Feeding and mouthpart morphology in the semaphore crabHeloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

The mouthparts of the Australian semaphore crabHeloecius cordiformis (H. Milne-Edwards, 1837) are described. Male and female semaphore crabs were observed and collected from mangrove swamps around the south side of Botany Bay, Australia between 1983 and 1987. Semaphore crabs inhabit mangrove mud/sand flats between the midlittoral intertidal zone and the supralittoral fringe of bordering saltflats. Scanning electron micrographs provide detailed pictures of mouthpart morphology and the setae present on the third, second, and first maxillipeds; the second and first maxillae; and the mandibles. Amongst other setal types, spoon-tipped, corn, and bottle-brush setae are described. While semaphore crabs are primarily deposit feeders (microphagous), they have well developed mandibles and are, therefore, also able to eat larger plant and animal material (macrophagous). A brief comparison is made between the mouthparts of semaphore crabs and fiddler crabs (Uca spp.), since the two genera are closely related, occupy similar niches, and resemble each other in appearance. This comparison reveals that while the second maxilliped setal morphology differs between the two genera (Heloecius possesses corn setae,Uca possesses spoontipped setae) these setae may have similar functions. The feeding behaviour ofH. cordiformis is related to substrate composition, burrow construction and various mouthpart specialisations. It is conlcuded that, within the context of the present study, certain structural e.g. mouthpart modifications allowing both scavenging and deposit feeding, and behavioural modifications e.g. mound building in wet muddy habitats, enable semaphore crabs to occupy a wide range of habitat types within the mangrove.Please address all correspondence and requests for reprints to Dr Maitland at his present address at the University of the Witwatersrand     

On the near-surface plankton of the eastern South Pacific Ocean

A study has been made of the plankton of the near-surface water layer (0 to 30 cm) of the eastern South Pacific Ocean in the region lying to the east of the meridian 90°W, between latitudes 5°N and 35°S. This region is influenced by the Peru Current: the current brings water from high latitudes, which results in a decrease in the number of species of the local fauna of copepods of the family Pontellidae, typical of tropical near-surface plankton. Some of the widely tropical and one bicentral species are absent or rare. Least affected by the Peru Current are the waters of equatorial structure in the northern part of the region. Here, 7 species of pontellids were recorded: the widely tropical Labidocera detruncata, Pontella tenuiremis, Pontellopsis regalis, the distant-neritic Pontella danae and Labidocera acuta, the bicentral Labidocera acutifrons, and the neritic Pontellopsis lubbockii. The dominant species among these are L. detruncata and L. acuta. To the west of the convergence, in the southern part of the region, live the southern central species Pontella valida and P. whiteleggei, with Pontellopsis regalis occurring occasionally. In these regions the copepod fauna is frequently dominated by pontellids. To the south of the boundary of the waters of equatorial structure, between the coast of South America and the line of convergence, lies a region most subjected to the effect of waters from high latitudes and of upwellings. It is inhabited by 2 pontellids only: Pontellopsis regalis and Labidocera acutifrons, but they too disappear close to the coast. In this particular region the copepods Calanus australis and Centropages brachiatus are common; they are found in a thicker water layer (0 to 200 m), and are often more abundant than the pontellids.     

Competition for inorganic carbon between photosynthesis and calcification in the symbiont-bearing foraminifer Amphistegina lobifera

The feeding behaviour of the subtropical, intertidal crab Gaetice depressus (He Haan) has been investigated. This species was found to be an omnivorous scavenger capable of ingesting both animal and plant tissues which are passed to the mouth using the chelipeds. Furthermore, the mouth-parts themselves are modified and bear elongated setae, notably on the third maxillae. The net-like structures which the setae give rise to can be repeatedly flailed through the seawater in unison enabling the crabs to feed on suspended material. Beating frequency decreased with crab size but rose with increasing suspension concentration. Experiments demonstrated that suspension feeding can contribute significantly to nutrient uptake and direct observations confirmed that the crabs use this method in situ. The crabs are also able to use the setose appendages to sweep deposited material from the underlying substrate towards the mouth, presumably for nutritive purposes. The significance of these different feeding methods is discussed.     

