Effects of anoxia on the viability of subitaneous eggs of planktonic copepods

The effect of anoxia on the viability (as evidenced by hatching) of newly spawned and fully developed subitaneous eggs of three species of copepods, Acartia tonsa (Dana), Centropages hamatus (Lilljeborg), and Labidocera aestiva (Wheeler) was determined for eggs produced in the laboratory by adults collected from inshore waters of the northeastern Gulf of Mexico between January and August 1992. Hatching success decreased to 50% or less when eggs were exposed to oxygen concentrations <0.06 mll^-1 for more than 12 d, except for newly spawned eggs of L. aestiva, which still showed 50% survival after 32 d of exposure to anoxia. For all three species, newly spawned eggs survived exposure to anoxia longer than fully developed eggs. The results indicate that the increasing occurrence of anoxia in estuarine and coastal waters could have a major impact on the population growth of these important food web organisms.     

Light-dependent magnetoreception in birds: interaction of at least two different receptors

Passerine migrants require light from the blue-green part of the spectrum for magnetic compass orientation; under yellow light, they are disoriented. European robins tested under a combination of yellow light and blue or green light showed a change in behavior, no longer preferring their seasonally appropriate migratory direction: in spring as well as in autumn, they preferred southerly headings under blue-and-yellow and northerly headings under green-and-yellow light. This clearly shows that yellow light is not neutral and suggests the involvement of at least two types of receptors in obtaining magnetic compass information, with the specific interaction of these receptors being rather complex.     

Subitaneous, diapause, and delayed-hatching eggs of planktonic copepods from the northern Gulf of Mexico: morphology and hatching success

Experiments were conducted to examine the morphology and hatching success of eggs, either spawned by freshly caught planktonic copepods or recovered from bottom sediments in the northern Gulf of Mexico. Collections were made between August 1992 and September 1995. Eggs of nine species were described and these differed in their diameter, color and surface attributes. Three types of eggs were distinguished: subitaneous, diapause, and delayed-hatching. Three species, Labidocera aestiva Wheeler, Acartia tonsa Dana, and Centropages velificatus (Oliveira) produced only subitaneous eggs. Hatching success varied greatly among these species. Two species, Labidocera mirabilis Fleminger and Centropages hamatus (Lilljeborg) produced diapause eggs and subitaneous eggs. The length of the refractory phase of the diapause eggs differed greatly both within and between these two species. A third type of dormant egg, delayed-hatching, was recognized in Labidocera scotti Giesbrecht and Pontella meadi Wheeler. The existence of delayed-hatching eggs may be an adaptive response of subtropical species to less seasonal fluctuation. Based upon morphological characteristics of the eggs and rearing of nauplii to an identifiable stage, benthic dormant eggs of eight species of calanoid copepods were also identified. Received: 9 September 1996 / Accepted: 1 October 1996     

Environmental effects on the distribution of corallimorpharians in Tanzania

This study examined the distribution and abundance of corallimorpharians (Cnidaria, Anthozoa) in Tanzania in relation to different aspects of the coral reef environment. Five reefs under varying degrees of human disturbance were investigated using the line intercept transect and point technique. Corallimorpharian growth and the composition of the substratum were quantified in different habitats within reefs: the inner and middle reef flat, the reef crest, and at the 2 and 4 m depths on the reef slope. Corallimorpharians occurred on all the reefs and 5 species were identified: Rhodactis rhodostoma, R. mussoides, Ricordea yuma, Actinodiscus unguja and A. nummiforme. R. rhodostoma was the dominant corallimorpharian at all sites. Within reefs, they had the highest densities in the shallow habitats. While R. rhodostoma occurred in all habitats, the other corallimorpharian species showed uneven distributions. Corallimorpharians ranked second, after scleractinian coral, in percent living cover. Results from this study suggested that corallimorpharians benefitted from disturbance compared with other sessile organisms. They preferred inhabiting areas with dead coral, rock and rubble whilst live coral was avoided. There was a positive relationship between percent cover of corallimorpharians and water turbidity and they dominated the more disturbed reefs, i.e. reefs that were affected by higher nutrient loads and fishing.     

