Natural food,foregut clearance-rate and activity of the crab Scylla serrata

The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e^0.033x , where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved.     

Abundance,breeding and growth of the crab Scylla serrata in two South African estuaries

Populations of the crab Scylla serrata (Forskal) were studied in two South African estuaries from 1971 until 1974. One estuary was open to the sea, the other was closed by a sandbar. Population density in the closed estuary was estimated by means of mark-release-recapture data from tagged crabs. The population of S. serrata was estimated as 1 crab/124m² and the production at 3.4 g/m²/annum. Catch per unit effort data from the closed estuary indicated a natural mortality of 41% in the crabs' second year and 60% in the third. Growth was studied in both estuaries by means of size-frequency analysis and from tagging returns. Growth was rapid in the first 12 to 15 months, when the crabs attained a carapace width of 80 to 160 mm. Thereafter growth slowed, and after 3 years crabs were between 140 and 180 mm in carapace width. Females mated in summer at a carapace width of 103 to 148 mm, males at 141 to 166 mm. After mating, females migrated out of both estuaries into the sea.     

A method to reconstruct anguilliform fishes from partially digested items

Estimating the amounts of resources consumed by individuals is important in many studies. For predators, allometric relationships can be used to extrapolate the size of preys from undigested remains found in the stomach and in the faeces. However, such equations are available for a limited number of species. Based on a large sample size gathered in New Caledonia on both predators (sea kraits) and their preys (anguilliform fishes), we provide the first allometric relationships that allow estimating accurately the mass and the size of various anguilliform fish species.     

Sexual selection and cuckoldry in a monogamous songbird: implications for sexual selection theory

Sexual selection is generally assumed to be weaker in monogamous than in polygynous animals. Recently, though, extra-pair fertilizations have been hailed as an important force in generating variance in reproductive success among males in socially monogamous species, thereby increasing the intensity of sexual selection. To see if extra-pair copulations contribute to variance in male reproductive success in the house finch (Carpodacus mexicanus), we used DNA fingerprinting to determine the paternity of chicks from 35 nests. This species is a socially monogamous passerine in which plumage brightness serves as a sexually selected indicator of male quality. Out of 119, nestlings 10 (8.3%) were fathered by a male other than the attending male, but cuckoldry occurred randomly with respect to the plumage colouration, size, or age of the attending male. Thus extra-pair fertilizations do not generate variance in male reproductive success with respect to plumage colour. On the other hand, a strongly male-biased sex ratio and asynchronous breeding by females may generate substantial variance in male reproductive success and could explain the evolution of ornamental colouration.     

Distribution of Juvenile,subadult and adult Scylla serrata (Crustacea: Portunidae) on tidal flats in Australia

In Deception Bay, northern Australia, during 1979–1981, a study was made of the distribution of Scylla serrata (Forskal) in an area having a broad intertidal zone. Juveniles (20 to 99 mm carapace width) were resident in the mangrove zone, remaining there during low tide. The majority of subadult crabs (100 to 149 mm) migrated into the intertidal zone to feed at high tide and retreated to subtidal waters at low tide. Adults (150 mm and larger) were caught mainly subtidally and only small numbers were captured in the intertidal at high tide. Few crabs were captured in the coolest months (May to August). Adults were captured on the flats mainly in the warmest months (January to April), but subadults could be captured over the entire summer (September to March). Juveniles were found in the upper intertidal throughout the year.     

Salinity and temperature tolerance of zoeae of the portunid crab Scylla serrata

The tolerances of the first zoeal stage of the crab Scylla serrata (Forskal) have been investigated in 64 different temperature-salinity combinations. Exposure to temperatures above 25°C or to salinities below 17.5 caused considerable mortality; therefore, zoeae are unsuited to estuarine conditions. The larvae can tolerate temperatures down to 5°C is they are inactive below 10°C. It is suggested that 10°C is probably a lower limit and that female crabs which migrate to sea to release their eggs do not enter water with a temperature below 12°C. Hydrological conditions along the south-east coast of Africa indicate that females would, therefore, migrate less than 10 km offshore.     

