Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). I.<Emphasis Type="Italic"> Mysis mixta</Emphasis> (Mysidacea)

Seasonal population dynamics of Mysis mixta Lilljeborg were studied from December 1998 to November 2000 at a 240 m deep site in Conception Bay, Newfoundland. At this depth, temperature was <0°C and salinity between 32.0 and 34.0 psu year-round. The spring phytoplankton bloom began in early or late March and reached a maximum in late April to mid-May. M. mixta exhibited a highly synchronised life cycle, with spawning and mating occurring in October to November, embryos brooded for ~5 months, and juveniles released during spring bloom sedimentation in April and May. Females were semelparous and died at age 2.5 years, following release of juveniles in spring, whereas the majority of mature males died at age 2 years, following mating in November. The biennial life cycle of this population resulted in the presence of two cohorts in the hyperbenthos at any given time. Variation in density and biomass was low among cohorts but high within cohorts, the latter probably due to the high motility of mysids. Densities in 1999 and 2000 were 242±379 and 544±987 ind. per 100 m³ (mean±SD), respectively. Although growth rates were similar between years, rates measured from changes in dry mass differed both seasonally and among life-history stages (range from –4 to 7 mg month^–1). Annual secondary production was estimated at 29–73 mg C m^–2 in 1999 and 53–205 mg C m^–2 in 2000. The annual P/B ratios were 1.62 and 1.19 in 1999 and 2000, respectively.Communicated by J.P. Grassle, New Brunswick     

Feeding and respiration rates of a planktonic copepod (<Emphasis Type="Italic">Calanus sinicus</Emphasis>) oversummering in Yellow Sea Cold Bottom Waters

The distribution, feeding and oxygen consumption of Calanus sinicus were studied in August 2001 on a transect across Yellow Sea Cold Bottom Waters (YSCBW) and two additional transects nearby. The distribution of C. sinicus adults and copepodites stage CV appeared to be well correlated with water temperature. They tended to concentrate in the YSCBW (>10,000 ind. m^–2) to avoid high surface temperature. Gut pigment contents varied from 0.44 to 2.53 ng chlorophyll a equivalents (chl a equiv.) ind.^–1 for adults, and from 0.24 to 2.24 ng chl a equiv. ind.^–1 for CV copepodites. We found no relationship between gut pigment contents and the ambient chl a concentrations. Although the gut evacuation rate constants are consistent with those measured for other copepods, their low gut pigment contents meant an estimated daily herbivorous ingestion of <3% of body carbon in the YSCBW and <10% outside the YSCBW. However, based on estimates of clearance rates, C. sinicus feeds actively whether in the YSCBW or not, so the low ingestion rates probably reflect shortage of food. Oxygen consumption rates of C. sinicus ranged from 0.21 to 0.84 l O₂ ind.^–1 h^–1, with high rates often associated with high temperature. From the oxygen consumption rates, daily loss of body carbon was estimated to be 4.0–13.7%, which exceeds our estimates of their carbon ingestion rates. C. sinicus was probably not in diapause, either within or outside the YSCBW, but this cold-water layer provides C. sinicus with a refuge to live through the hot, low-food summer.Communicated by T. Ikeda, Hakodate     

Trophodynamic function of copepods,appendicularians and protozooplankton in the late summer zooplankton community in the Skagerrak

The study was carried out in the Skagerrak during late summer when population development in the pelagic cycle culminated in the yearly maximum in zooplankton biomass. The cyclonic circulation of surface water masses created the characteristic dome-shaped pycnocline across the Skagerrak. The large dinoflagellate Ceratium furca dominated the phytoplankton biomass. Ciliates and heterotrophic dinoflagellates were the major grazers and, potentially, consumed 43–166% of daily primary production. The grazing impact of copepods was estimated from specific egg production rates and grazing experiments. The degree of herbivory differed between species (14–85%), but coprophagy (e.g. feeding on fecal pellets) and ingestion of microzooplankton were also important. The appendicularian Oikopleura dioica was present in lower numbers than copepods, but cleared a large volume of water. The grazing impact of copepods and O. dioica was estimated to 57±24% and 12±12% of daily primary production, respectively. Sedimentation of organic material (30 m) varied between 169 and 708 mg C m^–2 day^–1, and the contribution from the mesozooplankton (copepod fecal pellets and mucus houses with attached phytodetritus of O. dioica) was 5–33% of this sedimentation. Recycling of fecal pellets and mucus houses in the euphotic zone was 59% and 36%, respectively. However, there was a high respiration of organic material by microorganisms in the mid-water column, and 34% of the sedimenting material actually reached the benthic community in the deep, central part of the Skagerrak.     

