Vertical distribution of chitons (Mollusca: Polyplacophora) in the rocky intertidal zone of central Chile

The patterns of vertical distribution of chitons in various exposed rocky shore habitats of central Chile are described. The density and size of the individuals were determined at different levels on intertidal rock walls, in pools and on boulders. A group of four species was found on rock walls while another group of four species was found in tidal pools and on boulders. The species showed vertical separation on rock walls and segregation according to a range of increasing frequency of water movement in pools and on boulders. Only the two species with largest adult individuals (Acanthopleura echinata (Barnes) and Chitonlatus Sowerby) showed vertical segregation in size. Small-sized species and small individuals of large-sized species were found higher on rock walls or in zones where water movement is less; large chitons occur in zones of greatest water impact. This suggests that water movement may be a significant factor in setting the lower limits of distribution of these herbivores. Some of the species examined were extremely abundant (600·m^-2) with densities of one to two orders of magnitude greater than for other chiton species elsewhere.     

Vertical distribution of the European sardine (Sardina pilchardus) larvae and its implications for their survival

This study presents results of the vertical behaviour of theEuropean sardine (Sardina pilchardus) larvae as observed atsea off the NW Iberian coast during an oceanographic cruiseconducted in May 2002. Samples were taken in a grid of 38 stations(conductivity-temperature-depth [CTD] measurements and LonghurstHardy Plankton Recorder [LHPR] plankton hauls); a 69-h fixedstation study was also performed (hourly CTD measurements andLHPR/neuston hauls every 2 h). The horizontal distribution oflarvae is closely related to the circulation patterns measuredby a current metre-mooring array deployed during the cruise.Larvae were mainly distributed in the upper 20–25 m ofthe water column, in evident association with the waters ofthe Western Iberia Buoyant Plume (WIBP). Large (older) larvaeare found mainly in the surface layers, and larval size decreaseswith depth. A diel rhythm of migration to the neuston layerwas observed, correlated with the inflation/deflation activityof the swim bladder. Larvae with lengths greater than 12.5 mmand inflated swim bladders were only found in this layer. Consideringthe near surface stratification conditions for food availabilityand Ekman transport in the upper few metres, even small verticalmigrations of larvae can be very important for their survivaland subsequent recruitment success.     

Vertical distribution of coralline algae in the rocky intertidal of northern Chile

Studies on crustose corallines present in the intertidal region at three localities in northern Chile (30°S), show that these algae are well represented in exposed and protected sites, reaching up to 90% cover. Species composition differs between sites with the common occurrence of species or morphological variants of Spongites and a single taxon attributed to Phymatolithon at the most exposed sites, and species of Lithophyllum and Titanoderma at more protected localities. The two Lithophyllum taxa recorded are distinguished by the presence/absence of protuberances, cell size and degree of calcification, while Titanoderma taxa are segregated by the thickness of the thallus, hypothallic and perithallic cell size and shape. Spongites taxa are distinguished on the basis of external morphology and anatomical features such as cell size, degree of calcification and percentage of fusions between cells. The variability of these features within each species is still unknown thus, the taxa remain without specific epithet until further studies. Examination of specific types recorded for nearby regions are also required in order to clarify the taxonomy of the group in these coasts.     

Across-shelf transport of gastropod larvae in the central Bahamas: rapid responses to local wind conditions

Surveys for veliger larvae of the large gastropods Strombusgigas and Strombus costatus were carried out in duplicate transectsrunning offshore (0.26–5 km) from Lee Stocking Island,Exuma Cays, Bahamas. The across-shelf distribution of the larvaeduring the 1991 spawning season was highly variable over periodsof 3–6 days. Larvae of both species are known to inhabitthe upper few meters of the water column, and analysis of windstress patterns over the study period showed that across-shelfdistribution of the larvae was affected by wind forcing. Seaward(recruitment-unfavorable) transport near Lee Stocking Islandwas most highly correlated with wind stress toward the north-northwest(335–357). The resultant wind stress during the studywas toward 279, suggesting that recruitment of conch to nurserygrounds on the Great Bahama Bank in the Exuma Cays occurs underanomalous summer wind conditions. The correlation between theacross-shelf distribution of conch veligers and wind stresswas highest with extinction coefficients of 0.17–0.23in the exponentially filtered wind stress. This indicates thatlarval distribution over the 5-km-long transects responded rapidlyto changes in wind stress. Over 75% of the effective wind stressoccurred over just 6–8 h preceding collections; therefore,short-term changes in wind stress, such as afternoon strengtheningof the trade winds, may have a significant influence on across-shelflarval transport. ³Present address: Northeast Fisheries Science Center, NationalMarine Fisheries Service NOAA, 74 Magruder Road, Highlands,NJ 07732, USA     