Role of the bivalveCorbicula japonica in the nitrogen cycle in a mesohaline lagoon

The effect of the bivalveCorbicula japonica on the nitrogen cycle in Lake Shinji, a mesohaline brackish lagoon in Japan, was examined quantitatively based on field surveys and laboratory experiments carried out in the summer of 1982 and 1983. The biomass of the flesh ofC. japonica comprised 97% of the total biomass of the macrozoobenthos in summer. Total biomass ofC. japonica in the lake was estimated 30 986 t fresh wt. The concentration of suspended solids immediately above the lake bottom, whereC. japonica filters the water, was 1.5 to 4 times higher than that in the surface water. In laboratory experiments, the filtration rate was 5.0 litres g dry flesh wt^-1 h^-1, the excretion rates of ammonia and of feces and pseudofeces ofC. japonica were 200×10^-6 g N g dry flesh wt^-1 h^-1 and 33.4 mg dry wt g dry flesh wt^-1 h^-1, respectively at 27°C, the average summer water temperature in the lake. From our study, we estimated thatC. japonica filters almost the same amounts of particulate organic nitrogen produced in the lake by phytoplankton and that supplied from rivers, and that it excretes 30% of filtered nitrogen as feces or pseudofeces and 18% as ammonia.     

Subitaneous, diapause, and delayed-hatching eggs of planktonic copepods from the northern Gulf of Mexico: morphology and hatching success

Experiments were conducted to examine the morphology and hatching success of eggs, either spawned by freshly caught planktonic copepods or recovered from bottom sediments in the northern Gulf of Mexico. Collections were made between August 1992 and September 1995. Eggs of nine species were described and these differed in their diameter, color and surface attributes. Three types of eggs were distinguished: subitaneous, diapause, and delayed-hatching. Three species, Labidocera aestiva Wheeler, Acartia tonsa Dana, and Centropages velificatus (Oliveira) produced only subitaneous eggs. Hatching success varied greatly among these species. Two species, Labidocera mirabilis Fleminger and Centropages hamatus (Lilljeborg) produced diapause eggs and subitaneous eggs. The length of the refractory phase of the diapause eggs differed greatly both within and between these two species. A third type of dormant egg, delayed-hatching, was recognized in Labidocera scotti Giesbrecht and Pontella meadi Wheeler. The existence of delayed-hatching eggs may be an adaptive response of subtropical species to less seasonal fluctuation. Based upon morphological characteristics of the eggs and rearing of nauplii to an identifiable stage, benthic dormant eggs of eight species of calanoid copepods were also identified. Received: 9 September 1996 / Accepted: 1 October 1996     

Distribution of overwintering calanoid copepod eggs in sea-bed sediments around southern Britain

Eggs of the calanoid copepodsLabidocera wollastoni (Lubbock) andCentropages hamatus (Lilljeborg) and others, which could not be reliably assigned to species, were identified from sediment samples taken during three cruises in December 1984, January 1986, and February 1987 in the southern North Sea, the English Channel, the Irish Sea and the Celtic Sea. Eggs were most abundant in sediment samples taken between 20 and 80 m depth, with bottom stress less than 10 dyn cm^–2, and near to the positions of tidal fronts. It is suggested that sedimentation, resuspension and sediment transport contribute to the causes of these distributions, which have been found to be consistent with the distributions of species which are known to produce diapause eggs as an overwintering strategy. Nauplii ofL. wollastoni, C. hamatus, C. typicus (Krøyer)Temora longicornis (Müller) andAcartia sp. hatched from incubated sediment samples. The last noted hatchings ofL. wollastoni, Centropages spp. andT. longicornis all occurred more than 1 yr after the start of the incubation experiments.     

Feeding preferences of periwinkles among four species ofFucus

A widely accepted view of intertidal community organizatiton in the NW Atlantic proposes that fucoid vegetation is maintained by the actions of predators which remove species competitively superior toFucus species. Herbivory is an important component of these predatory interactions, but has been studied largely with reference to the interaction betweenF. vesiculosus andLittorina littorea. There are many species of fucoids and herbivorous invertebrates on the shores of the NW Atlantic and this paper reports field and laboratory experiments performed in 1987 (in or near Halifax, Canada) on the effects of grazing by three species ofLittorina on adults and juveniles of four species ofFucus. In laboratory experiments, portions ofFucus species were presented singly (no choice) or together (multiple choice) to single species ofLittorina. AdultF. distichus was grazed to only a small extent.F. evanescens andF. vesiculosus adult tissues were heavily grazed in most laboratory experiments.F. spiralis adults were heavily grazed in no choice experiments, but were grazed only slightly in multiple choice tests. When adult fucoid tissues were exposed to a mixed suite of grazers in the field, onlyF. vesiculosus was grazed heavily. Tests done on adult tissues showed clearly thatFucus species are highly variable in their vunerability to grazers. Moreover, we found variability among periwinkle species in grazing rates on adultFucus. We also found a great disparity in the feeding rates of different periwinkle species on juveniles ofFucus. Therefore, it is not possible to extrapolate from a single periwinkle species/single fucoid species interaction when attempting to identify vegetation structuring processes.     