Rearing Pandalus borealis larvae in the laboratory

Larvae of the northern shrimp Pandalus borealis (Krøyer) are pelagic. In the Estuary and Gulf of St. Lawrence, Canada, the early stages are found in the upper 25-m of the water column in spring and early summer and are expected to experience a range of water temperatures from as low as 0°C to as high at 6°C. Little is known of the impact of water temperature on metabolic requirements of northern shrimp larvae. In this study, routine respiration (VO₂), maximum respiration (electron transport system activity, ETSA) and metabolic scope for growth (MS, ETSA–VO₂) of northern shrimp larvae were measured as a function of temperature (3, 5 and 8°C), developmental stage (I–V at 3°C, I–VII at 5°C and 8°C) and growth rate in dry mass. After logarithmic transformation, all three metabolic variables were linearly related to dry mass. The increase in VO₂ with body mass was faster at 5°C than at 3 or 8°C, whereas with ETSA this increase was slower. As a result, MS increased more slowly with dry mass at 5°C than at 3 and 8°C. However, MS did not limit growth in this study, since it explained only 39% of the variability in growth. All three metabolic variables as well as growth varied together as a function of temperature and ontogeny. Q₁₀ of all three metabolic variables ranged from 1.6 and 2.2 for stages I–V larvae, except for VO₂ at stage I (3.9) and stage III (2.9).     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. I. Centropages abdominalis

Population dynamics and production of the calanoid copepod Centropages abdominalis were studied from November 1986 to November 1987 in Fukuyama Harbor, in the central part of the Inland Sea of Japan. This species was present in the plankton during a cold-water period from November to June (temperature range: 8.9 to 21.1 °C), with a peak abundance (23 600 ind m^–3) in February. During this period, six generations could be detected, and each generation time agreed well with that predicted from food-satiated laboratory experiments, indicating that the natural population was not food-limited. The population suffered extremely high mortality during the period from egg to naupliar stage (N) II: only 0.02 to 4% of the eggs survived to NII. However, the mortality in stages older than NII was almost negligible. The growth rate of C. abdominalis increased exponentially with increasing temperature. Its biomass and production rate showed marked seasonal variations largely in parallel with numerical abundance. The estimated production between 7 November 1986 and 29 May 1987 was 355 mg C m^–3 or 2.66 g C m^–2, 95% of which occurred during February and March. The daily production rate to biomass ratio increased exponentially with temperature from 0.18 at 8.9°C to 0.37 at 19°C.     

Primary productivity and particulate organic matter flow in an estuarine mangrove-wetland in Hong Kong

Net primary productivity and organic matter flow of a mangrove-dominated wetland was estimated by following production and detritus dynamics in a tidal pond in north west Hong Kong in 1986–1988 (9.1 ha). Total productivity was 12.47 t dry wt ha^–1 yr^–1, of which >90% was from emergent macrophytes (the mangroveKandelia candel and the reedPhragmites communis). High turbidity and high summer temperatures probably limited respective production by phytoplankton and benthic macroalgae (dominated byEnteromorpha crinata). Despite the high total productivity, little detritus was exported from the emergent macrophyte stands, due to the low inundation frequency. This created a net water column carbon deficit which was provided for by the high organic matter import (mean = 4.42 g ash free dry wt m^–2 d^–1) from the incoming water. This same sediment and particulate organic carbon input giving a high accretion rate of 1.7 cm yr^–1 was probably also the force behind progressive dis-coupling of emergent macrophyte production from water column consumers. This resulted in a tendency to retain production in the emergent macrophyte stands while the water column community increasingly relied on allochthonous carbon. This shift from a net exporter to a net importer of carbon in landward wetlands is probably characteristic of the transition into nutrient-conservative terrestrial systems.     

