Effects of density dependence, zooplankton and temperature on blue whiting Micromesistius poutassou growth

Blue whiting Micromesistius poutassou mean total length at age in the north-east Atlantic Ocean was found to vary by around ±6% during the period 2004–2011 and mean mass at age by ±22% during the years 1981–2013. Linear modelling provided strong evidence that these phenotypic growth variations can be explained by trophic conditions, mainly negative density dependence and also food availability, and a negative long-term temperature effect on asymptotic siz

Age-dependence of cultured pearl grade and colour in the black-lipped pearl oyster Pinctada margaritifera

Pinctada margaritifera is an economically important marine bivalve species for cultured pearl production in French Polynesian aquaculture. In order to evaluate the influence of donor oyster age on pearl quality traits, experiments were conducted over 6 years using both grafts and surgreffe operations. At harvest, 6 pearl quality traits were recorded and compared: surface defects, luster, grade, darkness level, and visual color. Analyzing the quality traits of pearls harvested in the initial graft process and those of pearls obtained from surgreffe experiments allowed a comparison of the influence of pearl sac cells originating from the initial mantle graft, which aged together with their recipient oysters. The results demonstrated a significant decrease between these successive grafts in luster, grade (A-B-C,) darkness level, and green color – traits that are of major importance in the pearl market. The duplicated graft experiment allowed the comparison of donor oyster families at 2 and 5 years old, where a mantle graft was inserted into recipient oysters aged 2.5 years old. The results showed the same tendencies to a lesser extent, with 1) an improved pearl grade, predominantly through a most important rate of 0 surface defect category, and 2) a green / grey ratio in favor of the younger donor. A comparison between the graft-surgreffe and the duplicated graft experiments also highlighted: 1) the indirect role played by the younger recipient oysters, which must be optimized for optimal pearl quality realization, and 2) the complex interplay between donor and recipient oysters.

Lipid and lipid carbon stable isotope composition of the hydrothermal vent shrimp Mirocaris fortunata: evidence for nutritional dependence on photosynthetically fixed carbon

Mirocaris fortunata were sampled from the Lucky Strike hydrothermal vent area (Eiffel Tower site) on the mid-Atlantic ridge during the French DIVA 2 cruise (June 1994). Small adults (17 to 22 mm total length), although morphologically identical, could be divided into 2 categories on the basis of pigmentation, lipid composition and C-13/C-12 stable isotope ratios of fatty acids. Highly pigmented small adults (8.6 to 9.2 mu g carotenoid shrimp(-1)) contained higher levels of total lipid than similar-sized individuals containing lower levels of pigment (0.9 to 2.9 mu g carotenoid shrimp(-1)). Lipid class analysis indicated that wax esters comprised 62.5% of total lipid in the former group. These pigmented shrimp also contained high proportions of polyunsaturated fatty acids (PUFA), particularly the phototrophic microplanktonic markers 20:5(n-3) and 22:6(n-3) (14.0 and 33.5% respectively). By contrast small adults (22 mm) and adult shrimp (25 to 26 mm) with low levels of carotenoid pigmentation contained lower amounts of total lipid, little or no wax ester and low levels of 20:5(n-3) and 22:6(n-3), but did contain 16:2(n-4) and 18:2(n-4) and the non-methylene interrupted dienes 20:2 Delta 5,13 and 22:2 Delta 7,15. GC-IRMS analysis of all fatty acids and fatty alcohols in the pigmented small adults indicated delta(13)C values of -18.2 to -27.7 parts per thousand, which is consistent with a photosynthetic carbon source for these compounds. The C-13/C-12 isotope composition of fatty acids from low-pigmented small adults and adults was more variable (-12.5 to -33.1 parts per thousand) and suggests a bimodal distribution which may be attributable to differing nutritional sources or the physiological/reproductive status of these shrimp. Samples of eggs, which are carried by the female on the pleopods, represented approximately 57% of total somatic lipid which indicates a substantial reproductive investment by this species. The egg lipids comprised high proportions of triacylglycerols (64.4 to 78.0% of total lipid) whilst the fatty acid composition was dominated by the monounsaturated fatty acids 16:1(n-7), 18:1(n-7) and 18:1(n-9), which accounted for 65.7 to 33.5% of total fatty acids. By contrast, PUFA were relatively minor components of egg lipids, particularly 20:5(n-3) and 22:6(n-3), which accounted for only 1.1 and 2.9% of total egg fatty acids respectively. This indicates that the reproductive investment by this species is supported mainly by material derived from bacterial chemosynthesis. The potential for M. fortunata hedge betting by producing larvae which either metamorphose at the vent site or adopt a bathypelagic lifestyle and delay metamorphosis to facilitate more widespread dispersal is discussed.