Cytotoxic haplosclerid sponges preferred: a field study on the diet of the dotted sea slug<Emphasis Type="Italic"> Peltodoris atromaculata</Emphasis> (Doridoidea: Nudibranchia)

Trophic specializations are widespread among opisthobranch molluscs. One purported example from the Mediterranean Sea is the dotted sea slug Peltodoris atromaculata. It has been hypothesized that this species is strongly monophagous on the sponge Petrosia ficiformis. However, the small amount of evidence that has been found for this hypothesis is based just on laboratory tests. Here we study the feeding habits and the diet of Peltodoris atromaculata in its natural habitat. We observed and videotaped 161 individuals together with the organisms on which they were found (their living substrata). Feeding scars were identified and videotaped as well. Individuals and their living substrata were sampled for further analysis in the laboratory. The composition of faeces of Peltodoris, especially undigested sponge spicules, was analyzed by light and scanning electron microscopy and compared to the composition of the living substrata. Most of the faecal samples consisted of undigested sponge spicules. Although Peltodoris was found on 11 species of sponges, only 2 of them, Petrosia spp. and Haliclona fulva, form its diet (76% out of n=121 samples). In accordance with this, feeding scars in the habitats were exclusively observed on these two sponges. Estimation of electivity indices suggests that Haliclona is preferred over Petrosia. One remarkable feature of the exclusive feeding of Peltodoris on Petrosia and Haliclona is that both sponges share specific fulvinol-like polyacetylenes that show cytotoxic activity in bioassays. Potential benefits and evolutionary aspects of this trophic specialization are discussed. Besides sponge-containing faeces, we found spicule-free faeces (24%, n= 29). These were very small in volume compared to sponge-containing faeces, and only few distinct structures were present. However, the use of food other than sponges is not necessarily indicated by this, because the spicule-free faeces might also represent left-overs from the stomach and digestive gland after sponge spicules have been released.Communicated by O. Kinne, Oldendorf/Luhe     

Anatomical and experimental evidence for particulate feeding in<Emphasis Type="Italic"> Lucinoma aequizonata</Emphasis> and<Emphasis Type="Italic"> Parvilucina tenuisculpta</Emphasis> (Bivalvia: Lucinidae) from the Santa Barbara Basin

Previous nutritional models for adults of the lucinid bivalve Lucinoma aequizonata contend that symbiotic chemoautotrophic bacteria provide most of the organic carbon for the host. The existence of this symbiosis, coupled with the hosts distinctive anatomical features, shaped the impression that particulate feeding was not a significant part of L. aequizonata nutrition. Here, we use several techniques to show that particulate feeding is a consistent and important part of the L. aequizonata nutritional strategy. Histological and scanning electron microscopy observations reveal that the gills of L. aequizonata, like those of the lucinid Parvilucina tenuisculpta, have functional mucociliary epithelia, able to transport captured particles to the mouth. Observations of gut content and radiolabeled feeding experiments indicate that L. aequizonata does ingest and assimilate carbon from particulate organic matter. Furthermore, molecular identification of a broad spectrum of organisms in the guts of native adult specimens demonstrates that L. aequizonata is non-selective when ingesting organic material, and has a mixotrophic diet.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by P.W. Sammarco, Chauvin     

Sympatry and allopatry in the deeply divergent mitochondrial DNA clades of the estuarine pulmonate gastropod genus <Emphasis Type="Italic">Phallomedusa</Emphasis> (Mollusca,Gastropoda)

DNA sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene were collected from estuarine snails in the genus Phallomedusa to examine the effects of estuarine isolation on population structure and gene flow. Three clades were recovered, one corresponding to Phallomedusa austrina and two others with the morphology of Phallomedusa solida. The haplotype diversity in all three clades indicated recent population expansion. Phallomedusa austrina was restricted to the west of a previous land bridge in the Bass Strait between mainland Australia and Tasmania, and P. solida to its east and to northern Tasmania. Phylogeographic analysis of P. austrina and P. solida shows strong geographic separation of species, but no local genetic structure indicative of regional or estuarine isolation. The clades of P. solida exhibit substantial genetic divergence and were sympatric across their entire distribution in eastern Tasmania and mainland Australia. Such a situation, which has not previously been observed in phylogeographic studies of southeast Australia, suggests that P. solida has had a complex refugial history during periods of environmental challenge.     