Population dynamics of Euterpina acutifrons (Copepoda: Harpacticoida) from North Inlet,South Carolina,with reference to Dimorphic Males

The population dynamics of Euterpina acutifrons (Dana), a pelagic, harpacticoid copepod, are summarized in a life table based on field data. Highest mortality occurred in the last naupliar stage (NVI) and the first copepodite stage (CI). Overall survival in the field was 0.06% from the first naupliar stage (NI) to adult (CVI). The net reproductive rate (R _o=55.590) and intrinsic rate of increase (I _m=0.28) were sufficiently high to maintain a population with such a low survival rate in nature. E. acutifrons was present and breeding in the field from April through December. Low temperatures limited breeding, which began when the temperature reached 16.5°C and ceased when it fell to 11°C. Optimum temperature for North Inlet E. acutifrons was 25°C, with a maximum laboratory survival of 15.3% and a generation time of 10.3 days. Generation time in the field (20°C) was 14 days. Temperature also affected the abundance of dimorphic males. Small males were always most abundant, but peaked during the coldest month; large males became equal in abundance only during the varmest months.Contribution No. 298 from the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. III.Paracalanus sp.

Population dynamics and production of the calanoid copepodParacalanus sp. were studied from November 1986 to November 1987 in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan. This species was perennial, with a large abundance peak in June/July and small peaks in September/October and November/December. During a year of investigation, 15 generations Gould be detected. For each generation, the mean population egg production rate and the mean daily midstage abundance front NIII to CV were determined to obtain a survival curve from egg to CV. The mortality was extremely high during the early life stages: on average only 7.1% of the eggs produced might survive into NIII. This high mortality might be caused by predation by sympatric omnivorous copepods, in addition to sinking loss of eggs from the waten column. The biomass ofParacalanus sp. showed marked seasonal variations largely in parallel with numerical abundance. The instantaneous growth rate of each developmental stage increased exponentially with temperature up to 20 °C, above which the rate was constant. The annual integrated production rate was 734 mg C m^–3 yr^–1 or 5.5 g C m^–2 yr^–1.     

Glucosephosphate isomerase genotype frequencies,homozygous excess and size relationships in the sand flounder Rhombosolea plebeia

Genetic variation was studied at two polymorphic loci for 3 yr (November 1978–February 1982) in juvenile sand flounder (Rhombosolea plebeia) in Wellington Harbour, New Zealand. The Gpi-1 locus showed a heterogeneity in genotype frequencies, but this was not clearly related to season or to fish length. At the Gpi-2 locus, genotype frequencies were dependent upon length and showed a significant excess of homozygotes in juveniles but not in adults. This latter phenomenon has been reported previously in several species of marine molluscs, and so may be common to marine organisms producing large numbers of pelagic larvae. Reasons for the excess of homozygotes are discussed, and it is suggested that assortative mating is the most likely explanation and that this is an area of marine population genetic research which has been over-looked.     

Divide or broadcast: Interrelation of asexual and sexual reproduction in a population of the fissiparous hermaphroditic seastar Nepanthia belcheri (Asteroidea: Asterinidae)

Asexual and sexual reproduction were studied in an intertidal population of Nepanthia belcheri (Perrier) at Townsville, Queensland, Australia, by regular sampling over a year (March 1976-March 1977) and by histological analysis of gonads. Fission reached a peak in early winter (April–June), when about 45% of the population showed evidence of recent fission. Propensity for fission was unrelated to longest arm length. Seven-armed seastars predominated in the population and these underwent fission in two stages to produce one 3-armed fragment and two 2-armed fragments. Fission planes were not related to numbers or positions of madreporites. Hermaphroditism was a normal sexual condition in the population. Almost all gonads contained oocytes, but some gonads functioned as ovaries (without spermatogenic tissue) while others functioned as testes. Seastars with mature ovaries were significantly larger than those with mature testes, indicating protandry, as in other hermaphroditic asteroids. However, fission complicates the pattern of gonad development by causing regression or retardation of gonads and by apparently having a masculinizing effect, so that ovaries may change to testes in fission products. There was a period of sexual reproduction in early summer (October–November). This followed the period of intense fission and regeneration, and a population change from predominately functional females to males. Consequently there was an extreme imbalance against mature females at sexual reproduction, further reducing potential fecundity. Thus, sexual reproduction was very subordinate to fission as the means of recruitment. The 450 m diam eggs probably give rise to pelagic lecithotrophic development and, if this is the case, N. belcheri retains the advantage of complementing reliable recruitment from fission with a dispersive phase. The combination of fission and hermaphroditism is particularly advantageous for a very sparse dispersal of larvae, as a functionally dioecious population may develop from one larva settling in a new locality.     