Phytoplankton activity and standing crop in an impoundment of central Chile

Seasonal and spatial variations of the primary productivitywere measured in Rapel reservoir, Chile in 1976 and 1977. Chlorophylla, phytoplankton and several environmental factors were alsomeasured. The results show that primary productivity began toincrease in September, and remained at high levels until thefollowing June near the dam. The same pattern, slightly displacedin time (October – May) was observed near the main riverinflow areas. Standing crops were high at the beginning andat the end of those periods. The photosynthetic behavior ofthe phytoplankton was shown to be affected mainly by absolutelight availability and the dimension of the illuminated watercolumn. The phytoplankton composition and standing crop seemsto be controlled by water temperature and flow.     

Vertical distribution of zooplankton: density dependence and evidence for an ideal free distribution with costs

Background  

In lakes with a deep-water algal maximum, herbivorous zooplankton are faced with a trade-off between high temperature but low food availability in the surface layers and low temperature but sufficient food in deep layers. It has been suggested that zooplankton (Daphnia) faced with this trade-off distribute vertically according to an "Ideal Free Distribution (IFD) with Costs". An experiment has been designed to test the density (competition) dependence of the vertical distribution as this is a basic assumption of IFD theory.     

Vertical distribution of denitrification in an estuarine sediment: integrating sediment flowthrough reactor experiments and microprofiling via reactive transport modeling

Denitrifying activity in a sediment from the freshwater part of a polluted estuary in northwest Europe was quantified using two independent approaches. High-resolution N(2)O microprofiles were recorded in sediment cores to which acetylene was added to the overlying water and injected laterally into the sediment. The vertical distribution of the rate of denitrification supported by nitrate uptake from the overlying water was then derived from the time series N(2)O concentration profiles. The rates obtained for the core incubations were compared to the rates predicted by a forward reactive transport model, which included rate expression for denitrification calibrated with potential rate measurements obtained in flowthrough reactors containing undisturbed, 1-cm-thick sediment slices. The two approaches yielded comparable rate profiles, with a near-surface, 2- to 3-mm narrow zone of denitrification and maximum in situ rates on the order of 200 to 300 nmol cm(-3) h(-1). The maximum in situ rates were about twofold lower than the maximum potential rate for the 0- to 1-cm depth interval of the sediment, indicating that in situ denitrification was nitrate limited. The experimentally and model-derived rates of denitrification implied that there was nitrate uptake by the sediment at a rate that was on the order of 50 (+/- 10) nmol cm(-2) h(-1), which agreed well with direct nitrate flux measurements for core incubations. Reactive transport model calculations showed that benthic uptake of nitrate at the site is particularly sensitive to the nitrate concentration in the overlying water and the maximum potential rate of denitrification in the sediment.     

Vertical distribution behaviour and its spatial variation in late-stage larvae of coral-reef fishes during the day

Daytime vertical distribution behaviour of settlement-stage reef-fish larvae in the upper 18?m was documented by diver observations of 497 pelagic larvae of 7 species 100–1000?m offshore of Lizard Island, Great Barrier Reef. Four species were studied on 2 sides of the island. Depth amplitude and depth frequency differed among species, locations and times. Four pomacentrids had modal depths in the upper 30–50% of the water column. A lutjanid and 2 chaetodontids had modal depths 0–2?m deeper than the deepest-swimming pomacentrid. On the leeward side, 6 of 7 species swam deeper and/or more variably offshore. On the windward side, 1 of 4 species swam deeper or more variably offshore. No larvae swam deeper than 18?m on the leeward side, but 31% of larvae of 3 species did so on the windward side. Three of 4 species swam deeper and/or more variably on the windward than leeward side. Vertical distributions in relatively shallow water are apparently strongly influenced by water-column depth and bottom type.     

