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Abstract: The genome sizes of 8 species of amphipods collected from the Canadian Arctic were estimated by flow cytometry. Haploid genome sizes ranged from 2.94 [+ or -] 0.04 pg [...]

Contest behavior of amphipod, Gammarus pulex, during precopula is analyzed. Males assess their own resource-holding potential during struggles with females. Physiological state of the loser is examined.

Although the visual systems of animals living in the cold, dark water of the deep sea have been investigated for some time, little is known about vision in animals inhabiting polar oceans, where temperatures are even colder and irradiance fluctuates dramatically with ice cover and season. Physiology of the compound eye of the amphipod Abyssorchomene plebs (Gammaridea: Lysianassoidea), a common Antarctic benthic scavenger, was studied electrophysiologically by electroretinography. A. plebs has a monochromatic visual system with a spectral sensitivity maximum at 487 nm, and higher sensitivity at ultraviolet wavelengths than predicted by a visual pigment template. While irradiance sensitivity determined from V/log I curves is comparable to that of mesopelagic crustaceans, temporal resolution calculated from response waveform dynamics and as determined by critical flicker fusion frequency suggest that the A. plebs eye is slower than that of crustaceans from the deep sea. A. plebs photoreceptors are physiologically adapted for a slow lifestyle in a low-light environment, where maximizing photon capture occurs at the expense of detecting fast events in the visual scene., Introduction Visual systems may be uniquely adapted structurally and physiologically to the light environment in which they must function (reviewed in Lythgoe, 1979). Structural adaptations include modifications to dioptric elements, […]

Abstract: Benthic surveys were conducted in the southern basin of Lake Michigan and throughout the lake to assess trends in benthic populations, emphasizing recent changes in densities of the benthic [...]

Four species of scavenging amphipod are studied to present an account of the structure and vertical zonation of the scavenging guild residing in the hadal habitat of the Tonga and Kermadec Trenches (SW Pacific Ocean). Observations reveal that each species occupy a distinct vertical zone of 3.5 km or less and separation of habitat in conjunction with deviations in reproductive traits, behaviors and nutritional strategies facilitate the coexistence of the four related species in the harsh and confining habitat.

Abstract: Infection by larval parasites can have severe consequences on intermediate hosts that affect transmission, fecundity and fitness of the host, and host population structure. This study examines the pathogenic [...]

Orientation experiments were carried out on Talitrus saltator (Crustacea Amphipoda) at four points along 3 km on a dynamic sandy beach inside the Maremma Regional Park (Grosseto, Italy) to highlight behavioural variation related to distance from a river mouth, to erosion or accretion of shoreline, and to human trampling on the beach. Tests were performed using circular transparent Plexiglas arenas, contemporaneously at the four points. Replicates were made in 2 different months (September 2002 and May 2003), on 2-3 successive days, in the morning and afternoon. The distributions of the angles of orientation were compared for the different points and seasons, and multiple regression analysis was performed to test the effects of environmental and intrinsic variables on orientation. Sandhoppers showed the highest scatter at the eroded shoreline, intermediate scatter at the accreting beach most distant from the river mouth, and consistent orientation seaward at the least disturbed point. Orientation of sandhoppers was significantly affected by season, global radiation, time of day, distance from the river mouth, and human trampling. Sex and air humidity were of minor significance in the multiple regression model. The results, on the one hand, confirm plasticity in orientation of sandhoppers living on a dynamic shoreline, and on the other hand, show that variation in orientation could potentially be used as a bioindicator of shoreline changes., Introduction This article describes the sun orientation behaviour of the sandhopper Talitrus saltator (Crustacea: Amphipoda), collected at sites with different geophysical characteristics, on a single beach in Tuscany, Italy, and [...]