Population structure in Banggai cardinalfish,<Emphasis Type="Italic"> Pterapogon kauderni</Emphasis>, a coral reef species lacking a pelagic larval phase

Previous studies on two reef fish lacking a pelagic larval phase (Acanthochromis polyacanthus and Embiotoca jacksoni) revealed features that may be characteristic of their lifestyle: (1) low levels of gene flow, (2) frequent population bottlenecks, and (3) strong phylogeographic breaks, all within their over 1,000 km coastal geographic ranges. The present study tested the predictive nature of these three characteristics in another species lacking a pelagic larval stage, but with a very restricted distribution (<10,000 km²). The Banggai cardinalfish, Pterapogon kauderni Koumans, 1933, is a mouthbrooding species occurring in the Banggai Archipelago (eastern Indonesia). Fish were captured in January and February (2001, 2002). The mitochondrial control region of 122 individuals from 22 locations was sequenced. P. kauderni individuals clustered in two reciprocally monophyletic clades corresponding to a southwestern population (restricted to the southwest of Bangkulu Island) and all northern and eastern populations, which included all the remaining samples. Data were compatible with reduced gene flow and the presence of severe bottlenecks; however, small sample sizes and limited genetic variability in P. kauderni prevented a definitive conclusion. Further studies using larger samples and more rapidly evolving molecular markers may provide enough power to conclusively test our hypotheses.Communicated by J.P. Grassle, New Brunswick     

Population biology of hyperbenthic crustaceans in a cold water environment (Conception Bay,Newfoundland). II.<Emphasis Type="Italic"> Acanthostepheia malmgreni</Emphasis> (Amphipoda)

Seasonal population dynamics of the gammarid Acanthostepheia malmgreni Goës in Conception Bay, Newfoundland, were examined from October 1998 to November 2000. This species exhibited a 2.5-year life span, with the reproductive cycle correlating with seasonal phytoplankton flux. Females were semelparous and died following a 5-month brooding period and the subsequent release of juveniles in April and May. The biennial life cycle of this population should result in the presence of two cohorts in the hyperbenthos at any given time. However, the cohorts alternated in strength from year to year, which affected annual density, biomass and production during the study period. Densities were 64±87 ind. per 100 m³ in 1999 and 491±492 ind. per 100 m³ (mean±SD) in 2000. Secondary production was estimated at 18–44 mg C m^–2 in 1999 and 180–311 mg C m^–2 in 2000. The annual P/B ratios were 0.89 and 2.27 in 1999 and 2000, respectively. Growth varied both among and within cohorts, with different life-history stages exhibiting variable growth rates ranging from 0 to 12 mg dry mass month^–1.Communicated by J.P. Grassle, New Brunswick     

Zooplankton biomass in the ice-covered Weddell Sea,Antarctica

Zooplankton was sampled by a Rectangular Midwater Trawl (RMT 1 + 8) in Weddell Sea surface waters (0 to 300 m) between 66 and 78°S during austral summer (February – March 1983). Sixty-nine taxa including different developmental stages were considered and divided into 16 size classes between <1 and >39.5 mm length. Biomass was determined by taxon and size class for three different meso- and macroplankton communities in the oceanic region, on the northeastern shelf and on the southern shelf of the Weddell Sea. The highest biomass of 11.2 mg DW m^–3 (3.4 g DW m^–2) was found in the northeastern shelf community (70 to 74°S), where juvenile and adultEuphausia crystallorophias accounted for 3.7 mg DW m^–3 (1.1 g DW m^–2). Although not quantitatively sampled, early copepodite stages (CI to CIII) ofCalanoides acutus andCalanus propinquus ranked second with 2.7 mg DW m^–3 (0.8 g DW m^–2). Biomass in the northeastern shelf community was concentrated in the size ranges 1 to 4 mm and 19.5 to 39.5 mm. The oceanic community of the central Weddell Sea was dominated by copepods smaller than 5 mm, which made up half of the total oceanic biomass. The tunicateSalpa thompsoni (7.0 to 8.5 mm) was the dominant single species with 1.6 mg DW m^–3 (0.5 g DW m^–2). Euphausiids, mainly juvenile and adult krillEuphausia superba, comprised 1.2 mg DW m^–3 (0.4 g DW m^–2). Total standing stock in the oceanic community was 9.4 mg DWm^–3 (2.8 g DW m^–2). Lowest biomass values were found in the southern shelf community (south of 75°S) with 4.0 mg DW m^–3 (1.2 g DW m^–2), concentrated in the 1 to 4 mm and 14.5 to 34.5 mm size classes. Abundant species were the pteropodLimacina helicina (1 to 2 mm; 0.7 mg DW m^–3; 0.2 g DW m^–2) andE. crystallorophias (24.5 to 39.5 mm; 0.9 mg DW m^–3; 0.3 g DW m^–2). The data reveal that it is essential to distinguish among subsystems in the Southern Ocean. This leads to a better understanding of the structure and function of those pelagic food webs which represent alternatives to the paradigmatic krill-centered system.     

