Ecological and biological features of a mesopelagic ostracod,Conchoecia pseudodiscophora,in the Japan Sea

The abundance and vertical distribution pattern of a halocyprid ostracod,Conchoecia pseudodiscophora, were investigated in the Japan Sea in 1985, 1987 and 1989. Vertical sampling from 500 m depth to the surface in the water around Yamato Rise revealed that this ostracod was second in dominance by number and third to fourth by biomass of the total zooplankton collected with a 0.35 mm mesh Norpac net. Horizontal net tows in Toyama Bay indicated that the major population ofC. pseudodiscophora was distributed below 250 to 300 m depth. No diel migration pattern was evident. Its contribution to total zooplankton there was 5 to 10% or more in terms of biomass. A total of five subadult instars (II to VI) and adult males and females were identified from instar analysis based on sizes and morphological characteristics of specimens collected with 0.10 mm mesh Norpac nets. Data on body length, wet weight and dry weight of each instar are presented. Carbon content of 35 to 48% of dry weight, and nitrogen content of 5.3 to 7.3% of dry weight, were recorded on fresh, freeze-dried specimens of selected instars (subadult Instars IV to VI, adult females). Water and ash contents of mixed specimens of these four instars were 76% of wet weight and 25% of dry weight, respectively. Feasibility of laboratory maintenance ofC. pseudodiscophora was tested, and it produced characteristic J shaped faecal pellets. Oxygen consumption rates of subadult instars V and VI, and adult female ranged 0.011 to 0.021µl O₂ ind.^–1 h^–1 at 1 °C, or 2.9 to 6.1µl O₂ (mg body N)^–0.85 h^–1 in terms of Adjusted Metabolic Rate (AMR_{o 2}). There was no appreciable metabolic reduction inC. pseudodiscophora compared to other ostracods, despite their mesopelagic life mode. Subdominance in total zooplankton and nonreduced metabolic activity ofC. pseudodiscophora suggest that this species may be an important link in mesopelagic energy-flow and matter cycling in the Japan Sea.     

Development, maturation, brood size and generation length of the mesopelagic amphipod Cyphocaris challengeri (Gammaridea: Lysianassidae) off southwest Hokkaido, Japan

 Using the number of segments of pleopod rami as a marker of instar number, the population structure (instar composition) of the mesopelagic gammarid amphipod Cyphocaris challengeri was investigated by monthly samplings from May 1997 to April 1999 at a station off southwest Hokkaido, Japan. Laboratory-rearing experiments were also conducted to establish the relationship between the number of segments of pleopod rami and instar number, and to estimate the growth pattern of this gammarid based on the intermolt period and molt-increment data. Stratified sampling in the field (0 to 200 and 200 to 400 m depth strata) showed this species occurred mainly at 200 to 400 m depth during the day. Instar analysis indicated that C. challengeri has 12 instars in females and 11 instars in males. Based on observations of secondary sexual characters, Instars 1 to 6 were designated juveniles (Instars 1 to 3 occurred in the marsupia of gravid females); in males, 7 to 9 were immature and 10 and 11 were mature, while in females 7 and 8 were immature and 9 to 12 were mature. Off southwest Hokkaido, Instar 4 (just released from a female's marsupium) was found throughout the year, with a peak abundance occurring in April to July of each year. A sequential development of Instar 4 to 9 (youngest adult instar) through the year was observed. Generation length (i.e. the time required to grow from Instar 4 to 10) was estimated from a laboratory-obtained growth curve to be 216 to 584 d at the in situ temperature range (2 to 5 °C), which is consistent with observations on field populations. Specimens older than Instar 9 were rare in the field and could not be used in laboratory-rearing experiments, so longevity could not be estimated. Eggs were oval and measured 0.6 mm (large diameter). Brood size ranged from 20 to 65. Comparing the present results with those of epipelagic hyperiid amphipods, the nearly identical growth rates together with the production of fewer but larger eggs seen in C. challengeri appear to reflect to the typical life mode of deep-living pelagic crustaceans. Received: 14 February 2000 / Accepted: 6 July 2000     

Abundance, growth and life cycle of the mesopelagic amphipod Primno abyssalis (Hyperiidea: Phrosinidae) in the Oyashio region, western subarctic Pacific

