Search

The long-term dynamics of production of the glacial relict amphipod Monoporeia affinis was examined in a small subarctic lake. The aims of this study were: (1) to compare the production of amphipods with their biomass; (2) to relate the changes in amphipod population with environmental variables. I hypothesized secondary production could provide better insight into M. affinis population dynamics, than abundance and biomass alone. Production (increment-summation method) and its standard error were estimated based on benthic samples taken at a sublittoral site from June 2002 to May 2019 (as a rule, 4–5 times a year). Production and biomass were highly correlated with each other. The annual P/B ratio varied twofold. However, the majority of estimates did not differ significantly from the mean P/B value for the study period. Effects of environmental variables (water temperature and chlorophyll-a concentration) were pronounced for offspring and juvenile amphipods only. The older amphipods showed no significant correlation with any environmental variables. Despite the initial prediction, no reliable evidence was found that production revealed greater insight into population dynamics of M. affinis. This long-term study confirms that benthic production is mainly a function of biomass. [ABSTRACT FROM AUTHOR]

In most European freshwater ecosystems, the invasive gammarids Gammarus tigrinus and Dikerogammarus villosus strongly impair recipient communities through predation of a wide range of native invertebrates. Due to the effects of temperature on both the physiology and the behaviour of such ectotherms, understanding how global warming may influence their ecological impact is a research priority. These species were therefore exposed to three different food types to determine their detritivorous, herbivorous and carnivorous characters, and predation was measured characterizing the Holling's functional response. The effect of increasing water temperatures (15, 20, 25°C) on both the food choice and predatory activities was investigated. Both species showed a significant preference for animal tissues at all temperatures. The total food intake increased with temperature for G. tigrinus but did not change for D. villosus, which may result from specific species differences in metabolic requirements. The consumption of live prey strongly increased with temperature. The main differences were an increased searching efficiency in G. tigrinus and a decreased handling time in D. villosus as temperature increased, which may result from differences in foraging strategies. These results suggest that climate change is likely to increase the predation pressure of both invasive gammarids on prey species. [ABSTRACT FROM AUTHOR]

Macrophyte complexity has been associated with high abundance and richness of macroinvertebrates. While the effect on richness has been attributed to an increase in the number of niches, the effect on abundance has been explained by a higher availability of space for small individuals, refuge, and/or food. For studying effects of complexity on macroinvertebrates, we used complementary approaches of laboratory choice and field colonization experiments, with macrophytes ( Egeria densa and Elodea ernstae) and plastic imitations of contrasting fractal dimension. We investigated whether macroinvertebrates may actively select complex habitats by Hyalella sp. choice experiments. Then, we tested effects of complexity on macroinvertebrate density, biomass, richness, diversity, and body size using colonization experiments. Finally, a caging experiment was performed to study interacting effects of complexity and predation. The active choice of complex substrates by Hyalella sp., and the significant positive relationship between macrophyte fractal dimension and macroinvertebrate density support the existence of a positive effect of complexity on abundance. As macroinvertebrate length was not associated with fractal dimension, such differences could not be attributed to a higher space available for smaller invertebrates in complex plants. Finally, neither macroinvertebrate density nor size was reduced by fish predation in the Las Flores stream. [ABSTRACT FROM AUTHOR]

Deposits of detached macrophytes, known as wrack, are a common feature on shore lines and can represent an important subsidy of organic material from subtidal systems to low productivity intertidal and terrestrial systems. On beaches, these support high densities of consumers that have an important role in wrack decomposition. The feeding behavior of wrack consumers is poorly known relative to the marine herbivores that consume marine macrophytes in situ. To understand how feeding behavior relates to the quality of wrack for an abundant wrack consumer, the talitrid amphipod Notorchestia sp., we test for habitat preferences, differences in feeding rates, and survival among four species of macroalgae and seagrasses in an estuary in New South Wales, Australia. Notorchestia displayed strong preferences for Sargassum sp. and Zostera capricorni as habitat, but consumed only Sargassum in feeding experiments, and only this alga supported high survival in a longer term performance assay. The differences in food quality, as measured by survival over 30 days, did not translate to differences in the abundance of amphipods colonizing each food resource in the field. Our results suggest that feeding by Notorchestia will result in the rapid loss of Sargassum in the wrack, and that other consumers or microbial degradation may be more important in the decomposition of seagrass. [ABSTRACT FROM AUTHOR]