Female amphipods carry their eggs and offspring in a ventral brood pouch. Previous research has demonstrated that females of species inhabiting harsh environmental conditions expend additional energy in active parental care such as ventilating eggs by beating their pleopods. This study investigated whether similar forms of care could be detected in amphipods collected from spring fed ponds and streams. Two behaviors reported to function in parental care in other species were observed in ovigerous females, but were absent in nonovigerous females and males. Ovigerous females were also shown to beat their pleopods significantly longer than males or nonovigerous females, suggesting that this is another form of active parental care. The duration of pleopod beating varied considerably depending on both the season and the habitat from which the amphipods were collected. Differences were most pronounced for ovigerous females. Similarly, the duration of pleopod beating was significantly longer, especially for ovigerous females, when amphipods were placed in water with experimentally reduced levels of oxygen. These results suggest that even in habitats with high water quality, anaphipods can show active parental care and that females have a phenotypically plastic response to environmental conditions in determining the amount of care provided. The potential fitness effect of such response may have important implications for water quality management.

The toxic reactive oxygen species (ROS), produced naturally in an oxygenated environment, led to the development of antioxidant defenses by aerobic organisms to prevent tissue damage. Polar marine waters are regarded as a strongly prooxidant ecosystem, due to the high dissolved oxygen level and intense UV radiation during summer, while the deep waters are considered refuges against oxidative stress. In order to further elucidate the prooxidant and antioxidant forces associated with cold-water ecosystems and the implications of UV radiation, we sampled three amphipod species living at three different depths in the same water mass of the Arctic Ocean, characterized by low temperature (ca. 0oC), high oxygen level, and high ROS concentration in the surface water. The three species were the deep-sea amphipod Eurvthenes grvllus, the benthic sublittoral amphipod Anonyx nugax and the surface-water species Gammarus wilkitzkii inhabiting the ice pack. The total oxyradical scavenging capacity (TOSC) was measured in the cytosolic fraction of the digestive gland and in the cell-free hemolymph of the three amphipod species. A significantly low TOSC toward peroxyl and peroxynitrite radicals (P0.05) was noted in G. wilkitzkii. These data suggest that A. nugax is highly susceptible to oxidative stress and that G. wilkitzkii is characterized by a mechanism that prevents the diffusion of exogenous ROS through the gills or allows excretion of internal [H.sub.2][O.sub.2] through the gills to the environment.

Changes in the abundance of an endemic amphipod, Jesogammarus annandalei, that inhabits the profundal zone of Lake Biwa were examined from 1966 to 1999. The abundance of J. annandalei increased suddenly during the mid-1980s and thereafter stayed at a level that was sevenfold higher than that before 1980. Compared with the amphipod in the 1960s, both the clutch and body size of the matured individuals decreased during the 1990s, which suggests that per capita food supply decreased. Thus, the increase in the abundance of J. annandalei appeared to be due largely to an increase in their survival rate and not their growth or reproduction rates. In accord with the increase in amphipod abundance, the fishery catch of an endemic gobiid fish species that is dominant in the profundal zone and preys on this amphipod as a major food, decreased dramatically during the mid 1980s. These results suggest that long-term changes in abundance of J. annandalei in Lake Biwa are mainly regulated by fish predation rather than by food supply.

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. pacifica 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[degrees]C, 5[degrees]C, 8[degrees]C and 12[degrees]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[degrees]C were computed as 32 days (12[degrees]C) and 224 days (2[degrees]C), respectively, for T. pacifica, and 66 days (12[degrees]C) and 358 days (2[degrees]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.

The effect of oxygen on 15 size spectra worldwide, established by compiling maximum length data of more than 2000 amphipod species is investigated. Data indicate that there is a small, but significant increase in minimum amphipod size with increasing oxygen.

