Microbial transformations in deep-sea sediments: free-vehicle studies

Radiotracer techniques can be used to assess eitherin-situ metabolic activities of natural microbial populations or potential turnover rates of specific substrates under the givenin-situ conditions. The second approach has been used in deep-sea sediment studies where steady-state conditions are unlikely to occur because of the heterogeneous distribution of nutrients as a result of a patchy input by depositing particulates. Recent sediment trap studies have shown that particulate matter reaching the deep sea does contain simple organic compounds. Therefore, the present experiments dealt with the measurement of carbon incorporation and respiration of¹⁴C-labeled acetate, glucose, glutamate and trimethylamine in deepsea sediments. Free vehicles, i.e. aluminum framed tripods that descend untethered to the deep sea floor and return automatically, were used for thein-situ injection and incubation of cores at depths of 2600 to 5330 m. The data were compared to those obtained from (1) parallel samples incubated at 1 atm andin-situ temperature and (2) a shallow-water station (Buzzards Bay, 12 m). Rates measuredin situ generally decrease with water depth as well as with depth in the upper 9 cm of top sediment. In most experiments, rates measured in the 1 atm controls were higher than those observedin situ. This fact supports the general notion that natural populations of deep-sea sediment contain barotolerant and barophilic microorganisms in varying proportions.     

Offshore spawning by the portunid crabScylla serrata (Crustacea: Decapoda)

The portunid crabScylla serrata (Forskål) is shown to migrate offshore to spawn. Records of 447S. serrata caught as bycatch by trawlers in the tropical waters of northern Australia were analysed with respect to area, depth, distance offshore and month of capture as well as the sex and size of the crabs and whether the females were ovigerous. The crabs were caught mainly in three areas that correspond to the tiger prawn trawl fishery, at between 10 and 60 m depth (mean 28.5 m), 3 to 95 km offshore (mean 17.9 km). Most (87%) of the crabs were captured in October and November, which suggests they move offshore in September and October. No crabs were reported from offshore by February. Over 97% of the crabs caught offshore were female, of these 61.5% were ovigerous. The size range of females (100–109 to 200–209 mm carapace-width size classes) and males (120–129 to 200–209 mm carapace-width size classes) caught was similar. The frequent occurrence in coastal waters of females that are larger than the modal size at spawning, as well as mature females with spent ovaries, suggests that many females return to the coast after spawning. Although some species of portunid crab are euryhaline, mature females of estuarine species migrate to the sea to spawn. The migration byS. serrata described here is far more extensive than would be required to reach sea water salinities; it probably provides a dispersal mechanism for larvae to enable the megalopa stage to recruit to habitats distant from those of the parents.     

Geographic and bathymetric patterns of mitochondrial 16S rRNA sequence divergence among deep-sea amphipods,Eurythenes gryllus

The physical uniformity of the deep sea suggests a lack of absolute barriers to faunal dispersal, and thus genetic homogeneity in broadly distributed species is expected. The deep-sea amphipod Eurythenes gryllus Lichtenstein (Crustacea: Lysianassoidea) is considered a panoceanic, cold-water stenotherm, with a vertical depth distribution from 184 to 6500 m. We surveyed mtDNA sequence diversity in E. gryllus to assess genetic diversity and population structure in different oceans and across traditionally defined bathyal and abyssal zones. DNA sequences (437 nucleotides length) from the mitochondrial large-subunit ribosomal RNA gene (16S rRNA) of 95 individuals, collected between 1982 and 1990 from 14 locations in the central North Pacific (including multiple samples on the slope of a seamount), castern and western North Atlantic, and the Arctic Ocean, were obtained. Our analysis of DNA sequence diversity indicates (1) genetic homogeneity among sites within the same depth zone at the scale of ocean basins; and (2) genetically divergent, cryptic taxa distributed at different depths, with the greatest diversity in the bathyal zone. These observations suggest that ecological and physical conditions are important isolating mechanisms that may lead to speciation in this group.     

