Aspects of the Ecology of the Deep-water Fauna of the Gulf of Mexico

Recent transects across the continental slope off western Louisiana,the Mississippi River delta, and the Florida peninsula in thegeneral depth range of 300–3,000 m have provided informationon habitat variables and on faunal composition, density, anddepth zonation. In the meiofauna (retained by 63µm screens)nematodes, harpacticoid copepods, nauplii, polychaetes, ostracods,and kinorynchs were numerically dominant, in that order, andtogether these groups made up 98% of the fauna. The macrofauna(retained by 0.3 mm screens) was dominated by polychaetes, ostracods,bivalves, tanaids, bryozoans, and isopods in that order, andtogether these made up 86% of the fauna. Densities of both groupswere highest on the Central Transect, and densities of bothtended to decrease with depth. Between the depths of 300 m and3,000 m there was a threefold decrease in meiofaunal and a twofolddecrease in macrofaunal density. Among the megafauna (collectedby otter trawl) invertebrate densities, dominated by crustaceans,were four to five times as great as fish densities at all depthsand on all transects. Densities were greatest on the Easternand least on the Central Transect, and on all transects theydecreased with depth. On the slope off Louisiana and East Texas,in the depth range of 400–900 m, dense biological communitieshave been encountered at about 40 locations aggregated aroundoil and gas seeps. These organisms include clusters of largetube worms (vestimentiferans), vesicomyid clams, mussels, galatheidcrabs, bresiliid shrimps, neogastropods, limpets, and fishes.This community is trophically dependent upon chemoautotrophicbacteria (which utilize hydrogen sulfide), although some musselsdirectly utilize methane as a carbon source. This communityis closely related to that of the hydrothermal vent systemsof the East Pacific Rise and to the seep communities at thebase of the Florida escarpment. The megafauna of the northernand eastern Gulf of Mexico falls naturally into the followingdepth distribution pattern: Shelf/Slope Transition Zone (118–475m), Archibenthal Zone—Horizon A (500–775 m), ArchibenthalZone—Horizon B (800–975 m), Upper Abyssal Zone (1,000–2,275m), Mesoabyssal Zone (2,300–3,225 m), and Lower AbyssalZone (3,250–3,850 m). Biological characteristics of eachzone are discussed.     

Long-term history of chemoautotrophic clam-dominated faunas of petroleum seeps in the Northwestern Gulf of Mexico

Summary Chemoautotrophic clam-dominated assemblages are commonly associated with petroleum seepage on the continental slope of the Gulf of Mexico. We examine the persistence and resilence of these communities by evaluating downcore trends in abundance, biomass, and trophodynamics in communities from four separate petroleum seep sites on the Louisiana continental slope. Some petroleum seep sites retained optimal habitat for some species continuously over geologically-relevant periods of time. More commonly, however, habitat optimality varied substantially over time scales of hundreds of years. Thus, one important characteristic of these sites was the degree of persistence of the chemoautotrophic biota. A fauna typically was persistent over a time span of a few hundred years, but was typically not persistent over a longer time span. The mechanisms producing local extinction remain unclear, however temporal variations in juvenile survivorship seem to be substantially larger than temporal variations in larval settlement, to the extent that the heavily taphonomically-biased record of juvenile individuals permits such a conclusion. When local extinctions occurred in the chemoautotrophic biota, the biota was replaced by a normal slope biota or a mixture of a normal slope biota and the juveniles of chemoautotrophic species that failed to survive to adulthood. Thus, the only faunal transitions were between specific chemoautotrophic faunas and the non-chemoautotrophic fauna. Not one distinctive faunal transition between two chemoautotrophic faunas was observed. Accordingly, each discrete chemoautotrophic fauna was resilient over long time scales; time scales of geological importance.     