Populations of the vent amphipod Bouvierellu curtirama were compared from two sites in the Lucky Strike vent field on the Mid-Atlantic Ridge. The two sites (Sintra and Eiffel Tower) are chemically distinct, fed by different bydrothermal sources, but separated by only about 400 m. Both sites are characterized by dense beds of the mussel Bathymodiolus azoricus, though the proportion of methanotrophic and thiotrophic endosymbionts supported by the mussel and its isotopic composition vary significantly between the sites. Such differences presumably reflect the availability of primary resources and would be expected to impinge on other members of the mussel bed community, such as B. curtirama, which was abundant at both sites. A detailed comparative study of the amphipod showed that, although the overall population structure (in terms of growth stages) was similar at the two sites, reproductive output was significantly greater at Sintra, a result of females maturing at a smaller body size and producing more broods of a greater size. The reproductive output at both sites was relatively low, with a proportion of surviving females failing to mature. The plasticity of response of the two populations is discussed in relation to food availability (quantity and quality). Grazing predation, resulting in loss of antennal flagellum articles, was high at both sites. Such damage is discussed in terms of predation impact. Damage to the antennae of the holotype has resulted in an inaccurate species description, which is remedied here.

The lysianassid amphipod Orchomenella aahu was associated with small-scale mass mortality of Ecklonia radiata, the dominant laminarian alga in north-eastern New Zealand. O. aahu burrowed into and hollowed out stipes with severe bleaching, accelerating mortality by 12-14 months. Meristoderm tissue of bleached plants contained approximately one-third of the phlorotannin content (~4% dry mass) present in unbleached, apparently healthier, sporophytes (~12% dry mass). Unbleached stages consistently lacked amphipod damage. O. aahu also colonised plants when non-lethal storm damage afforded entry into the cortical layers of the primary lamina, and ultimately the stipe. O. aahu typically consumed both medullary and cortical tissue of the stipes, forming networked brood-chambers within them, with increasing populations often reducing the plant to the holdfast. There was synchronised mortality across sites and between depths over spatial scales of metres. Following loss of the mature canopy, recruitment of E. radiata was generally within 2 months at most study sites where mortality had occurred.

Animals in the intertidal, both mobile and sessile, generally exhibit some zonation pattern, in which each species shows a preference for, or is confined to, some height levels. The study of zonation patterns is, however, almost exclusively based on surveys made during low tide, when many animals are relatively inactive. We studied zonation patterns of amphipods and isopods on rocky shores in southwestern Iceland, both by traditional sampling at low tide as well as by sampling during high tide. The distributional patterns seen at high tide differed significantly from that at low tide. One amphipod, Anonyx sarsi, was common around baits at all levels at high tide but absent from the intertidal at low ride. Several other species were either relatively more common or tended to be recorded higher, or in one instance, lower on the shore when the tide was in than at low tide. There was also evidence of some species changing habitats within the intertidal with the tidal cycle. Many species, however, moved little away from their respective zones occupied at low tide, and for some species, including some capable of rapid swimming, very limited mobility was indicated. We conclude that low-tide surveys of the intertidal give an incomplete picture of the community structure, and even key species may be missed in such surveys.

During three 'Polarstern' cruises to the ice-covered Greenland Sea (spring 1997, summer 1994, autumn 1995) studies on the under-ice habitat (morphology, hydrography, ice-algal biomass) and on the macrofaunal, autochthonous under-ice amphipods (species diversity, abundance) were carried out in order to describe environmental controls and seasonal patterns in this community. In spring, the ice underside was rather smooth and whitish, while in summer melting structures and sloughed-off ice-algal threads were observed, in autumn detritus clumps accumulated in depressions at the ice underside. Only in summer, a thin layer of warm (up to -0.6 [degrees] C) and less saline (as low as S = 6.3) water was found at the ice-water interface above Polar Water. Integrated ice-algal biomass was highest during autumn (2.6 mg chl a [m.sup.-2]) and lowest during summer (1.2 mg chl a [m.sup.-2]). Four species of under-ice amphipods occurred in spring and summer (Apherusa glacialis, Onisimus glacialis, O. nanseni, Gammarus wilkitzkii), but only the last species was observed at the ice underside in autumn. A. glacialis and G. wilkitzkii were equally abundant in spring; A. glacialis dominated in summer. The highest total abundance of amphipods occurred during summer (31.9 ind. [m.sup.-2]), compared to lower abundances in spring and autumn (5.3 and 1.1 ind. [m.sup.-2], respectively). A factor analysis revealed seasonal patterns in the data set, which mainly influences. A. glacialis, and species-specific relations between several environmental factors and the distribution of under-ice amphipods. Abundance of A. glacialis was closely related to the under-ice hydrography and ice-legal biomass, whereas the other amphipod species were more influenced by the under-ice morphology. It is therefore stated that the observed thinning of the Arctic sea ice and the resulting increased meltwater input and change in morphology of floes will have a profoundly adverse effect on the under-ice amphipods.