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.     

Rates of fission, somatic growth and gonadal development of a fissiparous sea star, Allostichaster insignis, in New Zealand

Seasonal changes in population structure and incidence of fission were measured in intertidal and subtidal populations of Allostichaster insignis, a fissiparous sea star. Population size structure was stable over the course of the 1-year study. Sea stars in the subtidal zone attained greater maximum size (mean arm length, R = 35 mm) than those in the intertidal population (20 mm). Fission rates were greatest among small individuals (R < 20 mm). The frequency of fission ranged from 5 to 32% with peaks in early austral summer in the intertidal zone, and in autumn and winter in the subtidal zone. Sexual reproduction occurred in early spring in sea stars larger than 12 mm. The populations were heavily biased toward males. In the laboratory, A. insignis of three size classes (small, R = 9–13 mm; medium, 19–21 mm; and large, 29–31 mm) were fed mussels ad libitum or starved (not fed macroscopic food) for ∼1 year in a 3 × 2 factorial experiment. Small and medium-sized sea stars divided throughout the experiment and the ramets of most individuals regenerated sufficiently to divide again after 6–9 months. Unfed sea stars did not undergo fission (with one exception), had a higher mortality rate, and did not grow. Small, fed sea stars grew significantly faster than medium-sized or large individuals. At the end of the experiment, the pyloric caeca index (a measure of nutritional condition) was greater in fed than in unfed animals. Gonads (only testes were observed) developed in medium-sized and large, fed sea stars. Our field and laboratory results indicate that asexual reproduction in A. insignis predominantly occurs in small, well-nourished individuals. Ramets grow gradually through repeated fission and regeneration to a size (mean length of regenerating arms, R _r ∼ 20 mm) at which they begin to switch to sexual reproduction as the dominant reproductive mode.     

Crossing the frontier: vertical transit rates of deep diving cormorants reveal depth zone of neutral buoyancy

Knowing the depth zone of neutral buoyancy of divers is important because buoyancy can determine how animals manage their energy budget. In this study, we estimate the depth zone of neutral buoyancy of free-ranging cormorants for the first time, using time-depth recorders. We discovered that vertical ascent rates of 12 Crozet and 15 Kerguelen diving blue-eyed shags (respectively Phalacrocorax melanogenis and P. verrucosus) slowed down considerably at the 50–60 m depth zone. We suggest this was due to birds trying to reach the surface from that point upwards using reduced locomotor activity because the force of buoyancy becomes greater than the force of gravity at that depth. The results show a shift of this depth zone in relation to maximum targeted dive depth, suggesting cormorants may control buoyancy through respiratory air volume adjustment. Interestingly, 60 m is close to the maximum depth zone reached by these two species during dives lasting 4 min, their estimated behavioural aerobic dive limit. This suggests that the decision to swim deeper has a direct consequence on the energy budget, with time spent recovering at the surface (time thus lost to foraging) strongly increasing relative to the preceding time of submergence. Resources found in deeper waters must be of sufficient quantity or quality to justify crossing the frontier of physical neutral buoyancy.     

Growth of the deep-sea irregular sea urchins Echinosigra phiale and Hemiaster expergitus in the Rockall Trough (N.E. Atlantic Ocean)

