Age estimation methods in the marine gastropod Buccinanops globulosus comparing shell marks and opercula growth rings

Age determination in gastropods is an essential tool for understanding the main aspects of population dynamics that allow for the formation of fisheries policies. Small-scale fisheries of the nassariid gastropod Buccinanops globulosus from northern Patagonia are not yet regulated, although it is locally consumed while an incipient commercialization is taking place. The aim of this study was to show the suitability of opercula readings for age estimation in B. globulosus, compared with shell marks, previously validated by the analysis of the stable isotope of oxygen. The individual age estimated by the opercula rings reading method did not match the estimation made by the shell marks reading method. Stable isotope analyses confirmed that shell marks were deposited annually. Proper age estimation for B. globulosus, based on recognizable external shell marks, reached up to 9 years.     

High incidence of otolith abnormality in juvenile European flounder Platichthys flesus from a tidal freshwater area

Otolith abnormality has been reported for a wide range of freshwater and marine fish species. In this study, the sagittal otolith morphology and mineralogy of juvenile European flounder, Platichthys flesus, were examined to describe the incidence and types of structural deformities in this species. Juvenile flounder were collected over the years 2013–2015 in the tidal freshwater section of an estuarine nursery (Minho estuary, NW Portugal). Otolith abnormality was found in 43% of the individuals and, in most cases, occurred in both otoliths. Despite an abnormal mineralogy confirmed by scanning electron microscopy, the morphometry and the mineral polymorph composition of abnormal otoliths did not differ from normal ones (i.e. aragonite). This contrasts with other studies where vaterite and/or calcite were found to replace aragonite in abnormal otoliths. Further studies are needed to elucidate whether abrupt salinity changes associated with habitat transitions may have played a role in the abnormal otolith biomineralization in this species.     

Comparative study on the surface ultrastructures of fertilized eggs of three Sebastes species

Fertilized eggs of Sebastes schlegelii, Sebastes pachycephalus and Sebastes hubbsi are morphologically similar under stereomicroscope. However, under the scanning electron microscope, significant differences in the ultrastructures of the egg surface among the three species were observed, and herein, a taxonomic key was proposed for future applications. A clustering analysis based on the ultrastructures of the egg surface and the diameter of the oil globule suggested that among the three species, S. hubbsi and S. pachycephalus were more genetically similar, while S. schlegelii had diverged earlier. The results agree with the conclusions drawn from morphological and molecular analyses on adult samples of the same species.     

Seasonal and annual variability in the phytoplankton community of the Raunefjord,west coast of Norway from 2001–2006

Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by Skeletonema marinoi and Chaetoceros socialis, and other Chaetoceros and Thalassiosira spp. Blooms of the haptophytes Phaeocystis pouchetii and Emiliania huxleyi were irregular and in some years totally absent. Although E. huxleyi was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes.     

Mysid shrimp dynamics in relation to abiotic and biotic factors in the coastal lagoons of Maryland,Mid-West Atlantic,USA

The distribution and densities of two mysid species, Neomysis americana and Americamysis bahia in the coastal lagoons of Maryland were investigated using data collected monthly from March 2012 to December 2013. Mysid density was higher in the northern than southern bays in 2013 for Americamysis (P?=?0.043) and Neomysis (P?=?0.004). Neomysis americana density was inversely correlated with temperature (P?Neomysis densities (nos. m^?2?±?S.E) were negatively related to the catch-per-unit effort (CPUE?±?S.E) of fish predators (r?=??0.40, ?0.81; P?=?0.051, 0.002, respectively). Mysid density was higher in winter (March, 1.3?±?0.8 and spring, May, 1.4?±?1.3) 2012, when the CPUE of bay anchovy (Anchoa mitchilli) was relatively low (April: 5.8?±?2.3; and May: 11.9?±?4.5, 2012), than during summer (August, 0.003?±?0.002 nos. m^?2), when fish CPUE was relatively high (191.7?±?66.5). The observed seasonal patterns of mysid and fish densities, supported by the fact that mysids comprise 53–97% by weight of the diet of some of the abundant fish species in the bays, suggests a top-down control of mysids by fish predation. However, summer high temperatures in the bays exceeded 22°C, at which juveniles of N. americana have been reported to suffer high mortality, and perhaps contributed to the lower density of mysids in the summer.     

Movement,connectivity and population structure of the intertidal fish Lipophrys pholis as revealed by otolith oxygen and carbon stable isotopes