Field measurements were used to test and quantify the population dynamics of Nosema granulosis, a parasitic sex ratio distorter, and Gammarus duebeni, its amphipod host, over a two-year period. Findings suggest that while N. granulosis creates a slight reduction in G. duebeni female fecundity, it is not likely to produce extinction and recolonization cycles.

Research suggests that Monoporeia affinis recolonises macroscopic life depleted sulfide-rich sediments as long as the overlaying water is oxygenated. Data indicate that amphipods avoid high concentrations of sulphide in the sediments and form aggregated pockets where oxygen concentration is high.

Instar analysis show that Cyphocaris challengeri exhibit 12 instars in females and 11 in males with maturation occurring in some but not all based on secondary sexual characters. Brood size ranges from 20 to 65 eggs with a generation length of 216 to 584 days.

The population dynamics and reproductive biology of an ascidian- and a sponge-dwelling amphipod were examined. The two undescribed amphipod species, Leucothoe 'ascidicola' and L. 'spongicola', are closely related to each other, and occur in ascidians and sponges, respectively, along the Florida Atlantic coast. L. 'ascidicola' was abundant in solitary ascidians during fall 1997, disappeared during spring/early summer, and became abundant again in September 1998. During the time when L. 'ascidicola' were absent from their hosts, a copepod became a frequent inhabitant of the ascidians but disappeared again when L. 'ascidicola' returned to the ascidians in September 1998. The numbers of L. 'spongicola' in sponges increased substantially during spring, when high reproductive activity was observed. Following this reproductive peak, both adult and juvenile amphipods apparently left the sponges, and during the summer amphipod numbers in the sponges were very low. Another small amphipod species, which often co-occurred with L. 'spongicola', showed less seasonal variation and was found in sponges throughout the whole study period. The percentage of ovigerous females per host unit was usually lower in the ascidian-dwelling than in the sponge-dwelling amphipods. In solitary ascidians, L. 'ascidicola' amphipods usually occurred in groups of several adults, yet there never was more than one ovigerous female per ascidian. In contrast, several ovigerous L. 'spongicola' females were found to cohabit in the same spongocoel. This suggests that intrasexual aggression may be stronger among reproductive amphipod females in the ascidians than in sponges. The size distributions of juvenile cohorts indicate that juvenile L. 'ascidicola' remain for relatively long time periods in the parental ascidian, where they may reach sexual maturity. In contrast, in L. 'spongicola', only cohorts of very small juveniles could be identified, indicating that juveniles disperse shortly after emerging from the female's brood pouch. It is concluded that extended parental care is of very short duration or does not occur in the sponge-dwelling amphipod L. 'spongicola', possibly because fast-growing sponges with a highly branched spongocoel system do not allow long-lasting coexistence of parent-offspring groups. In contrast, the discrete character of the solitary ascidians may enhance the potential for exclusion of other species, resource monopolization by reproductive females, and furthermore for long-lasting extended parental care in the ascidian-dwelling amphipod. Groups of single parents together with cohorts of large juveniles are reported in the literature for amphipods and isopods from brachiopods, bivalves and ascidians, suggesting that these discrete biotic microhabitats may favor the evolution of extended parental care in peracarid crustaceans.