Genetic differentiation of populations of the planktonic copepod Labidocera aestiva

Planktonic populations of the calanoid copepod Labidocera aestiva show significant biochemical genetic heterogeneity along the Atlantic coast of the USA. In summer, 1981, copepods were collected by surface tows at Beaufort Inlet, North Carolina; Fort Pierce Inlet, Florida; and Vineyard Sound, Massachusetts. Genetic variation within each population and genetic differentiation among the three populations were studied by micro-acrylamide gel electrophoresis of six loci encoding four enzymes. All six enzyme loci were polymorphic when all populations were considered together, but the North Carolina population was monomorphic at two loci. High genetic variability was indicated by the following: (1) the number of alleles per locus averaged over all loci was 2.57±0.26 SD; (2) the average proportion of loci for which the frequency of the most common allele was not greater than 0.95 was 0.78±0.10; (3) the frequency of heterozygous individuals was 0.25±0.07. Genetic differentiation among population samples in the three regions was demonstrated in several ways: allele frequencies at one aminopeptidase-I locus, Lap-1, differed significantly among samples of the three populations, and there were unique alleles of high frequency at this locus in two population samples. Values of the statistic of genetic distance (D) averaged 0.20±0.08 for pairwise comparisons between all samples. Compared to expected heterozygosity if individuals across the entire range sampled mated at random, there were highly significant heterozygote deficiencies at five of the six loci. Genetic differentiation of populations of L. aestiva may result from (1) differential selection on populations in the three regions, or (2) restricted gene flow between the populations. Gene flow may be limited by geographic separation or differences in life history, such as seasonal presence in the plankton and diapause egg production.Contribution No. 5810 of Woods Hole Oceanographic Institution     

Social foraging and dominance relationships: the effects of socially mediated interference

In socially foraging animals, it is widely acknowledged that the position of an individual within the dominance hierarchy of the group has a large effect upon its foraging behaviour and energetic intake, where the intake of subordinates can be reduced through socially mediated interference. In this paper, we explore the effects of interference upon group dynamics and individual behaviour, using a spatially explicit individual-based model. Each individual follows a simple behavioural rule based upon its energetic reserves and the actions of its neighbours (where the rule is derived from game theory models). We show that dominant individuals should have larger energetic reserves than their subordinates, and the size of this difference increases when either food is scarce, the intensity of interference suffered by the subordinates increases, or the distance over which dominant individuals affect subordinates increases. Unlike previous models, the results presented in this paper about differences in reserves are not based upon prior assumptions of the effects of social hierarchy and energetic reserves upon predation risk, and emerge through nothing more than a reduction in energetic intake by the subordinates when dominants are present. Furthermore, we show that increasing interference intensity, food availability or the distance over which dominants have an effect also causes the difference in movement between ranks to increase (where subordinates move more than dominants), and the distance over which dominants have an effect changes the size of the groups that the different ranks are found in. These results are discussed in relation to previous studies of intra- and interspecific dominance hierarchies.     

桑给巴尔岛附近硬珊瑚的分布和丰度模式

东非珊瑚礁的特点是它位于一个离散的动物地理学分区[1],具有经由赤道流接纳和重新分配偏远的种属物质的潜在重要性[2].尽管如此,该地区仍然是世界上研究最少的地区之一.例如,在坦桑尼亚,尽管珊瑚礁是众多的人赖以为生的重要自然资源,却没有受到应有的重视和研究[3～5].为数不多的研究定量分析过坦桑尼亚的珊瑚礁结构[6～13],而且大部分只是限于对一些礁砰进行基线研究.     

Integrating corporate social responsibility,health improvement,and community support in development programmes: a case for enhancing the application of health impact assessment in programme implementation in the Niger Delta region

Transnational corporations (TNCs) invest enormous resources in their corporate social responsibility (CSR) programmes in the Niger Delta region of Nigeria. However, the effectiveness and mode of execution of these CSR activities have been subjects of continuing debate. This research was therefore carried out to elicit the perspectives of members of four local communities about the impact of the CSR interventions in the areas of health improvement and participation by members of the communities in the Niger Delta. Semi-structured questionnaires were self-completed by 182 members of the local communities in the Niger Delta; the respondents gave detailed feedback about community feelings for TNCs and their CSR efforts. The findings showed that the people generally have negative views towards the CSR practices of the TNCs. The result of a two-paired t-test showed this to be true for both men and women (P =?.888, CI 95). While 69.8% of the respondents felt that the TNCs did not bring any development to their community, 87.9% had high fear of getting a disease due to the community they live in; interestingly, 90.1% wanted to be involved in decisions concerning their communities. This research therefore proposes the increased use of health impact assessment as an approach to integrate health considerations and community participation into the evaluation and implementation of development programmes in the Niger Delta. Such an approach has the potential to make CSR initiatives more effective, transparent, and minimise the tensions between communities and TNCs.     

Identifying pathways to visions of future land use in Europe

Regional Environmental Change - Plausible scenarios of future land use derived from model projections may differ substantially from what is actually desired by society, and identifying such...