Bacteria and Archaea Physically Associated with Gulf of Mexico Gas Hydrates

Although there is significant interest in the potential interactions of microbes with gas hydrate, no direct physical association between them has been demonstrated. We examined several intact samples of naturally occurring gas hydrate from the Gulf of Mexico for evidence of microbes. All samples were collected from anaerobic hemipelagic mud within the gas hydrate stability zone, at water depths in the ca. 540- to 2,000-m range. The δ¹³C of hydrate-bound methane varied from −45.1‰ Peedee belemnite (PDB) to −74.7‰ PDB, reflecting different gas origins. Stable isotope composition data indicated microbial consumption of methane or propane in some of the samples. Evidence of the presence of microbes was initially determined by 4,6-diamidino 2-phenylindole dihydrochloride (DAPI) total direct counts of hydrate-associated sediments (mean = 1.5 × 10⁹ cells g⁻¹) and gas hydrate (mean = 1.0 × 10⁶ cells ml⁻¹). Small-subunit rRNA phylogenetic characterization was performed to assess the composition of the microbial community in one gas hydrate sample (AT425) that had no detectable associated sediment and showed evidence of microbial methane consumption. Bacteria were moderately diverse within AT425 and were dominated by gene sequences related to several groups of Proteobacteria, as well as Actinobacteria and low-G + C Firmicutes. In contrast, there was low diversity of Archaea, nearly all of which were related to methanogenic Archaea, with the majority specifically related to Methanosaeta spp. The results of this study suggest that there is a direct association between microbes and gas hydrate, a finding that may have significance for hydrocarbon flux into the Gulf of Mexico and for life in extreme environments.     

Composition and seasonal fluctuations of intertidal fish assemblage in Kohr al-Zubair, Northwestern Arabian Gulf

A total of 2,851 fishes belonging to 34 species and weighing 177.15 kg were caught between July 1983 and June 1984 near Kohr al-Zubair in the northwestern Arabian Gulf, using four types of fixed gillnets with different mesh sizes. Four species (Thryssa hamiltoni, Liza macrolepis, T. mystax and Nematalosa nasus) formed 82.1% of all fish while 3 species (L. macrolepis, T. hamiltoni, Pomadasys argenteus) comprised 50.3 % of the total wet weight. The abundance of species was highest during autumn and spring, clearly reflecting the high values for the diverse indices during these periods and indicating the differing biological fish utilization of Kohr al-Zubair. The high positive correlation of temperature to number of species played an important role in this abiotic factor of fish migration to and from Kohr al-Zubair. Quantitative clustering of common fish species based on individual samples showed six distinctive groups. Group I included four resident species, while groups II-VI comprised mainly seasonal species that entered the Kohr area during either warm or cold seasons.     

Long -Term Changes in the Fish Fauna of the Karkinitsky Gulf of the Black Sea

Russian Journal of Marine Biology - The summarized composition of the fish fauna of the Karkinitsky Gulf of the Black Sea was established for the first time on the basis of literature and original...     

川西北高寒草甸蚁丘植物群落演替：种类组成与物种多样性

蚂蚁通过构建蚁丘,提高了群落生境异质性,影响群落物种组成,甚至生态系统结构和功能。我们在川西北典型高寒草甸调查了平地（非蚁丘,即距离蚁丘4～5m的草地）和不同大小广布弓背蚁（Cam-ponotus herculeanus）蚁丘（小蚁丘、中蚁丘和大蚁丘3种,平均面积大小分别为309．45cm^2、948．45cm^2、2124．90cm^2）上的植物种类组成、物种多样性,以及每个物种的高度,盖度和多度,在此基础上分析了蚁丘植物群落演替进程中的优势种变迁及其机制。调查发现,与平地相比,天气晴朗条件下蚁丘的土壤温度在白天较高,而在夜晚较低,日变化的波动性较大;蚁丘中心的相对湿度低于边缘,更低于平地。群落结构分析表明,不同大小蚁丘之间植物物种丰富度和多样性差异不显著,但是优势种变化明显。随蚁丘增大,钩状嵩草（Kobresia uncinoides）的群落地位（重要值）逐渐上升,小、中、大蚁丘上的次优种分别为拉拉藤（Galium aparine）、羊茅（Festuca ovina）、垂穗披碱草（Elymus nutans）。蚁丘上禾草类优势度显著高于平地,而杂草类优势度则显著低于平地。平地上菊科（Compositae）和毛莨科（Ranunculaceae）植物占优势,蚁丘上莎草科（Cyperaceae）和禾本科（Gramineae）植物占优势。文中还讨论了蚁丘植物群落演替的可能机制,以及蚁丘对整个草甸群落组成和动态的潜在意义。     

