Gammarid Amphipods Research Articles

Effects of hypoxia on the feeding intensity and somatic condition of the blackfin flounder Glyptocephalus stelleri in Funka Bay, Japan

To clarify effects of hypoxia on feeding and somatic condition of blackfin flounder Glyptocephalus stelleri, we studied the temporal relationship between hypoxia and feeding intensity as well as the condition of this species in May and August 2006–2012. Hypoxia occurred near the seafloor in August between 2010 and 2012 but not in May. Population densities of gammarid amphipods Ampelisca brevicornis and Melita sp., the main prey items of blackfin flounder, were consistently low; however, the somatic condition and feeding intensity of blackfin flounder increased during hypoxia. Such an increase was not detected in May 2012 under non-hypoxic conditions. These facts imply that the hypoxia increased prey availability for blackfin flounder through the increased exposure of the gammarids over the sea floor, and, thus, resulted in improved body condition in August 2011 and 2012. Hypoxia positively would influence the somatic condition and feeding intensity of blackfin flounder in Funka Bay in August 2011 and 2012; however, the somatic condition during this period did not reach the levels recorded in 1983, suggesting that habitat quality for blackfin flounder in Funka Bay in 2011 and 2012 was worse than that in 1983.

Reproduction, growth and early life history of the Antarctic gammarid amphipod Paramoera walkeri

The gammarid Paramoera walkeri is one of the most abundant amphipods in near-shore Antarctic waters. There has been increasing interest in P. walkeri as a test species for ecotoxicology studies and bio-monitoring for contaminants in Antarctica, but further information is needed to improve understanding of its biology including reproduction, growth and early life history. Female P. walkeri brooding late-stage embryos were collected in summer from coastal waters in the Vestfold Hills region, East Antarctica, and were maintained in the laboratory. Timing of neonate release, brood size and early post-marsupial survival and growth (total length) of juveniles were recorded. Brood size ranged from 26 to 86 neonates per female, and juvenile survival rates were high (96 %). The increase in body length of juveniles ranged from 0.017 to 0.043 mm/day with a mean growth rate of 0.028 mm/day (0.94 % per day) over 11 weeks with strong evidence for exponential growth over time. The body lengths of laboratory-raised juveniles were not significantly different to those of wild-caught juveniles with the same number of segments (15) in the first antennae, indicating that growth may have progressed at a similar rate in vivo and in situ. Juvenile growth was similar when modelled over time or by addition of first antennal segments. This study provides new information on the reproductive biology and early life history of P. walkeri, with further evidence that Antarctic amphipods exhibit slow growth, even when food is not a limiting factor, compared with species from lower latitudes.

Temporal variation of the gammaridean fauna (Crustacea, Amphipoda) associated with the sponge Mycale angulosa (Porifera, Demospongiae) in southeastern Brazil

Marine sponges are advantageous microhabitats because of their complex architecture. The system of internal canals provides circulation of water and deposition of particulate organic matter, ensuring availability of food and shelter. Diminutive amphipods have little difficulty penetrating the spaces of sponges and remain in their aquiferous systems as one of the most abundant taxa in this association. This study evaluated the temporal variation of the gammaridean amphipod species associated with the sponge Mycale angulosa. Sponge samples were collected every three months over one year at Pontal da Cruz Beach, Sao Sebastiao Channel, southeastern Brazil. The amphipod assembly varied over time, while the amphipod density and sponge biomass remained approximately constant. Six species contributed to the temporal variation infaunal composition, highlighting the importance of the natural history of each species.

