Spatio-temporal distribution of the microphytobenthic biomass in intertidal flats of Tagus Estuary (Portugal)

A study on spatio-temporal distribution of microphytobhethos in intertidal zones of Tagus Estuary was carried out from 1990 to 1992. Near Lisbon, Portugal, Tagus Estuary is a shallow mesotidal estuary, covering an area of 320 km². The intertidal area ranges from 20 to 40% off the total area and it is constituted mainly by mudflats. Intertidal flats are richly populated by microalgae, diatoms being the most important and ubiquitos group.Spatial variation of microphytobethos was studied in spring 1990, 21 different sites were sampled. Microphytobenthos biomass was evaluated as chlorophyll a content of the surface centimeter, ranging from 10 to 240 mg m^–2. A Principal Component Analysis showed that 62% of the total variability found in intertidal flats of Tagus estuary could be attributed to two major factors: sediment type and tidal height. A hierarchical grouping defined 3 major groups of similar stations, each one representing a different strata of the ecosystem.One station from each group was chosen for the study of the temporal variation. A sampling, rogram took place from April 1991 to April 1992, with fortnightly sampling, the Chl a ranged from 20–300 mg m^–2. No clear seasonal variation was found, and our results indicated that tidal height of sampledsite played an essential role in temporal biomass evolution, thus upper littoral sites were influenced by climatic parameters, whereas in lower sites action of tides mainly controlled microphytic biomass.

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Résumé Une étude sur l'hétérogénéité spatio-temporelle du microphytobenthos dans les sédiments intertidaux de l'Estuaire du Tage a été accompli de 1990 á 1992.L'Estuaire du Tage, prés de Lisbonne (Portugal) est un estuaire peu profond, mesotidal, avec une aire total de 320 km². L'aire intertidale est comprise entre 20 et 40% du total, et constituéé surtout par des vasiéres. Ces slikkes sont peuplées par une communauté assez riche de microalgues, ou les diatomées sont les plus abundantes.La variation spatialle du microphytobenthos était évalué au Printemps 1990, ou 21 différentes stations étaient échantillonnées. La biomasse était évalué par la concentration enchlorophylle a du premier centimétre de sédiment, qui a varié de 10 á 240 mg Chl a m^–2. Une Analyse en Composants Principales a montré que 62% de la variabilité de la biomasse était lié á deux facteurs: le sédiment et l'hauteur vis-á-vis la marée. Une classification hiérarchique des stations par similitude a établi 3 groupes principaux, représantantles différents strates de écecosytéme.Une station de chaque groupement a été choisie pour l'étude de la variation temporelle, qui s'est deroulé d'avril 1991 á avril 1992, avec des prélévements deux fois par mois. Les valeurs de Chl a obtenus vont de 20 á 300 mg m^–2. Les variations saisonniéres observées ne sont pas claires: nos résultats indiquent que l'hauteur de la station (m) joue un rôle essentiel dans l'évolution temporel de la biomasse, c'est á dire, la biomasse microalgal des sites du supra-littoral est influencié par les paramétres climatiques, tandis que dans l'infra-littoral c'est l'action des marées le facteur principal.

     

Factors controlling the growth of field populations of Hydrodictyon reticulatum in New Zealand

Since Hydrodictyon reticulatum was introduced to New Zealand it has spread rapidly and produced persistent annual nuisance growths in areas where nuisance algal had not occurred previously. Field bioassays were conducted at 10 sites between August 1993 and February 1995 to evaluate the seasonal growth patterns and the factors controlling growth under natural conditions. H. reticulatum exhibited a strong seasonal growth pattern with growth rates up to 0.33 doublings d^-1 from August to March, are duction in growth rate in April and little or no growth from May to July. The H. reticulatum present in New Zealand has are latively low requirement for dissolved inorganic nitrogen (DIN) in comparison with other nuisance species, with its growth rate being saturated at 200 mg m^-3. This and the high affinity for DIN as shown by a K_s of 29 mg m^-3 have been key factors in the establishment of nuisance growths of H. reticulatum in New Zealand. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal cycle of nitrogen and phytoplankton biomass in a well-mixed coastal system (Eastern English Channel)

