Reproduction and developmental variability in the opisthobranchTenellia pallida

Pelagic and non-pelagic development occurs within a single population of the nudibranchTenellia pallida (Alder and Hancock) from South Carolina (USA). Both developmental types occurred simultaneously, under identical conditions, and without the aid of nurse eggs. Adults laid either ≈70 μm diameter eggs that hatched as pelagic (planktotrophic?) veligers in 68 to 122 h, or ≈100 μm diameter eggs that became well-developed veligers, metamorphosed within their egg capsules, and hatched as shelled juveniles in 140 to 190 h (15°C, 30‰ S). Adults that produced pelagic larvae laid more eggs per day and per egg mass and twice the daily egg volume produced by adults of the opposing type.     

Reproduction of<Emphasis Type="Italic"> Ophiactis resiliens</Emphasis> (Echinodermata: Ophiuroidea) in New South Wales with observations on recruitment

Reproduction of the ophiuroid Ophiactis resiliens Lyman 1879, a common species in the shallow waters around Australia, was examined over 1 year in two populations near Sydney, New South Wales. Gametogenesis was documented by histological examination of the gonads. Vitellogenesis in females and spermatocyte proliferation in males started in February and March. O. resiliens had an annual spawning period from May to September/October with peak gamete release from May to July. Thereafter, spawning occurred in some specimens through November. Gravid gonads were present for approximately 2 months longer in O. resiliens from Clovelly Bay than in those from Little Bay. At both sites spawning was episodic and gametogenesis continued through most of the spawning season. Most specimens (50–100%) collected from November to March had indeterminate/recovery stage gonads, the sex of which, could not be determined. The timing of gametogenic renewal during these months varied among individuals. O. resiliens has a 3-month planktonic stage and the presence of juveniles, 0.5 –1.5 mm disk diameter, in the coralline algal turf at Little Bay from February to May, suggests that settlement occurs in summer and autumn at this site. In contrast, juveniles were rarely encountered in coralline turf at Clovelly.     

Genetic structure in native and non-native populations of the direct-developing gastropod Crepidula convexa

In many marine invertebrate species, larval development plays an important role in population connectivity and gene flow: species with direct benthic development generally show more genetic structure than those with planktonic development. We used nuclear markers (microsatellites) to determine population genetic structure of the direct-developing snail Crepidula convexa (Gastropoda: Calyptraeidae) in seven populations with 15–85 individuals each within its native range of the northwest Atlantic and compared it to Crepidula fornicata, a congener with planktonic development. Our results are consistent with general expectations and previous work in these species with other markers: C. convexa had greater population structure and even at a regional scale shows significant isolation-by-distance, in contrast to C. fornicata. We also genotyped a single population of C. convexa introduced to the northeastern Pacific to investigate the prediction of reduced genetic diversity following introduction (founder effect). We did not find a reduction in genetic diversity, suggesting that this non-native population may be characterized by multiple introductions. This pattern is consistent with many other introduced populations of marine invertebrates, including C. fornicata.     

Habitat selection in the tropical polychaeteSpirobranchus giganteus

Total body weight, tube length, abdomen weight and branchial crown weight of individualSpirobranchus giganteus (Pallas) living on four different coral species on the bank reef on the west coast of Barbados were investigated in 1986. Worms onDiploria strigosa were larger in all size parameters than those onMontastrea annularis, which were larger than those onMontastrea cavernosa, which were larger than those onPorites porites. The differences between worms onM. annularis andM. cavernosa were not significant. Variation in worm size on the different corals could result from variation in mortality and/or variation in growth. Whichever the case, larger worms may have higher lifetime reproductive success. Abdomen weight is an index of gamete production inS. giganteus, and increases with increasing body weight for worms on all corals. Moreover, larger worms do not have lower abdomen weight at a given body size than smaller worms. This may imply that faster growth does not reduce gamete production at body size. The coral species on which worms are largest are those most preferred by worm larvae in the laboratory and most heavily colonised by adult worms in the field. The results suggest adaptive habitat selection by planktonic larvae ofS. giganteus.     