Why do plants ‘talk’?

Summary Plant defence can be induced by herbivory. This is true for both direct and indirect plant defence. Induced direct defence has been the most studied of the two. However, in most cases induced direct defence does not appear to be a water-tight defence option. In contrast, induced indirect defence through the production of herbivore-induced carnivore attractants can be a decisive factor in the extermination of herbivore populations. In this paper the main characteristics of induced attraction of carnivores by plants are reviewed. This includes the similarities and dissimilarities among tritrophic systems. There are two main patterns of induced carnivore attraction. (1) Through the emission of the same bouquet as that emitted by mechanically damaged plants, but in larger quantities and for a longer period of time after damage. (2) Through emission of large amounts of new volatiles that are synthesizedde novo in response to herbivore feeding andnot in response to mechanical wounding.Herbivore populations may be decimated by carnivores. Therefore it should be realized that herbivoreinduced carnivore attractants are essential in an important step in carnivore foraging,i.e. long-distance herbivore location. Once herbivores have started feeding on a plant and direct defence is not effective, induced indirect defence may be decisive for plant survival. Therefore, it is concluded that indirect defence is an essential aspect of induced plant defence directed at herbivorous arthropods.     

Defensive secretions from the larvae ofApatania fimbriata (Pictet) (Trichoptera: Limnephilidae)

Summary When the larvae of the caddis flyApatania fimbriata (Pictet) are threatened, drops of fluid appear on their head capsules. The secretions are produced in a gland in the dorsal part of the prothorax. The neck region contains an eversible sac with numerous single setae, groups of 3 setae, or rows of setae on the surface. The secretion is released through two paris of orifices on the lateral sides of the sac. For the most part the secretion is composed of some 30 fatty acids, with the major components having 12–14 carbon atoms and up to 4 double bonds (approx. 1–2 µg secretion per specimen). Biotests with synthetic saturated acids (C₆–C₁₂) in a stream and in the laboratory demonstrated a paralysing effect on small invertebrate predators (Rhyacophila sp.,Plectrocnemia conspersa, Hydropsyche sp., larvae, all Trichoptera). In choice experiments,Rhyacophila sp. larvae preferred larvae ofAgapetus fuscipes andDrusus annulatus (Trichoptera) as food as compared withApatania fimbriata larvae. Larger predators, such asDinocras cephalotes (Insecta, Plecoptera) and the fishCottus gobio, did not discriminate betweenApatania fimbriata and other prey species. The use of fatty acids in defensive secretions is interpreted as an adaptation to the running water environment. They are effective repellents againstRhyacophila sp. larvae, the most important predator in the natural environment ofApatania larvae.     

Growth and reproduction of the generalist opisthobranch Haloa japonica: effect of algal seasonality on growth rate

The life history of Haloa japonica (Pilsbry), especially the seasonality of growth and reproduction, was investigated from 1992 to 1995 on a flat rocky shore exposed at low tide at Kattoshi, Hakodate Bay, Japan. To estimate the effect of environmental seasonality on growth rate, we conducted two sets of field cage experiments in which algal food was controlled. H. japonica was shown to have an annual life cycle. Spawning occurred from late April to mid-July. Recruitment occurred in June. Simultaneously, large adults disappeared from the habitat. A rapid increase in wet weight of H. japonica was observed in early spring, and coincided with the bloom of the membranous green alga, Monostroma angicava. Under field cage experiments, individuals feeding on both M. angicava and Polysiphonia japonica grew faster than those feeding on only P. japonica. Growth rates of H. japonica feeding on only P. japonica, however, did not vary from February to April. These results suggest that seasonal variation in the algal community limits the growth of H. japonica in early spring at Kattoshi. This factor is relatively more important as a limiting factor on the growth of H. japonica than the physical environment in this season.     