The abundance and biomass of Corophium multisetosum Stock, 1952 were determined from benthic corer samples collected monthly over 1 yr in the upper reaches of Canal de Mira (Ria de Aveiro, Portugal). Both density and biomass over the sampling period were negatively correlated with water temperature and positively correlated with chlorophyll a concentration in the sediment. C. multisetosum density was significantly negatively correlated with plant biomass and positively correlated with salinity. The nature of the sediment, favourable environmental conditions, high availability of food and low interspecific competition allowed the population to reach a maximal density of 200 x [10.sup.3] individuals [m.sup.-2] and a maximal biomass (ash-free dry wt, AFDW) of 62 [g.sub.AFDW] [m.sup.-2]. The population was highly productive, especially during the autumn/winter period. Production, estimated by two different methods (Hynes method: 251 [g.sub.AFDW] [m.sup.-2] [yr.sup.-1]; Morin-Bourassa method: 308 [g.sub.DW] [m.sup.-2] [yr.sup.-1]), was much higher than the values reported for other Corophium species. The annual P:B ratio (10) was high, but similar to values reported for Swedish populations of C. volutator and lower than the values estimated from Mediterranean populations of C. insidiosum.

A solar simulator was used to compare the sensitivity of five species of freshwater invertebrates to enhanced levels of UV-B radiation. Effects were strongest on the cladoceran Scapholeberis kingii, while Ceriodaphnia reticulata, Daphnia magna and the amphipod Hyalella azteca were moderately affected, and the ostracod Cyprinotus incongruens was highly tolerant to UV-B radiation. Median lethal dose values were identified for each species, with a range from 4.2 to 84.0 muW(cm-2).

Research was conducted to examine patterns in diversity, species replacement and species composition of benthic gammaridean amphipodsin across the Greenland-Iceland-Faeroe Ridge and to analyze the environmental factors shaping the patterns. A comparison of the fauna patterns of two sites in the Arctic Ocean and the North Atlantic Ocean was performed. Results indicate that different factors such as salinity and water temperature were the crucial environmental variables that explain the species composition in the area.

Sampling conducted by personnel of two separate laboratories of the U.S. Environmental Protection Agency showed a single amphipod species, Crangonyx pseudogracilis, present in the Ohio River before the early 1970s. Subsequent sampling by personnel of both laboratories, along with invertebrate collections made by the West Virginia Department of Natural Resources and the first author of this paper showed that this species disappeared from the river in approximately 1973. Another amphipod species, Gammarus nr. fasciatus, invaded the Ohio River in 1973. Gammarus nr. fasciatus spread rapidly throughout the Ohio River, and is now one of its most common macroinvertebrate species. Although the evidence is circumstantial, it seems likely that the elimination of C. pseudogracilis from the Ohio River was caused by the damming of the river, especially the use of high-lift dams, completed from 1936 through the present. Experimental evidence indicates that the existing amphipod, G. nr. fasciatus, has a proclivity for slow-water conditions, which have been favored by the installation of the high-lift dams., INTRODUCTION Recently, Carlton (1996) pointed out that ecologists and biogeographers routinely categorize species as native with a confidence belying the quality of the supporting data. Although the spread of a [...]

The dry weight (DW), carbon (C) and nitrogen (N) components of four species of caprellid amphipods inhabiting Sargassum yezoense were examined. Collected from the Otsuchi Bay in northeastern Japan, the Caprella danilevskii, C. subinermis, C. penantis and C. verrucosa were kept in laboratory aquariums with running sea water and sorted within 24 hours after collection. Results showed that males have a greater pereonite II length, higher DW, C and N contents in all four species. Regressions of female pereonite II length in DW, C and N significantly varied from males in all four species.

The reproduction and population biology of the endobenthic amphipod Leptocheirus pinguis at mean low water in muddy sediment in Lowes Cove, ME, were investigated. Findings revealed that this soft-sediment dwelling amphipod uses extensive parental care which appears to be a successful reproductive strategy where there is plenty of food. However, the possibility for evolution of advanced social behavior for this species is low because parental burrows in soft muds have limited expandability and stability.