The hydrological structure of the French coastal part of the eastern English Channel is strongly linked with tidal regimes and riverine input. Two distinct water masses are separated by a frontal area and drift along the coast in SW–NE direction. These two water masses are well-mixed during the entire year. We studied the seasonal dynamic of nitrogenous nutrients, chlorophyll a and organic particulate carbon and nitrogen at two stations, characteristic of these water masses, during the year 1994. Results show (i) a winter stock of nitrate and ammonium, (ii) a pre-bloom period corresponding to the use of ammonium, (iii) a high bloom period of short duration using nitrate, (iv) a post-bloom period with little phytoplanktonic activity probably limited by nutrients other than nitrogen and (v) an autumnal period of reconstitution of stock. The essential difference between the two stations is the importance of winter stock of nutrients and of bloom chlorophyll a concentration, with the coastal station richer than the offshore one. An assumption about the nitrogen available for new production in this area gives a value of 57% of the winter stock of inorganic nitrogen.     

REPRODUCTION IN THE FEMALE SUBANTARCTIC FUR SEAL, ARCTOCEPHALUS TROPICALIS

The reproductive tracts of 89 female subantarctic fur seals, taken at Gough Island between November 1977 and October 1978, were examined. Females started ovulating at age 4 yr and all 6-yr-old females were sexually mature. They are mono-ovulatory, alternating between ovaries, and only single embryos were found. Females older than 13 yr ( n = 11) showed poor follicular development and some failed to ovulate. The gestation period (first recorded ovulation to first recorded birth) was 360 d, while delayed implantation (first recorded ovulation to first recorded implantation) lasted for 139 days. Follicle numbers in the functional ovary declined sharply after ovulation while the corpus luteum increased in size until at least 1 mo prior to parturition. The number of follicles in the contralateral ovary increased after midwinter (June/July), and the mean size of the largest follicles peaked prior to ovulation in December. The mean size of the largest follicles increased in both ovaries near implantation time, after reaching a low subsequent to, ovulation. The regressing corpus albicans, conspicuous for approximately 3 mo after parturition, could not be detected macroscopically within one year postpartum. Subantarctic fur seals at Gough Island have a distinct postreproductive class of older females. The pregnancy rate for all females ≥4 yr of age was 79%, and it was 84.5% for the sexually mature group of ≥6 yr of age, while the mean age at puberty was 4.80 yr.     

Nocturnal foraging habitats of French and bluestriped grunts,Haemulon flavolineatum and H. sciurus,at Tobacco Caye,Belize

Synopsis Nocturnal foraging habitats of Haemulon flavolineatum and H. sciurus were investigated in the backreef habitat around Tobacco Caye, Belize. Grunts leave the reef at dusk to forage in the grass beds and sand flats surrounding the reef. The hypothesis that French and bluestriped grunts use separate foraging habitats was examined by following tagged fishes from their diurnal territories or schooling sites to nocturnal foraging grounds. The tag consisted of a small, glowing Cyalume light stick sutured to the dorsal musculature of the fish, next to the first dorsal fin. Surveys of foraging habitats were done to support the tracking study. Large quadrats (225 m²) were set out over the sand flats and grass beds during the day. The numbers of French and bluestriped grunts feeding in each habitat were counted one hour after dark. Foraging French grunts used sand flats, whereas bluestriped grunts usually fed in grass beds. Repeated sightings of two French grunts and one bluestriped grunt in the same individual night-time locations support the hypothesis that nocturnal foraging sites may be used repeatedly by the same individuals.     