Growth in the deep-sea irregular sea urchins Echinosigra phiale (family Pourtalesiidae) and Hemiaster expergitus (family Hemiasteridae) was studied from deep-sea samples taken during the years 1973 to 1985 from two stations at 2900 and 2200 m depth in the Rockall Trough (N.E. Atlantic Ocean). Growth zones, similar to those described from sea urchins in shallow water, are present as a series of wide white bands separated by narrow, dark rings in the calcite stereom of the test plates after heating to 350°C. In shallow water, such growth zones seem to result from seasonally varying growth rates. In the supposedly constant conditions in the deep sea, a seasonal growth pattern is unexpected but may occur in response to recently discovered annual pulses in downward flux of detritus from the euphotic zone, providing a seasonally varying food supply for such deposit-feeding species living in the bottom sediment. On this assumption, growth curves were fitted to counts of growth zones (as representing age in years), in the larger lateral and ventral test plates of E. phiale and H. expergitus. The opportunity was also taken to fit growth curves derived from counts of growth zones in samples of the inshore spatangoids Spatangus purpureus and Echinocardium pennatifidum. Plots of counts against test length of Echinosigra phiale and H. expergitus, although scattered and not clearly asymptotic, indicate, growth to be slower than in the two inshore spatangoids, and than in the coastal species Echinocardium cordatum, for which there are good recent growth data, available.     

Diatoms of the microphytobenthic community in a tropical intertidal sand flat influenced by monsoons: spatial and temporal variations

Seasonal variations in the microphytobenthic diatom community were investigated in an intertidal sand flat of a tropical marine environment influenced by monsoons. Cores of sediments were collected along the beach gradient: low tide, mid tide and high tide zone up to a depth of 15 cm.. Diatom abundance was lowest during the monsoons and highest during the post-monsoons and the early pre-monsoon season throughout the intertidal transect. Diatom diversity was highest at the mid tide, followed by the high and low tide zones. Diatoms were viable up to a depth of 15 cm throughout the intertidal transect. The diatom community included the pennates, the permanent residents of this area, centric genera, which lead an attached mode of life and also some planktonic genera, brought in from ambient waters. Among the pennates, Navicula and Amphora were the dominant genera whereas in the case of centrics, Thalassiosira dominated the community throughout the intertidal transect down to a 15 cm depth. . Grain size fractions, which served as predictors of some diatom genera changed with tidal zones. The effect of winds on the resuspension of the pennate diatoms was evident only at the low tide zone down to a depth of 5 cm . Chlorophyll a concentration proved to be a good predictor of both pennate and centric diatom abundance at the low tide zone down to a depth of 10 cm and at the mid tide zone down to a depth of 5 cm.. However, even though chlorophyll a concentrations failed to reveal any positive correlation with the diatom abundance at both the deeper sediment layers and the high tide zone, the fact that viable cells were present at these areas reveal that the diatoms adopt survival strategies, contributing significantly to the carbon budgets of such unstable habitats.     

Habitat associations and diet of young-of-the-year Pacific cod (<Emphasis Type="Italic">Gadus macrocephalus</Emphasis>) near Kodiak,Alaska

The influence of environmental variables and habitat on growth and survival of juvenile gadoid species in the Atlantic has been clearly demonstrated; conversely, in the North Pacific little is known about the habitat and ecology of juvenile Pacific cod (Gadus macrocephalus Tilesius). The hypothesis that density of young-of-the-year (YOY) Pacific cod in nearshore habitats is predicted by shallow depth and the presence of eelgrass and macroalgae was tested in a variety of nearshore habitats adjacent to commercial fishing grounds near Kodiak Island, AK. From 10 to 22 August 2002, a beach seine and small-meshed beam trawl were used to capture YOY Pacific cod (n = 254) ranging from 42 to 110 mm fork length. Depth, water temperature, salinity, sediment grain size, and percent cover by emergent structure (i.e. tube-dwelling polychaetes, sea cucumber mounds, macroalgae) were measured prior to fishing. Density of YOY Pacific cod was highest in areas of moderate depth (15–20 m) and positively and linearly related to percent cover by sea cucumber mounds and to salinity. No previous studies have documented fish utilizing sea cucumber mounds as habitat. Furthermore, eelgrass and macroalgae were inconsequential to cod distribution. Diets consisted mainly of small calanoid copepods, mysids, and gammarid amphipods and were significantly related to cod length and depth. This work provides important information on previously undocumented factors that affect distribution and feeding of YOY Pacific cod, which ultimately influence growth and survival in this species.     