Phototaxis and cannibalism in gammaridean amphipods

Development changes in phototaxis were investigated in three species of estuarine amphipods: Gammarus lawrencianus. G. tigrinus, and G. mucronatus. In water of salinity 16 S, juveniles of G. tigrinus and G. mucronatus were initially photoneutral and became photonegative within two days after hatching. Juveniles of G. lawrencianus were photopositive on hatching and became photoneutral approximately 11 d later. In all three species, the change in phototactic behaviour coincided with the age at which juveniles became less vulnerable to cannibalism by adults. Evidence is presented showing genetic variation for phototactic behaviour in G. lawrencianus. Our data are consistent with the hypothesis that juvenile phototaxis is an evolutionary adaptation to minimise cannibalism by adults.     

Ecology of the northern Red Sea crinoids and their Epi- and Endozoic fauna

Fourteen crinoid species are found along the coral reefs of the northern Red Sea that form aggregations of different species at various depths. The shallowest aggregation consists partly of Lamprometra klunzingeri and Capillaster multiradiatus, occurring subtidal to a depth of 2 to 5 m. Of this group, Heterometra savignii inhabits depths down to 12–15 m. Further down, another group of 10-armed crinoids occurs, dominated by Decametra chadwicki and Oligometra serripinna. The deepest aggregation of crinoids occurs at 45 m; its most common members are Colobometra arabica and Comaster distinctus. Feeding on micro- and nanoplankton, shallow-water crinoids show a circadian activity rhythm; in deeper aggregations (10 to 12 m), this behaviour changes with decreasing illumination, to a diurnal activity rhythm. The symbiotic animals living on crinoids comprise 27 taxons, among them Copepoda (6 species), Mollusca (2 species), Polychaeta (11 species, especially Myzostomida); Ophiurida (1 species), Crustacea, Decapoda (6 species); and the clingfish Lepadichthys lineatus. These symbiotic animals form food webs at various depths, according to the distribution of their crinoid host. The occurrence of Indo-West Pacific and Mediterranean commensals on the same crinoid in the Gulf of Aqaba is of special interest.     

Effects of temperature and delayed feeding on growth and survival of larvae of three species of subtropical marine fishes

In larvae of the bay anchovy Anchoa mitchilli (Valenciennes), the sea bream Archosargus rhomboidalis (Linnaeus), and the lined sole Achirus lineatus (Linnaeus), growth, survival, and starvation times were investigated at temperatures of 22° to 32°C. The rate at which hours after hatching until starvation decreased in relation to temperature for unfed larvae did not differ significantly among the 3 species, ranging from-5.4 to-6.3 h per degree increase in temperature. The total number of hours until starvation did differ for all 3 species: lined soles survived longest, bay anchovies were intermediate, and sea bream survived the least time. At 28°C, unfed sea bream could survive 90.1 h, bay anchovy 102.3 h, and lined sole 119.8 h. The eyes pigmented at nearly the same time after hatching for sea bream and bay anchovy, but took about 20 h longer at all temperatures for lined sole. Quadratic equations best described the relationship between hours after hatching when the eyes became pigmented and temperature. Eye-pigmentation times became nearly constant for all 3 species at temperatures above 28°C. At 28°C, eyes pigmented about 27 h after hatching for bay anchovy and sea bream but not until 47 h for lined sole. Hours after eye pigmentation when unfed larvae starved was a measure of the effective time that larvae had to commence feeding. Bay anchovies and lined soles were nearly alike in this respect, but sea bream starved at tewer hours after eye pigmentation. Slopes of regressions representing decrease in times to staration for increasing temperatures ranged from-3.7 to-4.4 h per degree increase in temperature, and were not significantly different among the 3 species. At 28°C, unfed lined soles starved at 70 a after eye pigmentation, bay anchovies starved at 72.5 h, and sea bream at only 62 h. Yolk absorption was most rapid for all species during the first 20 h after hatching, and was faster at higher temperatures. Amounts of yolk remaining at the time eyes became pigmented were less at higher temperatures for bay anchovy and lined sole, but were greater for sea bream, suggesting that sea bream used yolk more efficiently at higher temperatures. Either no yolk or small traces (>0.20%) remained at 24 h after eye pigmentation in all 3 species. Feeding was delayed for periods of 8, 16, 24, 32, 40 and 48 h after eye pigmentation for all species at a series of experimental temperatures from 24° to 32°C. Growth and survival were affected when food was withheld for more than 24 h at 28°C, but survival did not decrease markedly until food was withheld at least 8 h longer. At lower temperatures food could be withheld longer and at higher temperatures for less time. Feeding can be initiated by most larvae for several hours after all visible yolk reserves have been exhausted. All species tested can survive for 24 to 40 h after eye pigmentation at 24° to 28°C without food and still have relatively good growth and survival when food is offered. If the “critical period” is considered relative to time of hatching, lined soles need not find food for 3 to 3.5 days after hatching, but bay anchovy and sea bream must feed within 2.5 days of hatching.     