Population age structure and rhizome growth of<Emphasis Type="Italic"> Cymodocea nodosa</Emphasis> in the Ria Formosa (southern Portugal)

The population age structure and derived population dynamics (recruitment, growth and mortality), rhizome growth and flowering effort of Cymodocea nodosa in the Ria Formosa (south of Portugal) were examined using reconstruction techniques. The horizontal rhizome elongation rates were low (13.8–30.7 cm year^–1), which is consistent with the low population growth rate (–2.35 to 0.29 year^–1). The vertical elongation rate was proportional to the horizontal growth except for one stand that was subjected to sand movements and had higher elongation rates. The mean leaf production varied from 11.8 to 14 leaves year^–1. The average shoot age varied from 0.70 to 1.04 years, and the oldest shoot found was 7.6 years. The mortality rates were the highest as yet reported for this species (0.99–3.70 year^–1). Observed low growth and high mortality are possibly associated with the development of eutrophic conditions in the Ria Formosa. The flowering probability found in Ria Formosa stands (<0.009–0.90 shoots^–1 year^–1) was comparable to that found in the Mediterranean and off the Canary Islands. Only two stands with flowering events were found inthe Ria Formosa population, which indicates that the stands are highly dependent on clonal growth to maintain themselves inthe Ria Formosa.Communicated by O. Kinne, Oldendorf/Luhe     

Gonadal development in the coral reef damselfish<Emphasis Type="Italic"> Dascyllus flavicaudus</Emphasis> from Moorea,French Polynesia

The present study investigated the sexual pattern of the yellow-tailed dascyllus, Dascyllus flavicaudus (Randall and Allen), through histological examination of the process of gonadal differentiation and maturation and through male-removal experiments in the laboratory. The study was conducted in Moorea, French Polynesia (17°32S; 149°50W), from 31 December 1994 to 11 March 1995. For gonadal histology, two populations were sampled, one consisting of large aggregations (n=54) and the other consisting of small- to medium-sized groups around isolated corals (n=55). An additional small sample (n=21) was also collected from a population that consisted of small groups around isolated corals. After an initially undifferentiated state, gonads of D. flavicaudus developed an ovarian lumen, followed by oocytes in the primary growth stage. From this ovarian state or from more developed ovaries with cortical-alveolus stage oocytes, some gonads developed into testes through degeneration of oocytes and development of spermatogenic tissue. In all three populations, spermatogenic tissue developed only in gonads that contained pre-vitellogenic oocytes (termed as mixed stage 1–2 gonads). The two main populations did not differ in their expression of sex change despite differences in their social organization. In both populations, size of individuals with mixed stage 1–2 gonads overlapped mainly with the size range of immature females, which suggests that functional female-to-male sex change was rare. The hypothesis that D. flavicaudus is primarily gonochoristic is further supported by removal experiments in laboratory groups, in which removal of a dominant male(s) failed to induce sex change in any of the high-ranking females. Yet, in all three field populations, some fish with mixed stage 1–2 gonads were found within the size ranges of mature females, which indicates possible occurrences of functional sex change. These conflicting results indicate that it may be premature to draw any definitive conclusions about the sexual pattern of D. flavicaudus.Communicated by T. Ikeda, Hakodate     

MtDNA population structure and gene flow in lingcod (<Emphasis Type="Italic">Ophiodon elongatus</Emphasis>): limited connectivity despite long-lived pelagic larvae

