New development in the MOCNESS,an apparatus for sampling zooplankton and micronekton

Four variants of the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) have been constructed to sample a broad size spectrum of oceanic animals from microzooplankton to micronekton. The systems differ in mouth opening dimensions (ranging from 1/4 to 20 m²), the number of nets carried (from 5 to 20), and the mesh size of the netting (from 64 m to 3.0 mm). A new electronics package enables an operator to send commands down a single conductor, armored cable to open/close the nets and provides 12-bit resolution for the environmental (temperature, depth, conductivity) and net operation data (flow, net-frame angle, net-bar release), which are transmitted up the cable to the deck unit at 2-s intervals. A microcomputer system, interfaced to the deck unit, calculates salinity, volume filtered by a net, net trajectory velocity, and vertical velocity. The data are printed out and stored on disc, and profiles of temperature and salinity versus depth are plotted during the course of the tow. Analysis of the relationship between the geometry of the MOCNESS under tow and the past and present methods used to estimate the water filtered by a net revealed that significant bias is introduced when the ascent or descent angle of a net is disregarded. The bias is a function of the ratio of vertical velocity to net trajectory velocity and results in an underestimate of volume filtered while shooting a net and an overestimate while hauling.     

Growth and recruitment of the deep-sea urchin Echinus affinis

Large samples of the sea urchin Echinus affinis Mortensen were obtained from a time-series of Agassiz trawlings from a 2 200 m-deep permanent station (Station M), and at neighbouring positions, in the Rockall Trough (North-east Atlantic Ocean) over a period of 7 yr (1978 to 1985). Counts of growth zones visible in the skeletal elements of the test were used to age individuals. Various growth functions were fitted to counts from a full range of the sizes available. Functions giving a sigmoidal growth curve fit the early phase of growth better than the von Bertalanffy model, although the latter provided better fit amongst larger sizes. The fit of a robust and flexible model recently developed by Preece and Baines to describe the human growth curve overcame this limitation. Skeletal banding is thought to result from seasonally varying growth as a result of annually pulsed fallout of phyto-detrital food to the deep-sea floor. Early stages were found in only a few of a time series of samples obtained with a fine-meshed epibenthic sledge, suggesting that recruitment to the population from its annual breeding may only occasionally be successful. Postlarval growth was estimated from samples taken soon after presumed settlement and later in the year. The fitted growth curve showed good agreement to that obtained from annual banding, and corroborates an initially exponentially increasing growth rate. Postlarval survivorship was estimated, by means of computer simulation, from a sample that included postlarvae along with a range in juvenile size, to be about 10% amongst postlarvae after settlement and thereafter about 90% yr^-1. Adults are inferred to be up to about 28 yr old. A markedly uneven representation of ages in a large subsample of aged adults of even frequency in size is interpreted by means of simulations as probably reflecting multi-year cycles in recruitment success. The possible causes of a varying size structure amongst large samples of adults, which showed some spatial segregation in relation to the track of the trawl on the bottom at Station M, are discussed.     

Stereophotography for the field biologist: measurement of lengths and three-dimensional positions of free-swimming sharks

A stereophotographic technique for determining size and relative position of free-swimming sharks is described and illustrated for schooling scalloped hammerhead sharks (Sphyrna lewini). The method yields total length and nearest-neighbor, interindividual distance; and each of these dimensions is expressed as a function of the shark's distance into a school on the vertical and horizontal planes. Stereopairs of photographs were taken by an aligned, beam-mounted pair of cameras (Nikonos III). The scale to determine the length of a shark from the paired photographic images was obtained from the horizontal displacement between the images. Displacement was correlated with optical axis separation from photographs of a scaled staff at known distances from the camera. Image dimensions on the photographs were measured by projecting a scale onto the stage through a camera lucida. The precision of repeated measurements of a 50 cm section of a scaled staff at increasing distances from the cameras of 2, 4, and 8 m was ±5.0%. Lengths of the sharks ranged from 109 to 371 cm, with a median of 178 cm, for 3 offshore sites in the Gulf of California during July and August 1979. At one site, El Bajo Gorda, lengths increased with both distance from the camera and distance into the group; in contrast, the interindividual distances (head-to-head) did not vary with distance into the group and possessed a median of 232 cm.     

Measurement of photosynthetic production of a marine phytoplankton population using a stable 13C isotope

The use of stable isotope of carbon, ¹³C, for the determination of the photosynthetic rate of a marine phytoplankton population was examined. Particular concern was paid to the effects of non-phytoplanktonic organic carbon and the enrichment of inorganic carbon on the estimation of the photosynthetic rate. Photosynthetic rates determined by the ¹³C method showed a remarkable agreement with those determined by the ¹⁴C method. Insitu determinations of photosynthetic rate were made in three different water types: open ocean, coastal and neritic waters, which included oligo- and mesotrophic waters, by using the ¹³C method established.     

Synergistic effects of nitrate and ammonium ion on the growth and uptake kinetics of Monochrysis lutheri in continuous culture

Continuous-culture results for Monochrysis lutheri grown on 12 h light-12 h dark cycles with a spectrum of ratios of nitrate and ammonium serving as limiting nutrients are compared with continuous light, exclusively nitrate, and exclusively ammonium-limited data for this species. The diel effects of the light regime on the maximum specific uptake rate are examined for both nitrate and ammonium. Synergistic effects on uptake by various initial concentrations of these two nutrients are presented. Preconditioning with light-dark cycles did not affect maximum uptake rate, but preconditioning on a combination of nitrate and ammonium gave much lower uptake rates than those observed for populations preconditioned on either nutrient exclusively. The implications of high maximum specific-uptake rates compared to maximum specific-growth rates in terms of the range of nitrate and ammonium ion concentrations associated with nutrient limitation are reviewed.Hawaii Institute of Marine Biology Contribution No. 477.     