Connectivity in solitary ascidians: Is a 24-h propagule duration sufficient to maintain large-scale genetic homogeneity?

Ascidians are considered to have lower dispersal potential than most other sessile marine invertebrates with planktonic propagules by virtue of a very brief propagule duration. The larvae of colonial forms remain in the water column for only a few minutes, whereas most solitary forms settle in less than 24 h. This difference in propagule duration has been used to explain why allozyme data from colonial ascidians on the Australian east coast were genetically distinct at different sampling sites, whereas a solitary species exhibited no genetic structure. Spatial homogeneity in solitary species is surprising because genetic structure of species with much higher dispersal potential can be characterised by isolation by geographic distance, suggesting that these disperse by means of a stepping-stone pattern of dispersal. I reassessed the dispersal potential of solitary ascidians using DNA sequence data from the mitochondrial cytochrome oxidase subunit 1 gene and the intron of the nuclear adenine nucleotide transporter gene of a common south-eastern Australian solitary ascidian, Pyura praeputialis, using samples that span the species’ distribution range. Congruent with earlier findings, there was no evidence for stepping-stone dispersal, but it must be conceded that these results could be strongly affected by frequent adult dispersal, particularly by means of anthropogenic vectors, as well as insufficient marker resolution.     

Respiration of Sepia officinalis during embryonic and early juvenile life

Adult Sepia officinalis L. were caught in June 1984, in the coastal waters of Wimereux (France). Deposition of the eggs took place in the seawater aquaria of the Station Marine. The oxygen consumption of S. officinalis was measured during embryonic and juvenile development. Aerobic metabolism occurs as soon as the early embryonic Stage 21. Oxygen diffuses through the initially thick egg shell; the oxygen level in the perivitelline liquid reaches a maximal value just before hatching (116.7±6.9 mm Hg). Hatchings display only a slight increase in oxygen consumption compared to embryos in the last stage of development. Respiration experiments with 40 d old juveniles showed that oxygen consumption increases with temperature, but is not affected by photoperiod. Experiments under increasing hypoxia revealed that S. officinalis juveniles are good regulators and maintain a constant oxygen consumption in the range of 4 to 7 mg O₂l^-1. Juveniles successfully recover from an hypoxic stress of 2 mg O₂l^-1 maintained for 1 h. This suggests that the respiratory pigments (pre-hemocyanins) of 40 d-old juveniles have a high oxygen affinity and/or that these juveniles have the ability to adapt to anaerobic conditions.     

Latitudinal variation in the life history features of the black turban snail Tegula funebralis (Prosobranchia: Trochidae)

At higher latitudes along the west coast of the USA the herbivorous intertidal snail Tegula funebralis (Adams, 1854) lives longer, grows more slowly, but attains a larger size than further south. To the north, age distributions are less predictable and often far from stationary. The differences, which have some generality, can be explained either by a primary temperature effect joined with increased hazards to planktonic larvae in the north, or else may result from a combination of interactions between intensity of predation, population density and food supply. Growth rates of transplanted individuals suggest a genetic basis for the latitudinal differences.     

Larval biology of six species of the genus Conus (Gastropoda: Toxoglossa) in Hawaii,USA

Among the Hawaiian species in the genus Conus, larval life histories range from long-term planktotrophy to nonpelagic lecithotrophy. Prehatching developmental time, hatching size, pelagic period and total prejuvenile developmental time are all significantly correlated with egg size, while settling size is correlated with none of these larval characteristics. Therefore, larval life history patterns in the genus Conus appear to be determined by 2 sets of selective forces: the first influencing egg size, and the second stipulating settling size. As egg sizes become larger, hatching sizes and prehatching developmental time increase while pelagic periods and total prejuvenile developmental times decrease. Settling size appears to be related to water depth, but food requirements of newly metamorphosed juveniles may also be important.     