An introduced species meets the local fauna: predatory behavior of the crab Rhithropanopeus harrisii in the Northern Baltic Sea

Crabs are some of the most successful introduced species among marine organisms, and they can be an important structuring force in marine communities. Recently, the North American white-fingered mud crab, Rhithropanopeus harrisii, has invaded the Northern Baltic Sea. This is an area where no native crab species exist, and the addition of a novel functional species to the low species diversity of the Baltic Sea could have large community-level impacts i.e. modifying biotic interactions and/or altering ecosystem functioning. We examined the predatory behavior of introduced R. harrisii both in the laboratory and field focusing in shallow, hard bottom habitats dominated by the alga Fucus vesiculosus. In the laboratory environment, R. harrisii was an effective predator of littoral grazers, readily consuming both sessile fauna (Mytilus trossulus) and also mobile species such as isopods (Idotea balthica) and gammarid amphipods (Gammarus sp.). When studying the predation of different sized prey items, R. harrisii preyed upon small and medium sized prey of both mobile and sessile species. However, in the field experiment with the native faunal community associated with F. vesiculosus, R. harrisii negatively impacted only the abundance of the snail Theodoxus fluviatilis, possibly through indirect effects. Nevertheless, R. harrisii significantly decreased both the prey species richness and diversity but not the total number of potential prey individuals associated with F. vesiculosus. In conclusion, predatory behavior of this novel crab has the potential to impact the native macroinvertebrate littoral community, but the realized predation pressure in the field is lower than could be expected from laboratory experiments.

High fecundity and predation pressure of the invasive Gammarus tigrinus cause decline of indigenous gammarids

The North American amphipod Gammarus tigrinus is one of the most aggressive invaders recently expanding its distribution in the European waters. The species was detected in the north-eastern Baltic Sea in 2003 and has rapidly expanded its distribution ever since. This invasive amphipod has been notably successful in shallow, soft and mixed bottom habitats becoming one of the most abundant gammarid colonizing such environments. This study carried out two experiments: (1) an outdoor aquarium experiment to assess interspecific competition among the invasive G. tigrinus and the native Gammarus duebeni and compare their reproductive potential, and (2) an in situ meshbag experiment to determine the effect of adult G. tigrinus and native gammarids on juvenile gammarid amphipods. These demonstrated that the adult G. tigrinus had no effects on the adult G. duebeni; however, the invasive amphipod had higher reproductive potential compared to the native species such as G. duebeni. Moreover, almost all adult gammarids exerted a significant predation pressure on juvenile amphipods. Thus, the combined effect of predation on juvenile amphipods and large brood production of G. tigrinus could be plausible explanations describing increased abundance of G. tigrinus and decrease of local gammarid populations in the north-eastern Baltic Sea but plausibly in similar shallow water habitats in other seas.

Feeding relationships among juveniles of abundant fish species inhabiting tropical seagrass beds in Cockle Bay, North Queensland, Australia

Dietary analysis was conducted on juveniles of 10 numerically abundant fish species inhabiting tropical seagrass beds in North Queensland, Australia. Gammarid amphipods were consumed by all of the species, but their contribution to the diet of each varied. Crab larvae and copepods contributed to the diets of Leiognathus bindus, Pranesus endrachtensis and Stolephorus sp.; polychaetes and isopods were consumed by Sillago maculata burrus, Lethrinus sp., Pelates sexlineatus and Siganus canaliculatus; and Favonigobius reichei, Coris caudimacula and Arothron manilensis fed on bivalves. Seagrass and gastropods were rarely ingested by most of these fishes, but made a moderate contribution to the diet of A. manilensis. With the exception of L. bindus, the diet of each species was correlated with size: smaller species consumed copepods, crab larvae and gammarid amphipods, while larger species ate polychaetes, bivalves, isopods and gastropods. Non-metric multidimensional scaling (MDS) ordination plots emphasised the variation in dietary composition between species, and showed that this was often correlated with mouth length and width of the fish—for example, species with larger mouth dimensions tended to have broader diets. These interspecific differences in dietary composition increase the number of food resources available to these fishes, thereby reducing the potential competition for resources within the fish community.

Indirect effects of predators control herbivore richness and abundance in a benthic eelgrass (Zostera marina) mesograzer community.