Seasonal Phenology and Species Composition of the Aphid Fauna in a Northern Crop Production Area

Background

The species diversity of aphids and seasonal timing of their flight activity can have significant impacts on crop production, as aphid species differ in their ability to transmit plant viruses and flight timing affects virus epidemiology. The aim of the study was to characterise the species composition and phenology of aphid fauna in Finland in one of the northernmost intensive crop production areas of the world (latitude 64°).

Methodology/Principal Findings

Flight activity was monitored in four growing seasons (2007–010) using yellow pan traps (YPTs) placed in 4–8 seed potato fields and a Rothamsted suction trap. A total of 58,528 winged aphids were obtained, identified to 83 taxa based on morphology, and 34 species were additionally characterised by DNA barcoding. Seasonal flight activity patterns analysed based on YPT catch fell into three main phenology clusters. Monoecious taxa showed early or middle-season flight activity and belonged to species living on shrubs/trees or herbaceous plants, respectively. Heteroecious taxa occurred over the entire potato growing season (ca. 90 days). Abundance of aphids followed a clear 3-year cycle based on suction trap data covering a decade. Rhopalosiphum padi occurring at the end of the potato growing season was the most abundant species. The flight activity of Aphis fabae, the main vector of Potato virus Y in the region, and Aphis gossypii peaked in the beginning of potato growing season.

Conclusions/Significance

Detailed information was obtained on phenology of a large number aphid species, of which many are agriculturally important pests acting as vectors of plant viruses. Aphis gossypii is known as a pest in greenhouses, but our study shows that it occurs also in the field, even far in the north. The novel information on aphid phenology and ecology has wide implications for prospective pest management, particularly in light of climate change.     

Incidence of Plasmids in Marine Vibrio spp. Isolated from an Oil Field in the Northwestern Gulf of Mexico

Presumptive marine Vibrio spp. were collected from an operational oil field and control site located in the northwestern Gulf of Mexico. Of 440 isolates analyzed for the presence of extrachromosomal deoxyribonucleic acid elements or plasmids by using the cleared lysate and agarose gel techniques, 31% showed distinct plasmid bands on agarose gels. A majority of the plasmids detected were estimated to have molecular masses of 10 × 10⁶ or less. Multiple plasmids were observed in approximately half of the plasmid-containing strains. A number of isolates contained plasmids with similar banding and mobility patterns. The oil field area had noticeably more plasmid-containing strains (35 versus 23% in the control site) and a greater number of plasmids per plasmid-containing strain (an average of 2.5 plasmids, versus 1.5 in the control site). Oil field discharges might have resulted in increased plasmid incidence and diversity.     

Edge Effects on Species Composition and Exotic Species Abundance in the North Carolina Piedmont

Edges between forest and non-forest habitats often have significant effects on forest microclimate and resource availability, with corresponding effects on species composition and abundance. Exotic species are often increased in abundance near forest edges. This increase in abundance could be either because of the increase in resource availability near edges, or because of increased dispersal into forest edges. We measured species composition and a set of geospatial variables on transects at 66 edges in the North Carolina Piedmont in an attempt to distinguish between these two factors. Mantel tests show that species composition is significantly different in forest edges than in the forest interior, but that this effect only penetrates about 5 m into the forest. Indicator species analysis finds several species that are indicative of edge communities, including trumpet vine (Campsis radicans), two drought-tolerant oak species (Quercus stellata and Q. falcata), a serviceberry (Amelanchier arboreum), and a common exotic species, tree-of-heaven (Ailanthus altissima). Poisson regression techniques showed that in both the seedling and tree strata of the forest, exotic species increased in abundance on flat sites with a high potential seed source. Mapping predicted exotic species abundance onto the landscape. We find that large-scale variation in exotic species abundance is due mostly to variation in potential seed sources, while small-scale variation relates more to edaphic factors. Our results stress that both dispersal and environmental filters are important for determining exotic species abundance, but potentially the filters operate at different spatial scales.     