The Baltic benthic amphipod Monoporeia affinis was found to contain hemocyanin as a respiratory pigment. Hemocyanin was observed to be composed of ca. 90% of the total protein in the hemolymph. Oxygen affinity of the pigment was low and the Bohr factor was also low. The pigment properties indicated a modest role of the hemocyanin which is contrary to the usual sediment-living amphipods.

The influence of the presence of Saduria entomon on populations the benthic amphpod Bathyporeia pilosa under varying oxygen conditions and prey conditions was investigated through functional response studies. Results have shown that Bathyporeia pilosa obtained refuge from S. entomon at low densities in normal oxygen conditions. The functional response of S. entomon was altered by short-term exposure to impoverished oxygen iconditions.

The marine amphipod species Eogammarus oclaire is found in significantly reduced numbers when its oyster shells are unfragmented. Mating pairs of amphipods appear to be more susceptible to predators if they have whole shells. Scientists believe that crab predators find it easier to move around on whole shells. However, numbers of the E. oclaire predator crab Cancer magister remain unchanged regardless of the depth of oyster-shell layer or shell fragmentation levels.

Epidermal cells on the medial side of coxal plates of the beachflea Orchestia gammarellus have filipodial extensions that extend into a gap of about 0.2 micro-m separating the epidermis and the epithelium. The diffusion distance across the coxal plates is a third of that across coxal gills. The coxal plates could act as regions of extrabranchial aerial gas-exchange. In the coxal gills, gas-exchange occurs across the thin-type epithelial cells rather than the thick-type epithelial cells. The coxal gills are permeable to chloride ions.

Water uptake, temperature, and development of major organs of the oocyte influence the egg size of the Gammarus insensibilis. A decrease in temperature is associated with an increase in egg size. The maximum volume increase occurs during the late egg stages which is attributed to the formation and development of major body organs. Water uptake by the embryo and changes in the body-wall permeability increase the size of the egg during hatching. The seasonal variation in egg volume is associated with the seasonal patterns of size-dependent growth and mortality.

The physiology of the amphipods Monoporeia affinis and Pontoporeia femorata, determined by the rate of ammonium excretion (V NH4+), total lipid content and lipid concentration, shows spatial and in some cases seasonal variations at different places in the Baltic Sea. The difference in V NH4+ of M. affinis is not due to a difference in body size, lipid concentration or composition. Total nitrogen release is controlled by seasonal differences in V NH4+. However at all the sites the concentration of lipids and triacylglycerols in P. femorata is less than that in M. affinis.

The rapid digestion rate in scavenging lysianassoid amphipods (Eurythenes gryllus) conforms to the batch reactor feeding model. Digestion rates varies with the nature of the bait. The rapid digestion and assimilation rates in E. gryllus allows additional feeding during unpredictable food supply. Digestion and assimilation rates with timed exposure to bait was studied at various depths in the Canada Basin of the Arctic Ocean and Sohm Abyssal Plains in the Atlantic Ocean.

The comparative study of Hyalella species indicates that the significance of male body size as a factor of reproductive success may be restricted in the lake species by the demographic outcome of size-based predation in the lake habitat. The promotion of a better comprehension of the interactive impact of sexual and feasibility selection on trait evolution which includes the creation of predictive models will need more research.

A study of production, population dynamics and intertidal distribution of the talitrid amphipod Uhlorchestia spartinophila in a salt march in GA reveals the species importance to trophic dynamics. The period between January and May, when adults attain maximum size-specific mass, was the most conducive for reproduction. The species also displayed a broad intertidal distribution.

An investigation of bioturbation by Corophium volutator, an amphipod, reveals enhanced rates of nitrification and denitrification. The denitrification of microcosms having 3,000 to 6,000 ind per sq m is 1.2 to 1.7 times higher than that of control microcosms. Burrow construction and irrigation caused by the benthic organism enhances the total mineralization processes. The ratio of the benthic fluxes between CO2 and O2 are increased in microcosms inhabited by 0 and 6,000 ind per sq m.

