Buoyancy Changes as Related to Respiratory Behavior in an Amphibious Snail, Pomacea Urceus (Müller), from Venezuela

The ampullariid Pomacea urceus uses its ctenidium and lung in respiration. The snails reach the surface with their siphon and ventilate their lung by withdrawing their head-foot in a pumping action. The lung gas also serves to change the buoyancy of the snails. After a ventilation a snail does not necessarily return to the same buoyancy level. They may achieve overall specific gravities of \u3c1 to \u3e 1 after a ventilation. They may remain submerged (s.g. \u3e 1) or float (s.g

Early and Middle Holocene Hunter-Gatherer Occupations in Western Amazonia: The Hidden Shell Middens

We report on previously unknown early archaeological sites in the Bolivian lowlands, demonstrating for the first time early and middle Holocene human presence in western Amazonia. Multidisciplinary research in forest islands situated in seasonally-inundated savannahs has revealed stratified shell middens produced by human foragers as early as 10,000 years ago, making them the oldest archaeological sites in the region. The absence of stone resources and partial burial by recent alluvial sediments has meant that these kinds of deposits have, until now, remained unidentified. We conducted core sampling, archaeological excavations and an interdisciplinary study of the stratigraphy and recovered materials from three shell midden mounds. Based on multiple lines of evidence, including radiocarbon dating, sedimentary proxies (elements, steroids and black carbon), micromorphology and faunal analysis, we demonstrate the anthropogenic origin and antiquity of these sites. In a tropical and geomorphologically active landscape often considered challenging both for early human occupation and for the preservation of hunter-gatherer sites, the newly discovered shell middens provide evidence for early to middle Holocene occupation and illustrate the potential for identifying and interpreting early open-air archaeological sites in western Amazonia. The existence of early hunter-gatherer sites in the Bolivian lowlands sheds new light on the region's past and offers a new context within which the late Holocene "Earthmovers" of the Llanos de Moxos could have emerged. © 2013 Lombardo et al

Geographic and seasonal patterns and limits on the adaptive response to temperature of European Mytilus spp. and Macoma balthica populations

Seasonal variations in seawater temperature require extensive metabolic acclimatization in cold-blooded organisms inhabiting the coastal waters of Europe. Given the energetic costs of acclimatization, differences in adaptive capacity to climatic conditions are to be expected among distinct populations of species that are distributed over a wide geographic range. We studied seasonal variations in the metabolic adjustments of two very common bivalve taxa at European scale. To this end we sampled 16 populations of Mytilus spp. and 10 Macoma balthica populations distributed from 39° to 69°N. The results from this large-scale comprehensive comparison demonstrated seasonal cycles in metabolic rates which were maximized during winter and springtime, and often reduced in the summer and autumn. Studying the sensitivity of metabolic rates to thermal variations, we found that a broad range of Q10 values occurred under relatively cold conditions. As habitat temperatures increased the range of Q10 narrowed, reaching a bottleneck in southern marginal populations during summer. For Mytilus spp., genetic-group-specific clines and limits on Q10 values were observed at temperatures corresponding to the maximum climatic conditions these geographic populations presently experience. Such specific limitations indicate differential thermal adaptation among these divergent groups. They may explain currently observed migrations in mussel distributions and invasions. Our results provide a practical framework for the thermal ecophysiology of bivalves, the assessment of environmental changes due to climate change and its impact on (and consequences for) aquaculture

Seasonal Respiratory Variation and Acclimation in the Pea Clam, Pisidium Walkeri Sterki

1. Seasonal respiratory variation at field temperatures and at 10° and 20°C are presented for field acclimated clams. Values are presented as QO2s based on shell-free tissue dry weight and shell-free tissue N2. 2. Q10 values are presented for all seasons with winter and summer values of about one and three respectively. 3. No size rate differences were found for measurements of oxygen consumption. 4. The seasonal acclimation pattern is complex with the data of early spring indicating Precht\u27s Type I pattern of over-compensation for the over-wintering generation and some of the summer-fall data suggesting Precht\u27s Type V reverse acclimation for the summer generation. Seasonal acclimation is discussed in an ecological-environmental context. © 1976

Effect of water removal on introduced caddisflies from a tropical mountain stream

Tropical island streams worldwide are being threatened by existing or proposed dams and diversions. Numerous streams of the Hawaiian Islands have diversions that remove freshwater for human use; however, little research has addressed diversion effects on aquatic insect communities in tropical streams. We studied the effect of water removal by a stream diversion on density and biomass of two introduced Trichoptera, Cheumatopsyche analis (Banks) (Hydropsychidae) and Hydroptila potosina (Buenoa-Soria) (Hydroptilidae), in Iao Stream, Maui, Hawaii, from April-August 2000. Both species seem to have multivoltine life cycles. Pooled Trichoptera (both species) biomass was significantly greater above the diversion (178.3 mg.m-2 and 112.9 mg.m-2 for upstream and downstream, respectively). For each individual species the mean total instar biomass was significantly reduced below the diversion (38 % and 54 % reduction for C. analis and H. potosina, respectively). Both species had greater densities above the diversion; however, individual larval mass of H. potosina instars, but not C. analis instars, was significantly lower below the diversion. Our results suggest that reduced habitat quality, due to lowered stream flow, limits density of both species below the diversion, whereas lowered food quantity and quality may differentially affect H. potosina biomass through reduced body sizes. These data suggest that water removal not only reduces habitat quality, but significantly lowers the community biomass of these introduced Trichoptera species, affecting the trophic energetics of stream reaches downstream of a diversion in Hawaii. Similar changes to macroinvertebrate communities would be expected below dams and diversions of streams in other tropical regions

