Processing of allochthonous macrophyte subsidies by sandy beach consumers: estimates of feeding rates and impacts on food resources

Allochthonous subsidies of organic material can profoundly influence population and community structure; however, the role of consumers in the processing of these inputs is less understood but may be closely linked to community and ecosystem function. Inputs of drift macrophytes subsidize sandy beach communities and food webs in many regions. We estimated feeding rates of dominant sandy beach consumers, the talitrid amphipods (Megalorchestia corniculata, in southern California, USA, and Talitrus saltator, in southern Galicia, Spain), and their impacts on drift macrophyte subsidies in field and laboratory experiments. Feeding rate varied with macrophyte type and, for T. saltator, air temperature. Size-specific feeding rates of talitrid amphipods were greatest on brown macroalgae (Macrocystis, Egregia, Saccorhiza and Fucus). Rates for large individuals of both species ranged from ∼40 mg wet wt individual⁻¹12 h⁻¹ on brown macroalgae to negligible feeding by M. corniculata on a vascular plant (surfgrass). Amphipod growth rates were also greatest on Macrocystis and lowest on surfgrass, Phyllospadix. For a Californian beach with substantial inputs of macrophyte wrack (>70 kg wet wt m⁻¹ month⁻¹ in summer), we estimated that the population of talitrid amphipods could process an average of 55% of the palatable Macrocystis input. Our results indicate that talitrid amphipod populations can have a significant impact on drift macrophyte processing and fate and that the quantity and composition of drift macrophytes could, in turn, limit populations of beach consumers.     

Omnivory and grazer functional composition moderate cascading trophic effects in experimental <Emphasis Type="Italic">Fucus vesiculosus</Emphasis> habitats

We tested the relative strength of direct versus indirect effects of an aquatic omnivore depending on the functional composition of grazers by manipulating the presence of gastropod and amphipod grazers and omnivorous shrimp in outdoor mesocosms. By selectively preying upon amphipods and reducing their abundance by 70–80%, omnivorous shrimp favoured the dominance of gastropods. While gastropods were the main microalgal grazers, amphipods controlled macroalgal biomass in the experiment. However, strong predation on the amphipod by the shrimp had no significant indirect effects on macroalgal biomass, indicating that when amphipod abundances declined, complementary feeding by the omnivore on macroalgae may have suppressed a trophic cascade. Accordingly, in the absence of amphipods, the shrimp grazed significantly on green algae and thereby suppressed the diversity of the macroalgal community. Our experiment demonstrates direct consumer effects by an omnivore on both the grazer and producer trophic levels in an aquatic food web, regulated by prey availability.     

Survival and bioturbation of the amphipod Monoporeia affinis in sulphide-rich sediments

Laboratory experiments were conducted to investigate the survival rate of Monoporeia affinis in sulphide-rich sediment with oxic overlying water, and the effect of amphipod bioturbation on sulphide and oxygen profiles. As long as the oxygen content in the water is high, the amphipods seem to avoid quite high concentrations (>200 μmol l⁻¹) of sulphide in the sediment by creating microhabitats where sulphide is rapidly oxidised. In cores with amphipods, a decrease of sulphide concentration was found in upper layers, while an increase of sulphide was found in deeper layers. Aggregation of amphipods generated pockets of light-brown sediment, characterised by high oxygen concentrations and no sulphide, and their depth was clearly dependent on amphipod density. This indicates that M. affinis has a potential to recolonise sulphide-rich sediments, devoid of macroscopic life, after the overlying water column has become oxygenated. Received: 13 April 2000 / Accepted: 8 September 2000     

The effect of micrograzers on algal community structure in a coral reef microcosm