A prior survey of Michigan populations of a freshwater amphipod, Hyalella azteca, indicated that populations occur as one of two morphotypes that differ in body size and life history traits. Population types, which may represent separate species, are associated with distinct habitat types. Generally, lakes with centrarchid fish contain a small-bodied form, and fishless ponds and marshes contain a large-bodied form. In this comparative study of two Hyalella populations, I examine the potential role of size-biased feeding by major predators in maintaining, and perhaps generating, the pattern of association between Hyalella morphotype and habitat type. In Duck Lake (centrarchid fish present), overall mortality generally increased with body size in each of two study years, and adult mortality exceeded juvenile mortality. The opposite pattern was observed in a nearby fishless habitat, Duck Marsh, where mortality generally declined with size, so that juvenile mortality exceeded adult mortality. To determine the degree to which size-biased predation might cause the observed mortality patterns, I used stomach content analysis to assess prey size preferences of fish in the lake habitat and laboratory foraging trials to examine size-biased predation by invertebrate predators from the marsh. Fish predators displayed a strong tendency to prey on larger, adult Hyalella. Size preferences exhibited by larval dragonflies, the principal invertebrate predators in the marsh habitat, depended on predator body size, with small larvae preferring juvenile Hyalella and the largest larvae preferring adults. In general, size-selective predation by major predators in each habitat appeared to contribute importantly to overall mortality patterns, the exception being the marsh habitat in a year of low predator density. Observed differences in life history traits between populations are in close agreement with predictions derived from life history models addressing the influence of size-biased mortality on the evolution of reproductive allocation, size at maturity, and egg size. Life history characteristics of Hyalella were measured both on field-collected individuals and on individuals reared for approximately two generations in replicated predator-free artificial ponds. In field samples, the lake Hyalella population exhibited a smaller mean adult body size, smaller size at maturity, smaller egg size, and higher size-specific fecundity and reproductive investment than the marsh population. These life history differences were also observed in the artificial pond experiment, indicating that these traits are genetically based and nonplastic. Key words: amphipod; body size; demography; egg size; fish predation; Hyalella; life history; Michigan; predation; reproductive investment; size at maturity; size-selective predation.

Populations of the scorpion Cercophonius squama and the terrestrial amphipod, Family Tallitridae, were monitored by pitfall trapping in southeastern Australia for 8 yr as part of a field experiment to study the effects of habitat fragmentation and remnant habitat patch size on biological diversity, for 3 yr prior to the fragmentation treatment, and 5 yr thereafter. The abundance of scorpions did not change significantly with habitat fragmentation and there was no discernible effect of remnant size. The abundance of amphipods in the remnants relative to that in the controls decreased markedly after fragmentation, more so on smaller remnants than on larger ones. By reason of their ecological and biological characteristics, scorpions seem resistant to the changed ecological conditions brought about by habitat fragmentation, at least in the short term, whereas amphipods are more susceptible. It is not yet possible to generalize about the responses of species to habitat fragmentation. Management of fragmented ecosystems to maintain biological diversity should be directed at populations of species because different species respond differently. Key words: Cercophonius squama; Family Tallitridae; field experiment; habitat fragmentation; population persistence; southeastern Australia.

The deep-sea amphipod Eurythenes gryllus, captured with and without baits in the Canada Basin of the Arctic Ocean, show extended meal intervals by gut size. Allometric regression of body length and wet weight, by estimating the meal sizes for instars segregated by body length, shows no sex-linked differences in the length-weight relationships. Size of meals was < 50% of empty-gut body weight for the 1-5th instars, more than 60% for mature males above 8th instar and > 75% for mature females above 14/15th instar. Ingested plus stored body lipid energy sustains 1-6 months of respiration in juveniles, 14-22 months in mature females and 9-14 months in mature males.

