Latitudinal range of epiplanktonic chaetognatha and ostracoda in the western tropical Indian Ocean

An account of the chaetognath and ostracod species obtained from zooplankton samples collected along a transect in the Western Indian Ocean between 9° N–20° S and 57° 18–68° 43E in January–February 1981 is given. Species richness was maximum north of 10° S. The latitudinal variation of thirteen species of chaetognaths indicated that many of the typical Indo-Pacific species are restricted to the tropical zone with limited penetration into the subtropical region. All the sixteen species of planktonic ostracods were cosmopolitan. Based on the available information on the distribution of chaetognaths and ostracods, the species assemblages in the Indian Ocean are discussed.     

Detailed analysis of the microdiversity of Prochlorococcus populations along a North-South Atlantic Ocean transect

In order to understand how environmental factors shape the diversity of Prochlorococcus in the Atlantic Ocean, we have elucidated the microdiversity along a north–south transect. The polymerase chain reaction-restriction fragment length polymorphism analysis of the genetic diversity of rpoC1 gene fragments of Prochlorococcus at 12 sampling sites revealed a latitudinal pattern in Prochlorococcus RFLP-type diversity in the samples collected from two depths. At the depth to which 14% of surface irradiance penetrated, HLII clones dominated the stations closest to the equator. The percentage of HLI clones increased with distance from the equator and LL clones were found only at the most northern and southern stations. In contrast, deeper (1% light depth) water samples did not show any overall trend in Prochlorococcus diversity or clade dominance. Multivariate statistical analyses indicated that Prochlorococcus diversity was linked to water temperature (partially an effect of latitude) and depth (which was linked to light penetration and turbidity). Phylogenetic analysis of the sequences obtained from the 423 different environmental RFLP-types detected in this study indicated that the HLII and HLI populations were composed of a wide range of genetically different clones, while the LL Prochlorococcus clade was less diverse, although half of the samples screened in this study derived from the 1% light depth.     

Distribution of myctophid resources in the Indian Ocean

Mesopelagics are one of the largest under-exploited marine resources with wide distribution in the world oceans. Lanternfishes are the key members of mesopelagic communities and the total resource in the world oceans is estimated at 600 million tons. Lanternfishes belong to the family Myctophidae which comprises of about 250 species in 35 genera. Myctophids account for about 75% of total global catch of small mesopelagic fishes. They are known to exhibit diel vertical migration, concentrating during the day time between 400 and 1,000 m, and between 5 and 100 m, during the night. In this paper, an attempt is made to review the existing information on the occurrence and distribution of myctophid resources in the Indian Ocean. 137 myctophid species have been reported from the entire Indian Ocean. Studies in the Arabian Sea have indicated that the area is rich in the midwater fish stocks dominated by myctophids with an estimated potential of 100 million tons.     

Distribution of small phytoflagellates along an Arctic fjord transect

Phytoflagellates < 10 μm substantially contribute to the abundance, biomass and primary production in polar waters, but information on the distribution of specific groups is scarce. We applied catalysed reporter deposition‐fluorescence in situ hybridization to investigate the distribution of total phytoflagellates and of eight specific groups along a 100 km transect west off Kongsfjorden (Spitsbergen) from 29 to 31 July 2010. Phytoflagellates contributed to > 75% of the depth‐integrated abundance and biomass of total eukaryotes < 10 μm at all stations. Their depth‐integrated abundance and biomass decreased along the transect from 1.5 × 10¹² cells m^?2 (6.6 × 10¹² pgC m^?2) at the outermost station to 1.7 × 10¹⁰ cells m^?2 (4.7 × 10¹⁰ pgC m^?2) at the innermost station. Chlorophytes contributed to the total abundance of phytoflagellates with a range from 13% to 87% (0.7–30.5 × 10³ cells ml^?1), and predominated in open waters. The contribution of haptophytes was < 1–38% (10–4500 cells ml^?1). The other groups represented < 10%. The temperature and salinity positively correlated with the total abundance of phytoflagellates, chlorophytes, haptophytes, bolidophytes and pelagophytes. Cryptophytes, pedinellids and pavlovophytes were negatively associated with the nutrient concentrations. The community composition of phytoflagellates changed along the transect, which could have implications on food web dynamics and biogeochemical cycles between the open ocean environment and Kongsfjorden investigated here.     

Distribution of seagrasses along the Indian coast

Seagrass environments, from the main coast of India, Lakshadweep and Andaman Islands, were surveyed for seagrass and marine algal composition. Extensive seagrass meadows and the maximum number of species (seven genera and 12 species) occurred along the Tamil Nadu coast. Seagrasses were observed from intertidal to subtidal regions down to 8 m depth. Thalassia hemprichii (Ehrenberg) Aschers. and Cymodocea serrulata (R. Brown) Aschers. & Magnus were the dominant seagrasses in the subtidal zones. Halophila beccarii Aschers. was restricted to the intertidal mudflats in association with mangroves. The rich growth of seagrasses along the Tamil Nadu coast and Lakshadweep can be attributed mainly to high salinity, clarity of the water and sandy substratum. One hundred species of marine algae were recorded from the seagrass environments of India.     