Distribution of euphausiid and decapod larvae in the spring plankton of the southern Barents Sea

New data have been obtained on the spatial distribution of the early developmental stages of Malacostraca in the mesozooplankton of the southern Barents Sea. In spring 2007, the euphausiid stages with the highest abundance (over 80%) were eggs and nauplii. Decapod larvae were represented by zoeae of Paralithodes camtschaticus, Pagurus pubescens, and Hyas araneus; their abundance was at most 1.5% of total zooplankton abundance. The larvaton groups dominant by abundance were furciliae of Euphasiacea (14.5 ± 6.2 mg/m³) and zoeae of P. camtschaticus (32.7 ± 15.9 mg/m³). The size structure of larval hemipopulations was similar over the studied water area. Comparison with data on the larval body length obtained in other areas of the sea leads to a conclusion on the independence of the decapod groups of Eastern and Western Murman.     

Vertical and radial profiles in tracheid characteristics along the trunk of Douglas-fir trees with implications for water transport

The main stems of three young Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirbel) Franco) trees were dissected to obtain samples of secondary xylem from internodes axially along the trunk and radially within each internode. From these samples, measurements were obtained of tracheid diameter, length, the number of inter-tracheid pits per tracheid, and the diameter of the pit membranes. In addition, samples were obtained along the trunks of three old growth trees and also a small sample of roots for measurement of tracheid diameter. A gradient was apparent in all measured anatomical characters vertically along a sequence among the outer growth rings. These gradients arose not because of a gradient vertically along the internodes, but because of the strong gradients present at each internode among growth rings out from the pith. Tracheid characteristics were correlated: wider and longer tracheids had more numerous pits and wider pits, such that total pit area was about 6% of tracheid wall area independent of tracheid size. A stem model combining growth rings in parallel and internodes in series allowed for estimates of whole trunk conductance as a function of tree age. Conductance of the stem (xylem area specific conductivity) declined during the early growth of the trees, but appeared to approach a stable value as the trees aged.     

Vertical distribution of organic constituents in an Antarctic lake: Lake Vanda

Vertical distribution of organic constituents, i.e. total organic carbon (TOC), extractable organic carbon with ethyl acetate (EOC), hydrocarbons, phytol, sterols, fatty acids and phenolic acids in Lake Vanda was studied to elucidate their features in relation to the stratification of lake water and the distribution of lake organisms. The concentrations of TOC, EOC and sterols increased with depth and attained the maximum values of 25 and 1.5 mgC l^–1 and 1.4 g l^–1 in the bottom, respectively, while those of fatty acids showed the maximum value of 61 g l^–1 at a depth of 55.4 m, along with the highest value of the ratio of unsaturated (UC₁₆, uC₁₈) to saturated (C₁₆, C₁₈) acids (8.5) and with the highest carbon preference index (35). Hydrocarbons were only found in the bottom layers (60.4 and 65.9 m) and bottom sediment. These results suggest strongly that the vertical distribution of lake organisms and their activity are quite different due to depth. In the bottom warm anoxic layers the degradation of organic materials must have occurred significantly and thus refractory organic materials should be concentrated.     

Vertical distribution of epiphytic bryophytes in an Indonesian rainforest

We studied species richness, composition and vertical distribution of epiphytic bryophytes in submontane rainforest of Central Sulawesi. Bryophytes were sampled on eight canopy trees and on eight trees in the forest understorey. Microclimate was measured at trunk bases and at crown bases. The total recorded number of 146 epiphytic bryophyte species is among the highest ever reported for tropical forests and underlines the importance of the Malesian region as a global biodiversity hotspot. Species composition differed significantly between understorey trees and canopy tree trunks on the one hand, and the forest canopy on the other. Fourty-five percent of the bryophyte species were restricted to canopy tree crowns, 12% to the understorey. Dendroid and fan-like species mainly occurred in the forest understorey whereas tufts were most species rich in the tree crowns. The findings reflect the different microclimatic regimes and substrates found in the understorey and in the forest canopy. The results indicate that assessments of the bryophyte diversity of tropical forests are inadequate when understorey trees and tree crowns are excluded.     