Population dynamics of the acorn barnacles, Tetraclita squamosa and Tetraclita japonica (Cirripedia: Balanomorpha), in Hong Kong

Tetraclita squamosa and Tetraclita japonica are common, intertidal barnacles. In Hong Kong, the population dynamics of the two species exhibited spatial and temporal variation on two semi-exposed shores. T. squamosa produced egg masses from May–June and annual settlement and recruitment occurred from June–July. In contrast, settlement and recruitment of T. japonica was sparse from March–May, but intensified in July–October. Mature gonads and egg masses were, however, only present from September–November, suggesting the larvae from the two settlement pulses originated from other locations as well as Hong Kong populations. Settlement intensity and post-recruitment mortality of the two species varied between sites, possibly due to spatial variation in free rock space, physical transport of larvae and abundance of food in the water column.Communicated by T. Ikeda, Hakodate     

Etude de la respiration chez des copépodes de niveaux bathymétriques variés dans la région sud marocaine et canarienne

The results of 281 respiration analyses of pelagic copepods sampled in the South Moroccan and Canarian area are described. The copepods used in experimentation were collected from various bathymetric levels: hyponeustonic species (Anomalocera patersoni, Pontellopsis villosa, P. regalis, Labidocera wollastoni, Pontella lo biancoi), epipelagic species (Centropages typicus, Temora stylifera, Calanus helgolandicus, Acartia clausi), meso and bathypelagic species (Pleuromma xiphias, P. abdominalis, Euchaeta acuta, Undeuchaeta plumosa and some other rare species). Analysis of the metabolismtemperature curve makes it possible to describe different modes of adaptation in relation to geographical distribution, altitudinal repartition, and dietary characteristics. When all species are studied together, a strong correlation exists between the log of respiration and the log of weight. The regression coefficient varies with temperature; it is strongest at a temperature near that of the natural thermic conditions.     

Functional mouthpart morphology of the squat lobster Munida sarsi, with comparison to other anomurans

 The mouthparts of Munida sarsi Huus, 1935, including the labrum and paragnaths, are described using LM and SEM, with special attention to the setal composition and its function. We also used high-resolution macrovideo equipment to record the feeding processes and monitor setae in action. This combination of morphological and preliminary behavioral data enabled us to arrive at a more comprehensive understanding of the functional morphology. M. sarsi was found to be an opportunist and capable of handling and eating most kinds of animal tissue. The species can also be a selective deposit feeder, sorting the sediment by quality and not by size. This sorting is performed by the setae on the medial rim of the bases of maxilla 1, maxilla 2 and maxilliped 1. Many of the other mouthpart functions ranging from food detection to ingestion are mapped with comparison to what has been found for other anomurans. Grooming was shown to be a significant function of many mouthparts, especially the endopod of maxilliped 3. In general the mouthparts closest to the mouth have the least complex movements and functional scheme, with the mandibles being able to perform only one movement, i.e. cutting or crunching food objects. Some functions are attributed to the paragnath, the endopod of maxilla 2 and the epipod of maxilliped 1. Received: 3 October 1999 / Accepted: 22 March 2000     

Stable isotope analysis of two species of anguilliform leptocephali (<Emphasis Type="Italic">Anguilla japonica</Emphasis> and <Emphasis Type="Italic">Ariosoma major</Emphasis>) relative to their feeding depth in the North Equatorial Current region

Anguilla japonica leptocephali are transported from their offshore spawning area to their recruitment areas in East Asia, but their depth distributions, food sources and feeding are still poorly known. This study analyzed carbon and nitrogen stable isotope ratios of leptocephali of A. japonica, Ariosoma major and Ariosoma spp., and of particulate organic matter (POM), their likely food source, at five different depths in 2004–2009. We used mixing models to show that A. japonica appeared to be feeding at depths between 5 and 50 m, but sometimes deeper. A. major appeared to have a tendency of mostly feeding at depths of 50 m or shallower. Although the A. japonica and Ariosoma spp. collected in the same area during the leptocephalus stage appeared to have different feeding ecologies possibly related to different types of POM, their different depth distributions, sizes and transport histories may also help explain these differences.     