Halocyprid ostracods in Atlantic neuston

Twenty-one species of halocyprid ostracods were identified from 7778 specimens caught in 144 neuston net hauls taken from the research vessel “Walther Herwig” in the Atlantic Ocean. Hauls taken during dusk were richer both in specimens and in species than later in the night. Few if any specimens occurred in daytime catches. Eighty-eight percent of the specimens were male Conchoecia spinirostris, which were observed to swarm at the surface at dusk in two positions. Many of the species occurred over a wide range of hydrographic conditions, and only in the region 40°S; 39°W did representatives of the cold-water fauna appear. The species could be categorised into 5 groups, depending on zoogeographical ranges and daytime depth distributions; the majority of the species ranged from 40°N–40°S, and had daytime maxima in the upper 100 m. It is concluded that ostracods only constitute important food items for carnivores feeding in the neuston when the latter are permanently in the neuston; the occurrence of vertically migrating carnivores does not coincide with the maximum occurrence of ostracods in the neuston.     

Morphometric and genetic analysis as proof of the existence of two sturgeon species in the Guadalquivir river

Morphometric and genetic methods were used to identify two sturgeon species, Acipenser naccarii Bonaparte, 1836, and A. sturio Linnaeus, 1758, captured in some of the principal rivers of the Iberian Peninsula, including the Guadalquivir. After measuring 25 Iberian specimens from a fishery and several Spanish and Portuguese museums and applying stepwise discriminant analysis (SDA), four specimens preserved in different museums [two specimens from the Guadalquivir river (EBD-8173 and EBD-8174), one specimen from the Tagus river (MUC1) and one specimen from the Mondego river (MUC46B)], as well as five specimens captured in the Guadalquivir river in the 1940s but not preserved (CM1, CM2, CM3, CM4 and CM5), were identified as A. naccarii. After cloning and characterisation of a satellite-DNA family, HindIII, from A.␣naccarii genome, its absence from the genome of A.␣sturio was determined. Using this satellite-DNA as a genetic marker and by means of dot-blotting, we demonstrate that the DNA of the two specimens captured during the mid-1970s in the Guadalquivir river cross-hybridised with HindIII satellite-DNA sequences of A.␣naccarii. We conclude that A. naccarii is autochthonous to the Iberian Peninsula and is not, as was previously believed, endemic to the Adriatic Sea. Received: 28 November 1996 / Accepted: 10 March 1997     

Effects of salinity and dietary DHA (22:6n - 3) content on lipid composition and performance of Penaeus kerathurus postlarvae

A two-way ANOVA experiment was designed to study the effects of salinity and dietary docosahexaenoic acid (DHA; 22:6n-3) on lipid composition and performance of postlarvae from the marine shrimp Penaeus kerathurus (Forskål, 1775). Shrimp were reared from 1- to 8-d-old postlarvae at 35 and 25‰S with Kelko-enriched Artemia sp. [20.0 μg (n-3)?HUFA mg^?1 dry weight; 9.1 μg DHA mg^?1 dry weight] and nonenriched Artemia sp. [14.2 μg (n-3)?HUFA mg^?1 dry weight; 0.3 μg DHA mg^?1 dry weight]. Dietary DHA content did not affect either total length or survival but influenced the nutritional status represented by condition indices (triacylglycerol/total polar lipid and triacylglycerol/free cholesterol) of 8-d-old postlarvae at the end of the experiment. Culture salinity affected final total length and condition indices but did not show any effect on survival in the different experimental treatments. The interaction of dietary DHA and culture salinity was not significant for total length and survival but was significant for both condition indices used. P. kerathurus 8-d-old postlarvae showed better growth, survival and nutritional condition when reared at 35‰S and when fed on Kelko-enriched Artemia sp., but the differences with postlarvae from other treatments were very poorly marked. The results demonstrate that 8-d-old postlarvae may have sufficiently developed osmoregulatory capabilities to resist 25‰S under good conditions, although (n-3) HUFA-enriched diets may also enhance osmotic stress resistance, general performance and disease resistance.     

Certainty of paternity covaries with paternal care in birds

Summary Male investment in parental care has been hypothesized to be affected or not to be affected by their certainty of paternity, depending on the particular assumptions of theoretical models. We used data on paternal care and extra-pair paternity from 52 bird species to determine whether male parental care was related to certainity of paternity. Paternal care was measured as the relative male contribution to nest building, courtship feeding, incubation, and feeding of nestlings, respectively. Males of avian taxa did not provide less parental care during nest building, courtship feeding and incubation if the frequency of extra-pair paternity was high. However, male participation in feeding of offspring was significantly negatively related to the frequency of extra-pair paternity. This was also the case when the effects of potentially confounding variables such as developmental mode of offspring (which may result in males being freed from parental duties), extent of polygyny (which may result in less paternal care), and the frequency of multiple clutches during one breeding season (which may increase the probability of finding fertile females during the nestling period) were controlled statistically. These results suggest that the extent of paternal care has been affected by certainty of paternity, and that sex roles during the energetically most expensive parts of reproduction have been shaped by sperm competition.