Abundance and life-cycle features of the mesopelagic hyperiid amphipod Primno abyssalis (formerly P. macropa) in the Oyashio region, western subarctic Pacific, were investigated using samples collected between July 1996 and July 1998. P. abyssalis was collected throughout the entire survey period, with abundance peaks occurring in spring to autumn. While all maturity stages of males and females were observed throughout the study period, the peak reproduction season was in summer. Instar analysis based on the segment number of the pleopod rami indicated that hatched juveniles molted 10 times before becoming adult males and 13 times before becoming adult females. Judging from the dry and ash-free dry weights of each instar, males and females continued to feed throughout the final instar stage. Based on cohort analysis of seasonal samples and laboratory observations on molting frequencies, growth in body length of P. abyssalis was linear with time, and estimated generation lengths were 2.3-3.8 years for females and 1.4-1.9 years for males. Brood size of females ranged from 66 to 337 and increased with increasing female body length. Lifetime fecundity, calculated as the sum of six successive broods, was 1,004. Compared with P. abyssalis in the southern Sea of Japan, those in the Oyashio region have a larger number of adult instars (six versus five for females, three 3 vs one for males), a lower growth rate (0.014 mm day^-1 vs 0.021 mm day^-1), and mature earlier (instar 13 vs instar 15 for females; instar 10 vs instar 11 for males). These characteristics are considered to be advantageous life-history traits to counteract higher niche competition within the mesopelagic community and higher predation pressure by mesopelagic fishes in the Oyashio region than in the Sea of Japan.     

Ecdysial rhythms in megalopae and first instars of the Dungeness crab Cancer magister

Diel molting cycles of megalopae and first instar Dungeness crabs Cancer magister Dana captured in the Grays Harbor estuary (46° 55N; 124° 05 W) in May 1991 were studied under laboratory conditions. Sixtyone percent of the megalopae and 76% of the first instar crabs molted during periods of ambient darkness under a normal light — dark diel regime, and molting pattern was not affected by changes in the photoperiod (24 h daylight or 24 h darkness). Time until metamorphic molt increased as conspecific density increased. Habitat type (shell or mud) did not affect time until molt of megalopae and first instar crabs, nor did it affect daily molting rhythm of first instars. We hypothesize that nightly ecdysis of megalopae and first instar Dungeness crabs and density-dependent molting may be an adaptive response to predation and cannibalism among young-of-the-year.Contribution No. 875 from the School of Fisheries, WH-10, University of Washington, Seattle, Washington     

Bathymetric distribution of chaetognaths in the South Eastern Pacific Ocean

The bathymetric distribution of chaetognath fauna observed at planktonic stations in the South Eastern Pacific Ocean during three different expeditions, is presented quantitatively. The material from the cruises IFOP-01 (October–December, 1964) and IFOP-04 (November–December, 1965) was collected by vertical closing net, at regular intervals, from 2000 and 1000 m depth, respectively; the R.V. A. Bruun Cruise 13 data include vertical samples at usual depth intervals from 3000 m (see Table 12), Isaac-Kidd Midwater Trawl (IKMT) and surface collections. They allowed us to identify, for the first time, the meso and bathypelagic species of this region and to extend the longitudinal distribution of the epipelagic species, which had been previously limited to the coastal areas. Among the epiplanktonic species, it was shown that two, Sagitta serratodentata and S. bipunctata, do not penetrate into the Peru Coastal Current region, where the endemic S. bierri is to be found extending westwards to the west boundary of the Peru Coastal Current, and that both mesopelagic species, previously reported for the epipelagic level of this area, S. decipiens and Eukrohnia hamata, inhabit the upper mesopelagic level in the oceanic region, but also rise to the epipelagic level near the coast, where upwellings do occur. The lower mesopelagic levels (500 to 1000 m) are occupied by E. fowleri and S. macrocephala, this latter species being reported for the first time in the South Eastern Pacific Ocean. The other mesopelagic species, S. zetesios and S. bathypelagica, also found for the first time in this region, were not found in large enough numbers to obtain a correct view of their stratification. Eukrohnia bathyantarctica, described for the Southern Ocean and previously reported only in the bathypelagic levels of the Gulf of Mexico and Caribbean Sea, was found at only bathypelagic levels. The faunistic data from the R.V. A. Bruun Cruise 13, were compared with the corresponding hydrographical profiles.     

