Distribution patterns of larval myctophid fishes in the transition region of the western North Pacific

We examined the species composition and horizontal distribution of myctophid fish larvae in the transition region of the western North Pacific during the early summer. In total, 4,760 myctophid larvae were collected at 44 stations; 18 species of myctophids from 15 genera were collected, and the 8 most abundant species accounted for >95% of larvae. The distribution patterns of these larvae were well defined by the hydrographic structures of the study area including the Oyashio and Kuroshio fronts, the Subarctic Boundary, and a warm core ring. The horizontal distribution patterns of the eight dominant species were categorized into three groups: northern transition water (Stenobrachius nannochir, Tarletonbeania taylori, and Lampanyctus jordani), southern transition water (Symbolophorus californiensis, Diaphus theta, and Nannobrachium regale), and Kuroshio (Myctophum asperum and Diaphus garmani). The Subarctic Boundary defined the distributions of the northern and southern transition-water groups. The importance of areas of western North Pacific transition water as spawning and nursery grounds for subarctic, transitional, and subtropical myctophid fishes was indicated by the relationship between the horizontal distribution patterns of larvae, juveniles, and adults and the physical oceanographic structures.Communicated by T. Ikeda, Hakodate     

Male-male competition selects for delayed sex change in the protandrous shrimp<Emphasis Type="Italic"> Pandalus latirostris</Emphasis>

In most protandrous species, male size advantage is generally regarded as unimportant in determining the timing of protandrous sex change. In pandalid shrimp, the size/age of male sex change often fluctuates among years and populations, but the adaptive significance of late reversing males (LRMs) is not well understood. This study experimentally examined the adaptive significance of LRMs in the protandrous pandalid shrimp Pandalus latirostris Rathbun. Field and laboratory studies were carried out in August–September of 1998–2002 on P. latirostris in Notoro Lagoon, Japan (44°03′N; 144°10′E). Mature females that had molted (i.e. mate receptive) were tethered in the field and their mating behavior with wild males was observed. Copulations occurred with a single male at a time, although other males could sequentially mate with a tethered female. Because tethered females rejected male approaches, males had difficulty transferring their spermatophores. In the laboratory, males copulated with non-tethered, recently molted females for only 15 min after molting. Recently molted females are wary of potential predators, since their soft exoskeleton makes them particularly vulnerable. Fast access by males enhanced fertilization success in this shrimp. The effect of male size on mating success in the laboratory was examined. Both small and large males successfully inseminated females in the absence of competitors. In experiments where large, medium, and small males competed for a female, however, larger males guarded females longer than smaller males, until the female molted and became receptive. Moreover, large males were more successful at copulating once molting occurred. These results imply that male-male competition drives delayed sex change in some situations.     

Histological study of the effects of starvation on reared and wild-caught larval stone flounder,Kareius bicoloratus

Starvation tolerance of laboratory-reared larval stone flounder, Kareius bicoloratus, was examined at different temperatures and salinities during the winters of 1984, 1985 and 1986. Starvation tolerance decreased with increased temperature and exhibited low values with high salinities. The highest starvation tolerance observed at low salinity was just before the metamorphosis stage. Starvation tolerance showed little change until larvae were 11 d. It increased with age thereafter. Epithelial cell heights of the digestive tract and cell diameters of pancreas and liver were measured histologically in reared stone flounder during growth and starvation. These values decreased markedly in the starved condition. Aldehyde fuchsin positive granules in the rectal epithelium also disappeared during the short starved period. The nutitrional condition of wild-caught stone flounder larvae, collected in January and February 1986 from the Matsukawa-ura inlet, Fukushima, Japan, was also examined. Eighty percent of larvae were estimated to be in fed condition just before sampling. The changes in cell heights of digestive organs agreed with this estimate. These histological methods seem to be useful in assessing the nutritional condition of marine fish larvae.     

Effects on growth and reproduction of the coral Stylophora pistillata by the mutualistic damselfish Dascyllus marginatus

Although coral dwelling fishes are common on coral reefs, the nature of their effect on the host corals is poorly understood. The present study, conducted in the Gulf of Eilat (Red Sea) between July 1989 and August 1990, demonstrated that the branching coral Stylophora pistillata (Esper) benefits, in two components of coral fitness, from the presence of the damselfish Dascyllus marginatus (Rüppell), an obligate coral dweller. The growth rate of damselfish-inhabited corals was significantly higher than that of corals without damselfish. This was observed, using two growth assessment methods, in long-term (>7 mo) comparisons between: (1) corals where the damselfish were experimentally removed versus corals with unaltered fish groups; and (2) naturally inhabited versus non-inhabited corals. The presence of damselfish did not affect the coral's specific (per surface area) reproductive output, whether it was assessed by the number of female gonads per polyp or by the number of planulae released cm^-2 surface area d^-1. However, the more rapid increase in branch size in damselfish-inhabited corals resulted in an apparent increase in the total reproductive output, with age, in growing corals. These findings demonstrate that the association between the damselfish D. marginatus and its host coral, S. pistillata, is mutualistic.     