Species Distribution and Population Connectivity of Deep-Sea Mussels at Hydrocarbon Seeps in the Gulf of Mexico

Hydrocarbon seepage is widespread and patchy in the Gulf of Mexico, and six species of symbiont containing bathymodiolin mussels are found on active seeps over wide and overlapping depth and geographic ranges. We use mitochondrial genes to discriminate among the previously known and a newly discovered species and to assess the connectivity among populations of the same species in the northern Gulf of Mexico (GoM). Our results generally validate the morphologically based distribution of the three previously known GoM species of Bathymodiolus, although we found that approximately 10% of the morphologically based identifications were incorrect and this resulted in some inaccuracies with respect to their previously assigned depth and geographical distribution patterns. These data allowed us to confirm that sympatry of two species of Bathymodiolus within a single patch of mussels is common. A new species of bathymodiolin, Bathymodiolus sp. nov., closely related to B. heckerae was also discovered. The two species live at the same depths but have not been found in sympatry and both have small effective population sizes. We found evidence for genetic structure within populations of the three species of Bathymodiolinae for which we had samples from multiple sites and suggest limited connectivity for populations at some sites. Despite relatively small sample sizes, genetic diversity indices suggest the largest population sizes for B. childressi and Tamu fisheri and the smallest for B. heckerae and B. sp. nov. among the GoM bathymodiolins. Moreover, we detected an excess of rare variants indicating recent demographic changes and population expansions for the four species of bathymodiolins from the Gulf of Mexico.     

Seasonality and Structure of a Macrobenthic Seagrass Community on the Florida Gulf Coast

Macrofauna at two intertidal sites, quantitatively sampled monthly for 25 months, exhibited distinct reoccurring population fluctuations which were poorly correlated with abiotic parameters. Faunal dominants, Laeonereis culveri and Onuphis simoni, showed reciprocal fluctuations. Laeonereis exhibited non-synchronized reproduction and recruitment while Onuphis exhibited synchronized release. Laeonereis peaked before Onuphis while Oniphis fluctuated with the majority of other species. The faunal dominants exhibited one cycle in autumn at both sites but also exhibited a cycle at only one site in spring. Temperature is thus not indicated as causal and detrital input was suggested as the overriding factor. A hypothesis was advanced that Laeonereis is an opportunistic species exploiting fresh detritus, while Onuphis is a detritus feeder utilizing bacterial populations.     

Changes in Mammal Fauna of the Northern Palearctic and Living Range Dynamics of the Component Species

Changes in the distribution of game animals that have living ranges with northern and southern boundaries in the northwestern regions of Russia have been analyzed and compared to horological materials published by a group of researchers almost 50 years ago. An anthropogenic impact has been identified as the major factor for the changes named above.     

Changes in Microbial Plankton Assemblages Induced by Mesoscale Oceanographic Features in the Northern Gulf of Mexico