Distribution,growth and life cycle of the mesopelagic amphipod Primno abyssalis (Hyperiidea: Phrosinidae) in the southern Japan sea

The vertical distribution, growth, maturation, brood size and life cycle of the hyperiid amphipod Primno abyssalis (formerly P. macropa) were investigated using seasonal samples collected from Toyama Bay, southern Japan Sea, during the period June 1986 to September 1992. Over four different seasons of the year, P. abyssalis was most abundant in the 200 to 350 m strata at night and the 350 to 400 m strata during the day, indicating 100 to 150 m as the general distance of diel vertical movement. Some differences in vertical migrating behavior were noted among juveniles, adult males and females. Population-structure analysis revealed the occurrence of three cohorts aged 0+, 1+ and 2+ yr. Growth as body length in this species is linear with time. Estimated time to complete one life cycle is 1.8 to 2.5 yr for females, but only 0.8 yr for males. Maximum longevity is 2.8 yr. Instar analysis based on the segment number of pleopod rami indicated that newly hatched juveniles molt ten times to reach adult male, and four more times to reach adult female. Adult instar number was found to be only 1 for males and 5 for females. Ovigerous females occurred throughout the year, but the annual peak of release of juveniles from the female's marsupium is estimated to be arly March. Brood size was not correlated with female size, a maximum brood size of 214 eggs was recorded. The dry and ash-free dry weights of instars suggested that juveniles in the female marsupium, adult males, and older adult females are less active feeding or non-feeding stages. Except for the reduced growth rate and the occurrence of small, short-lived males, most characteristics of P. abyssalis are consistent with the present view of the life modes of mesopelagic animals, including linear growth in length, aseasonal reproduction, and smaller brood size coupled with larger eggs.     

Effects of prolonged starvation on O2 consumption,NH 4 + excretion,and chemical composition of the bathypelagic mysid Gnathophausia ingens

The large bathypelagic mysid Gnathophausia ingens was collected in January 1980 at 400 to 700 m depth from the San Clemente Basin off southern California. Instars 7-8 and Instars 10-12 were starved in the laboratory for up to 19 wk. Oxygen consumption and ammonia excretion rates, and water, protein, lipid, and ash contents were determined periodically during starvation. Protein and lipid were metabolized in approximately equal amounts by starved individuals after the initial weeks of food deprivation. Unidentified components (probably non-protein nitrogenous compounds) apparently were oxidized within the first 7 wk of starvation. Oxygen consumption and ammonia excretion by Instars 7-8 decreased steadily during 19 wk of starvation. In contrast, stable or increasing respiration and excretion rates were observed for fed mysids. The mean respiration rate of Instars 10-12 did not change significantly during 13 wk of starvation, although ammonia excretion rates decreased. Low metabolic rates and large lipid reserves probably help G. ingens to withstand long periods of starvation in the mesopelagic environment. Calculations based on the laboratory data demonstrate that small, infrequent meals could account for the rates of metabolism and growth observed for G. ingens in the field.     

Deep-water decapod crustacean communities in the Northwestern Mediterranean: influence of submarine canyons and season

The specific composition and abundance of bathyal decapods in the Catalan Sea were investigated. A total of 109 bottom trawls were effected at depths ranging from 141 to 730 m on the continental slope in the Catalan Sea (northwestern Mediterranean) during two sampling cruises in spring and autumn 1991. Multivariate analysis of the samples revealed four groups of the decapod crustacean communities: (1) A shelf-slope transition-zone group at depths between 146 and 296 m, primarily characterized by the presence of Plesionika heterocarpus; (2) an upper-slope community between 245 and 485 m, characterized by the presence of the mesopelagic species Pasiphaea sivado and Sergestes arcticus, with Processa nouveli, Solenocera membranacea and Nephrops norvegicus as secondary species; (3) a middle-slope community below 514 m, with Aristeus antennatus and Calocaris macandreae as the most abundant species; (4) a group at 430 to 515 m, comprising all samples collected exclusively within or in the vicinity of submarine canyons. Mesopelagic decapods were predominant on the slope, while benthopelagic fishes (Merluccius merluccius, Micromesistius poutassou, Gadiculus argenteus) replaced mesopelagic decapods on the shelf. There were seasonal variations, with higher densities of mesopelagic species in spring, which were probably related, among other factors, to variations in the photoperiod. Our surveys also revealed higher species richness in the canyons together with seasonal changes in the megafaunal biomass. Generally, the upper and middle-slope communities both displayed seasonal changes in the composition and abundance of megabenthos.     

Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs

Pelagic eggs of the scaled sardine Harengula pensacolae (Goode and Bean), have been hatched and reared in the laboratory for the first time. Larvae were reared in two 75 l aquaria under constant illumination, at an average temperature of 26.2°C. Zooplankton collected in a 35 mesh net was fed to the newly hatched larvae, and the diet was supplemented later with Artemia salina nauplii and a pelleted food. Larvae hatched at 4 mm TL (total length), and metamorphosed about 25 days later at 25 to 30 mm TL. Survivors averaged 76 mm TL 100 days after hatching. Of the 500 incubated eggs, 2.8% survived until 20 days, after which no significant natural mortality occurred. Sources of natural mortality included starvation, a copepod parasite (Caligus sp.), and injuries from contact with the sides of the tank. Larvae began feeding at 4.5 mm TL on copepod nauplii averaging 62 in body width. Scaled sardines were photopositive throughout the larval stage.Contribution No. 149, Bureau of Commercial Fisheries Tropical Atlantic Biological Laboratory, Miami, Florida 33149, USA.     

Mesopelagic-boundary community in Hawaii: Micronekton at the interface between neritic and oceanic ecosystems

The present study demonstrates that a distinct land-associated community of mesopelagic micronekton exists around the Hawaiian Islands. This mesopelagic-boundary community replaces the oceanic mesopelagic community over bottom depths of approx 400 to 700 m and includes about 14 species of fishes, 5 of shrimps and 4 of squids. Similar species of the mesopelagic micronekton have been reported in association with other landmasses at the boundary between the oceanic mesopelagic realm and upper continental or island slopes. These species may form a cosmopolitan mesopelagic-boundary community which shows regional differences in taxonomic composition, abundance and diversity. Boundary communities, with populations which are both tightly constrained geographically and relatively accessible to shore-based research programs, offer unique opportunities for studying biological processes of the mesopelagic realm and the interactions between neritic and oceanic populations. Data is presented from three midwater and two neuston sampling projects undertaken around the main Hawaiian Islands between 1987 and 1989; additional evidence from the literature is also discussed.     

Growth and reproduction in the mesopelagic-boundary squid Abralia trigonura

Abralia trigonura is a small squid that is an important member of the mesopelagic boundary community around Hawaii. Squids were aged by examining statolith growth increments, and various reproductive parameters were measured. Female longevity is 6 mo, and they become sexually mature at 3.5 mo. Male longevity is the same, but they become sexually mature at 2.5 mo. This species appears to be a multiple spawner, and peculiarities in the number of eggs found in the oviducts suggests that they spawn every few days. Possible advantages of this reproductive mode are examined.     

Inter-genotype aggression in the solitary sea anemone Actinia tenebrosa

The entire process of development from eggs to juveniles was observed in the sea-star Ctenopleura fisheri Hayashi. The breeding season of this sea-star in Toyama Bay, the Sea of Japan, occurs in the winter. The eggs are 465 in diameter, semitranslucent and pale brown in color. They develop into a barrel-shaped larva, neither bipinnaria nor brachiolaria, through a wrinkled blastula stage by holoblastic, radial cleavage. Larvae are free-swimming and do not feed during the larval stage. At metamorphosis the stalk, a larval organ, disappears by one of either 2 different processes; absorption into future body of the juveniles, or rupture and collapse. Fifteen days after insemination, metamorphosis is completed and the resulting juveniles, about 1 000 m in diameter, bear 2 pairs of tube-feet and a terminal tentacle in each arm.     

