摘要:

Abstract.Coulter counter data (from the upper 100 m of water) gathered during a cruise in October, 1976 in the Spanish waters of the Western Mediterranean are analysed in this paper. The ANOVA shows that the main sources of variability are the geographical situation and the depth level, while the sampling method especially affects the results for the larger particles. Repeating the counting in the same sample also introduces some changes which have less importance in the overall sense. Correlations of the particle counts with chlorophyll a, total POC and PON, POC and PON above 200u.m, estimated POC based on the particle size spectra, and SECCHI disc visibility were calculated and are discussed in order to assess the kind of information given by seston counts obtained from two different sampling methods and expressed both in absolute values (ppm by volume) and as a percentage of volume for the different channels.Some striking results arise which suggest that the use of a Coulter counter together with some kind of sample treatment might give an insight into the qualitative and quantitative characterization of the pelagic ecosystem.

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00121.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The horizontal distribution of phytoplankton in relation to changes in the physico‐chemical conditions of a eutrophic semi‐enclosed embayment is described. Phytoplanktonic populations derived from a station interval of 6 miles (coarse scale variations) were compared by quantitative (standing stock) and qualitative (species composition, diversity, Diatom/Flagellate ratio) criteria. The results showed that quantitative and qualitative parameters differed in their sensitivity and were affected differently by environmental perturbations. Along a horizontal transect with defined variations in nutrient concentrations, changes in standing stock levels were not significant, but differences in species composition existed and caused coefficients of variation between stations for species diversity up to 50% and of the Diatom/Flagellate ratio up to 120%. Furthermore, distributional differences among certain flagellate species (Prorocentrum micans, Prorocentrum balticum) and diatom species (Nitzschia closterium, Chaetoceros curvisetus) were recorded which showed that the flagellate species were distributed more uniformly than the diatoms along a transect with progressive decrease in nutrient concentrati

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00122.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Recruitment, migration, growth and longevity of populations of Penaeus semisulcatus along the southeastern coast of the Mediterranean were investigated. The general pattern of the life cycle of P. semisulcatus and the parameters affecting it were identified.Relative population density, measured by catch per unit effort, as well as relative age estimated by age group body length were used to study the pattern of the benthic phase of the life cycle.

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00123.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Over a period of two weeks in September, 1983 a high biomass macroepifauna community characteristic of a greater part of the Gulf of Trieste suffered mass mortality. The affected area is estimated to cover several hundred km2. Within 2–3 days all sponges and the brittle star Ophiothrix quinquemaculata, which together make up over 60 % of the community biomass, were dead. Benthic fish, mostly gobiids, were already affected on the first day and littered the bottom in great numbers. Concurrently the complete spectrum of macroinfauna species including (in order of emergence) holothurians, burrowing shrimp, echinoids, polychaetes, sipunculids and bivalves appeared on the sediment surface. Within one week sea stars and all remaining ophiurids had died. At this time hermit crabs were found lying dead next to their shells. Several anemones survived into the last week, although many showed signs of severe stress and lay on the surface with exposed pedal discs. Oxygen deficiency is the apparent immediate cause of this phenomenon and several possible factors leading to anoxic conditions in the Gulf are discussed. This ecological catastrophy provides evidence that the affected community, considered to have achieved relative stability by developing a strategy effectively dampening the effect of physical oscillations, has a distinct tolerance limit to stress. The Gulf of Trieste, among the most productive areas in the Mediterranean Sea, must be considered as sensitive; September is a particularly critical mont

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00124.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Feeding habits of adult female Acartia tonsa and Labidocera aestiva and L. aestiva CV copepodites were examined by comparing fecal pellet contents and available phytoplankton. Samples were collected from eight stations in the northern Gulf of Mexico near the mouth of the Mississippi River. Fecal pellets of both copepods contained remains of a wide variety of chain‐forming and solitary phytoplankters of various sizes, as well as remains of other crustaceans. Contents of fecal pellets generally mirrored the composition and relative abundance of fluctuating assemblages of available natural phytoplankton. Both species fed upon a wide size range of cells, from solitary centric diatoms of 2–8 um diameter up to large solitary centrics of 33–53 urn diameter. Both copepods also ingested the elongate solitary pennate diatom Thalassiothrix sp. (264–330 urn long) and chain‐forming diatoms such as Skeletonema costatum. Remains of large or chain‐forming diatoms and crustaceans were more dominant in fecal pellets of L. aestiva. This suggests that L. aestiva is primarily a raptorial feeder, grasping larger particles while A. tonsa is a more typical suspension feeder. Both copepods are opportunistic omnivores, however, and there is considerable overlap in

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00125.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Boonea (= Odostomia) impressa is a common ectoparasite of oysters. In the laboratory, small oysters (Crassostrea virginica) parasitized by natural densities of B. impressa produced 75 % less new shell than unparasitized oysters. Shell deposition rates of previously parasitized oysters increased significantly after all B. impressa were removed. Thus, the decrease in growth rate, although significant, apparently was not permanent. B. impressa preferentially parasitized small, living oysters (≤2.5cm) in the field, even though a higher percentage of large, living oysters (>2.5cm) was available. The snails maintained an aggregated distribution on the oyster reef. The number of B. impressa per oyster clump was positively correlated with the number of living oysters per clump, however some clumps with few or no living oysters had many B. impressa. Thus, food availability only partially explained the pattern of distribution. B. impressa was very mobile. About 50 % of the population moved in one week. Reproduction occurred throughout the year with a peak period in May. Recruitment was greatest in July, however new recruits were observed throughout the year. The reduction in growth rate of parasitized oysters, the snaiľs propensity towards parasitizing small oysters and the snail's tendency to be contagiously distributed suggests that B. impressa potentially exerts a significant influence on the population structure and health of oyster populatio

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00126.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

ISSN:0173-9565    

DOI:10.1111/j.1439-0485.1984.tb00127.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY