demands encountered by parents during breeding. If sex differences exist in how parents make the trade-off, sex-specific differences may exist in the contribution of each parent to those costs. Adaptations of offspring facing such costs are not well understood, but the hormone corticosterone probably plays a role. We manipulated breeding effort in Corys shearwaters (Calonectris diomedea) to increase costs to offspring and used an integrated measure of corticosterone from chick feathers to investigate how experimental variation in parental investment influences offspring physiology. Average foraging trip duration and foraging efficiency (FE) of breeding pairs were not related to chick corticosterone, but sex biases in FE were. Adult male investment was more strongly related to chick corticosterone than was female investment. Importantly, we show for the first time suppression of adrenocortical activity in nestling Procellariiform seabirds, and explain how our results indicate an adaptive mechanism invoked by chicks facing increased costs of parental trade-offs.

Effects of diet on fatty acid composition of body zones in larvae of the sea bass Dicentrarchus labrax: a chemometric study

Larvae of the sea bass Dicentrachus labrax were fed four Artemia sp. diets for 28 d. Three were nauplii enriched with emulsions of polyunsaturated fatty acids, and the fourth nauplii enriched with bakers yeast. At the end of the experimental period, the fatty acids of the bodies, heads and eyes of the larvae were analysed. A multivariate statistical method (discriminant analysis, DA) applied to the data revealed anatomical as well as dietary fatty acid pattern-discrimination. We propose here the use of discriminant analysis as a pattern-recognition method that will help to integrate the fatty acid information obtained in nutritional studies.

Sexual dimorphism in bill morphology and feeding ecology in Cory's shearwater (Calonectris diomedea).

The bill is a sexually dimorphic structure in many bird species and implicated in numerous functions. Sexual differences may arise from sexual selection or ecological divergence. Here, we examined differences in bill size and shape between males and females and explored to what extent these relate to feeding ecology of each sex in Corys shearwater (Calonectris diomedea). We applied linear measurements and geometric morphometric methods to examine sexual differences in bill size and shape. We investigated feeding ecology by tracking foraging movements during the breeding period and by analysing stable isotope signatures in blood during the breeding period and in feathers grown during the non-breeding period. Bill traits were all sexually dimorphic, both in absolute and relative terms, and scaled hypermetrically with body mass in several characters in males. However, males and females did not differ in their feeding areas or isotopic signatures and no significant correlation was observed between these traits and bill dimorphism. Therefore, we discard the foraging-niche divergence hypothesis, and suggest that sexual dimorphism in bill size in this species is more likely driven by sexual selection related to antagonistic interactions.

Effect of different dietary levels of docosahexaenoic acid (DHA, 22:6w-3) on the DHA composition of lipid classes in sea bass larvae eyes

The effect of different dietary levels of docosahexaenoic acid (DHA, 22:6w-3) on the corresponding composition of lipid classes of the eyes of sea bass, Dicentraxrchus labrax, larvae was studied using Artemia nauplii enriched with different products: oil emulsions, liposomes, a dry microalga and bakers yeast. DHA was found to be a major constituent of phosphatidylserine and phosphatidylethanolamine of visual tissues. The different DHA dietary levels were markedly reflected in the fatty acid composition of the lipid classes of eyes, suggesting a dose-dependent relationship between DHA in the food and in visual tissue lipids of sea bass larvae. The possible implications of this dietary effect are discussed.

Trophic Dynamics of Deep-Sea Megabenthos Are Mediated by Surface Productivity

Most deep-sea benthic ecosystems are food limited and, in the majority of cases, are driven by the organic matter falling from the surface or advected downslope. Species may adapt to this scarceness by applying a wide variety of responses, such as feeding specialisation, niche width variation, and reduction in metabolic rates. The Mediterranean Sea hosts a gradient of food availability at the deep seafloor over its wide longitudinal transect. In the Mediterranean, broad regional studies on trophic habits are almost absent, and the response of deep-sea benthos to different trophic conditions is still speculative. Here, we show that both primary and secondary production processes taking place at surface layers are key drivers of deep-sea food web structuring. By employing an innovative statistical tool, we interpreted bulk-tissue δ13C and δ15N isotope ratios in benthic megafauna, and associated surface and mesopelagic components from the 3 basins of the Mediterranean Sea at 3 different depths (1200, 2000, and 3000 m). The trophic niche width and the amplitude of primary carbon sources were positively correlated with both primary and secondary surface production indicators. Moreover, mesopelagic organic matter utilization processes showed an intermediate position between surface and deep benthic components. These results shed light on the understanding of deep-sea ecosystems functioning and, at the same time, they demand further investigation.

Feeding ecology and trophic position of a Mediterranean endemic ray: consistency between sexes, maturity stages and seasons

The study of trophic ecology of marine predators is crucial to better understand the ecological factors that condition their role within marine ecosystems. Here we investigated the trophic habits and position of a Mediterranean endemic predator, the starry ray, Raja asterias. Specifically, we quantified the diet composition of this endemic ray in a highly exploited area of the NW Mediterranean, and we evaluated the effects of sex, maturity-stage and season on its feeding habits. Our results revealed that the starry ray is a predator of crustaceans (crabs and shrimps), and to a lower extent on teleosts, molluscs and polychaetes. This species has a high trophic position within its food web and feeds mainly on crabs (mainly Liocarcinus depurator and Goneplax rhomboides), independent of their sex, maturity-stage or season. The great importance of crabs in the diet of starry ray may be due to the fact that crabs are the dominant crustaceans in terms of biomass and abundance in the area where starry rays were collected, thus allowing them to exploit the most abundant food resource. Since the starry ray has shown a progressive decline on the catch, further research is needed to analyse the main drivers of starry ray dynamics in the Western Mediterranean Sea. Our results present important new data that will allow us to further explore the population dynamics of starry rays and the role of crustacean availability and fishing activity.