Herbivore communities can be sensitive to changes in predator pressure (top-down effects) and resource availability (bottom-up effects) in a wide range of systems. However, it remains unclear whether such top-down and bottom-up effects reflect direct impacts of predators and/or resources on herbivores, or are indirect, reflecting altered interactions among herbivore species. We quantified direct and indirect effects of bottom-up and top-down processes on an eelgrass (Zostera marina) herbivore assemblage. In a field experiment, we factorially manipulated water column nutrients (with Osmocote(™) slow-release fertilizer) and predation pressure (with predator exclusion cages) and measured the effects on herbivore abundance, richness and beta diversity. We examined likely mechanisms of community responses by statistically exploring the response of individual herbivore species to trophic manipulations. Predators increased herbivore richness and total abundance, in both cases through indirect shifts in community composition. Increases in richness occurred through predator suppression of common gammarid amphipod species (Monocorophium acherusicum and Photis brevipes), permitting the inclusion of rarer gammarid species (Aoroides columbiae and Pontogeneia rostrata). Increased total herbivore abundance reflected increased abundance of a caprellid amphipod species (Caprella sp.), concurrent with declines in the abundance of other common species. Furthermore, predators decreased beta diversity by decreasing variability in Caprella sp. abundance among habitat patches. Osmocote(™) fertilization increased nutrient concentrations locally, but nutrients dissipated to background levels within 3m of the fertilizer. Nutrient addition weakly affected the herbivore assemblage, not affecting richness and increasing total abundance by increasing one herbivore species (Caprella sp.). Nutrient addition did not affect beta diversity. We demonstrated that assemblage-level effects of trophic manipulations on community structure are the result of distinct and often indirect responses of herbivore species. These results underscore the importance of understanding herbivore-herbivore interactions in a system commonly subjected to both eutrophication and overfishing.

Top–down control by great blue herons Ardea herodias regulates seagrass‐associated epifauna

Top predators can influence the structure and function of plant and animal communities. In coastal marine systems, fish, shark and mammal population declines are major drivers of recent ecosystem‐level change. Cascading effects of predatory wading birds, however, are less understood, even though wading bird populations have declined in many regions. We quantified the effects of predation by the piscivorous great blue heron Ardea herodias fannini on fish, invertebrates and epiphytes living in eelgrass Zostera marina. We found that herons forage on benthic fish in seagrass meadows, and foraging intensity increased from late spring until midsummer. When we experimentally excluded herons, benthic fish abundance increased, and the invertebrate assemblage shifted to more shrimp‐dominated assemblages while grazing gammarid amphipod abundance declined. These shifts were associated with reduced epiphyte abundance when herons were excluded, reflecting a four‐level trophic cascade and mediated by shifts in the grazer assemblage. In summary, we found that a piscivorous wading bird species exerts top down control in a subtidal seagrass ecosystem. Losses and recovery of wading birds could have ecosystem‐level ecological consequences that may need to be considered in the context of concern for overfishing and predator recovery in marine coastal management.

Trophic interactions between native and alien palaemonid prawns and an alien gammarid in a brackish water ecosystem

Macroalgae are an important habitat for small mobile invertebrates such as gammarid amphipods and palaemonid prawns. Gammarid amphipods are important grazers of micro- and macroalgae whereas palaemonid prawns are feeding on macroalgae and small aquatic invertebrates including gammarids. Recently the invasive palaemonid prawn Palaemon elegans established in the Baltic Sea. As P. elegans occurs within the same habitats as the native Palaemon adspersus, it is expected that this invasion modifies the existing trophic interactions. To address this question, we experimentally investigated the feeding of the native P. adspersus and the invasive P. elegans on the benthic macroalga Cladophora glomerata and on the invasive gammarid amphipod Gammarus tigrinus. In the course of the experiment neither G. tigrinus nor Palaemon spp. had effects on filamentous macroalgae. The presence of prawns drastically increased the mortality of amphipods with no difference in the feeding efficiency between the two prawn species. To conclude, the alien prawn does not add an extra function to the trophic system of the coastal ecosystem of the Baltic Sea. Nevertheless, due to its progressively increasing densities and wide habitat range, P. elegans is expected to exert stronger predation pressure on gammarid amphipods as compared to P. adspersus alone.