The effect of amphipod grazing on algal community structure was studied within a 75 l refuge tank connected to a 6500 l closed-system, coral reef microcosm. When amphipods (Ampithoe ramondi) were absent or present in low numbers, a high biomass of mostly filamentous algal species resulted, including Bryopsis hypnoides, Centroceras clavulatum, Ceramium flaccidum, Derbesia vaucheriaeformis, Enteromorpha prolifera, Giffordia rallsiae, and Polysiphonia havanensis. These microalgae disappeared when amphipod density increase beyond approximately 1 individual cm^-2 of tank surface. The macroalga Hypnea spinella germinated in the system in association with amphipod tube sites. H. spinella plants remained rare until filamentous species were eliminated by amphipod grazing. Feeding trials confirmed that H. spinella was protected from grazing by its size rather than a chemical defense strategy. The H. spinella community we observed is similar to the flora described on algal ridges where physical conditions exclude fish grazing. We suggest that amphipods and similar micrograzers are responsible for the algal community structure of these ridges. Caging experiments may be subject to similar effects from increased amphipod grazing on the algae. Introduction of fish that are amphipod predators into the refuge tank caused an increase in algal species diversity but total H. spinella growth rates fell from 25 g dry wt month^-1 to less than 8 g dry wt month^-1. We describe amphipod behavior in relation to changes in population density and food supply, and we stress the potential for increasing the productivity of commercial seaweeds through maintenance of appropriate amphipod species in mariculture facilities.     

Biochemical composition and trophic strategies of the amphipod Eurythenes gryllus at hadal depths (Atacama Trench,South Pacific)

Amphipods Eurythenes gryllus were collected at 7800?m depth in the Atacama Trench (South Pacific) for studying their biochemical composition (in terms of proteins, lipids and carbohydrates and fatty acid content) and to gather information on bioenergetic strategies and trophic habits of organisms living in this extreme environment. The effect of long-term formalin storage on the biochemical determinations was also determined. Proteins were the dominant biochemical class of organic compounds (39–53%D.W.), whereas carbohydrates accounted for a very small fraction (1–2%D.W.). Lipid concentrations of E. gryllus accounted for 7–18%D.W. and were much lower than those reported for other deep-sea amphipods. These differences are likely to be more dependent upon food availability in the Atacama Trench rather than upon temperature. Lipid composition of E. gryllus revealed the dominance of monounsaturated fatty acids with polyunsaturated fatty acids accounting for a very small fraction, suggesting that hadal amphipods are higher dependent upon lipid reserves than amphipods inhabiting at shallow depths. The ratio of C18:1Δ⁹ to C18:1Δ¹¹ was >11 confirming the necrophagous trophic habits of this hadal amphipod.     

Conflict of interest between a nematode and a trematode in an amphipod host: test of the "sabotage" hypothesis

Microphallus papillorobustus is a manipulative trematode that induces strong behavioural alterations in the gamaridean amphipod Gammarus insensibilis, making the amphipod more vulnerable to predation by aquatic birds (definitive hosts). Conversely, the sympatric nematode Gammarinema gammari uses Gammarus insensibilis as a habitat and a source of nutrition. We investigated the conflict of interest between these two parasite species by studying the consequences of mixed infection on amphipod behaviour associated with the trematode. In the field, some amphipods infected by the trematode did not display the altered behaviour. These normal amphipods also had more nematodes, suggesting that the nematode overpowered the manipulation of the trematode, a strategy that would prolong the nematode's life. We hypothesize that sabotage of the trematode by the nematode would be an adaptive strategy for the nematode consistent with recent speculation about co-operation and conflict in manipulative parasites. A behavioural test conducted in the laboratory from naturally infected amphipods yielded the same result. However, exposing amphipods to nematodes did not negate or decrease the manipulation exerted by the trematode. Similarly, experimental elimination of nematodes from amphipods did not permit trematodes to manipulate behaviour. These experimental data do not support the hypothesis that the negative association between nematodes and manipulation by the trematode is a result of the "sabotage" hypothesis.     

Herbivory and detritivory among gammaridean amphipods from a Florida seagrass community

