An experimental study on recolonization and succession of marine macrobenthos in defaunated sediment

Hypoxia/anoxia in coastal waters is a world wide problem which often results in mass mortality and defaunation of benthos. In this study, field experiments were carried out to examine recolonization and succession of macrobenthic infauna in defaunated sediments, and the time required for recovery from complete defaunation to a stable community. Trays (33 cm length × 25.5 cm width × 11 cm depth) of defaunated sediment were exposed at the subtidal of a pristine site in subtropical Hong Kong. Temporal changes of macrobenthic communities in defaunated sediment were analyzed by univariate and multivariate statistics, and compared with those in undisturbed natural sediment at the same site. Initial colonization of macrobenthos occurred rapidly. A total of 42 species was found, with an average of 258 animals per tray and 24 species per tray recorded in the first month. Abundance showed a small peak (496 animals per tray) after 3 months, reached a sharp peak (1154 animals per tray) after 6 months, and declined thereafter. Species number increased gradually, reached a maximum (68 species per tray) after 9 months, and then decreased. Recolonization was predominantly contributed by larval settlement rather than adult migration. Temporal changes in abundance, species number and diversity of the macrobenthic community in defaunated sediment resemble the spatial changes along a decreasing pollution gradient previously defined by other authors. Results of this experiment suggest that newly available sediment may allow more species to colonize (or coexist) than sediment pre-occupied by an established community. This is probably due to less interspecific competition in the former habitat. No significant difference in abundance or species richness was observed between defaunated and natural sediments after 15 months, suggesting that a stable community had been achieved, although minor variations in species composition were still discernible between defaunated and natural sediments. Received: 24 May 1999 / Accepted: 20 October 1999     

Humoral opsonin from the colonial ascidian Botryllus schlosseri as a member of the galectin family

The synthesis and secretion of the humoral opsonin from the colonial ascidian Botryllus schlosseri was studied by using specific polyclonal antibodies that recognise both of the bands obtained after SDS-PAGE of the purified lectin. The agglutinin was revealed on the surface of agglutinated yeast and red blood cells and in the cytoplasm of the phagocytes, either uniformly distributed or localised inside the cytoplasmic projections. A previous incubation of haemocytes with the agglutinin resulted in intense labelling of the surface that disappeared in the presence of D-galactose, whereas it was not affected by treatment with proteases. These results, together with the already published data, suggest that our molecule is a new member of the galectin family. Received: 16 July 1999 / Accepted: 7 February 2000     

Reef coral reproduction in the eastern Pacific: Costa Rica, Panamá and Galápagos Islands (Ecuador). IV. Agariciidae, recruitment and recovery of Pavona varians and Pavona sp.a

The reproductive ecology of two eastern Pacific zooxanthellate coral species was examined as part of a continuing series of studies relating bleaching/mortality events caused by the El Niño–Southern Oscillation disturbance, and is described for study sites in Costa Rica, Panamá, and the Galápagos Islands (Ecuador). This study deals with the sibling agariciid species Pavona varians and Pavona sp.a over a 13?yr period (1985 to 1997). Both Pavona species are broadcast-spawners with some gonochoric, but mostly sequential hermaphroditic colonies. Minimum colony sizes (and ages) at first reproduction were 5?cm (5?yr) and 3?cm (2 to 3?yr), respectively, in P. varians and Pavona sp.a. In the Panamá and Galápagos populations, gonochoric colonies spawn eggs or sperm at least monthly. Six fecundity attributes were not significantly different in the two species, but the eggs of P. varians are white to beige and positively buoyant, and those of Pavona sp.a are dark green and neutrally to negatively buoyant. Eggs of both species lack zooxanthellae. Both species are reproductively active year-round, with maximum activity in the dry season in the nonupwelling Gulf of Chiriquí, and in the wet season in the upwelling Gulf of Panamá. Spawning is predominantly during full moon, and possibly also at new moon at most study sites. Spawning in P. varians and Pavona sp.a is 12?h out of phase, with the former species spawning ～1?h before sunrise and the latter about 1?h after sunset. The fecundity of Pavona spp. at Caño and the Galápagos Islands was much greater (19?900 to 27?900 eggs cm^?2?yr^?1) than at all Panamá sites (14?800 to 19?800 eggs cm^?2?yr^?1). Intraspecific crosses in both species resulted in swimming planula larvae after 25 to 36?h. Recruitment of P. varians was highest in Panamá, moderate in Costa Rica, and nil in the Galápagos Islands, matching, respectively, the contributions of P. varians to the pre-1982/1983 El Niño coral-population abundances in these areas. Recruitment success of P. varians at Uva Island was significantly related to maximum monthly positive sea surface-temperature (SST) anomalies that occurred in the year preceding recruitment over the period 1982 to 1996; recruitment failed when SST anomalies exceeded 1.6 to 1.9?C° during the severe ENSO events of 1982/1983 and 1997/1998.     