Vertical distribution of organic constituents in an Antarctic lake: Lake Fryxell

Vertical distribution of organic constituents, i.e. total organic carbon (TOC), hydrocarbons, fatty acids and hydroxy acids in water and sediment samples from Lake Fryxell (77° 35 S, 163° 15 E) of southern Victoria Land, Antarctica were studied to elucidate their features in relation to stratification of the lake waters and likely distribution of microorganisms. The TOC content of the surface water (5.0 m; just below the ice cover of 4.50 m thickness) was 1.4 mg l^–1. It increased markedly with depth and attained a maximum value of 21.7 mg C l^–1 at a depth of 17.5 m, but decreased to the bottom (13.3 mg C l^–1). The high TOC content of the anoxic bottom layers (> 15 m) is attributable to the concentration of refractory organic substances over long periods following the degradation of labile organic constituents. Hydrocarbons were not found in the water column, but the major constituent of the bottom sediment was n-C_{29 : 2} alkene. Total concentrations of fatty acids in the oxic layers ( 10 m) were highest at 10.0 m and much higher than those in the anoxic layers (> 10 m), probably reflecting the phytoplankton population. The content of branched (iso and anteiso) fatty acids and 3-hydroxy acids in the anoxic layers were much greater than those in the oxic layers which would seem to reflect the distribution of bacterial abundance. The differences of organic composition between the water column and sediments imply that sinking dead organisms were quickly degraded in the lake bottom. Also, the composition of microorganisms in the water column must be very different from that in the sediments.     

Conservation of temperate forest birds in Chile: implications from the study of an isolated forest relict

We characterize the bird assemblage of an isolated relict temperaterainforest (Santa Inés) in terms of its structure, composition anddynamics. The relict character and long-term isolation of this forest remnant,immersed in a matrix of semiarid scrub, provide a natural experiment to assessthe consequences of long-term isolation and forest area reduction for temperatebird species. Bird surveys were conducted in a forest fragment and thesurrounding scrub matrix between April 1999 (austral autumn) and October 2000(austral spring) on a seasonal basis. Within the forest fragment wedistinguished two microhabitat types: creeks and areas far from creeks (i.e.slopes). A total of 36 species were recorded in the study site, of which 21were inside the relict forest. Highest bird abundance and richness wererecorded during winter and spring, and these were always higher in creek plotsrather than slope plots. Comparisons between this assemblage and thosedistributed in the continuous temperate forest (located more than 900km southwards) indicate that this bird assemblage shares moresimilarities, with regard to bird species composition, to southern temperateforest localities and to other relict forests, than to nearer scrub habitats.However, there are eight species, endemic to temperate forests in southern SouthAmerica, missing from our system. In this regard, our analyses indicate thatthese eight endemic species should be of great conservation concern and willlikely be the ones that will go extinct first if the fragmentation of thetemperate forest continues.     

Biogenic amines and DOPA in the central nervous system of decapod crustaceans

The biogenic amines serotonin (5-HT), dopamine (DA), noradrenaline (NA), octopamine (OA) and the amino acid dihydroxyphenylalanine (DOPA) were identified and measured in the brain and the eyestalks of five decapod crustacean species using high pressure liquid chromatography (HPLC) with electrochemical detection. The amounts fall within 0.01-1.1 micrograms/g or 0.17-60 pmoles, and OA is the dominating amine in most species. THe DOPA levels in many of the species varied considerably between different measurements. It is concluded that the biogenic amines and DOPA are ubiquitous in the central nervous system of decapod crustaceans and the presence of NA and DOPA increases the number of presumed neurotransmitter/modulator candidates in the crustacean nervous system.     

Short-term dynamics of a Melosira population in the plankton of an impoundment in central Chile

Relationships among the chlorophyll-specific photosyntheticbehaviour of a Melosira-dominated phytoplankton, net variationsin the quantity of Melosira in suspension, the rates of sinkingloss of Melosira cells and did fluctuations in water-columnstability were investigated in Embalse Rapel. central Chile.The short study was carried out during the autumnal equinoxialperiod (March. 1984) of maximal Melosira abundance to determinethe extent to which these various components might contributeto the distinctly bimodal seasonal distribution of phytoplanktonabundance in this reservoir. Diurnal photosynthetic productionwithin the illuminated layer and supposed column respirationwere found to be of a similar order, suggesting that net increasethrough cellular growth was already substantially limited byself-shading. Thus observed net changes in the standing populationmay have depended more on the relative magnitude of sinkingloss rates and recruitment through resuspension, which processesare profoundly influenced by alternations in wind-induced mixingand intense, near-surface, thermal stratification. As the relativefrequency and duration of these episodes vary during the year,so does the capacity of the Melosira to maintain or increaseits standing biomass. High cellular photosynthetic efficiencycoupled with rapid sinking rate appear to be of selective advantagewhen the cycle of alternation is approximately diel. The applicationof these findings to the seasonal distribution of M. granulatain the Rapel reservoir and to the ecology of planktonic Melosirapopulations elsewhere is briefly discussed.     