Composition and seasonal fluctuations of the ichthyoplankton community in a shallow tidal channel of Cadiz Bay (S.W. Spain)

The composition and seasonal variation of the ichthyoplankton community in a shallow tidal channel in Cadiz Bay was studied for 5 years (1984 1988), taking fortnightly samples with a conical tide-strained net (0.5 mm mesh). Thirty-nine species belonging to 21 families of teleosts were caught. Four species ( Pomutoschistus microps Kroyer, Atherina hoyeri Risso, Liza rumuda Risso and Lizu a lira Ia Risso) totalled more than 90% of the annual ichthyoplankton abundance. Three species, assumed to be permanent residents, dominated the number offish (837%), and were represented by all their developing stages; 26 species (66.7%) were temporary residents, contributing 17.2% to the total abundance and were represented only by early developing stages; the remaining 10 species were classified as rare. Monthly numbers of species and individuals showed seasonal variation with a main annual peak in spring and in late spring-early summer, respectively. The diversity (H') and evenness (S) indices of this community were low (0.13 to 1.83 and 0.03 to 0.71. respectively), with higher values in winter and late summer, and both were significantly correlated with the log-transformed density of temporary residents (r = 0.43 and 0.41, respectively; P<0.0l) and permanent residents (r=−0.75 and −0.79, respectively; P<0.01). Multivariate classification analysis of samples revealed that similar cyclical changes were taking place in the structure of this ichthyoplankton community every year; three periods could be differentiated: (1) a cool period of low fish density but relatively high diversity; (2) moderate temperature and salinity with high numbers of species and density but low diversity and (3) a warm period of moderate diversity and fish density.     

Nutrient enrichment experiments in three central Florida lakes of different trophic states

Seasonal nutrient enrichment experiments (short-term bioassays) were conducted in three Florida lakes of different trophic states to determine the effects of addition of various nutrient combinations upon chlorophyll a and phytoplankton standing crops. Nutrient enriched surface water samples with crustacean zooplankton removed were incubated in situ in clear polyethylene bags for 3 to 6 days. The 2⁵ factorial design employed two levels (ambient and enriched) of each of five nutrients [NH₄ ⁺, PO _inf4 ^sup3− , Fe⁻ -EDTA, SiO _inf3 ^sup2− and a cation (Ca²⁺ or K⁺) or trace elements]. Ammonium produced significant increases in chlorophyll a and phytoplankton standing crops in all experiments. Phosphate produced similar results in the mesotrophic lake, but the eutrophic lakes had both positive and nonsignificant responses which varied seasonally between lakes. Iron increased chlorophyll a in most experiments but affected total phytoplankton standing crop only during the summer and fall. Silicon had negative effects in some experiments. Cations and trace elements produced marked differences between lakes for chlorophyll a, but total phytoplankton standing crop showed few significant responses. Synergistic responses to two- and three-factor interactions were observed in all lakes. Differences in the responses of phytoplankton taxonomic divisions to enrichment may be responsible for much of the between lake variation in chlorophyll a and total phytoplankton volume responses. Nutrient limitations in these lakes are discussed and related to limnological factors and predictive models.     

辽宁省丹东地区吸血蠓类(双翅目:蠓科)生态调查

吸血蠓类对人畜危害较大,不仅是多种疾病的传播媒介,而且刺叮吸血骚扰性很大。1988年我们在辽宁省丹东地区东沟和风城二县郊区进行了采集和生态习性的调查,现将结果报道如下。材料和方法器材由军事医学科学院微生物流行病研究所提供的诱蠓帐、捕虫网和吸虫器。调查方法     

Seasonal variation in copper and zinc concentrations in three talitrid amphipods (Crustacea)

Cu and Zn concentrations were determined for three talitrid amphipods, Orchestia gammarellus (Pallas), O. mediterranea Costa and Talitrus saltator (Montagu), collected at two-monthly intervals in 1987 from sites on Great Cumbrae Island, Firth of Clyde, Scotland. To account for size effects, log transformed Cu and Zn concentrations were regressed against log dry weight for each bimonthly sample of each species, and compared by analysis of covariance. Copper concentrations in O. gammarellus were significantly raised in March 1987, and lowered in November 1987. Copper concentrations in O. mediterranea and T. saltator were significantly lowered in November 1987. Cu concentrations differed interspecifically in the order O. gammarellus > O. mediterranea > T. saltator. There was no significant intraspecific seasonal variation in zinc concentration in any of the three species. Zn concentrations differed interspecifically in the order T. saltator > O. gammarellus > O. mediterranea.