Influence of food concentration,temperature and salinity on the larval development ofBalanus amphitrite

Influence of food concentration (0.5, 1 and 2 x 10⁵ cell ml^–1 ofSkeletonema costatum), temperature (20 and 30°C) and salinity (15, 25 and 35) on the larval development ofBalanus amphitrite (Cirripedia: Thoracica) was examined. The mortality rate at 20°C was lower than at 30°C in general. Increase in food concentration from 0.5 to 1 x 105 cells ml^–1 improved the survival rate, but this was not evident when food concentration was increased to 2 x 105 cells ml^–1. The results indicate that food availability and temperature jointly determine the energy allocation for metamorphic progress. It was observed that the influence of the tested variables varied with instar. At 20 °C the mean duration of the second instar exceeded 3 d and was much longer than other instar durations. The fourth, fifth and sixth instars and the total naupliar period showed that the effect of different salinities at given food concentrations was negligible at 20°C, while at 30°C there was a marked decrease in duration with increasing salinity.     

The relationship between conspecific superparasitism and the outcome of in vitro contests staged between different larval instars of the solitary endoparasitoid Venturia canescens

When endoparasitoid wasps oviposit into hosts which have already been parasitized (= superparasitism), this results in potentially lethal interlarval competition. For solitary species, the decision to lay additional eggs should therefore be based on the probability of superparasite survival in any superparasitized host. In this study, in vitro contests staged between three larval instars of Venturia canescens Grav. (Hymenoptera: Ichneumonidae) reveal that the age difference between competitors affects the outcome of interlarval competition. Three parameters were used to assess parasitoid performance: the number of fights initiated, the number of bites inflicted, and the duration of each bite. When fighting takes place between two first instars, then both competitors were found to be evenly matched. However, at greater age differences, first-instar competitors appeared to win more fights than their larger second instar rivals. The advantage shown by younger competitors is most pronounced in contests staged between first and third instar larvae. These findings are consistent with the increasingly high levels of conspecific superparasitism shown by V. canescens in the first 5 days after initial host attack, suggesting that this parasitoid can deploy her use of deliberate superparasitism in an adaptive way. Received: 13 December 1995/Accepted after revision: 5 March 1996     

Spawning behaviour,egg and larval development of the myctophid fish Benthosema pterotum

The distribution of eggs and early larval stages of the myctophid fish Benthosema pterotum was studied during three cruises to the Gulf of Oman during January to February 1981 and February 1983. The eggs and yolk sac larvae were identified and described after artificial fertilization on board the Research Vessel Dr. Fridtjof Nansen. The mature fish spawn in the Gulf at 300 to 100 m depths during early night. The eggs and smallest larvae were found at 300 to 200 m depths. The eggs hatch within 12 h at 21°C. Hatching occurs before the slightly bouyant eggs reach the upper 50 m of the water column.     

On the ecology of Heterocypris salinus,H. incongruens and Cypridopsis aculeata (Crustacea: Ostracoda) from Baltic brackish-water rockpools

The ostracod fauna of Baltic brackish-water rockpools is made up of two groups: permanent members of the pools, and occasional guests from the littoral zone. The former group consists of Heterocypris salinus, H. incongruens and Cypridopsis aculeata. These species are characterized by rapid development (which starts when the water temperature approaches 15°C), a short life span, and 2 or 3 separate generations during the summer and autumn. The number of generations is determined by water temperature. Hibernation always takes place as eggs. Hatching and development during the late spring or early summer has been found to be mostly simultaneous. The spawning of the 3 species always starts epidemically. Reproduction is entirely parthenogenetic in the investigated area. Under natural conditions, C. aculeata may be found with either H. salinus or H. incongruens, but these two latter species have never been recorded together. H. incongruens is less tolerant to high salinities than the other 2 species and, even after successive adaptation, it does not resist salinities higher than 16. H. salinus has been found in 35.2 S in the field, and has been kept in 30 S in the laboratory after successive adaptation. The optimum salinity-temperature range for this species is 5 to 10 S and 15°C, when both survival and development are considered. Corresponding figures for C. aculeata are 0.5 to 20 S and 15°C, although this species, like H. salinus, survives longest at 5°C. The very rapid development, parthenogenetic reproduction and short life span of these species must be considered as favourable adaptations to the variable and unstable environment of the rockpool ecosystems.     