Disturbance-related patterns in unstable rocky benthic habitats of the north-eastern Baltic coast

Distinct patterns of benthic flora and fauna are produced when unstable rocky substrata are disturbed by water motion. This study investigated occurrence of disturbance-related patterns in benthic boulder habitats on the north-eastern Baltic coast. Sessile assemblages, mostly algae on tops of boulders and barnacles and bryozoans underneath, were found to differ between small (50–150 cm2 upperside surface area) and large (200–800 cm2) boulders. Densities of motile gammaridean amphipods were negatively correlated with boulder size. These patterns may be due to small boulders being displaced by water motion more frequently than large ones. Most of the barnacle shells/tests were remnant empty ones, and the proportion of empty tests and living barnacles was similar underneath small and large boulders, suggesting that degradation/removal of empty tests was not influenced by disturbance associated with boulder size. There was no consistent evidence of algae being affected by boulder size, but the tops of boulders had less algae than the edges, a pattern that is typically associated with high rates of overturning. Confirmation of disturbance as having caused these patterns and thus being an important process for structuring benthic biota in this region could be achieved by further manipulative experimentation.

Grazer Functional Roles, Induced Defenses, and Indirect Interactions: Implications for Eelgrass Restoration in San Francisco Bay

Understanding the individual and interactive roles of consumer species is more than academic when the host plant is a subject of intense conservation interest. In a mesocosm experiment, we compared effects of common invertebrate grazers in San Francisco Bay seagrass (Zostera marina, eelgrass) beds, finding that some species (a native opisthobranch, Phyllaplysia taylori; a native isopod, Idotea resecata; and an introduced gastropod, Ilyanassa obsoleta) enhanced eelgrass growth through removal of epiphytic algae, as is often predicted for small invertebrate grazers on seagrasses, while one (an introduced caprellid amphipod, Caprella cf. drepanochir) had neutral effects. In contrast, the putatively-introduced gammaridean amphipod, Ampithoe valida, had strong negative effects on eelgrass (in addition to epiphytes) through consumption, as we had previously observed in the field during restoration programs. We tested whether other common grazer species could influence the effects of the eelgrass-grazing Ampithoe, and found that Idotea induced production of phenolic compounds and limited eelgrass damage by Ampithoe, without affecting Ampithoe abundance. These results have implications for restoration strategies, and contribute to a growing awareness of the importance of trait-mediated indirect grazer interactions through grazer-induced changes in plant traits, providing the first example in a seagrass system.

New data on the Gammaridean amphipoda species composition of the Vietnam nearshore waters

New data on the Gammaridean amphipoda species composition of the Vietnam nearshore waters

New data on the gammaridean amphipoda species composition of the Vietnam Nearshore waters

New data on the gammaridean amphipoda species composition of the Vietnam Nearshore waters

Variation at multiple trophic levels mediates a novel seagrass-grazer interaction

Herbivores can have highly variable effects across their ranges, sometimes with unanticipated effects on trophic dynamics that in turn affect management and conservation programs. In seagrass beds, small invertebrate grazers (mesograzers) are expected to benefit the habitat-forming plants by removing competing algae; however, harm by mesograzers has been documented increasingly in a number of regions. In San Francisco Bay, California, USA, a gammaridean amphipod (Ampithoe valida), native to the US East Coast and putatively introduced to Pacific coastlines, reaches outbreak densities and consumes large quantities of eelgrass Zostera marina, while it is not known to do so elsewhere in its range. Using a series of mesocosm experiments, we manipulated predator (fish) identity and density, herbivore assemblage, and habitat complexity to test how variation at multiple trophic levels influences the abundance and role of A. valida. Reductions in A. valida abundance by native San Francisco Bay shiner surfperch and bay pipefish were less pronounced than by a pinfish brought in from North Carolina, USA; however, the former 2 predators enhanced eelgrass biomass, while consumption of both amphipods and eelgrass by pinfish netted limited benefits to eelgrass. Increasing density of the surfperch in a separate experiment did not further reduce A. valida abundance but nonetheless strengthened positive effects on eelgrass, presumably through behavioral response to increased threat. The presence of a second (introduced) grazer reduced predation pressure on A. valida, weakening the trophic cascade to the detriment of eelgrass. Increasing habitat complexity by substituting flowering shoots reduced predation success, leading to higher A. valida abundances. Our results point to the importance of predator control of A. valida to reduce eelgrass damage; however, the strength of the trophic cascade across this grazer’s range is likely to be modulated by composition of predator and grazer assemblages as well as flowering rates and phenology.