The gammaridean amphipods Cymadusa compta (Smith), Gammarus mucronatus Say, Melita nitida Smith and Grandidierella bonnieroides Stephensen from a seagrass community in the Indian River estuary of Florida (USA) fed variously upon large drift algae, small algae epiphytic on seagrasses and seagrass leaf debris and detritus. Consumption was measured in the laboratory using an index (CI) equivalent to mg ingested mg^-1 amphipod day^-1. Observations revealed that the amphipods fed by macrophagy, an attack upon large algae and seagrass debris, and by microphagy, small particle detritus feeding and scraping of plant surfaces for diatoms and other epiphytic algae. C. compta was a macrophagous feeder with a generalized diet of algae and seagrass debris, preferring epiphytic algae and drift algae at mean rates of 1.10 and 0.87 CI, respectively. Gammarus mucronatus fed upon epiphytes and seagrass debris equally at mean rates of 0.90 and 0.97 CI, respectively. The diet of M. nitida condisted primarily of epiphytes, consumed at an average rate of 1.05 CI. Grandidierella bonnieroides fed in a specialized microphagous manner, grooming plant surfaces for small particle detritus and diatoms at an approximate CI rate of 1.45. Assimilation of plants ingested, as reflected by carbon-14 uptake, varied similarly among the 4 amphipods. Epiphytic algae appeared to be most useful as food, providing means of 41 to 75% carbon-14 uptake as ingesta. Drift algae and seagrass debris were of less value, with means varying between 11 and 24 % of carbon-14 uptake by the amphipods. The data show a pattern of feeding which resembles resource partitioning of food both by size and kind. Other evidence, however, including population limitation by predators and an apparent overabundance of food, indicate that resource partitioning as seen may be an artifact, and one which has no co-evolutionary basis among the present species.Contribution No. 102 of Harbor Branch Foundation, Inc.     

Survival, growth and reproduction of the salt-marsh amphipod Uhlorchestia spartinophila reared on natural diets of senescent and dead Spartina alterniflora leaves

The talitrid amphipod Uhlorchestia spartinophila lives in close association with standing-dead leaves of the smooth cordgrass Spartina alterniflora Loisel in salt marshes along the Atlantic coast of North America. This study probed the strength of the trophic link between the amphipod population and the decomposition process in this detrital-based ecosystem. We measured survival, growth and reproductive output in groups of amphipods reared for 6 wk on five diets derived from sheath and blade portions of S. alterniflora leaves just prior to (senescent) and during (dead) decomposition. In unfed treatments, the daily specific mortality rate was 0.391 and starved amphipods survived no longer than 11 d. Among the fed treatments, a diet of senescent sheaths resulted in the lowest survival (20%) and yielded no offspring. Groups fed senescent blades, dead sheaths, dead blades and unwashed dead sheaths had survival rates of 56 to 84% and produced 5.0 to 12.5 offspring replicate⁻¹. Sex ratio usually favored females, but approached unity in treatments with high overall survival, suggesting that quality of available food resources may influence sex ratio in this species. Mean specific growth rates (mm mm⁻¹ d⁻¹) ranged from 0.013 to 0.016, and matched previous estimates of growth from field populations. Overall ecological performance (survival + growth + reproduction) was similar for all food treatments, except senescent sheaths, which yielded a final mean (±SD) dry biomass (0.4 ± 0.42 mg replicate⁻¹) of amphipods significantly lower than that of other diets (1.7 ± 0.81 to 2.6 ± 0.69 mg replicate⁻¹). Natural diets derived from decomposing cordgrass leaves can fulfill the nutritional requirements of U. spartinophila populations, but variation in initial amounts of living fungal biomass among the five experimental diets only partially explained the responses of amphipods in our experiment. Structural characteristics and variation in rates of fungal occupation within different portions of cordgrass leaves may affect the amphipod's ability to access plant production made available by decomposers. Received: 12 December 1996 / Accepted: 18 December 1996     

Grazing rates of organic matter and living fungal biomass of decaying Spartina alterniflora by three species of salt-marsh invertebrates

 The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg⁻¹ d⁻¹) and lowest for periwinkles (90 μg mg⁻¹ d⁻¹), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day. Received: 25 November 1998 / Accepted: 4 November 1999     

Patterns of selective predation by juvenile,benthivorous fish on estuarine macrofauna