A “source” for asteroid larvae?: recruitment of Pisaster ochraceus,Pycnopodia helianthoides and Dermasterias imbricata in Nootka Sound,British Columbia

A major recruitment of the forcipulate asteroid Pisaster ochraceus was observed in September 1987 in the channel leading into Boca del Infierno, a semi-enclosed bay on the southeastern shore of Nootka Island, on the west coast of Vancouver Island, British Columbia, Canada. Newly settled recruits were observed at high densities subtidally in the channel (mean maximal density=1.23x10⁴m^-2) and at nearby sites. Subsequent surveys in 1988 to 1991 and size-frequency distributions of adults indicated strong yearly recruitment of P. ochraceus. Recruits of P. ochraceus were found on all available substrata, including hard and soft bottoms and on benthic algae. The initial food of the recruits included newly settled mussels (Mytilus sp.), snails and barnacles. Recruitment of the forcipulate Pycnopodia helianthoides was observed in 1987 to 1989 and in 1991, while recruitment of the spinulosan Dermasterias imbricata occurred only in 1988. High densities of planktonic bipinnaria larvae were found in the bay of Boca del Infierno in late May. We hypothesise that the high density population of adult P. ochraceus found in the channel of Boca del Infierno spawns synchronously and most of the resulting embryos and larvae are retained within the bay. This area may act as a source of larvae that then disperse locally. Post-recruitment mortality was estimated by comparing the density of recruits of P. ochraceus in 1987 with the numbers of juveniles presumed to be 1 yr old in 1988. Post-recruitment mortality was in excess of 97% with few individuals surviving to 1 yr. Moreover, even after the first year, mortality or emigration of the juveniles resulted in the almost complete loss of the 1-yr cohort at North Saavedra between 1988 and 1989. This study provides evidence that the P. ochraceus population in this area of Nootka Island may not be open, but may be regularly supplied from a source of larvae in the bay of Boca del Infierno. Post-settlement processes may, however, have significant effects on the local population, resulting in a poor correlation between the rate of recruitment and the incorporation of yr-1 + individuals into the adult population.     

Effects of various environmental factors on egg development of several species of Acartia in Southern California

The hatching of the eggs of 3 Acartia species (A. tonsa, A. clausi, and Acartia sp. I) spawned in the laboratory and the eggs of Acartia (species undetermined) isolated from natural bottom sediments was examined under various environmental conditions (temperature, salinity and temperature combinations, oxygen concentration, illumination, and the presence of bottom mud). The range of temperature and salinity in which eggs hatched differed from one species to another. Egg hatching was inhibited under certain environmental conditions for all species, although egg viability under such conditions varied from one species to another. In relation to these findings, habitat separation of planktonic Acartia populations and the role of dormant eggs during their seasonal absence in the plankton of Southern California coastal waters are discussed.     

Larval durations and recruitment patterns of two Caribbean gobies (Gobiidae): contrasting early life histories in demersal spawners

The population dynamics of small tiger prawns (Penaeus esculentus and P. semisulcatus) were studied at three sites around north-western Groote Eylandt, Gulf of Carpentaria, Australia, between August 1983 and August 1984. Seagrasses typical of open-coastline, reef-flat and river-mouth communities were found in the shallow depths (2.5 m) at these sites. The temperature and salinity of the bottom waters did not differ among the shallowest depths of the three sites and mean values at night ranged from 21.9 to 32.0 °C, and from 30.1 to 37.5% S. Data from fortnightly sampling with beam trawls showed that virtually all post-larvae (90%) were caught in the intertidal and shallow subtidal waters (2.0 m deep). At one site, where the relationship between seagrass biomass, catches and depth could be studied in detail, high catches were confined to seagrass in shallow water, within 200 m of the high-water mark. This was despite the fact that seagrass beds of high biomass (>100 g m^-2 between August and February) were found nearby, in only slightly deeper water (2.5 m). It is likely, therefore, that only the seagrass beds in shallow waters of the Gulf of Carpentaria act as important settlement and nursery areas for tiger prawns. In general, catches of tiger prawn postlarvae (both P. esculentus and P. semisulcatus) and juvenile P. esculentus on the seagrass in the shallowest waters at each site were higher in the tropical prewet (October–December) and wet (January–March) seasons than at other times of the year. Juvenile P. semisulcatus catches were highest in the pre-wet season. While seasonal differences accounted for the highest proportion of variation in catches of tiger prawn postlarvae and juvenile P. semisulcatus, site was the most important factor for juvenile P. esculentus. In each season, catches of juvenile P. esculentus were highest in the shallow, open-coastline seagrass, where the biomass of seagrass was highest. The fact that the type of seagrass community appears to be more important to juvenile P. esculentus than to postlarvae, suggests that characteristics of the seagrass community may affect the survival or emigration of postlarval tiger prawns. Few prawns (<10%) from the seagrass communities in shallow waters exceeded 10.5 mm in carapace length. Despite the intensive sampling, growth was difficult to estimate because postlarvae recruited to the seagrass beds over a long period, and the residence times of juveniles in the sampling area were relatively short (8 wk).     