Mesoscale circulation generated by the Loop Current in the Northern Gulf of Mexico (NGOM) delivers growth-limiting nutrients to the microbial plankton of the euphotic zone. Consequences of physicochemically driven community shifts on higher order consumers and subsequent impacts on the biological carbon pump remain poorly understood. This study evaluates microbial plankton <10 μm abundance and community structure across both cyclonic and anti-cyclonic circulation features in the NGOM using flow cytometry (SYBR Green I and autofluorescence parameters). Non-parametric multivariate hierarchical cluster analyses indicated that significant spatial variability in community structure exists such that stations that clustered together were defined as having a specific ‘microbial signature’ (i.e. statistically homogeneous community structure profiles based on relative abundance of microbial groups). Salinity and a combination of sea surface height anomaly and sea surface temperature were determined by distance based linear modeling to be abiotic predictor variables significantly correlated to changes in microbial signatures. Correlations between increased microbial abundance and availability of nitrogen suggest nitrogen-limitation of microbial plankton in this open ocean area. Regions of combined coastal water entrainment and mesoscale convergence corresponded to increased heterotrophic prokaryote abundance relative to autotrophic plankton. The results provide an initial assessment of how mesoscale circulation potentially influences microbial plankton abundance and community structure in the NGOM.     

Horizontal Movements,Migration Patterns,and Population Structure of Whale Sharks in the Gulf of Mexico and Northwestern Caribbean Sea

Whale sharks, Rhincodon typus, aggregate by the hundreds in a summer feeding area off the northeastern Yucatan Peninsula, Mexico, where the Gulf of Mexico meets the Caribbean Sea. The aggregation remains in the nutrient-rich waters off Isla Holbox, Isla Contoy and Isla Mujeres, Quintana Roo for several months in the summer and then dissipates between August and October. Little has been known about where these sharks come from or migrate to after they disperse. From 2003–2012, we used conventional visual tags, photo-identification, and satellite tags to characterize the basic population structure and large-scale horizontal movements of whale sharks that come to this feeding area off Mexico. The aggregation comprised sharks ranging 2.5–10.0 m in total length and included juveniles, subadults, and adults of both sexes, with a male-biased sex ratio (72%). Individual sharks remained in the area for an estimated mean duration of 24–33 days with maximum residency up to about 6 months as determined by photo-identification. After leaving the feeding area the sharks showed horizontal movements in multiple directions throughout the Gulf of Mexico basin, the northwestern Caribbean Sea, and the Straits of Florida. Returns of individual sharks to the Quintana Roo feeding area in subsequent years were common, with some animals returning for six consecutive years. One female shark with an estimated total length of 7.5 m moved at least 7,213 km in 150 days, traveling through the northern Caribbean Sea and across the equator to the South Atlantic Ocean where her satellite tag popped up near the Mid-Atlantic Ridge. We hypothesize this journey to the open waters of the Mid-Atlantic was for reproductive purposes but alternative explanations are considered. The broad movements of whale sharks across multiple political boundaries corroborates genetics data supporting gene flow between geographically distinct areas and underscores the need for management and conservation strategies for this species on a global scale.     

Culture-Independent Characterization of Bacterial Communities Associated with the Cold-Water Coral Lophelia pertusa in the Northeastern Gulf of Mexico