Benthic feeding on macrofauna was studied in juveniles of the sparids Lithognathus lithognathus and Rhabdosargus holubi in the upper reaches of the Gamtoos Estuary, South Africa. Fish and benthic macrofauna were sampled simultaneously, and the selection of invertebrate prey assessed. Both fish species strongly selected for corophioid amphipods and consumed other benthic taxa in low numbers. R. holubi also exploited aquatic autotrophs, while L. lithognathus had a narrow prey-spectrum, feeding almost exclusively on the tube-dwelling amphipod Grandidierella lignorum. G. lignorum was the most abundant prey species, both in the benthos and the fish's diet. This species also showed prominent behavioural differences between the sexes; males were markedly more active on the sediment surface than females, who rarely left their tubes during the day. Males switched from an infaunal to epifaunal microhabitat in search of receptive females, concurrently increasing their exposure to fish predators. Consequently, L. lithognathus selected significantly more males than female amphipods, causing a marked bias towards females in the sex ratio and age-structure of the amphipod population. Juvenile amphipods were less preyed upon, presumably as a result of lower prey-detection or capture efficiency by the predators. Accepting current notions about predation as an important structuring element for benthic communities, our data also stress the prominence of size-and sex-selective predation in structuring individual prey populations.     

Trophic diversity in amphipods within a temperate eelgrass ecosystem as determined by gut contents and C and N isotope analysis

A conjoint analysis of gut contents and stable C and N isotopes was applied to determine the main food sources and feeding habits of dominant amphipods in an eelgrass bed (Zostera marina) in Gwangyang Bay, Korea. Gut content observations demonstrated that, while Gammaropsis japonicus and Jassa slatteryi are herbivorous, feeding on epiphytes and detritus, Pontogeneia rostrata and Monocorophium acherusicum are omnivorous, feeding on mesozooplankton fragments and detritus. Stable isotope data confirmed that epiphytes, detritus, and mesozooplankton fragments were major food sources for amphipods in the eelgrass bed. Isotopic mixing model calculations clearly showed an interspecific difference in diet composition. A high isotopic dissimilarity between amphipod taxa demonstrated interspecific trophic diversity, reflecting their herbivorous (G. japonicus and J. slatteryi) and omnivorous (P. rostrata and M. acherusicum) feeding habits and confirmed the detrivorous feeding habits of caprellids. Such trophic diversity at interspecific level of the amphipod species indicates that they use different food resources within their microhabitats and play species-specific functional roles as mediators in trophic pathways from producers to higher-level consumers of the eelgrass ecosystem. Finally, our findings suggest that information on the species-specific trophic ecology of amphipods is needed to better understand their potential role in the trophic dynamics and carbon flow of seagrass bed ecosystems.     

Importance of biotic and abiotic regulators of abundance of the intertidal amphipod Calliopius laeviusculus (Amphipoda: Gammaridae) and assessment of the accuracy and precision of sampling methods for detecting abundance changes

We examined seasonal patterns of abundance for the intertidal amphipod Calliopius laeviusculus (Amphipoda: Gammaridae). Amphipods were sampled with an epibenthic sled during the daytime high tide period from 18 May to 8 August 1988. Amphipod density increased from May to June and reached maxima in both late June and early August. Amphipod density was unrelated to any abiotic component measured in the intertidal community. These variables included sampling location, wave height, water column height, water temperature, salinity and cloud cover. Changes in abundance were related with sampling date and with the onset of capelin (Mallotus villosus) spawning activity in the intertidal. Capelin eggs are an important food item for amphipods. The accuracy of density estimates obtained with the epibenthic sled was assessed through comparison with densities obtained with a more efficient quadrat sampler. Sled samples consistently sampled ca. 1% of the amphipod population. We found that a large portion of the amphipod population burrowed into the sediment and was not effectively sampled by the sled. Sled sampler precision was roughly equivalent to that of quadrats with D (precision) ranging from 0.26 to 0.42 for sled samples and D=0.29 for quadrat samples. Although sample collection with the epibenthic sled was achieved more quickly and under a wider range of weather conditions than was possible with the quadrat sampler, the serious underestimate of amphipod density based on sled samples alone indicates that both sled and quadrat samples, obtained in concert, are required to obtain accurate measures of daily variation in C. laeviusculus abundance.Contribution to the program of GIROQ (Groupe interuniversitaire de recherches oceanographique du Quebec)     

Feeding habits and food requirements of some amphipods in the Black Sea

Food composition and food requirements of four amphipod species of the Black Sea — Dexamine spinosa (Mont.), Amphithoe vaillanti Lucas, Gammarellus carinatus (Rathke), Gammarus locusta L. — were studied and an attempt made to assess the quantitative composition of the food, daily rhythms of feeding, and daily food rations. The composition of the food of the above-named amphipods is similar and consists primarily of seaweeds. Daily feeding intensity is characterized by a distinct increase during the dark period (D. spinosa, A. vaillanti); however, in G. locusta feeding intensity increases in the morning. The daily food rations of amphipods vary greatly (from 1.7 to 360% of the specimens' body weight), depending upon factors such as the kind of food, age, sex, the physiology of specimens, and the water temperature. The total quantity of food eaten by the populations of these amphipods in the coastal zone of the Black Sea amounts to 4000 g organic matter per square metre within 1 year.     