The shanny Lipophrys pholis is an intertidal fish commonly found in Portuguese coastal waters. Spawning takes place from early autumn to mid spring, after which demersal eggs hatch and larvae disperse along the coast. Two to three months later, young juveniles return to the tide pools to settle. However, information on fish movement, habitat connectivity and population structure is scarce for this species. One hundred and twenty early juveniles (16–35?mm) were collected in April 2014 from six rocky beaches along the western and south Portuguese coasts (Agudela, Cabo do Mundo, Boa Nova, Peniche, Sines and Olhos de Água). δ¹⁸O and δ¹³C were determined by isotope-ratio mass spectrometry. Data were analysed to determine whether isotopic signatures could be used to assess the degree of separation between individuals collected from different locations. Mean δ¹³C and δ¹⁸O values ranged from ?0.02‰ to 1.14‰ and ?7.77‰ to ?6.62‰, respectively. Both seawater temperature and salinity caused differences in otolith δ¹⁸O among the four main sampling areas. The variation among areas in δ¹³C was most likely related to slight differences in the diet, growth and metabolism of fish. The distinct isotopic signatures, at least for the northern and central areas, suggested low levels of connectivity across large spatial scales during the juvenile stage. Furthermore, similar isotopic signatures within the same area indicated some degree of larval oceanic retention at short spatial scales. This study suggests that stable isotope records in otoliths could provide information about the home residency, movements and habitat connectivity of intertidal fishes.     

Interpopulation and context-related differences in responses of a marine gastropod to predation risk

We conducted laboratory experiments to investigate interpopulation differences in the behavioural responses of the whelk Buccinum undatum to the predatory lobster Homarus americanus and the asteroid Leptasterias polaris, both in the absence and presence of feeding opportunities. Whelks from three populations in the eastern North Atlantic (1) responded to lobsters by displaying avoidance behaviours (burrowing in the sediments or retreating inside their shell), (2) responded to asteroids by displaying escape responses (rapid crawling, shell rocking behaviour or foot contortions), and (3) more often refrained from feeding in the presence of a lobster than in the presence of an asteroid. Although whelks from the three populations responded similarly to lobsters and asteroids, interpopulation differences were evident. Thus, whelks from populations sympatric with a given predator more frequently displayed 'appropriate' antipredator behaviours (i.e. avoidance in the presence of a lobster, and escape in the presence of an asteroid) than did whelks allopatric with that predator. Also, whelks from a population sympatric with both predators fed less readily in the presence of a given predator than did whelks allopatric with that predator. However, the presence of a lobster or an asteroid had the same impact on the feeding response of whelks from two populations with contrasting predator fields, one sympatric with lobsters, but allopatric with asteroids, and one sympatric with asteroids, but allopatric with lobsters. The results of our study indicate that coexistence (over evolutionary or ecological time) with lobsters and asteroids increases the propensity of the whelk to display avoidance and escape behaviours in the presence of lobsters and asteroids, respectively, but has a less predictable effect on how whelks trade off predation risk and food acquisition. Studies are needed to investigate the roles of inheritance and experience on the development of antipredator behaviours and decision making by prey animals when predation risk conflicts with other fitness-related activities such as the acquisition of food or reproductive opportunities. Copyright 1999 The Association for the Study of Animal Behaviour.     

The adaptive value of phenotypic plasticity in two ecotypes of a marine gastropod

Background  

Few surveys have concentrated on studying the adaptive value of phenotypic plasticity within genetically-distinct conspecific ecotypes. Here, we conduct a test to assess the adaptive value that partial phenotypic plasticity may have for survival in the marine gastropod Littorina saxatilis. This species has evolved canalized ecotypes but, nevertheless, the ecotypes show some phenotypic plasticity for the traits under divergent selection between wave-exposed and high-predation habitats.     

Involvement of neurohormone in regulation of oxygen consumption in the marine gastropod,Onchidium verruculatum

Ablation of whole central nervous system (CNS) or pleurovisceral (PV) ganglia significantly inhibited O₂ uptake, after 4 hr through 24 hr of the operation over sham controls. Replacement of PV in PV-less animals restored their metabolic rates to the normal level. O₂ consumption of normal animals is significantly augmented by the macerates of CNS and PV, but not by cerebral and pleural ganglia, and body muscles. Reserpine was ineffective in lowering the O₂ uptake of PV-removed animals unlike in normal, intact individuals. The possible implication of a neurohormone originating from PV ganglia controlling whole body O₂ consumption, is discussed.     

Habitat disturbance and the stability of freshwater gastropod populations

Summary The interaction of population stability and habitat permanence has a major influence on the microdistribution of freshwater snails. For two years (February 1980–January 1982), we monitored the abundance of macrophytes and the abundance and size structure of four species of macrophyte-associated freshwater snails in an English pond. Previous work (Lodge, in press) showed that two species, the pulmonate Lymnaea peregra (Mull.) and the prosobranch Valvata piscinalis (Mull.), were associated with cubmersed macrophytes, while two other species, the pulnonate Planorbis vortex (Linn.), and the prosobranch Bithynia tentaculata (Linn.), were associated with emergent macrophytes. A dramatic decline of submersed macrophytes provided a test of the hypotheses that the population stability of Lymnaea and Valvata was 1) high, and 2) an important cause of the association of those two species with submersed macrophytes.When the submersed macrophytes declined in August 1980, >99% of the Lymnaea and about 35% of the Valvata population died. The populations of Planorbis and Bithynia were not reduced. In 1980, Lymnaea and Valvata had simple annual life cycles, but with the regrowth of submersed macrophytes in spring 1981, the Lymnaea and Valvata populations responded with early, high, and repeated reproduction with some overlap of generations. In both years, Planorbis had an annual semelparous life cycle, while Bithynia lived up to 3 years and bred iteroparously.Following the terminology of Connell and Sousa (1983), Lymnaea exhibited low resistance to habitat disturbance but high adjustment following the disturbance. Valvata showed higher resistance than Lymnaea, and also high adjustment. Although the population stability of Planorbis and Bithynia could not be rigorously evaluated, published accounts of those species' life cycles suggest that stability, specially the adjustment component, was low. We suggest that the population stability of the four species is a major determinant of the association of Lymnaea and Valvata with the impermanent macrophyte habitat and that of Planorbis and Bithynia with the permanent macrophyte habitat.     