Adaptation of light-harvesting pigments to downwelling light and the consequent photosynthetic performance of the eulittoral rockweeds Ascophyllum nodosum and Fucus vesiculosus

We compared the effect of habitat and water depth on the light-harvesting pigment content for Ascophyllum nodosum and Fucus vesiculosus at two near-shore stations in Long Island Sound (USA). Excised pieces of seaweeds were attached at depth intervals to a vertically buoyed line, and left in situ for 7 days. For comparison, fronds were collected from sun and shade habitats in the littoral zone. The three major antenna (light-harvesting) pigments increased in concentration with depth or shade. Chlorophyll c to a ratios remained stable at about 0.2. Fucoxanthin to chlorophyll a ratios decreased by 20 to 30% with depth or shade. Although pigment composition for the two rockweed species was equivalent, the maximum photosynthetic performance of F. vesiculosus exceeded that of A. nodosum by a factor of 2, while the compensation depths for 4 m-adapted A. nodosum and F. vesiculosus under natural limiting light conditions were equivalent. Plants held at 4 m had higher photosynthetic rates compared with plants held at 0 m, no matter the depth of measurement. Indirect evidence indicates that the enhanced photosynthesis of 4 m-adapted plants is due not only to higher concentrations of antenna pigments but to other physiological factors as well. We conclude that the clearly delineated vertical distribution of these two canopy species, the F. vesiculosus zone over the A. nodosum zone, is not determined by light quantity or quality, but by biotic factors as evidenced by the experiments of Menge which are cited herein.     

Reef-basel herbivores and the distribution of two seagrasses (Syringodium filiforme and Thalassia testudinum) in the San Blas Islands (Western Caribbean)

Two seagrasses, manatee grass (Syringodium filiforme) and turtle grass (Thalassia testudinum), predominated in the areas bordering Ukkup Tupo, San Blas Islands, Western Caribbean. These seagrasses occupied the following three concentric zones extending outward from the reef: a near-reef turtle grass zone, an intermediate manatee grass zone and an off-reef turtle grass zone. Feeding experiments between January and March 1980 indicate that the absence of manatee grass close to the reef resulted from grazing by reef-associated herbivores, mainly day-active fishes and night-active sea urchins (Diadema antillarum). Grazing on manatee grass by fishes was approximately six times greater than grazing by sea urchins; thus, it appears that herbivorous fishes restrict the near-reef distribution of manatee grass at the study area. Where grazing was heaviest, the inner boundary of the manatee grass zone was farthest from the reef. The volume of manatee grass grazed during experiments was five times the volume of turtle grass consumed, strongly suggesting that the former species is a preferred food item. This is the first evidence for selective grazing on seagrasses.     

Observations on the burrows and burrowing behaviour of two mud-dwelling decapod crustaceans,Nephrops norvegicus and Goneplax rhomboides

The burrows of the Norway lobster Nephrops norvegicus (L.) and of the crab Goneplax rhomboides (L.) were studied in Loch Torridon, Scotland. Polyester resin casts of burrows in the sea were made by divers to reveal their subsurface form. Tunnels made by N. norvegicus were usually simple, with two or more openings on the mud surface, and penetrated to a depth of about 30 cm. G. rhomboides burrows did not descend more than about 15 cm beneath the surface, but were usually more complex than the lobster burrows and had several openings. The methods of burrow construction used by the two crustaceans are described from aquarium observations. Neither N. norvegicus nor G. rhomboides show obvious morphological adaptations for burrowing, and it is suggested that the fossorial habit was adopted very early by decapods. The burrows of N. norvegicus do not seem to have assumed any functions in addition to the original one of providing refuge from predators. There is not sufficient known of the biology of the crab to indicate whether the same is true in its case.     