A study of the oxygen-binding properties of haemocyanins (Hc) of three gammaridean amphipod species confirms the Hc differences between aquatic and semi-terrestrial amphipod genera, and give credence to the theory that the Hc oxygen affinity, Bohr effect and effector sensitivity of amphipod crustaceans decreased when they migrated to the land. Hcs in aquatic gammarids and hyalids are characterized by high oxygen affinity, large Bohr effect and by a large L-lactase effect in gammarids.

Dives with the submersible Alvin revealed swarms of a pardaliscid amphipod at around 2520 and 2580 m depth in the East Pacific Rise vent field. Thin-layered shoals and scattered individuals were evident. Swarms were observed in relation to clams, mussels and tubeworms, and were situated over and just downstream to cracks with emerging hydrothermal water.

Allozyme electrophoresis is employed to study the population-level geographic variation among amphipods inhabiting deep-water basins of Southern California. Morphological differences are observed between different samples. Isolation by distance is weak, as exhibited by high gene flow among these populations. Large genetic differences are observed between deep-sill-basin species and shallow-sill-basin species.

The non-migratory behavior and the grouping together of hyperiid amphipods is due to a strong thermocline and an abundance of gelatinous zooplankton above the thermocline. Hyperiids and gelatinous zooplankton are closely associated as the hyperiids can partition their habitat. Forty-nine species of hyperiid amphipods, collected at the edge of the Benguela System during a major penetration in the Angola Current waters, were found in the uppermost 40 meter of the water column.

The role of benthic amphipod crustaceans in the Portuguese continental shelf ecosystem was examined through an analysis of their biodiversity and distributional ecology as gleaned from samples obtained in two benthic surveys. Of these, 113 species from 51 genera were identified, most of which were obtained from the shelf's lower limit. Species of the genus Ampelisca were found to be the most numerous and abundant of the group. These species were mostly found in sand bottoms, an area which had the most diversity. It was suggested that Ampelisca species might serve as an important source of food for secondary consumers in the area.

Data are presented on northern Bering Sea benthic amphipod growth rates and age at maturity, indicating that high latitude species grow slowly, require 2 to 4 years to mature, reach a large size, and have long lifespans. Data are also presented demonstrating predation by benthic amphipods on newly metamorphosed juveniles of a potential space competitor, the northern samd dollar Echinarachnius parma. Such facultative predation by the predominantly hebivorous amphipods may, in part explain the existence of alternative benthic communities in the eastern Bering Sea. Incorporation of the high latitude results into a review of benthic amphipod life histories revealed several important patterns. Amphipod growth rates and molting rates appear to be decoupled, resulting in small adults at warm temperatures and large adults at lower temperatures. We posit that molting rate is temperature-sensitive, that a warm temperatures molting occurs rapidly regardless of limited instar tissue growth, and that the amphipods reach sexual maturity after a fixed number of molts. Alternatively, gonad development is also temperature-dependent and may drive maturation, regardless of the number of molts experienced. Amphipods have linear or exponential growth rates, as opposed to the familiar asymptotic curve. Consequently, secondary production is highly dependent upon the proportion of large individuals in the population, in contrast to organisms with asymptotic growth in which production is largely determined by the proportion of young, growing individuals present. Production in amphipods is significantly correlated with standing stock. P:B ratios are not correlated with production in amphipods, and probably are not in other organisms with linear or exponential growth rates, and thus appear to have no comparative value other than as a possible index of generation times.

The phylogeographic structure of the amphipod Gammarus tigrinus is assessed to examine how habitat discreteness and dispersal barriers could enhance divergence in transitional estuarine environments, and provide insight to evolutionary mechanisms underlying marine and freshwater biodiversity. The occurrence of cryptic species and divergent population structure support limited dispersal, dispersed habitat distribution, and historical factors as important determinants of estuarine speciation and diversification.

Epibiotic filamentous bacteria living on the marine amphipod crustacean Urothoe poseidonis is identified in this study. These epibioants belong to the gamma proteobacteria.