Aluminum neurotoxicity in mammals

Although aluminum comprises a large percentage of the Earth's crust, it is excluded from body tissues, and especially from the central nervous system. When aluminum is experimentally introduced to the central nervous system, several neurotoxic effects are observed:i.e. neurofibrillary changes, behavioral and cognitive deficits and enzymatic and neurotransmitter changes, as well as certain types of epileptic seizures.The localization of relatively high levels of aluminum in Alzheimer disease, Guamanian amyotrophic lateral sclerosis and Parkinsonism-dementia has led to the implication of aluminum as a pathogenic factor in these diseases. Recent studies have shown that microtubule-associated proteins are part of the paired helical filaments which make up the intraneuronal neurofibrillary tangle. Other studies have identified the protein making the vascular and neuritic (senile) plaque amyloid and located the gene responsible for this protein to chromosome 21.Our electron microprobe analysis studies have not found the levels of aluminum or silicon in either the neurofibrillary tangles or amyloid cores reported elsewhere, nor have the levels of aluminum been elevated in approximately one half of the tangles and plaque cores examined to date.     

Variations de quelques facteurs estimatifs de la biomasse,et en particulier de l'ATP,chez plusieurs algues marines planctoniques

ATP, carbon, and nitrogen content, and cell volume have been measured in 7 marine algae in culture. Intraspecific differences are negligible during the phase of exponential growth; interspecific differences in ATP and carbon content are slight during this phase compared with those observed in the same cultures between the exponential and senescent phases. As the interspecific differences agree well with those reported for algae in situ, this leads the authors to believe that the greater part of the biomass in situ is always in a state of physiological youth. ATP content is higher in diatoms, and seems linked with silica shell synthesis. In non-silicified species, there is a significant correlation between the ATP: plasma ratio and the division rate, although the cellular volumes are quite different. In the author's opinion, ATP content allows a good estimation of biomass to be made, as well as, under controlled conditions, a suitable estimation of primary productivity; however, because of their high silica content, diatoms should be considered separately from other phytoplankters.     

Annual cycle of biomass of a threatened population of the intertidal seagrass Zostera japonica in Hong Kong

The phenology and primary productivity of a population of Zostera japonica (Aschers. & Graebn.) threatened by the construction of Hong Kong's new international airport were studied over a 12-month period. The need to conserve the population, and the small leaf size of Z. japonica rendered traditional destructive or marking techniques inapplicable for percentage cover and biomass estimation. A nondestructive method based on image analysis techniques was therefore devised for repeated estimation of percentage cover, biomass and leaf area index. This technique, which involved random quadrat sampling, photographic recording and image analysis, was able to provide data on the three parameters with acceptable precision and was cost-effective in the field. Z. japonica demonstrated a strongly seasonal cycle of vegetative growth, with different patterns for leaf density (peak in March) and overall bed area (peak in June). Total (above- and below-ground) net primary productivity was estimated at between 344 and 688 g AFDW m⁻² yr⁻¹. Percentage cover of Z. japonica was negatively correlated with total suspended solids (TSS) in the water column while total bed area was negatively correlated with water salinity. Increased sedimentation associated with the new airport project was identified as one important factor affecting the growth of the seagrass, as TSS reached the high level of ≈1 g DW l⁻¹ during the first half of the study period. Sediment traps set in the beds also recorded potential sedimentation rates at between 2.89 and 14.5 mg cm⁻² d⁻¹. This high turbidity resulted in a sharp decrease in the density of Clithon spp., the dominant grazers of epiphytic algae on Z. japonica. Effects of sedimentation and shading on growth of Z. japonica were investigated by field manipulative experiments. Experimental increase of sedimentation rate and shade both resulted in larger decreases in percentage cover and above-ground AFDW compared with the control. Received: 3 March 1997 / Accepted: 14 March 1997     

A Study of Plant Species Extinction in Singapore: Lessons for the Conservation of Tropical Biodiversity

The native vascular plant flora of the Republic of Singapore has suffered the extinction of 594 out of a total 2277 species. These represent local, not global, species extinctions. Coastal habitats, including mangroves, have lost 39% of their species, while inland forests have last 29%. Epiphytic species (62% loss) appear particularly prone to extinction, which is reflected in a similar disposition exhibited by the Orchidaceae. Deforestation and disturbance have been the main cause of plant species extinction in Singapore. The rich mangrove epiphyte flora has been totally exterminated, and a number of tree species are reduced to populations of a few mature individuals. Many more species continue to survive than the species-area relationship would predict given the 99.8% loss of primary forest. This is interpreted as a result of the failure of equilibrium to be achieved yet in the remnant forest fragments, even after more than a century of isolation. Singapore's secondary forests appear to accrete plant diversity very slowly, even if contiguous with primary forest areas. We conclude that remnant fragments of primary tropical forest, even of very small size, can play a major role in the conservation of tropical biodiversity. The patterns of extinction observed in Singapore indicate that coastal and estuarine sites are in greatest demand for development and therefore must be given high priority for conservation despite their somewhat lower biodiversity. Epiphyte and orchid diversity appear to be very good indicators of the degree of disturbance suffered by a habitat in the humid tropics.     

Photosynthetic carbon dioxide fixation in zooxanthellae

The carbon-fixation patterns of freshly isolated zooxanthellae from the hermatypic coral Acropora formosa were examined during a 15 min exposure to sodium mosa were examined during a 15 min exposure to sodium [¹⁴C]bicarbonate. The labelling pattern during the first 60 s exposure showed that the C₃ carbon-fixation pathway is the major route for photosynthetic carbon fixation in Symbiodinium sp. 3-Phosphoglyceric acid, which constituted >50% of the label after 5 s, steadily decreased over the first 60 s. Hexose phosphates, aspartate, malate and glucose were the other main products during the first 60 s. Over longer periods, significant amounts of the organic acids succinate, aspartate and glutamate were found in the extract along with glucose; but no glycerol.