Laboratory study of the effect of salinity and ionic composition of water on the mortality and osmoregulation of the gammarid amphipod Dikerogammarus haemobaphes (Eichwald, 1841): implications for understanding its invasive distribution pattern

The effect of salinity and ionic composition of ambient water on the mortality of the Ponto-Caspian gammarid amphipod Dikerogammarus haemobaphes (Eichwald, 1841) was measured in the laboratory and an osmoregulatory curve plotted. A three-day experiment showed that salinities both higher (15, 20 PSU) and lower (0.1, 3.5 PSU) than 7 PSU reduced survival. Salinity levels of 0.1 and 20 PSU were lethal after 20 and 55 h of exposure, respectively. Among the ions analysed (Cl−, , Na+, K+, Ca2+, Mg2+), Cl− and K+, and the ratios of Na+/K+ and Na+/Cl− had the greatest influence on the mortality of D. haemobaphes. Mortality was zero in waters where the concentrations and ratios of these ions most closely resembled those prevailing in the Caspian Sea. The osmoregulatory curve shows that D. haemobaphes is a eurytopic species i.e. osmoregulation is hyperosmotic within the salinity range of 0.1–20 PSU. The results of this study indicate ways in which inherent physiological capabilities affect the ability of an organism to tolerate environmental conditions outside its historical range. The results suggest some ways in which anthropogenic changes may have affected the spread of this species beyond its original range.

Diet composition and feeding ecology of the naked goby Gobiosoma bosc (Gobiidae) from four western Atlantic estuaries.

The feeding ecology of the small-bodied benthic naked goby Gobiosoma bosc, a western Atlantic species that occurs in estuaries and other inshore habitats from Connecticut to Texas U.S.A., was investigated in a total of four estuaries spanning South Carolina, North Carolina, Maryland and New Jersey. Gut content analysis of 391 individuals revealed that G. bosc is a benthic microcarnivore that feeds primarily on polychaetes, gammarid amphipods and harpacticoid copepods. Diet composition varied with body size, tidal creek within an estuary and geographic region. Analyses of gut fullness suggest that G. bosc is a daytime visual predator and that nest and egg guarding during the reproductive season reduce foraging activity in mature males. Additionally, G. bosc infected with adult digenean parasites of the gut foraged more intensely than uninfected individuals, a relationship that was strongest for reproductively mature males. Regionally, significant variation in dietary breadth was documented and may reflect a foraging response to a decrease in prey diversity moving from estuaries of higher salinity and lower latitude to estuaries of lower salinity and higher latitude. These results contribute to an understanding of the life history of G. bosc and the role played by this common species in estuarine food webs.

남해안 동대만 잘피밭에서 서식하는 해마(Hippocampus coronatus)의 출현량 및 먹이습성

A total of 164 individuals of Hippocampus coronatus were collected from an eelgrass bed in Dongdae Bay, Korea from September 2006 to August 2007. The number of individuals of H. coronatus was higher in September 2006. The size of H. coronatus ranged from 2.4 to 9.3cm in height (Ht), and most of individuals were small size below 5cm (Ht). H. coronatus was a carnivore which consumed mainly gammarid amphipods and copepods. Its diets also included a small amount ofmysids, ostracods, brachiopods, caprellid amphipods, bathynellaceas, isopods, tanaids, and ascothoracids. The diets of H. coronatus underwent size-related changes; smaller individuals consumed copepods, while larger individuals ate gammarid amphipods and mysids. The dietary breadth index of H. coronatus was increased with increasing of their size.