Comparative morphology and cytology of siphons and siphonal sensory organs in selected bivalve molluscs

 The form, anatomy and cytology of the water-passages in siphon-possessing and siphon-lacking species of a selected group of bivalve molluscs from the Red Sea (Callista florida, Circe currogata, C. crocea, Lucinia dentifera, Dosinia histrio, Pitar hebraea, Tridacna maxima, Pteria aegyptica), and from the Mediterranean Sea (Spondylus spinosus, Pinctada radiata, Pinna nobilis, Donax trunculus, D. semistriatus, Mactra stultorum, Tapes decussatus, Petricola lithophaga, Brachidontes pharaonis) were studied by means of light and electron microscopy. In the mytiloids, ostreoids and ptrioids studied, the water-passages are covered by a ciliated epithelium and the few tentacles around their openings are identical to those found on the mantle edges. Contrary to this, in the veneroids studied, the siphons are covered by a microvillar epithelium and their tentacles, especially of the inhalant siphon, reveal characteristic branching. The so-called Type I, Type II and Type III ciliated sensory organs on and within the siphons are similar to those observed in other bivalves, differing from each other in the dimension, number and form of cilia. In the studied mytiloid species only Type I and Type II organs were found. The form and structure of the siphons and the distribution of sensors on them can be used as markers for ecological as well as phylogenetic considerations. Received: 28 January 2000 / Accepted: 28 May 2000     

Genetic differentiation in a pelagic crustacean (Meganyctiphanes norvegica: Euphausiacea) from the North East Atlantic and the Mediterranean Sea

Meganyctiphanes norvegica (M. Sars)is a pelagic crustacean that plays a key role in marine food webs of North Atlantic Ocean and marginal seas. We studied eight population samples collected in the European Atlantic and Mediterranean Sea. By means of single strand conformation polymorphism analysis (SSCP) and direct sequencing, we investigated a segment of 158 base pairs of the mitochondrial gene coding for the subunit 1 of NADH dehydrogenase. We found 12 sequence variants among the 385 individuals studied. Analysis of molecular variance (AMOVA) showed that 14.75% of the total genetic variability was explained by differences between populations, thus indicating absence of panmixia for these populations. Pairwise comparisons revealed three distinct genetic pools: the first one represented by Cadiz Bay, the second one by the Ligurian Sea, and the third one included all the NE Atlantic samples. We also investigated one population from the Alboran Sea (within the Mediterranean basin, east of the Strait of Gibraltar). This population was found to be genetically intermediate between the NE Atlantic samples and the Ligurian sample, suggesting that the restriction to the gene flow is not associated with the Strait of Gibraltar, but possibly with the Oran–Almeria oceanographic front. The present work indicates that M. norvegica, although endowed with a high dispersal capacity because of its pelagic habit, can develop separate breeding units inside the same oceanic basin (the Atlantic). Furthermore, the Ligurian sample should be considered as a distinct evolutionary entity, separated from the Atlantic population. Received: 2 May 1999 / Accepted: 26 November 1999     

Mating behaviour of Macrophthalmus hirtipes (Brachyura: Ocypodidae)