Settlement, recruitment and potential predators and competitors of juvenile echinoderms in the rocky subtidal zone

Recruitment patterns of marine invertebrates are affected both by settlement and early post-settlement events. This study examined the settlement and recruitment patterns of echinoderms at three sites in the rocky subtidal zone of Bocabec Cove, Bay of Fundy, Canada using artificial turf collectors and quadrats on the natural substrate. Potential predators were quantified at two of the sites along transects and in 1-m² quadrats. Both potential predators and competitors were quantified in 0.0625-m² quadrats. Settlement varied across sites (1.5–3 km apart) and two years of sampling (2004, 2005). The site of most potential settlement differed for the three groups of echinoderms: sea urchins (Strongylocentrotus droebachiensis), sea stars (Asterias spp.) and sea cucumber (Psolus fabricii). Settlement densities on the artificial turf collectors tended to be greater than the densities of settlers on the natural substrate. On the natural substrate, the only significant difference between densities of juveniles over time was that newly settled sea stars were found in July and were not found the following October. Large lobsters and carnivorous worms were potential predators with densities that varied between sites. Potential competitors that differed in abundance between sites were herbivorous gastropods and conspecifics for sea urchins; and carnivorous worms for sea stars. This study suggests that patterns of recruitment are either set up by patterns of settlement or by events during the first few weeks/months on the benthic substrate for these echinoderms.     

Marine Protected Area Design and the Spatial and Temporal Distribution of Cetaceans in a Submarine Canyon

Abstract: The Gully, the largest submarine canyon off the coast of eastern Canada, is currently under consideration as a marine conservation area, primarily because of the increasing interest in oil and gas production on the Scotian Shelf. Cetaceans, as a guild of abundant, large organisms that are relatively sensitive to such threats, provide a reliable means to determine the boundaries for a conservation area in this region. We compared the abundance of cetaceans between the Gully and other parts of the Scotian Shelf and Slope and found that abundance was higher in the Gully. We also assessed cetacean distribution and relative abundance within the Gully relative to search effort for several spatial and temporal parameters: depth, slope, sea surface temperature, and month. Distribution within the Gully was most strongly correlated with depth, but was also significantly correlated with sea surface temperature and month. Five of the 11 cetacean species commonly found in the Gully, and all those for which the Gully formed significant habitat on the Scotian Shelf, were concentrated in the deep (200–2000 m) mouth of the canyon. We suggest that a year-round marine protected area is necessary for the Gully. A core protection zone should be defined in the Gully based on depth and bounded by the 200-m isobath. A buffer zone around the core zone should be defined to provide protection from activities with further-reaching effects, such as noise, dredging, and chemical pollution.     

Disposal of Coal Fly Ash at A Deep Water Site in the Eastern Mediterranean Off Israel - Six Years of Monitoring

Coal fly ash (CFA) is dumped at a deep sea disposal site (1,500m water depth) in the eastern Mediterranean, ca. 70km off the Israeli shore. Since 1989, about one million tons of CFA were dumped at the 200km² allocated area. Six years of monitoring at the dump-site shows that the CFA is heterogeneously distributed; there are areas where CFA covers about 1.3cm depth of the sea floor while at others no CFA is found. CFA is present as a fine powder, small aggregates and even as large blocks both in the dump-site as well as at its peripheries. Cadmium, copper and zinc concentrations in the CFA decreased as a result of the prolonged contact with sea water at in situ conditions while inconclusive changes in mercury, iron and manganese were detected. No changes were observed for lead, iron and aluminium concentrations. A controlled long term field experiment, now in progress at the site, is expected to clarify further chemical changes occurring in the CFA.     