Behaviour and distribution of the sand-beach amphipod Orchestoidea corniculata

The field distribution of Orchestoidea corniculata Stont a talitrid amphipod inhabiting the upper intertidal zone of sandy beaches, was measured by pitfall trap and subsurface core transects. Variations in the distribution of juveniles and adults were recorded. At Coal Oil Point (Goleta, California, USA), the population was concentrated on the leeward side of the Point and, with increasing distance from the Point, both the number and size of beachhoppers decreased. The amphipods burrowed in a 5 to 7 m wide band during the day, and were active over a 15 to 25 m area at night. When they emerged from their burrows, a net seaward movement of 3 m was observed for the population. Behavioural tests suggested that sand penetrability is an important factor determining the location of burrow sites. Diurnal orientation was investigated, and it was found that the amphipods oriented in a landward direction despite overcast sky conditions, beach slope, moisture gradients, or displacement to a new beach.     

Excess amylase in Gammarus palustris (Crustacea: Amphipoda); its release into and possible roles in the environment

Gammarus palustris Bousfield (1969) individuals, of both sexes, contain levels of amylase activity sufficient to hydrolyze their dry weight in starch in less than an hour. We suggest that this is in excess of their needs for internal digestion. Experiments show that amylase is released by the amphipod into the environment, especially when they are maintained in the presence of food. Gammarus palustris amylase can be recovered from their natural habitat. The enzymes retain activity over the wide salinity range (5 to 30) encountered by this species in nature. It is hypothesized that released amylase plays a role external to the amphipod, perhaps in predigestion of food, perhaps as an aid in finding food.     

Ciliated epibionts on the Arctic sympagic amphipod<Emphasis Type="Italic"> Gammarus wilkitzkii</Emphasis> as indicators for sympago–benthic coupling

In September 2003 specimens of the sympagic amphipod Gammarus wilkitzkii were sampled in drifting pack ice above 50 m water depth and in the pelagic/benthic environment beneath in the coastal waters off Svalbard (Norway). Abundance values ranged between 1.5 and 8 individuals m^–2 for the pelagic/benthic and the sympagic environments, respectively, and showed corresponding sex ratios of 1:1.4, favoring males. In the ice a significantly higher number of juveniles prevailed. In contrast, ovigerous females were more abundant among pelagic/benthic living specimens. Approximately 25% of the individuals hosted ciliated epibionts of the genera Ephelota, Cryptacineta, Acineta, Podophrya (all suctoria), and Epistylis (peritrichia). Cryptacineta and Ephelota were the most abundant epibionts on this amphipod species. Female specimens of G. wilkitzkii showed the highest degree of infestation (>2,100 individual epibionts per amphipod specimen: indE/A) followed by juveniles (>1,200 indE/A) and males (>220 indE/A). Highest densities of epibionts were found on anterior body parts with the antennae bearing up to 130 individuals. This is the first sighting of epibionts on crustacea from the sympagic environment. We interpret them as biomarkers that indicate the existence of sympago–benthic coupling processes between the ice and the underlying waters and the seafloor. The population structure and the proportion of infested specimens are equal for the amphipods sampled from both the sympagic and the pelagic/benthic environment, indicating the existence of exchange (coupling) processes between the two habitats. Considering the annual ice cycle, local ice drift patterns, and the shallow water depth in the sampling area, we hypothesize that ice amphipods spend ice-free periods near the seafloor where they may serve as basibionts for protozoans and eventually re-colonize the ice with the onset of ice formation. Our observations strongly emphasize that shallow coastal areas serve as both retention (rather than sink) areas for ice fauna during ice-free periods, and as stepping-stones for re-colonizing the ice when the ice is formed in winter.Communicated by M. Kühl, Helsingor     