 We examined the mating behaviour of the New Zealand ocypodid crab Macrophthalmus hirtipes in the laboratory between February and June 1998. This species has a discrete breeding season. Mating and moulting were not linked and only intermoult females with mobile gonopore opercula were attractive to males. Allometry and compatibility of gonopods and gonopores of different-sized crabs was investigated. Under laboratory conditions, the opercula of intermoult females remained mobile on average for 11.4 d, but the duration of receptivity did not appear to be under female control. The operational sex ratio in the laboratory fluctuated greatly, but was always male-dominated. During the period of opercular mobility, females mated many times with several different males. Matings in the absence of burrows were relatively short (mean duration = 23 min, max. = 122 min) and the mating behaviour of M. hirtipes lacked courtship and mate-guarding. Males used a search-intercept method to acquire mates, with very low levels of intrasexual competition. There was no evidence of mate preference in M. hirtipes, and males spent just as long mating with ovigerous females as with non-ovigerous ones. Although M. hirtipes has ventral-type spermathecae, as do several other ocypodid crabs, it is unclear whether this promotes last-male sperm precedence. The role of burrows in modifying the mating behaviour of M. hirtipes in the field remains to be established. Received: 7 January 2000 / Accepted: 5 June 2000     

Mitochondrial DNA sequence variation and phylogeography of oceanic insects (Hemiptera: Gerridae: Halobates spp.)

Relatively few insects have invaded the marine environment, and only five species of sea skaters, Halobates Eschscholtz (Hemiptera: Gerridae), have successfully colonized the surface of the open ocean. All five species occur in the Pacific Ocean, H. germanus White also occurs in the Indian Ocean, whereas H. micans Esch- scholtz is the only species found in the Atlantic Ocean. We sequenced a 780 bp long region of the mitochondrial cytochrome oxidase subunit I gene (COI) for a total of 66 specimens of the five oceanic Halobates species. Our purpose was to investigate the genetic variation within species and estimate the amount of gene flow between populations. We defined 27 haplotypes for H. micans and found that haplotype lineages from each of the major oceans occupied by this species are significantly different, having sequences containing five to seven unique base substitutions. We conclude that gene flow between populations of H. micans inhabiting the Atlantic, Pacific, and Indian Ocean is limited and hypothesize that these populations have been separated for 1 to 3 million years. Similarly, there may be limited gene flow between H. germanus populations found in the Pacific and Indian Ocean and between H. sericeus populations inhabiting the northern and southern parts of the Pacific Ocean. Finally, we discuss our findings in relation to recent hypotheses about the influence of oceanic diffusion on the distribution and population structure of oceanic Halobates spp. Received: 29 July 1999 / Accepted: 23 November 1999     

Has Economic Research Answered the Needs of Environmental Policy?

Efficient environmental regulation requires empirical estimates of the benefits and costs of environmental standards and policies. In the last 25 years, economists have made considerable progress in developing methods for measuring environmental benefits and in providing empirical estimates of costs and benefits. This paper reviews this progress. It examines by category of benefit the advancements made in providing estimates that can be used in benefit-cost analyses and identifies areas where additional research is required.     

Duetting and mate-guarding in Australian magpie-larks (Grallina cyanoleuca)

A recently favored hypothesis is that duetting in birds has a mate-guarding function: a male responds vocally to his partner’s song, thereby forming a duet that repels males who are attracted to her song. Previous studies have not provided unambiguous tests of the mate-guarding hypothesis because: (1) the probability of a male answering his partner’s song has not been shown to increase specifically when the female is fertile, and (2) the probability of a male answering his partner’s song has not been assessed separately from simply a higher song initiation rate. We investigated extra-pair paternity, mate-guarding, and duetting in the socially monogamous Australian magpie-lark (Grallina cyanoleuca). DNA fingerprinting revealed that 3% of young were the result of extra-pair paternity, and we found that males guarded fertile females by staying close to them. However, males did not initiate songs at a higher rate when females were fertile and actually reduced their probability of replying to female song during this period. We conclude that although male magpie-larks did guard fertile females in an attempt to prevent extra-pair copulations, they did not use duetting for this purpose. Received: 10 May 1999 / Received in revised form: 27 September 1999 / Accepted: 2 October 1999     

Life history costs of olfactory status signalling in mice

Large body size confers a competitive advantage in animal contests but does not always determine the outcome. Here we explore the trade-off between short-term achievement of high social status and longer-term life history costs in animals which vary in competitive ability. Using laboratory mice, Mus musculus, as a model system, we show that small competitors can initially maintain dominance over larger males by increasing investment in olfactory status signalling (scent-marking), but only at the cost of reduced growth rate and body size. As a result they become more vulnerable to dominance reversals later in life. Our results also provide the first empirical information about life history costs of olfactory status signals. Received: 15 December 1999 / Revised: 6 June 2000 / Accepted: 24 June 2000