First Recorded Family Odiidae (Crustacea, Amphipoda, Gammaridea) from the Korean Coast, with Description of Newly Recorded Species

A newly recorded species of gammaridean amphipod, Cryptodius kelleri (Br<TEX>$\ddot{u}$</TEX>ggen, 1907) belonging to the family Odiidae Coleman and Barnard, 1991 collected from the east coastal area of Korea. Cryptodius kelleri (Br<TEX>$\ddot{u}$</TEX>ggen) is characterized by the medially expanded maxillipedal palp article 2, smooth dorsal pereonites, propodochelate gnathopod 1, subchelate gnathopod 2, lacking the posterior process on the basis of pereopods 5-7, dorsal carination of pleonite 3, posterolateral upturned process of pleonite 3, and an entire telson. The species is described and fully illustrated in the present study. A key is also provided to the species of genus Cryptodius. This is the first record of the family Odiidae from Korea.

Detached macroalgae: Its importance to inshore sandy beach fauna

Kelp forests shed a large proportion of their biomass through storm-mediated defoliation, senescence of kelp blades, and constant erosion of particulate organic matter from the kelp fronds. Much of this detached macroalgae drifts in the water column and is deposited on intertidal zones of beaches. Detached macroalgae may provide inshore sandy beach fauna with refuge and food subsidies in an exposed and bare environment, with limited in situ primary production. We evaluated the relationship between detached macroalgae and the density of inshore fauna, where ‘inshore’ was the body of water extending from low water seawards for approximately 50 m. Inshore fauna were sampled using a push-net (1 mm mesh) on 11 beaches, and using a beam-trawl (4 mm mesh) on a subset of 8 beaches. On each beach, the density of detached macroalgae in the water column was quantified, together with a suite of physico-chemical beach characteristics. Push-net samples principally comprised omnivorous and detritivorous crustaceans such as gammarid amphipods, mysids and valviferan isopods, which have limited swimming abilities and reside inshore year-round. Beam-trawl fauna were mainly carnivorous decapods and fish, which undergo seasonal inshore-offshore migrations to utilize sandy beaches as nursery habitats. Linear models predicted increases of 11% (95% CI: 3.5–19%) and 2.4% (95% CI: 0.7–4.2%) in the density of push-net and beam-trawl fauna, respectively, with a 1 ℓ.100 m−3 increase in detached macroalgae. This suggests that detached macroalgae is more important in the provision of food and shelter to small, weak-swimming detritivores/omnivores than to larger and more mobile predators. The densities of large predators were mostly explained by physical beach characteristics, which overshadowed the role of macroalgae. Maximum abundances of decapods and fish were found on wide, flat beaches with low wave heights. Large accumulations of macroalgae may inhibit the foraging efficiencies of predatory fauna such as decapods and fish, and restrict their abundance.

Mating patterns of Gammarus lacustris (Amphipoda: Gammaridae) from three populations across a gradient on the Tibetan Plateau

The large-male mating advantage and size-assortative mating are two different size-based patterns which deviate from random mating in Gammarus species. The size-assortative pairing in gammarid amphipods may have arisen for microhabitat segregation, loading constraints, sexual selection, or a combination of them. This study investigated the mating patterns of Gammarus lacustris from three populations along an altitudinal gradient in the northeastern Tibetan plateau. We demonstrated that the species shows a size-related non-random mating pattern. There is a strong sexual size dimorphism (SSD) in G. lacustris, which does not vary along the altitudinal gradient. The ultimate cause of male-biased SSD is likely the stronger selection acting on male than on female body size, either because large males have a higher mating success than smaller males (large male advantage at the highest elevation population), or because they mate with larger females with more fecundity in three populations, or both, which results in size-assortative mating of G. lacustris. Additionally, the loading constraint hypothesis (size-assortative patterns potentially increased their fitness in fast-flowing water) cannot be excluded.