Lingcod, Ophiodon elongatus Girard, have a 3-month pelagic larval stage and are an important recreational and commercial species on the west coast of North America. Cytochrome-c oxidase I sequences from tissue samples were used to characterize population structure and infer patterns of gene flow from California to Alaska. No significant genetic structure was found when estimates of Wright’s F _ST (i.e., Φ_ST) were generated among all populations sampled. Nesting populations within regions, however, indicated that the inner coast of Washington State is distinct, a result corroborating previous allozyme work. Coalescent-based estimates of gene flow indicate that although migration can be high from an evolutionary perspective, nearly half of all comparisons among populations showed no gene flow in at least one direction. From an ecological perspective, moderate migration rates (Nm < 10) among most populations provide surprisingly limited connectivity at large (∼ 1,000 km) and small (∼100 km) spatial scales. Coalescent-based estimates also show that gene flow between the inner and the outer coasts is asymmetric, a result consistent with prevailing surface currents. Because the expected inter-locus variances for coalescent-based estimates of gene flow are likely large, future work will benefit from analyses of nuclear DNA markers. However, limited demographic connectivity on large spatial scales may help explain why stock recovery has been uneven, with greater recovery in the northern (87% rebuilt) than in the southern (24% rebuilt) fishery region, supporting a regional management strategy. These results suggest that despite a 3-month pelagic larval stage, some areas may be effectively closed with respect to both population dynamics and fishery management issues.     

Abundances,growth rates,and production of tropical neritic copepods off Kingston,Jamaica

Weekly samples were collected near Kingston, Jamaica in 27 m vertical hauls, using 200 and 64µm mesh plankton nets, from July 1985 to January 1987. Thirtytwo copepod species were identified; nauplii and all copepodite stages were enumerated. Total copepod abundance ranged from 2.56 to 87.3 × 10⁴ m^–2. The annual abundance cycle was bimodal with peaks in October–November and May–June corresponding to the rainy seasons. Mean annual copepodite biomass was 0.15 g AFDW m^–2 ranging from 0.03 to 0.41 g AFDW m^–2. Mean generation time (from egg to adult) at 28°C was 19.5 d for the common speciesCentropages velificatus, Paracalanus aculeatus, andTemora turbinata. Isochronal development was demonstrated for copepodites ofP. aculeatus andT. turbinata, but not forC. velificatus. Mean daily specific growth rates (G) were 0.63, 0.63, and 0.48 d^–1 forC. velificatus, P. aculeatus, andT. turbinata, respectively. In general, daily specific growth rates decreased in the later copepodite stages. Thus, it is postulated that growth of later stages and egg production may be food limited. Annual copepodite production was estimated as 419 kJ m^–2 yr^–1, while annual exuvial production and naupliar production were 35 and 50 kJ m^–2 yr^–1, respectively. Egg production was estimated as 44% (184 kJ m^–2 yr^–1) of the total copepodite production. Thus, mean total annual copepod production was 688 kJ m^–2 yr^–1. This estimate is within the range of copepod production estimates in coastal temperate regions.     

The echolocation and hunting behavior of Daubenton's bat,Myotis daubentoni

Summary The echolocation and hunting behavior of Daubenton's bat (Myotis daubentoni) were studied in the field under completely natural conditions using a multiflash photographic system synchronized with high-speed tape recordings. The hunting behavior of M. daubentoni is separated into four stages. In the search flight stage Daubenton's bat flies with an average speed of 3.4±0.6 m/s SD usually within 30 cm over water surfaces searching for insects. After the detection of potential prey, the approach flight stage occurs, during which the bat approaches the target in a goal-directed flight. The stage tail down indicates that M. daubentoni is close to the potential prey (approximately 10–22 cm) and is preparing for the catch. The insects are caught with the interfemoral membrane, the feet, and sometimes with the additional aid of a wing. In the stage head down, the bat seizes the prey during flight. Immediately afterwards, Daubenton's bat returns to search flight. M. daubentoni shows the typical echolocation behavior of a vespertilionid bat, emitting frequency-modulated (FM) echolocation signals. The three behavioral stages search, approach, and terminal phase (Griffin et al. 1960) are used to describe the pulse pattern of foraging M. daubentoni in the field. The terminal phase (or buzz) of Daubenton's bat is separated into two parts: buzz I and buzz II. Buzz II is distinguished from buzz I by the following characteristics: a sharp drop in terminal frequency, a distinct reduction in the bandwidth of the first harmonic, a continuous high repetition rate throughout the phase in the range 155–210 Hz, very short pulses (0,25–0.3 ms) and interpulse intervals (4.5–5.0 ms) at the end of the phase, and a distinct decrease in duty cycle. A pause in echolocation separates the end of the terminal phase from the ongoing search phase. The reduction in sound duration after the detection of a target and during pursuits with successfull or attempted catches is discussed in relation to the actual distance of the bat to the target at each stage. It is likely that Daubenton's bat reduces sound duration during approach and terminal phase in order to prevent an overlap of an outgoing pulse with the returning echo from the target. It is argued that the minimum detection distance can be estimated from the sound duration during search flight. Estimates of detection and reaction distances of M. daubentoni based upon synchronized photos and echolocation sequences are given to corroborate this hypothesis. An average detection distance of 128 cm and an average reaction distance of 112 cm were determined. Each behavioral stage of foraging M. daubentoni is characterized by a distinct pattern of echolocation signals and a distinct stage in hunting behavior. The approach flight in hunting behavior coincides with the approach phase and with buzz I in echolocation behavior. The stage tail down corresponds to buzz II. The stage head down is correlated with a pause in echolocation. Immediately afterwards, the bat returns into search flight and into the search phase, emitting search signals.     