Parasitism is emerging as one of the forces determining the outcome of biological invasions. Using field survey and laboratory experiments, we investigate parasitism as one of the factors mediating the interactions among invasive and native amphipods. An extensive survey (100 sites) of a small British island, revealed the native Gammarus duebeni celticus to be parasitised by the muscle wasting microsporidian Pleistophora mulleri and the acanthocephalan duck parasite Polymorphus minutus, the introduced European Gammarus pulex only by P. minutus and the North American Crangonyx pseudogracilis by neither. While Gammarus spp. were widespread in rivers (one or both species present in 64% of sites), C. pseudogracilis had a restricted distribution (7% of sites) and always co-occurred with Gammarus spp. In contrast, Gammarus spp. were absent from all pond/reservoir sites, with C. pseudogracilis present in over 90%. While the negative association of C. pseudogracilis with Gammarus spp. undoubtedly results from factors such as physico-chemical tolerance and predation as C. pseudogracilis can be heavily predated by Gammarus spp., it was notable that C. pseudogracilis co-occurred with Gammarus spp. more frequently when the latter were parasitised. Laboratory experiments clearly showed that predation on C. pseudogracilis was greatly diminished when G. d. celticus was parasitised by P. mulleri and G. pulex by P. minutus. Our study provides evidence that parasitism, by mediating a key interspecific interaction, is one of an array of interacting factors that may have a role in driving patterns of exclusion and co-existence in natives and invaders. [ABSTRACT FROM AUTHOR]

While the intensity of global shipping has increased dramatically over the last decades, species exchange between continents has likewise intensified. Ballast water of ships is recognized playing a major role in this process. Many of the larger sea ports have become bridgeheads for invasions. Ecological niche modeling is used to investigate the potential invasive range and high invasive risk ports of the North American amphipod Gammarus tigrinus. Sixty-two occurrences of G. tigrinus in its native range (North America) and 34 environmental data sets were compiled. Data on dispersal distances were used via ecological niche modeling to analyze the invasive potential of G. tigrinus. The invasive risk of large ports was analyzed according to modeling result, as well as their salinity in the main oceanic routes of the world. G. tigrinus had a rapid range extension on the British Isles and in the rest of Western Europe. Now it is invading the countries surrounding the Baltic Sea. Worldwide it has a vast potential invasive range. It has a high invasive risk for many large ports along the main oceanic routes, among which the ports of Shanghai, Buenos Aires and Montevideo have the highest invasive risk. G. tigrinus may become cosmopolitan through shipping, and this possibility is increasing. Particular emphasis should be placed on preventing human-mediated dispersal. Ports may be the first places G. tigrinus invades. This study can identify high invasive risk ports, especially those at risk of introduced North America species. More importantly, the water of large ports should be monitored regularly for exotic aquatic organisms that may survive temporarily or permanently. [ABSTRACT FROM AUTHOR]

The objective of the present study was to evaluate previously reported compartment models as a predictive tool, in particular, to investigate the potential of nonlinear predictions in case of saturation of the uptake process. Examples supporting this idea are presented for the amphipods Gammarus oceanicus from northern Norway and Themisto abyssorum from the Greenland Sea as well as for the copepod Calanoides acutus from the Weddell Sea. A further objective was to investigate verification of model parameters with independent experimental observations, aided by the statistical analysis of the results. This can be regarded as a first step toward a meta-analysis. While modeling results obtained for T. abyssorum in 1993 underestimated observed uptake of Pb and Cu in independent experiments (1999) in the same species, a good agreement was encountered between models obtained for T. abyssorum in 1993 and experimental data obtained for Themisto libellula (1999). Furthermore, a fairly good agreement was found between modeling results obtained for Pb in Calanus hyperboreus from the Greenland Sea (1993) and experimental data obtained for C. acutus (1999). Therefore, the biological species cannot be regarded as a “natural” unit in biomonitoring studies without further evaluation (viz. calibration as biomonitor), while even samples of animals belonging to different species may serve as such a unit, allowing for a comparison of bioaccumulation on large temporal and spatial scales. Finally, the concept of the sensitivity of zooplankton organisms for biomonitoring was elaborated in detail. These procedures involve analytical and experimental variability and model simulations based on previously derived parameters of compartment models. The minimal increments in exposure concentrations estimated in this way were 0.4–1.2 μg Pb l−1 for T. abyssorum, T. libellula, C. hyperboreus, and C. acutus. Corresponding results for Cu varied to a greater extent: 4–9 μg l−1 for the amphipods and 1–5 μg l−1 for the copepods. A correction of these values is proposed, taking into account the ratios of experimental (kinetic) and field bioconcentration factors; this yields exposure concentrations close to those reported for natural seawater. [ABSTRACT FROM AUTHOR]

We examined the seasonal diet of juvenile (≤32 mm total length) common bullies, Gobiomorphus cotidianus, in Lake Waihola, South Island, New Zealand and whether they preyed selectively on the amphipod, Paracalliope fluviatilis, which was a dominant prey item. Generally, ≥75% of all fish sampled had consumed amphipods, which comprised 80%, or more, of the total prey volumes in fish stomachs over most of a year except on one sampling occasion. Copepods, snails, chironomids, Daphnia, mysids and isopods also contributed to the diet. Comparisons of the size distribution of amphipods in fish stomachs and the lake on the date of sampling showed that on four occasions, juvenile bullies selectively consumed small amphipods. No selective feeding was detected on the other occasions. The dominance of primarily benthic amphipods in the diet of juvenile bullies which, in turn, are preyed on by piscivores, suggests a strong benthic-pelagic link in the transfer of energy in Lake Waihola. [ABSTRACT FROM AUTHOR]