Life cycle of a torrenticolous Hawaiian chironomid (Telmatogeton torrenticola) : stream flow and microhabitat effects

In this study we documented the instar densities and life cycle of Telmatogeton torrenticola Terry (Chironomidae : Telmatogetoninae) from Kinihapai Stream, Maui, Hawaii. Greatest larval densities of this midge are found on substrates of high velocity, shallow flows of cascades, and splash zones of waterfalls, with lower densities in riffles. In the summer of 1994 we compared the effects of two microhabitats (termed optimal and suboptimal) on inter-instar density and relative abundance. In a second year (1995), we evaluated the effect of long-term reduced stream flow on these variables only in optimal microhabitats. A significant reduction in stream flow from 1994 to 1995 was correlated with a similar reduction in larval densities that precluded larval colonization of suboptimal habitats in 1995, thereby preventing sampling in this microhabitat during that summer. Depth of optimal habitats of 1995 were significantly shallower than both habitats of 1994, with suboptimal habitats of 1994 the deepest. Total larval density was significantly higher in 1994 optimal habitats, while 1994 suboptimal and 1995 optimal habitats were statistically similar. Individual instar densities showed variable differences among habitats and years, with the first three instars always highest in 1994 optimal habitats. All instars and pupae were collected on most sampling dates in both years ; however, pupae were only collected on a two dates in suboptimal habitats of 1994. Based on larval size frequency histograms, T. torrenticola has a multivoltine, asynchronous life cycle, with continuous reproduction, which is variable among microhabitats characterized by different flow velocity and depth, and between years of differing stream discharge. Reduced stream flow during the summer of 1995 had effects of reducing densities and changing life cycle features similar to those found in 1994 (a year of higher stream flow) suboptimal habitats

The Ratio of Calcareous and Organic Shell Components of Freshwater Sphaeriid Clams in Relation to Water Hardness and Trophic Conditions

Shells from 14 populations of sphaeriid clams including Sphaerium striatinum, S. simile, Pisidium walkeri, Musculim partumeium and M. iransversum were analyzed for organic carbon (μgC mg−1 shell), nitrogen (μg,N mg−1 shell) and CaCOs (%CaCO3 of total clam dry weight). Habitat waters were assessed for total hardness (expressed as ppm CaCo3), ppm Ca, ppm Mg, conductivity (μmho) and suspended organic Carbon (μgCl−1). For all populations, shell organic C and N are positively correlated and there is an inverse relationship between the amounts of shell CaCO3 and shell organic carbon. Trophic considerations give the best correlation with shell type at the generic level of consideration since species of Musculium are found at the opposite end of the trophic scale (eutrophic) from all other populations studied. For S. striatinum, the most extensively studied species, the amount of shell CaCO3 is inversely related to water hardness. The selection of shells in the Sphaeriidae is discussed in relation to structural-functional needs and habitat conditions

Substrate Roughness, Velocity Refuges, and Macroinvertebrate Abundance on Artificial Substrates in the Lower Mississippi River

Articulated concrete mattress blocks (ACM) are now used almost exclusively for erosion control of banks along the lower Mississippi River (LMR) and provide habitat for macroinvertebrates and fishes which could not otherwise colonize the unstable substrate of the natural river channel. We studied the distribution and abundance of macroinvertebrates in the LMR on ACM blocks with smooth, rough, and grooved surfaces. Additionally, the effects of block surface modifications on substrate velocity profiles were determined at three flow velocities in a laboratory flume using a thermistor-based current meter. Total density of macroinvertebrates and the densities of individual taxa were significantly different on the three surface types after 3 mo of colonization; rough blocks had 1.4× greater densities than smooth blocks, and densities on grooved blocks were 2.3× higher than smooth and 1.6× higher than rough blocks. The caddisfly Hydropsyche orris and the amphipod Corophium lacustre were significantly denser on grooved than on the other block types. In a flume, velocities in groove bottoms were 7-24× lower than ambient water column velocities (0.12, 0.23, and 0.44 m/s) and increased significantly from 1 mm to 65 mm above the block surface at all flume velocities. For all surface types there was a negative relationship between height above the block surface and measured variance in velocities and a positive relationship between flume velocities and the measured variance in velocity readings which could be attributed to increased turbulence over the block surfaces. In the field, H. orris in grooves built retreats with the anterior opening containing the feeding nets extending up into the near-surface flows over the grooves. Low velocity eddies in the grooves provided a velocity refuge while still allowing the feeding structures to contact feeding flows over the block surface. Grooved blocks in the LMR supported, on average, more than twice the invertebrate density as smooth blocks, and are recommended for future deployment of mattress blocks