Cobalamin and microbial plankton dynamics along a coastal to offshore transect in the Eastern North Atlantic Ocean

Cobalamin (B12) is an essential cofactor that is exclusively synthesized by some prokaryotes while many prokaryotes and eukaryotes require an external supply of B12. The spatial and temporal availability of B12 is poorly understood in marine ecosystems. Field measurements of B12 along with a large set of ancillary biotic and abiotic factors were obtained during three oceanographic cruises in the NW Iberian Peninsula, covering different spatial and temporal scales. B12 concentrations were remarkably low (<1.5 pM) in all samples, being significantly higher at the subsurface Eastern North Atlantic Central Water than at shallower depths, suggesting that B12 supply in this water mass is greater than demand. Multiple regression models excluded B12 concentration as predictive variable for phytoplankton biomass or production, regardless of the presence of B12-requiring algae. Prokaryote production was the best predictor for primary production, and eukaryote community composition was better correlated with prokaryote community composition than with nutritional resources, suggesting that biotic interactions play a significant role in regulating microbial communities. Interestingly, co-occurrence network analyses based on 16S and 18S rRNA sequences allowed the identification of significant associations between potential B12 producers and consumers (e.g. Thaumarchaeota and Dynophyceae, or Amylibacter and Ostreococcus respectively), which can now be investigated using model systems in the laboratory.     

Macrobenthos composition,abundance and biomass in the Arctic Ocean along a transect between Svalbard and the Makarov Basin

Macrofauna has been sampled at 30 stations, at water depths of 1018–4478 m, along a transect extending between Northern Svalbard and the Makarov Basin, as a basis for understanding aspects of the benthic ecology of the Arctic Ocean. Species numbers, abundances and biomasses were extremely low, and generally varied between 0 to 11/0.02 m², 0 to 850 individuals/m², and 0 to 82.65 g/m², respectively. A total of 42 species was found. The Amphipod Jassa marmorata was the most common species. Both numbers and biomasses of suspension-feeding species increased towards the Lomonosov Ridge, probably due to lateral transport of organic material by deep currents along the ridge.     

Pollen-rain-vegetation relationships along a forest-savanna transect in southeastern Cameroon

Modern soil and litter samples from southeastern Cameroon, collected along a continuous forest–savanna transect were analysed for pollen content to define modern pollen–vegetation relationships. The pollen results, completed and compared with botanical inventories, leaf area index and basal area measurements performed in the same area, clearly registered the physiognomy, the main floristic composition and floral richness of the two sampled ecosystems. Distortions were observed between sampled vegetations and their pollen rain, related to important differences in pollen production and dispersal of plant species: this is a general feature in many tropical regions. The pollen data in the area studied reflected well the recent transgression of forest versus savanna. This permitted us to define inside the forest ecosystem more successional vegetation communities than the botanical surveys allowed.     

Simulating vegetation processes along the Kalahari transect

The Sheffield Dynamic Global Vegetation Model has simulated the structure and net carbon exchange of vegetation at five sites along the Kalahari transect where there is a strong gradient in precipitation from 299 to 918 mm yr^?1. There has been a decline in precipitation of 8 mm yr^?1 along the whole of the transect since about 1970. Simulations of vegetation dynamics and structure indicate that this decline has exerted a notable effect on the vegetation, with reductions in woody plant cover at the dry end of the transect and reductions in tree density at the wetter end. These changes were driven primarily by reductions in the net primary production and increased rates of mortality, with rather small impacts of fire.     

