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     

Grazing rates of organic matter and living fungal biomass of decaying Spartina alterniflora by three species of salt-marsh invertebrates

 The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg⁻¹ d⁻¹) and lowest for periwinkles (90 μg mg⁻¹ d⁻¹), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day. Received: 25 November 1998 / Accepted: 4 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.     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

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     

Gender- and oxygen-related irrigation behaviour of the decapod Nephrops norvegicus

The Norway lobster Nephrops norvegicus (L.) inhabits burrows in muddy clay sediments (e.g. on the Swedish west coast), where an autumnal oxygen deficiency in the bottom water can occur. Our experiments investigated whether the irrigation of the burrows would reflect a behavioural adaptation to hypoxia, and whether any gender differences of such behaviour exist. Irrigation is performed by the pleopods which may compensate for a decreasing oxygen tension. Pleopod activity (total number of strokes per sampling time), associated with oxygen concentration and gender, was studied in N. norvegicus kept in artificial burrows resembling their natural habitat. Male and female lobsters were separately exposed to either normoxia (70% oxygen saturation) or hypoxia (30% oxygen saturation). A sexual difference in behaviour was found, where females irrigated the burrow less than males during normoxia. Females showed a significant increase of pleopod activity in hypoxia compared with normoxic conditions, which was not displayed by the males probably due to the degree of individual variation found. However, when only males were studied during progressive hypoxia (from 60 to 5% oxygen saturation), following any changes of irrigational behaviour, a significant increase of accumulated pleopod activity occurred. A major increase of pleopod activity appeared between 60 and 50% oxygen saturation, below which the activity remained high until a critical point (<10% saturation, 11 °C, 33 psu) where irrigation dropped to a level close to that of normoxic values. Activity sessions during hypoxia were longer and had a higher stroke rate than during normoxia. Received: 22 October 1997 / Accepted: 26 February 1998     

Distribution and relative abundance of Pseudocalanus moultoni and P. newmani (Copepoda: Calanoida) on Georges Bank using molecular identification of sibling species

The sibling species, Pseudocalanus moultoni (Frost, 1989) and P. newmani (Frost, 1989), occur sympatrically on Georges Bank. Taxonomic discrimination of the species relies on subtle morphological characteristics, making routine identification of the species very difficult. DNA sequence variation of two mitochondrial genes, 16S rRNA and cytochrome oxidase I (COI), reliably discriminated P. moultoni and P.␣newmani. Levels of DNA sequence variation for both genes were consistent with those between species of calanoid copepods. A molecular systematic protocol (based on allele-specific PCR amplification) was designed from the COI sequences and used to discriminate females of the two species. The distributions and relative abundances of the two species were mapped for April 1996 based on samples of 15 to 30 females from 12 collections across Georges Bank. The results of this study indicated that P. moultoni females predominated along the northern flank of Georges Bank, while P. newmani females were common on the southern flank, deeper than the 60-m isobath. Received: 16 May 1997 / Accepted: 26 April 1998     

Recovery of benthic communities at Macquarie Island (sub-Antarctic) following a small oil spill

Intertidal communities at Macquarie Island (sub-Antarctic) were re-evaluated seven years after a small oil spill resulting from the grounding of the “Nella Dan”, and six years after the first assessment of biological impact. Sampling was conducted to evaluate community structure in three zones of the exposed rocky shore (upper red, kelp, and lower red) and in samples of Durvillaea antarctica holdfasts. There were no significant differences between the community structure in oiled and control locations in any of the three shore zones, but holdfast macrofaunal communities at oiled sites still showed evidence of impact. Holdfast community-structure in samples from heavily oiled sites showed moderate levels of recovery, with increased abundances of species which were considered sensitive to the oiling in the first post-impact studies and decreased abundances of opportunistic polychaete and oligochaete worms. In contrast, samples collected from the moderately oiled location at Secluded Bay showed little evidence of recovery. Holdfasts at this site were filled with sediment containing traces of diesel oil, and the macrofaunal community was dominated by opportunistic worms. This study clearly indicates that even small incidents of anthropogenic perturbation can have long-lasting consequences for marine communities at Macquarie Island. Received: 23 July 1997 / Accepted: 5 February 1998     

Factors influencing food choice by the seaweed-eating marine snail Norrisianorrisi (Trochidae)

Through two-choice gustatory experiments, a␣preference hierarchy was established␣for␣the␣herbivorous gastropod Norrisianorrisi Sowerby, with laminarialean kelps preferred over all other seaweeds. Among the kelps, laminae of Macrocystispyrifera were slightly preferred over Egregiamenziesii, and both were strongly preferred over sporophylls of Eiseniaarborea. E.arborea, the least preferred kelp, was consistently chosen over other algae common in the snail's habitat (Halidrysdioica, Dictyotaflabellata, and Pterocladiacapillacea) and over seaweeds believed to be edible and palatable based on their morphology, structure, and secondary chemistry (Endarachnebinghamiae, Mazzaellaflaccida, and Ulvalobata). The morphologies and structural toughness of tested seaweeds varied significantly as did their nutritional (% carbon, % nitrogen, C:N ratio, and % ash) contents and phlorotannin concentrations; however, snails preferred to feed on kelps regardless of nutritional content, toughness or phlorotannin concentration; and among kelps preferred to feed on the least tough species (based on penetrometer measurements), which also were those containing the lowest phlorotannin concentrations. Preference for kelp was not upheld in experiments using agarose thalli to which freeze-dried powder, of either the kelp Eiseniaarborea or non-kelp Endarachnebinghamiae was added, suggesting the destruction of attractant chemicals during the making of the artificial foods. Our data suggest that the preference of N. norrisi for kelps over other potentially edible and palatable seaweeds may not be related to nutritional content, but instead may have evolved in response to factors such as availability, habitat provision, or refuge from predation. Received: 27 September 1996 / Accepted: 7 October 1997     

Settlement-competency periods of larvae of three species of scleractinian corals

The pattern of settlement over time of three broadcast spawning coral species (Cyphastrea serailia, Acanthastrea lordhowensis, and Goniastrea australensis) from the Solitary Islands (30°00′S; 153°20′E) was studied in 1995 and 1996 in order to determine the maximum length of time these larvae could remain in the water column and still retain the ability to settle and metamorphose. Larvae were maintained in aquaria and the number which had settled on biologically-conditioned tile pairs was monitored every 5 to 10 d. While the majority of larvae settled quickly after becoming competent, some larvae survived and settled for extended periods after spawning. Competency periods ranged from 26 d for C. serailia to 56 d for G. australensis and 78 d for A. lordhowensis. These data greatly extend the known competency periods for larvae of broadcast-spawning corals and indicate the potential for transport of broadcast-spawned coral larvae over large distances. Medium to long-distance larval dispersal of the species studied provides a mechanism for their widespread distribution in subtropical regions, on reefs which are often widely spaced and relatively isolated. Received: 27 May 1997 / Accepted: 27 November 1997