Animal-sediment relations in Cape Cod Bay,Massachusetts I. A transect study

Benthic macrofauna and bottom sediments were sampled at 7 stations along a 24 km long onshore-offshore transect ranging in depth from 12 to 42 m in Cape Cod Bay, Massachusetts, USA. High faunal density, biomass and species diversity were recorded at stations densely populated by tubicolous polychaetes. These tube mats bind and stabilize the substratum, providing solid surfaces for attachment of epizoans. Three suspension-feeding species, Euchone incolor (polychaete), Thyasira gouldi (bivalve) and Aeginina longicornis (amphipod), co-occur with deposit-feeding species on muds resuspended by tidal currents. Hydrographic profiles of temperature, salinity and turbidity indicate that resuspended silt-clay particles are entrapped in dense water below the summer thermocline, which persists from mid-April to mid-October. The zone of intersection of the thermocline with the sea floor in about 22 m of water defines a major biofacies-lithofacies transition. This ecotone is characterized by high faunal density, biomass, and species diversity. Benthic populations of macrofauna from Cape Cod Bay are larger than those from Buzzards Bay, Massachusetts, and have a widely different taxonomic and trophic composition.Contribution No. 235 of the Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts, USA.     

Human impact on <Emphasis Type="Italic">Paracentrotus lividus</Emphasis>: the result of harvest restrictions and accessibility of locations

The sea urchin Paracentrotus lividus is common in the Mediterranean Sea in shallow subtidal rocky habitats, and it is intensely harvested for commercial and recreational purposes. This study is aimed at investigating whether the effects of harvest restrictions of P. lividus in rocky reef habitats interact with the accessibility of locations in structuring sea urchin population (total and commercial-sized individuals). These results are important for generating hypotheses about the influence of human harvesting on P. lividus and for addressing suitable measures of conservation. Paracentrotus lividus was sampled after the end of the sea urchin harvesting period (May–July 2007) within the Gulf of Alghero (North West Sardinia), where the Capo Caccia–Isola Piana Marine Protected Area (MPA) was established since 2002. Paracentrotus lividus was sampled at sixteen locations and attributed in groups of four to 4 combinations of harvest restrictions (Restricted Harvest, RH, vs. Unlimited Harvest, UH) and accessibility (Boat vs. Car), which correspond to a gradient of potential human activity on P. lividus in the ranked order of very low (RHBoatfar), low (RHBoatclose), moderate (RHCar) and high (UHCar). At each location, two depth ranges of 3–7 and 8–12 m were considered. At each of these depths, two areas of about 100-m² size were chosen. The density of P. lividus was assessed in ten quadrats of 1 × 1 m, and the size of 100 individuals (test diameter) was considered. Human activity has been found to significantly affect population structure of P. lividus influencing the proportion of individuals larger than 50 mm. Although harvest was restricted by MPA regulations, a significantly lower abundance of large individuals was found at sites accessible by car. This result highlights that there is an effect of harvest restrictions in relation to accessibility and emphasizes the need to carefully address the enforcement of the MPA toward easily accessible sites. Thus, surveillance and investment in enforcement of marine reserves seem crucial points that may provide the greatest return on maintaining the ecological benefits to the fishery activities.     

Surface sequestration of chemical feeding deterrents in the Antarctic sponge<Emphasis Type="Italic"> Latrunculia apicalis</Emphasis> as an optimal defense against sea star spongivory

Latrunculia apicalis is a spherically shaped demosponge that previous investigations have shown is rarely preyed upon by sea stars which are the dominant spongivores in antarctic benthic communities. Prior studies have also demonstrated that L. apicalis produces organic compounds that elicit a tube foot retraction response in the keystone spongivorous sea star Perknaster fuscus that can be used as a reliable assay for feeding deterrence. L. apicalis is known to contain discorhabdin alkaloids which serve, among other roles, as the source of its green coloration. To assess the defensive nature of the discorhabdin alkaloids toward P. fuscus, we have determined discorhabdin G concentrations in discrete sponge layers and evaluated those concentrations in the P. fuscus bioassay. In discorhabdin G-bearing sponges, we found a gradient of discorhabdin G that falls off rapidly toward the center of the sponge. On average, 52% of total discorhabdin G in a given sponge was found within 2 mm of the sponge surface. Tube foot retraction responses to extracts from the surface tissues (0–2 mm depth) of L. apicalis were compared to those of an inner layer (8–10 mm depth) and to a sample comprised of the same inner layer spiked with discorhabdin G at a concentration equivalent to that of the surface tissues. Tube foot retraction response times to extracts of the surface layers and the spiked inner layers were not statistically different, but were significantly greater than responses to the unaltered inner layer and controls. These results support the predictions of the optimal defense theory as L. apicalis sequesters its defensive chemistry (discorhabdin G) in its most vulnerable surface tissues, where the likelihood of predation from sea stars is highest. As antarctic sponges are generally preyed upon by extraoral feeding sea stars rather than deeper biting predators such as fish, surface sequestration may be uniquely adaptive in sessile macroinvertebrates occurring in antarctic marine benthic environments.Communicated by P.W. Sammarco, Chauvin     