Climatic calibration of 80 aeropollinic taxa along a European transect

The aim of calibration is to measure the relationships between climate and taxa, in order to use the taxa as indicators for the estimation of bioclimates. The indicator capacity of a taxon (ICT) measures the probability of two events, together or separately, either the ordering of abundance, within the range of a factor, or the confining of presences inside a limited part of the range. ICT is obtained from numbering inequalities or matches, on such orderings, without any arithmetical operation upon the initial data. ICT measures the indicator capacity of a taxon for a factor, even if the taxon is intermittent or if its gradient is irregular.ICT increases with the threshold of the sum of temperatures, for some taxa, such as Arbutus, Celtis, Cistus, Coriaria, Cupressaceae, Helianthemum, Olea, Onobrychis, Pistacia, Silene, Thymelaeaceae. These taxa indicate a superior threshold above the classical one of 0 °C. Conversely, ICT decreases when the threshold increases, for other taxa, such as Abies, Aesculus, Fraxinus, Juglans, Mercurialis, Populus, Resedaceae, Salix, Thalictrum, Tilia. A taxon may be an indicator for the whole range of a temperature, if its abundance increases rather regularly, such as Chenopodiaceae, Erica, Olea, Plantago, Tamarix, Umbelliferae, Vitis, or if its abundance decreases, as for Betula, Filicidae, Fraxinus, Juglans, Tilia. Conversely, some other taxa are indicators only in a part of the range, such as Calluna, Galium and Platanus.The indicator capacity is used to estimate the thermic climate according to the flora. For each taxon, ICT depends on A and F, which are the ranks of abundance and thermal factor. For a given rank A, observed in a spectrum, ICT depends on F; ICT is the probability of the spectrum to be in the rank F. The maximum value of ICT, for all taxa in the spectrum, indicates the probable rank of that spectrum. Along the transect, the estimated temperatures happen to be equal to the measured ones for all the tested spectra (except one) and for all the factors, even if a small part of the flora is tested.     

Methanogen communities along a primary succession transect of mire ecosystems

Peat accumulating mires are important sources of the greenhouse gas methane. Methane emissions and methanogenic Archaea communities have been shown to differ between fens and bogs, implying that mire succession includes an ecological succession in methanogen communities. We investigated methane production and the methanogen communities along a chronosequence of mires (ca. 100-2,500 years), which consisted of five sites (1-5) located on the land-uplift coast of the Gulf of Bothnia. Methane production was measured in a laboratory incubation experiment. Methanogen communities were determined by amplification of a methyl coenzyme M-reductase (mcr) gene marker and analyzed by terminal-restriction fragment length polymorphism. The terminal-restriction fragment length polymorphism fingerprinting resulted in 15 terminal restriction fragments. The ordination configuration of the terminal restriction fragments data, using nonmetric multidimensional scaling, showed a clear gradient in the methanogen community structure along the mire chronosequence. In addition, fingerprint patterns of samples from the water table level and 40 cm below differed from one another in the bog site (site 5). Methane production was negligible in the three youngest fen sites (sites 1-3) and showed the highest rates in the oligotrophic fen site (site 4). Successful PCR amplification using mcr gene primers revealed the presence of a methanogen community in all five sites along the study transect.     

Distribution of biomass of species differing in photosynthetic pathway along an altitudinal transect in southeastern wyoming grassland

Summary Based on the physiological characteristics and responses of C₃, C₄, and CAM plants to environmental factors, it is generally predicted that C₄ and CAM plants will become more abundant with increasing temperature and decreasing precipitation. To test this prediction, the relative contribution of each photosynthetic type to total plant community biomass was examined at seven study areas along an altitudinal transect in southeastern Wyoming grassland. In going from high (2,652 m) to low (1,405 m) elevation along this transect, mean annual temperature increased and annual precipitation decreased.The percentage of C₄ biomass composing each study area decreased with increasing elevation, while the percentage of C₃ biomass increased. All elevations had a significantly higher percentage of C₄ biomass in August than in June, reflecting the warm season growth characteristic of C₄ plants. Regressions of relative abundance of photosynthetic types on climatic variables showed that both mean annual temperature and annual precipitation were equally reliable as predictors of C₃–C₄ biomass, although we feel that temperature is of primary importance in explaining our observations. CAM species were present at all elevations, but showed no trends in biomass distribution with respect to elevation.     

Planktonic foraminifera of the northern Indian Ocean: Distribution and preservation in surface sediments

In the northern Indian Ocean, planktonic foraminiferal tests accumulate in a wide variety of surface-water environments and depositional settings. This variability enables us to isolate the effects that surface-water ecology and differential dissolution have on the distribution of planktonic foraminifera from 251 geographically widespread surface sediment samples.Foraminiferal abundance varies from 0 to > 10⁴ whole foraminifera in the greater than 150 μm fraction per gram dry sediment. Values < 10 characterize the three deep basins of the equatorial Indian Ocean and the western Bay of Bengal. Foraminiferal tests are most abundant on carbonate covered Ninety-East and Carlsberg Ridges. Absolute abundance patterns are mainly controlled by non-ecological processes. Variations in dissolution resistant species (RSP) with water depth reveal that the foraminiferal lysocline (FL) varies regionally. The FL is deepest (3,800 m) in the equatorial region, rises abruptly to 3,300 m in the Arabian Sea, and varies from 2,600 m to near 2,000 m moving northward in the Bay of Bengal. Deep samples with anomalously low RSP (< 30%) suggest redeposition.Systematic geographic and depth-related variation is observed for the 17 most abundant foraminiferal species. Dissolution resistant species (G. menardii, G. tumida, G. dutertrei, P. obliquiloculata) generally exhibit a rapid and continuous increase in relative abundance at and below the FL. Susceptible species (G. ruber, G. bulloides, G. glutinata, for example) exhibit a rapid and continuous decrease in relative abundance at and below the FL. Moderately susceptible species (G. conglobatus, G. aequilateralis, G. conglomerata, for example) rapidly increase in abundance at the FL and systematically decrease with depth below the FL.Principal components analysis (PCA) of faunal data from minimally dissolved (< 30% RSP) samples reveals important ecologically related species intercorrelations. The major biogeographic gradient is the negative covarying relationship between aG. bulloides-G. glutinata species pair and a grouping ofG. sacculifer, G. conglobatus, G. aequilateralis, andG. ruber. PCA of all samples demonstrates how differential dissolution alters this and other species relationships. Species groupings that incorporateG. ruber, G. menardii, andG. dutertrei are particularly affected by dissolution.Comparison of average faunal data from minimally dissolved samples in the northern Indian Ocean with similar samples from other tropical regions suggests varying environmental factors produce distinct faunas within the tropical ocean. For example,G. bulloides, G. falconensis, andG. hexagona are significantly more abundant in northern Indian Ocean surface sediments while such species asG. ruber, G. sacculifer, G. dutertrei, andP. obliquiloculata dominate in other tropical regions.     