Parasites and headless chaetognaths in the Indian Ocean

Typhloscolecid polychaetes, assigned to the genera Typhloscolex (Typhloscolex muelleri) and Travisiopsis (Travisiopsis dubia), feeding on chaetognaths are reported for the first time from the Indian Ocean. These parasitic/predatory polychaetes cause decapitation in the chaetognath Flacisagitta enflata, either by eating the head or by causing injuries to the neck or body. Data from eastern Africa to western India showed a peak of polychaete infestation and decapitation of F. enflata in the Seychelles. A 5% peak occurrence (turnover rate is unknown) of decapitated individuals indicates that this parasitism/predation may have an important impact on local F. enflata populations. The harpacticoid copepod Microsetella norwegica was found feeding on the head and the reproductive organs of F. enflata. Therefore, this copepod may cause both decapitation and castration. Flatworm parasites are reported from the body cavity of F. enflata. Digeneans probably belonging to the genera Aphanurus, Parahemiurus, Accacladocoelium and Opechona, along with the accacoeliid Cercaria owreae and didymozoid metacercariae, were found. Cestode larvae were also recovered. No nematodes were found inside chaetognaths in this study.Communicated by O. Kinne, Oldendorf/Luhe     

Late Pleistocene dispersal of Indian-Pacific sardine populations in an ancient lineage of the genusSardinops

Temperate sardines fall into two related monotypic genera,Sardina andSardinops. Sardina exists as a cluster of subpopulations in the northeastern Atlantic and Mediterranean, andSardinops encompasses five geographically-isolated regional populations: (1) South Africa-Namibia, (2) Australia-New Zealand, (3) Chile-Peru, (4) Mexico-California and (5) Japan-Russia. We surveyed electrophoretic variability in the products of 34 protein encoding loci inSardina (N=26) and the five Indian-Pacific populations ofSardinops (N=222), collected from 1983 to 1991. Nei's genetic distances () between samples ofSardina andSardinops averaged 1.04 and are typical of distances between species of related genera.s between the regional forms ofSardinops were <-0.011, indicating thatSardinops consists of a single species with widely-scattered subpopulations. Assuming a molecular clock calibrated by the rise of the Panama Isthmus and the opening of the Bering Strait, these genetic distances correspond to times since divergence of <200 000 yr. AlthoughSardinops populations showed a significant degree of allele-frequency heterogeneity (F _ST, a measure of population differentiation, averaged 0.085 over 8 polymorphic loci), the distribution of genetic distances and tests of allele-frequency heterogeneity could not distinguished between hypotheses of north-south antitropical or east-west oceanic dispersal. Low levels of gene diversity inSardinops and mutation-drift disequilibria are consistent with a strong reduction in population size before the Late Pleistocene dispersal to the corners of the Indian-Pacific Oceans of an ancestralSardinops population.     

Comparative life-history study on sympatric hyperiid amphipods (<Emphasis Type="Italic">Themisto pacifica</Emphasis> and <Emphasis Type="Italic">T</Emphasis>. <Emphasis Type="Italic">japonica</Emphasis>) in the Oyashio region,western North Pacific

Life-history features of the sympatric amphipods Themisto pacifica and T. japonica in the western North Pacific were analyzed based on seasonal field samples collected from July 1996 through July 1998, and data from laboratory rearing experiments. T. pacfica occurred throughout the year, with populations peaking from spring to summer. In contrast, T. japonica were rare from autumn to early winter, but became abundant in late winter to spring. Mature T. pacifica females and juveniles occurred together throughout the year, indicating year-round reproduction. Mature T. japonica females were observed only in spring, and juveniles occurred irregularly in small numbers, suggesting limited, early-spring reproduction in this study area. Size composition analysis of T. pacifica identified a total of eight cohorts over the 2 years of the study. Due to the smaller sample size and rarity of mature females (>9.6 mm) and males (>7.1 mm), cohort analyses of T. japonica were not comparable. Laboratory rearing of specimens at 2°C, 5°C, 8°C and 12°C revealed that a linear equation best expressed body length growth by T. pacifica, while a logistic equation best expressed body length growth by T. japoncia. Combining these laboratory-derived growth patterns with maturity sizes of wild specimens, the minimum and maximum generation times of females at a temperature range of 2–12°C were computed as 32 days (12°C) and 224 days (2°C), respectively, for T. pacifica, and 66 days (12°C) and 358 days (2°C), respectively, for T. japonica. The numbers of eggs or juveniles in females marsupia increased with female body length and ranged from 23 to 64 for T. pacifica and from 152 to 601 for T. japonica. Taking into account the number of mature female instars, lifetime fecundities were estimated as 342 eggs for T. pacifica and 1195 eggs for T. japonica. Possible mechanisms for the coexistence of these two amphipods in the Oyashio region are also discussed.Communicated by O. Kinne, Oldendorf/Luhe