Mucus secretion and transport in amphioxus larvae: organization and ultrastructure of the food trapping system, and implications for head evolution

A low-to-medium power transmission electron microscopy survey of the larval head of amphioxus was used to re-examine the position and constituent cell types of the mucus-secreting organs involved in feeding. Previously unreported features include cells with fibril-filled paraciliary processes in the recessed (pit) portion of the preoral organ, which probably assist in generating the mucus string produced by this structure, and the cell responsible for driving the current through the club-shaped gland, which appears to depend on a mechanism analogous to Archimedes' screw. Pharyngeal structures are dramatically repositioned during larval growth and metamorphosis. Mapping these changes shows that they are most easily explained if the positioning of the mouth is not directly controlled by the mechanism used to pattern the rest of the ventral pharynx. This accords with the predictions of the dorsoventral inversion hypothesis, which requires that an originally dorsal mouth in the inverted chordate ancestor be secondarily shifted to the ventral surface. It is argued here, on this basis, that the repositioning of the larval mouth in amphioxus, from the left side to the ventral midline, represents a partial recapitulation of past evolutionary events.     

The influence of coastal upwelling on the distribution of Calanus chilensis in the Mejillones Peninsula (northern Chile): implications for its population dynamics

A field experiment was carried out in October 1998 during active upwelling in a coastal area off the Mejillones Peninsula (23° S). Zooplankton was sampled at day and night, during two subsequent days at 4 stations inside and outside of the upwelling plume. Three depth strata were sampled: 0–20 m, 20–80 m and 80–200 m. Oceanographic data were obtained in a grid of 23 stations using a CTDO, a fluorometer and a Doppler current meter. Calanus chilensis was mostly represented by late stages, i.e. copepodid C5 and adult males and females. There were no day/night effects on vertical distribution, and abundance was significantly higher inside the upwelling plume in the upper 20-m layer at nearly 14 ind. m^–3, compared to ca. 5 ind. m^–3 outside the upwelling plume. Temperature at 10 m depth and biomass, estimated from stage numbers and their mean dry weights, were used to estimate growth and daily production of Calanus at temperature-dependent rates. The potential loss of biomass from the upwelling center because of advection in the upwelling plume was estimated from current data in the Ekman layer and biomass density. The mean cross-shelf component of the current was estimated at 10.4 km d^–1 within the upwelling plume. This yielded a loss of biomass of 9.7 mg dry weight m^–2 . Production, estimated by a temperature-dependent approach, ranged between 44 and 35 mg dry weight m^–2 d^–1, at mean temperatures of 14.6 °C and 15.8 °C inside and outside of the upwelling plume respectively. Within the plume, as much as 22% of daily production may be advected offshore. However, a higher concentration of biomass in the upwelling plume allowed a greater production compared to surrounding areas. A mass balance approach suggests that advective losses may not have a major impact on the C. chilensis population, because of very high daily production at temperature-dependent rates.     

The decline of an endangered temperate ecosystem: the ruil (Nothofagus alessandrii) forest in central Chile

We describe the current state of the ruil (Nothofagus alessandrii) forest, a rare and endemic temperate forest in central Chile. Because of a long history of land-use, the ruil forest has suffered intense deforestation and fragmentation. By 1991, there remained 352.2 ha of forest in 183 fragments, most of them small and regular and a few large and irregular. From 1981 to 1991 the forest disappeared at a rate of 8.15% per year, to our knowledge, the highest value reported in forest fragmentation. Fragments are surrounded by a matrix of Pinus radiata plantations. Only 42 ha of forest (12% of the total area) are protected in a public reserve. An analysis of the composition of the forest shows that 13.8% of the total species are introduced. Pinus radiata is the only tree that has invaded this forest successfully. The 45.4% of native tree species are shade-tolerant and dependent on biotic pollinators and dispersers. These species should be the targets for future conservation efforts as they are particularly sensitive to fragmentation. We conclude that the current situation of the ruil forest is critical, and it will disappear in the next decade unless we conduct an active strategy of conservation, including integrated efforts both inside and outside protected areas and between landowners and public agencies.