Factors regulating population dynamics of the marine bivalve Gemma gemma: intraspecific competition and salinity

A population of Gemma gemma (Totten) was investigated for 6 yr (1978–1983) in Connecticut, USA to determine the relationship between population fluctuations, life tables of successive cohorts and factors affecting life table parameters. Seasonal cycles occurred from 1978–1981. Although density was not abnormally low in summer of 1982, the population declined rapidly thereafter because individuals present during the reproductive season were smaller than the minimal size for reproduction. Forecasts of population size from a time series model based on past densities were compared to forecasts from the intrinsic rates of growth from four separate clam life tables. The latter approach was less precise but more consistent at successfully predicting temporal trends in population abundance. Two factors were identified that potentially controlled population density and structure during the study. Correlational evidence indicated that intraspecific competition between juveniles and adults was intense in 1978 but was reduced during subsequent years. This interaction reduced the size and subsequent fecundity of the young-of-the-year. Correlational evidence also indicated that low salinity in spring of 1978, 1979, 1982 and 1983 reduced juvenile survival, but not that of adults. Qualitative evidence indicated that a third factor, predation, might also have affected G. gemma's population size and structure.     

Exceptionally high concentrations of the insect repellent N,N-diethyl-m-toluamide (DEET) in surface waters from Jakarta,Indonesia

Jakarta is a booming coastal megacity in Indonesia with over 10 million inhabitants. The rivers flowing through the city district receive enormous amounts of untreated wastewaters from households and industries and discharge high pollutant loads into Jakarta Bay. Applying a screening approach for the identification of characteristic site-specific and harmful organic contaminants, we frequently found the insect repellent N,N-diethyl-m-toluamide (DEET) in river water and seawater samples from Jakarta. The compound was previously reported as persistent aquatic contaminant in industrial countries, and we present here the first data set from a tropical megacity. Concentrations in river water and seawater from Jakarta were exceptionally high, up to 24,000 ng L^?1, and exceeded by far all published concentrations in surface waters worldwide. We explained this with massive usage of the compound, lack of wastewater treatment and low average river flow as compared to rivers in other tropical megacities. The usage and properties of DEET indicate its suitability as molecular marker of municipal wastewaters. Such markers are useful to trace emissions from specific pollution sources in aquatic systems as a basis for the investigation of related impacts. We show here that DEET is in particular useful to trace the long-range distribution of municipal wastewaters in tropical freshwater and coastal systems. This application is of great value for tracing such inputs in tropical coastal habitats which are sensitive to changing water quality like coral reefs. This assists to uncover whether specific conditions in these systems could be related to pollutant inputs from land.     

Dimethyl disulfide and dimethyl trisulfide: so similar yet so different in evoking biological responses in saprophilous flies

Dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) are used by saprophilous insects to locate breeding sites (decaying organic matter), and by brood-site deceptive flowers to attract such insects. However, little is known about the relative importance of these two compounds in eliciting electrophysiological and behavioral responses in the insects. Here, we compared the relative attractiveness of DMDS and DMTS to saprophilous flies in field choice experiments and tested whether potential differences in field responses can be explained by differences in electrophysiological antennal responses to these compounds. Field experiments revealed that the attractiveness of a mixture of these compounds is due to DMTS alone. This result was confirmed by electroantennographic recordings in which flies of four tested species of Calliphoridae (Lucilia sericata, L. caesar, Calliphora vicina, Protocalliphora azurea) and one Muscidae (Musca domestica) respond clearly to DMTS, but not to DMDS. In house flies, however, DMTS elicited electrophysiological responses only, not reflected in behavioral assays. Despite the fact that DMTS and DMDS exhibit similar chemical structures, both the electroantennographic and field responses from saprophilous flies to these two compounds strongly differed. Our study suggests that oligosulfide-responsive saprophilous flies rely on DMTS and not DMDS for finding appropriate breeding sites and that DMTS and not DMDS could act as a key mediator for pollinator attraction in brood-site deceptive plants.