Autecology of the tailed jay butterfly Graphium agamemnon (Lepidoptera : Rhopalocera : Papilionidae)

The Tailed Jay Graphium agamemnon is one of the attractive papilionid butterflies that enliven the environment of Visakhapatnam. It occurs throughout the year. It lays eggs singly on young leaves of the mast tree Polyalthia longifolia var. pendula (Annonaceae). The eggs take 3-4 days to hatch. The larvae go through 5 instars over a period of 15-16 days. The pupal period is 13-14 days. The total period from egg to adult emergence spans over 33-36 days. Based on this short life cycle, and larval and pupal development success studied every month, this butterfly can be multivoltine with a minimum of 7-8 broods in a year. Both CI and GR decreased with the age of larva, their average figures being 3.78 and 0.43 respectively. AD values are high (average 92%) and decreased through successive instars. Both ECD and ECI followed a similar pattern with an increase from instar I up to II, then a decrease up to IV and again an increase in instar V and the highest value is with fifth instar. Adults frequently visited flowers (12-35 flowers in a min) spending 1.0 to 3.2 seconds on a flower. The nectar concentration ranged between 16 and 58%. Peak foraging activity mostly fell between 0900-1000 h. The proboscis received pollen in most of the floral species visited, thus satisfying one of the characteristics of butterfly pollination. Being a fast and strong flier it is treated as "high energy" pollinator promoting cross-pollination.     

Vertical community structure and ontogenetic distribution of chaetognaths in upper pelagic waters of the Eastern Mediterranean

The vertical distribution of chaetognaths and their developmental stages were investigated in the pelagic waters (0 to 500 m) of the Eastern Mediterranean Sea. Twenty vertical hauls were taken during autumn 1991 in the Ionian, Cretan, Levantine and Rhodes Seas. The chaetognaths Sagitta bipunctata and S. enflata had the same median depth distributions, which differed from those of S. minima, S. serratodentata, S. lyra, Krohnitta subtilis, and S. decipiens, while S. hexaptera occurred only sporadically. S. bipunctata and S. enflata were mainly restricted to <50 m, and while their distributions co-occurred their stage composition differed. The remaining species took up progressively deeper positions in the water column. Ontogenetic vertical distributions, with the older stages occurring at greater depth, were only observed for the mesopelagic species S. lyra and S. decipiens. Diurnal vertical migration was not detected in any of the species nor in their developmental stages.     

Distribution and diel vertical movements of mesopelagic scattering layers in the Red Sea

The mesopelagic zone of the Red Sea represents an extreme environment due to low food concentrations, high temperatures and low oxygen waters. Nevertheless, a 38 kHz echosounder identified at least four distinct scattering layers during the daytime, of which the 2 deepest layers resided entirely within the mesopelagic zone. Two of the acoustic layers were found above a mesopelagic oxygen minimum zone (OMZ), one layer overlapped with the OMZ, and one layer was found below the OMZ. Almost all organisms in the deep layers migrated to the near-surface waters during the night. Backscatter from a 300 kHz lowered Acoustic Doppler Current Profiler indicated a layer of zooplankton within the OMZ. They carried out DVM, yet a portion remained at mesopelagic depths during the night. Our acoustic measurements showed that the bulk of the acoustic backscatter was restricted to waters shallower than 800 m, suggesting that most of the biomass in the Red Sea resides above this depth.     

Potential effects of a resuspension event on the vertical distribution of copepod eggs in the sea bed: a laboratory simulation

Adult female Acartia tonsa and Labidocera aestiva were obtained from inshore marine waters near Turkey Point, Florida (29°54.5N;84°31W) during April and May 1991. For each species, eggs spawned overnight in the laboratory were collected, mixed with sediment, and added to a plastic tube (26 to 29 cm longx5 cm diam) to yield a 2 cm-thick layer. This tube was connected to a 245 cm-long tube, seawater was added and the contents were thoroughly mixed by turning the assembly end-over-end several times. The vertical distribution of eggs in the sediments following resuspension varied according to the grain size of the sediments. For sediments of 125 m particle-diameter, 68 to 72%, and 70 to 73% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm.For sediments 63 to <125 m particle-diameter, 34 to 36% of the eggs of A. tonsa and L. aestiva, respectively, occurred in the upper 4 mm. For sediments of <63 m particle-diameter, egg distribution was uniform for both species throughout the 2 cm layer. The results indicate that the vertical distribution of eggs in the sea bed following a resuspension event should be highly dependent upon the grain-size composition of the sediments.