Abundance

The gas phase chemistry of silicon in dense interstellar clouds has been investigated using a pseudo-time-dependent model. Based on new ion-molecule reaction studies as well as on improvements in the knowledge of the thermochemistry of silicon-bearing species, the model contains approximately 300 gas phase reactions involving such species. Calculated abundances are presented for a number of silicon-containing molecules including those

The composition of the mesozooplanktonic community was studied in the Punta Morales estuary, Gulf of Nicoya, Pacific coast of Costa Rica, during 1997. Oblique plankton hauls were performed during high and low tide using a 280 microm mesh screen net equipped with a flowmeter. The community was characterized by holoplanktonic and meroplanktonic organisms. For the holoplanktonic community, the main groups were copepods (80%) and chaetognaths (16%). The most abundant species were the copepods Acartia lilljeborgii and Paracalanus parvus. A. lilljeborgii is a typical estuarine species that maintains high populations in estuarine systems. Meroplankton was represented mainly by crustacean larvae (66%), and icthyoplankton (18%). The dominance of crustacean larvae and icthyoplankton is an evidence of the ecological importance of the Punta Morales zone.

The seasonal dynamics of diversity, abundance and horizontal distribution of the psammobiotic testaceans in four selected sandy beaches from the Bulgarian Black Sea Coast have been studied. A total of 2774 specimens of thirty-three psammobiotic species from 19 genera were observed. Pseudocorythion wailesi and Corythionella minima showed the highest relative abundance (20% and 17% of the established specimens, respectively). The genera Psammonobiotus (5 species), Centropyxiella (4), Corythionella (3) and Ogdeniella (3) had the biggest diversity. The data on seasonal dynamics of the diversity and abundance of the interstitial testacean communities showed that there were a well-expressed maximum of these parameters in the summer (from 10 to 21 species and an average abundance about of 70–175 specimens/cm³) and a minimum in the autumn-winter period (2–12 species and about of 3–60 specimens/cm³). Further situated zones away of the marine waterline (6 m and 9 m) are more favorable for the...

The sea urchin Diadema africanum is considered a key herbivore in sublittoral ecosystems of the Canary Islands. Spatial and temporal variability in population structure was carried out at Gran Canaria. We performed a morphometric and population density analysis during 2005, 2006 and 2007 at four sites in zones of Gran Canaria. The study considered a vertical gradient (5, 10 and 20 m depth) during both seasons, the cold season (February and March) and the warm season (October and November). The sea urchin D. africanum in Gran Canaria exhibited an overall density of 7.59 ± 2.92 urchin m−2. A two-way ANOVA evidenced spatial differences in mean abundance of the species, while seasonality was not relevant. The vertical analysis of the abundance of D. africanum showed differences, the smaller sizes appeared at greater depths. The Aristotle's lantern width decreased in a vertical gradient, being remarkable between 10 and 20 m. Findings of uniformity in size over time, a stable range of...

The humpback whale (Megaptera novaeangliae) population that uses Abrolhos Bank, off the east coast of Brazil as a breeding ground is increasing. To describe temporal changes in the relative abundance of humpback whales around Abrolhos, seven years (1998–2004) of whale count data were collected during July through to November. During one-hour-scans, observers determined group size within 9.3 km (5 n.m.) of a land-based observing station. A total of 930 scans, comprising 7996 sightings of adults and 2044 calves were analysed using generalized linear models that included variables for time of day, day of the season, years and two-way interactions as possible predictors. The pattern observed was the gradual build-up and decline in whale counts within seasons. Patterns and peaks of adult and calf counts varied among years. Although fluctuation was observed, there was generally an increasing trend in adult counts among years. Calf counts increased only in 2004. These fluctuations may have...

Received 11 April 2009; revised 18 May 2009; accepted 19 May 2009; published 20 June 2009. [1] The sodium and potassium exospheres of Europa are described as well as the variations of the Na/K ratio from Europa's surface up to about 20 Europa radii. Observations carried ...

We quantified habitat associations and evaluated the conservation status of a recently identified, undescribed species of dwarf chameleon, Bradypodion sp. nov. Dhlinza, endemic to scarp forest remnants in KwaZulu-Natal Province, South Africa. At the microhabitat scale the Dhlinza dwarf chameleon was found more often in forest gaps and near paths than highly disturbed edges or forest interior. Chameleon presence was not explained by forest physiognomic variables such as vine cover, shrub and tree density, or canopy cover. Presence near gaps may be better explained by the combined effects of the thermal microenvironment and food availability. The species is moderately common where it occurs, with estimated densities of 4.7, 8.7 and 29.7 individuals per ha within forest interior, edges and gaps respectively. At the landscape scale, the chameleon occurs only in three remnant forests: the Dhlinza, Entumeni and Ongoye Forests. The…

Atlantic cod ( Gadus morhua ) was the dominant demersal fish and most important predator in the southern Gulf of St. Lawrence ecosystem as recently as the 1980s. However, productivity of southern Gulf cod has declined, and the population is no longer viable even in the absence of fishing. We conducted population projections taking into account uncertainty in current abundance-at-age and uncertainty or variability in each of the components of population productivity (i.e., rates of recruitment, individual growth, and adult natural mortality). We defined extirpation as a spawning stock biomass less than 1000 t (<0.3% of historical levels). Based on these projections, at its current level of productivity, this population is certain to be extirpated within 40 years in the absence of fishing and in 20 years with fishery removals at the level of the total allowable catch in 2007 and 2008 (2000 t). Elevated natural mortality of adult cod (M) is the main factor contributing to the low pr...