Nematode Community Structure along the Continental Slope off the Kenyan Coast,Western Indian Ocean

Metazoan meiofauna and in particular nematode densities, diversity, community structure were studied in relation to water depth (20 m, 50 m, 500 m, 1000 m and 2000 m) along four bathymetric transects in the Western Indian Ocean off the Kenyan coast. Nematode densities ranged between 276–944 ind./10 cm², which is comparable to values from other oligotrophic areas in the world. Densities was correlated with oxygen concentrations in the overlying water, since they were lowest at mid‐depth (500–1000 m) coinciding with the minimum oxygen level. Nematode community structure (at genus level) resembles communities found in temperate slope regions, which are also characterized by a low productivity. The community structure showed correlations with sediment composition, water depth and oxygen levels in the overlying water. Sediment composition was mainly important at the shelf where nematodes separated into a silty sediment‐dwelling community with high abundances of Daptonema, Dorylaimopsis, Terschellingia and Halalaimus, and a sandy sediment‐dwelling community characterised by high abundances of Microlaimus and Halalaimus. The genera Monhystera, Acantholaimus, Sabatieria, Molgolaimus and Halalaimus dominated the slope communities. The characteristic deep‐sea taxa, the monhysterids and Acantholaimus increased in relative abundance with increasing depth, to become dominant at the lower slope (2000 m). The upper (500 m) and mid‐slope (1000 m), which coincided with the lowest oxygen concentrations, were colonised by Sabatieria, a genus that is known to inhabit suboxic sediments. Diversity at the level of the genera showed an unimodal trend along the sampled gradient, with highest values at mid‐depth (500 m). Although the oxygen minimum at mid depths is much less pronounced than in adjacent areas, the results of this study suggest an impact on the present communities.     

Diversity of terrestrial isopod species along a transect through northern Israel

The distribution of isopod species along a 70 km transect through northern Israel is described. The transect started from the Mediterranean seashore through Mt. Carmel and the Gilboa Mts. to the Jordan Valley. The habitats ranged from grassland, macqui to woodland in the Mediterranean region, onto grassland in the semi-arid region. Thirty isopod species were found, of these only one species was common to all the regions, and two species were found in four out of five regions. The largest number of species inhabited the mountainous habitats of Mt. Carmel and the Gilboa Mts: 20 and 14 species, respectively. Twelve species were found in the Coastal Plain; five of these were found exclusively there. Two of the four species found in the Jordan Valley were characteristic of that semi-arid region. Beta-diversity was found to be low in most cases and especially in the comparison between Mediterranean and semi-arid habitats.     

Epipelagic siphonophore assemblages associated with water masses along a transect between Chile and Easter Island (eastern South Pacific Ocean)

We analyze for the first time the spatial distribution of siphonophoresin relation to water masses along a 3750-km oceanic transectbetween the Chilean coast and the Easter Island (27° S),a sector scarcely known of eastern South Pacific Ocean. Thirty-onesiphonophore species were identified; Sulculeolaria turgidaand Vogtia glabra were recorded for the first time in this sector.The most abundant species were Muggiaea atlantica (29.2%), Eudoxoidesspiralis (24.5%) and Lensia subtilis (13.1%). Two differentsiphonophore assemblages east and west of 76 W, associated respectivelywith Subantarctic Water and Subtropical Water masses, can beused as water mass indicators. The former included the threemost abundant species, whereas the latter showed greater speciesrichness. This study provides basic knowledge on spatial distributionof siphonophores, which is important to develop future researchfocused on understanding the ecological role and biologicalprocesses driven by planktonic organisms in the southeasternPacific Ocean.