Annual life cycle of the copepod<Emphasis Type="Italic"> Eucalanus inermis</Emphasis> at a coastal upwelling site off Mejillones (23°S), northern Chile

Eucalanus inermis is an abundant species in the eastern tropical and subtropical South Pacific, including the oceanic and coastal waters off Chile and Peru. Its annual life cycle was studied through a time-series sampling (weekly intervals) during 2002, at a fixed coastal station at an upwelling site (Mejillones Bay, 23°S) off northern Chile. The more-or-less continuous occurrence and abundance of naupliar and copepodid stages indicated that the species reproduces during most of the year, with two peaks: one during the austral spring and the other during the summer. Thereafter, an abrupt decline in the population was observed during winter. The abundances of E. inermis copepodids and nauplii were positively correlated with sea surface temperature, suggesting temperature-dependent development and growth during the spring–summer period. Three cohorts could be distinguished during one annual cycle, with generation times >30 days. The estimate of mean weight-specific daily growth (0.12 day^–1) is lower than that of other species in the area, but it is consistent with a slower development rate. The distribution of this copepod is associated with the equatorial subsurface waters characterized by low-oxygen content (<0.5 ml l^–1). The ascent of this water mass to the near-surface during coastal upwelling in the spring–summer period and the presence of E. inermis adults favor their reproduction and the development of cohorts in the food-rich upwelling environment. The wintertime disappearance of E. inermis from shallow waters is, thus, interpreted as a movement to deep waters (>200 m depth), probably in a lethargic mode, within the oxygen minimum zone in the adjacent oceanic area.Communicated by P.W. Sammarco, Chauvin     

Effects of temperature,salinity, and predators on mortality of and colonization by the invasive hydrozoan<Emphasis Type="Italic"> Moerisia lyonsi</Emphasis>

The successful invasion of non-indigeneous species depends on initial colonization as well as establishing a self-maintaining population. The invasive hydrozoan Moerisia lyonsi (Boulenger, 1908), possibly originating from low-salinity waters in the Black Sea and Middle East regions, has become established in low-salinity waters in several estuaries of North America, including Chesapeake Bay. The effects of temperature and salinity on mortality of M. lyonsi polyps were examined in the laboratory in February 2001 in the presence of abundant food. The polyps of M. lyonsi were directly transferred from 20°C and 10 salinity to one of 45 combinations of temperature (10–29°C) and salinity (1–40). Polyp mortality within 7 days occurred only in low-temperature treatments with salinities of 35–40. Surviving polyps reproduced asexually in salinities of 1–40 at 20–29°C, and in salinities of 1–25 at 15°C, but not in any salinities at 10°C. The greatest asexual reproduction rates, an index for population survival potential, occurred at salinities of 5–20. Survival and reproduction of M. lyonsi over such broad temperature and salinity ranges indicate that M. lyonsi may colonize and establish populations throughout the Chesapeake Bay; however, M. lyonsi medusae were reported only at salinities <9.3 there. This discrepancy may be due to the effects of predators. The scyphomedusan Chrysaora quinquecirrha (Desor, 1848), but not the ctenophore Mnemiopsis leidyi (A. Agassiz, 1865) consumed M. lyonsi medusae in laboratory experiments in August–September 2001. Populations of M. lyonsi do not appear to be limited by temperature and salinity conditions; however, their distribution in Chesapeake Bay may be restricted to low salinities not inhabited by predators.Communicated by J.P. Grassle, New Brunswick