Feeding by the sand crab Portunus pelagicus on material discarded from prawn trawlers in Moreton Bay,Australia

A field and laboratory study in 1984–1985 using the foregut contents of crabs caught in Moreton Bay, Queensland, when trawling was underway, showed that animals discarded from trawls constituted about 33% of the diet. Portunus pelagicus can fill its foregut in about 8 min and clear it completely of tissues in about 6 h, except for fish bone which requires about 24 h. P. pelagicus used a zigzag search pattern to find food and moved towards it at a mean point-to-point speed of 290 m h^-1 (8 cm s^-1). Underwater still photography on the trawl grounds showed that P. pelagicus was the most common scavenger attracted to a bait that simulated trawl-discards, and that it was most active at dusk. Trawler-discards at periods of high food demand in summer may allow larger populations of P. pelagicus to exist than would otherwise occur.     

Consistent association of crenarchaeal Archaea with sponges of the genus Axinella

The association of sponges with microorganisms has been accepted to be a common feature of the phylum Porifera. Herein we describe the association between filamentous Archaea and three Mediterranean species of sponges from the family Axinellidae (Porifera: Demospongiae). Axinella damicornis, A. verrucosa and Axinella sp. harbor a high concentration of filamentous Archaea in the collagen that surrounds the siliceous spicules that form their skeleton. These Archaea have been found in every axinellid specimen studied, regardless of their environment and collection time. The morphology of the filaments has been studied using transmission electron microscopy, and they all show similar characteristics. Their nature has been determined by in situ hybridization experiments and by PCR amplification and sequencing of their 16S DNA. Each sponge species contains a single filamentous archaeal phylotype. The Archaea of the three sponges are closely related to each other and to the marine "group 1" crenarchaeotes. Our findings suggest that this newly described association could be defined as a symbiosis, where biochemical and/or metabolic relationships between the sponge hosts and their symbionts remain to be determined.     

Mathematical model for the microbial metabolism of glucose induced enhanced biological phosphorus removal in an anaerobic/aerobic sequential batch reactor

Glucose plays a significant role in enhanced biological phosphorus removal (EBPR). Previous experimental studies have shown that in addition to acetate, glucose can induce and maintain a successful EBPR performance under certain operating procedures. Mathematical modeling of the EBPR metabolism is an important consideration that is necessary to produce a deeper insight into this process. In this study, four anaerobic reactions plus four aerobic reactions with fourteen kinetic constants are structured to describe the dynamic behavior of the key metabolic components in the glucose induced EBPR system. The development of the stoichiometric coefficients for the reactions is based on fundamental biochemical principles. The model describes the dynamics of the important storage compounds, which are considered separately from the active biomass. Sequential batch experiments were performed to find the optimum model parameters using sludges exhibiting stable EBPR from glucose fed system. The maximum specific substrate conversion rate in the glucose model is composed of two factors: the maximum specific rates of glucose direct conversion to PHV (q _gv ^max ) and glucose conversion to glycogen q _gl ^max , which are 14.1 and 699.7 C-mmol/C-mmol·h, respectively. The maximum specific rate of polyphosphate synthesis k _pp ^max is 0.2 P-mmol/C-mmol·h. The model with the best-fit parameters satisfactorily simulates the dynamic behavior of the key components during both anaerobic and aerobic conditions.     

Very low versus undetectable maternal serum alpha-fetoprotein values and fetal death

Very low maternal serum alpha-fetoprotein (MSAFP) levels (<10 ng/mL) are known to be associated with non-viable pregnancies, including conditions such as fetal death, molar pregnancies, and non-pregnancies. There has not been agreement, however, as to whether very low MSAFP levels indicate already existing fetal deaths or are actually predictive. We analysed 230 pregnancies with MSAFP levels <10 ng/mL from among 15 807 women (1.5 per cent) screened consecutively during a three-year period and identified 26 non-viable pregnancies, 22 of which were diagnosed sonographically as part of the screening process (17 missed abortions, 3 blighted ova, 2 non-pregnancies). Furthermore, 20 of these 22 pregnancies were associated with essentially undetectable MSAFP levels (<5 ng/mL). Our data indicate that pregnancies with MSAFP values <5 ng/mL are the group most strongly associated with fetal non-viability and that very low MSAFP values are not strongly predictive for fetal death.