Sea Snake Harvest in the Gulf of Thailand

Conservation of sea snakes is virtually nonexistent in Asia, and its role in human–snake interactions in terms of catch, trade, and snakebites as an occupational hazard is mostly unexplored. We collected data on sea snake landings from the Gulf of Thailand, a hotspot for sea snake harvest by squid fishers operating out of the ports of Song Doc and Khanh Hoi, Ca Mau Province, Vietnam. The data were collected during documentation of the steps of the trading process and through interviewers with participants in the trade. Squid vessels return to ports once per lunar synodic cycle and fishers sell snakes to merchants who sort, package, and ship the snakes to various destinations in Vietnam and China for human consumption and as a source of traditional remedies. Annually, 82 t, roughly equal to 225,500 individuals, of live sea snakes are brought to ports. To our knowledge, this rate of harvest constitutes one of the largest venomous snake and marine reptile harvest activities in the world today. Lapemis curtus and Hydrophis cyanocinctus constituted about 85% of the snake biomass, and Acalyptophis peronii, Aipysurus eydouxii, Hydrophis atriceps, H. belcheri, H. lamberti, and H. ornatus made up the remainder. Our results establish a quantitative baseline for characteristics of catch, trade, and uses of sea snakes. Other key observations include the timing of the trade to the lunar cycle, a decline of sea snakes harvested over the study period (approximately 30% decline in mass over 4 years), and the treatment of sea snake bites with rhinoceros horn. Emerging markets in Southeast Asia drive the harvest of venomous sea snakes in the Gulf of Thailand and sea snake bites present a potentially lethal occupational hazard. We call for implementation of monitoring programs to further address the conservation implications of this large‐scale marine reptile exploitation. Cosecha de Serpientes Marinas en el Golfo de Tailandia     

Body mass and parental decisions in the Antarctic petrel Thalassoica antarctica : how long should the parents guard the chick?

In Procellariiformes, the parents guard the chick after it has attained homeothermy. This strategy may reduce the probability that a small chick is taken by predators, but is costly as only one parent can forage at a time. The decision to leave the chick may therefore be a compromise between the chick's vulnerability to predators, the body condition of the parent on the nest and whether the foraging parent returns in time. We studied how the number of days that parents guarded the chick was related to the body mass of the parent at the nest and the time the foraging parent spent at sea in the Antarctic petrel Thalassoica antarctica. We also examined how the body mass of the parent on the nest and the duration of the foraging trips influenced the chicks' body condition at the end of the guarding period. When the foraging parent did not return to the nest in time to relieve its mate, the number of days the parent on the nest kept guarding the chick was positively related to its body mass on arrival in the colony. The number of days the foraging parent spent at sea was positively related to the body mass of its mate, but those that returned in time had a shorter stay at sea relative to their mate's body mass than those that did not return before their mate had left. Apparently, both the body mass of the parent at the nest and the ability of the foraging parent to adjust its stay at sea to the mate's body mass is important for the number of days the parents guard the chick and also the chick's body condition at this point. The inability to return to the nest before the mate has left may be the result of needing a minimum amount of time at sea to find food, or because some parents having low foraging success and therefore prolong their stay at sea. Received: 10 October 1997 / Accepted after revision: 14 March 1998