Population and reproductive biology of two sibling amphipod species from ascidians and sponges

 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. Received: 30 July 1999 / Accepted: 8 May 2000     

Herbivory in the gammarid amphipod Aora typica: relationships between consumption rates, performance and abundance across ten seaweed species

This paper reveals a substantial capacity for herbivory of seaweeds in the gammarid amphipod Aora typica, adults eating seven of ten taxonomically and morphologically diverse seaweed species offered to them in a no-choice assay. The green algae Ulva spathulata and Enteromorpha intestinalis were consumed at the highest rates in both no-choice (2.3–2.5 mg blotted weight individual⁻¹ day⁻¹) and multiple-choice assays (0.5–1.3 mg blotted weight individual⁻¹ day⁻¹). Adult A. typica collected from two different species of brown seaweeds had very similar feeding preferences to each other. Juvenile A. typica grew to reproductive maturity on the green algae E. intestinalis and U. spathulata, and the brown algae Carpophyllum maschalocarpum and Ecklonia radiata. In common with previous studies on members of other amphipod families, survivorship of juvenile amphipods was positively correlated with feeding preferences of adults across seaweed species (r ²=0.43, P=0.04). However, densities of A. typica on seaweeds in the field (excluding the intertidal E. intestinalis and U. spathulata) were not significantly correlated with feeding preferences of adults (r ²=0.07, P=0.5) or survivorship of juveniles (r ²=0.17, P=0.31). This suggests that either host seaweeds are not a major dietary component of these amphipods in nature, or that the host’s value as a food source is overridden by other properties such as the degree of shelter it affords from larger consumers. This study provides the first demonstration that a member of the cosmopolitan amphipod family Aoridae is capable of consuming a diverse range of seaweeds.     

Scavenging deep-sea amphipods: Effects of food odor on oxygen consumption and a proposed metabolic strategy

In situ respiration rates as a response to the odor of food were measured for two species of scavenging amphipods, Paralicella caperesca from 3 650 m in the western North Atlantic Ocean and Orchomene sp. B from 1 300 m in the Santa Catalina Basin off southern California (USA). In addition, complementary laboratory starvation/respiration rates for a shallow-water species, Orchomene sp. A, were determined. Initial elevated O₂ consumption rates were found for up to 8 h in all deep-sea amphipods exposed to bait odor, followed by a period of lowered respiration equivalent to rates observed in individuals not exposed to bait. Orchomene sp. A revealed a response similar to that observed in the deep-sea species. A metabolic strategy is proposed whereby scavenging amphipods efficiently utilize large episodic organic falls in the food-limited environment of the deep sea. This strategy involves (1) the ability to withstand long periods of starvation, (2) rapid response to an organic fall, (3) rapid location of the organic fall, (4) maximal rate of food consumption with maximal quantity ingested, and (5) efficient utilization of the consumed food. Each of these attributes are explored with the expected and observed mechanisms employed to achieve them.     

Life history and reproduction of the amphipod Synchelidium trioostegitum (Crustacea, Oedicerotidae) on a sandy shore in Korea

The life history and reproductive strategy of the amphipod Synchelidium trioostegitum were studied on a sandy shore at Dolsando, South Korea. Samples were taken once a month for 1 year using a 0.3-mm sledge net on the bottom in 1 m of water at spring tide low water. The highest density of S. trioostegitum occurred from February through March. Ovigerous females were recorded virtually year-round, with a particularly high proportion in fall and early spring, indicating continuous recruitment with two dominant periods. The occurrence of ovigerous females was not correlated with environmental factors, such as temperature and salinity, and no significant difference between the body lengths of females and males was observed. The mean adult body length was greater in the early spring breeding period than in the fall. Brood size and embryo volume were positively correlated with the body length of ovigerous females. Brood size significantly decreased with increases in embryonic developmental stage. Embryo volume was significantly larger in the fall than in the early spring, but brood size was significantly smaller in fall, suggesting a strategy of using the same amount of reproductive energy during breeding periods. This type of reproductive effort is different from that of other Synchelidium amphipods having the same habitat and feeding regime. Our results suggest that interspecific competition for food and territory may be important in defining the reproductive strategy.