Singchia and Gunnaria, two new genera of Orchidaceae

Singchia Z. J. Liu ＆ L. J. Chen, a new orchid genus, is established based on the new species S. malipoensis Z. J. Liu ＆ L. J. Chen found in southeast Yunnan, China. The new genus is related to Pteroceras, from which it differs by having a lip with its basal margins immovably adnate to the lower part of the pendent column foot, a thin-walled spur, and very unequally and deeply split pollinia, each with a distinct caudicle. In addition to a discussion on Ascocentrum pusillum, a species of questionable placement, another new genus, namely Gunnaria S. C. Chen ex Z. J. Liu ＆ L. J. Chen, is set up and a new combination, namely G. pusilla （Aver.） Z. J. Liu ＆ L. J. Chen, is made. The new genus Gunnaria differs from its allyAscocentrum by having a cross-shaped pollinarium, sulcate or split pollinia, each with a distinct caudicle attached to a common linear stipe much longer than either pollinia or viscidium, and strongly incurved side lobes of the lip.     

Aggressive behaviour of female prairie deer mice in laboratory populations

Prairie deer mice (Peromyscus maniculatus bairdii), living in asymptotic laboratory populations established two years earlier, were observed for agonistic responses to conspecific intruders. In the first experiment, intruders of six age-sex classes were placed into 10 of the populations for 10 min. The sex of the intruder did not influence the behaviour of the residents, but juveniles elicited more aggression than did adults. A second experiment revealed that female residents were responsible for almost all of the attacks upon juveniles. Experiment 3, in which the responses of pairs of deer mice to juvenile intruders were recorded, demonstrated that the aggressiveness of a female was enhanced by the presence of a male. In the final experiment, females were observed to be highly aggressive during the first few days after giving birth. The aggressive behaviour of the female deer mouse may have greater significance for population dynamics than that of the male.     

First characterisation of the populations and immune-related activities of hemocytes from two edible gastropod species,the disk abalone,Haliotis discus discus and the spiny top shell,Turbo cornutus

The disk abalone Haliotis discus discus and the spiny top shell Turbo cornutus are edible gastropod species of high economic value, mainly in Asia. Mortality outbreaks and variations in worldwide stock abundance have been reported and suggested to be associated, at least in part, with pathogenic infections. Ecology, biology and immunology of both species are currently not well documented. The characterisation of the immune systems of these species is necessary to further assess the responses of H. discus discus and T. cornutus to environmental, chemical and disease stresses. In the present study, we investigated the morphology and immune-related activities of hemocytes in both species using light microscopy and flow cytometry. Two types of hemocytes were identified in the disk abalone hemolymph, blast-like cells and hyalinocytes; whereas four main hemocyte types were distinguished in the spiny top shell, blast-like cells, type I and II hyalinocytes, and granulocytes. Flow cytometric analysis also revealed differences between cell types in immune-related activities. Three subsets of hemocytes, defined by differing lysosomal characteristics, were observed in the hemolymph of the spiny top shell, and only one in the disk abalone. Phagocytic activity was higher in H. discus discus hemocytes than in T. cornutus hemocytes, and the kinetics of PMA-stimulated oxidative activity was different between hemocytes of the disk abalone and the spiny top shell. Finally our results suggest for the first time a predominant mitochondrial origin of oxidative activity in gastropod hemocytes.     

Structural differences in two biochemically defined populations of cardiac mitochondria

To determine whether there are structural differences in two topologically separated, biochemically defined mitochondrial populations in rat heart myocytes, the interior of these organelles was examined by high-resolution scanning electron microscopy. On the basis of a count of 159 in situ subsarcolemmal mitochondria (SSM, i.e., those that directly abut the sarcolemma), these organelles possess mainly lamelliform cristae (77%), whereas the cristae in in situ interfibrillar mitochondria (IFM, i.e., those situated between the myofibrils, n = 300) are mainly tubular (55%) or a mixture of tubular and lamelliform (24%). Isolated SSM (n = 374), similar to their in situ counterparts, have predominantly lamelliform cristae (75%). The proportions of crista types in isolated IFM (n = 337) have been altered, with only 20% of these organelles retaining exclusively tubular cristae, whereas 58% are mixed; of the latter, lamelliform cristae predominate. This finding suggests that, in contrast to SSM, the cristae in IFM are structurally plastic, changing during isolation. These observations on >1,000 organelles provide the first quantitative morphological evidence for definitive differences between the two populations of cardiac mitochondria.