Bacteria are recognized as an important part of the total biology of shallow-water corals. Studies of shallow-water corals suggest that associated bacteria may benefit the corals by cycling carbon, fixing nitrogen, chelating iron, and producing antibiotics that protect the coral from other microbes. Cold-water or deep-sea corals have a fundamentally different ecology due to their adaptation to cold, dark, high-pressure environments and as such have novel microbiota. The goal of this study was to characterize the microbial associates of Lophelia pertusa in the northeastern Gulf of Mexico. This is the first study to collect the coral samples in individual insulated containers and to preserve coral samples at depth in an effort to minimize thermal shock and evaluate the effects of environmental gradients on the microbial diversity of samples. Molecular analysis of bacterial diversity showed a marked difference between the two study sites, Viosca Knoll 906/862 (VK906/862) and Viosca Knoll 826 (VK826). The bacterial communities from VK826 were dominated by a variety of unknown mycoplasmal members of the Tenericutes and Bacteroidetes, whereas the libraries from VK906/862 were dominated by members of the Proteobacteria. In addition to novel sequences, the 16S rRNA gene clone libraries revealed many bacterial sequences in common between Gulf of Mexico Lophelia corals and Norwegian fjord Lophelia corals, as well as shallow-water corals. Two Lophelia-specific bacterial groups were identified: a cluster of gammaproteobacteria related to sulfide-oxidizing gill symbionts of seep clams and a group of Mycoplasma spp. The presence of these groups in both Gulf and Norwegian Lophelia corals indicates that in spite of the geographic heterogeneity observed in Lophelia-associated bacterial communities, there are Lophelia-specific microbes.Cold-water and deep-sea corals have become a topic of interest due to conservation concerns over the impacts of trawling, exploration for oil and gas, and climate change (51, 52). Although the existence of these corals has been known since the 1800s, our knowledge of their distribution, ecology, and biology is limited due to the technical difficulties of studying them. Lophelia pertusa is a globally distributed cold-water scleractinian coral (53). In the Gulf of Mexico, Lophelia reefs occur primarily along the continental shelf break (300- to 500-m depth), providing an important complex habitat for a wide variety of fishes, crustaceans, and other invertebrates living below the photic zone (48).The microbial ecology of cold-water corals in deep water is fundamentally different from that of shallow-water corals due to the ambient environmental parameters (e.g., darkness, low temperature, and increased pressure) and the absence of symbiotic zooxanthellae. A few studies have begun to address the microbial associates of deep-sea corals, focusing on octocorals (9, 44) and on L. pertusa (27, 41, 42, 57, 72). To date, all the Lophelia studies have been conducted on the eastern side of the Atlantic: the Mediterranean basin (72), Mingulay Bay, Scotland (27), and Norwegian fjords (41, 42, 57). These studies have confirmed that the Lophelia-associated bacterial community is distinct from that of the surrounding seawater and sediments (27, 42, 57, 72). A variety of community profile methods (automated rRNA intergenic spacer analysis, terminal restriction fragment length polymorphism, and denaturing gradient gel electrophoresis [DGGE]) were used to demonstrate differences between samples within a geographic area, suggesting that the Lophelia-associated microbial community varies depending on regional environmental factors (27, 42, 57). Sequencing of 16S rRNA genes was done in only two studies, and there was no overlap between their data (42, 72). However, different methods of collection, extraction, amplification, and sequencing were employed, so the lack of commonality may be due to methodology rather than biogeography.Methodology is a concern, particularly the care with which samples need to be collected for microbial ecology studies. Deep-sea coral samples are typically collected by a trawl, net, or dredge or by a submersible/remotely operated vehicle (ROV). With these methods, many corals may be combined in a single container, which is not acceptable for microbiological studies because the microbial community of one coral could contaminate that of the other. Similarly, contact with sediment, other invertebrates, mobile fauna, or water masses between the collection point and the surface could contaminate the coral samples. Unlike the case with the northeastern Atlantic and Norwegian fjords, the temperature and salinity gradients in the Gulf of Mexico during the warm months of the year can be considerable. In the case of the Viosca Knoll sites, the bottom temperature was 8 to 11°C, compared to a surface temperature of ≥30°C. Coral samples collected in uninsulated containers in this area have been observed to be affected (e.g., polyps retracted and copious stress mucus production) compared to those in insulated containers. Viosca Knoll is also impacted by the Mississippi River plume. The surface waters at these sites were turbid and green and had a salinity of 30 practical salinity units (psu), but below the plume the waters were clear and had a salinity of 35 psu. With this in mind, we designed a sampling container that would protect the coral samples from dramatic changes in temperature and salinity by sealing them in individual insulated compartments (see Fig. S1 in the supplemental material). However, the question remained whether environmental gradients in light and pressure would have an effect on the microbial diversity of the samples. To address this question, each sample was collected in duplicate: one piece was sealed in a compartment alive, and a replicate piece was sealed in another compartment and preserved at depth with a fixative solution. Both sample types (“live” versus “fixed”) were sealed and insulated, so temperature and salinity gradients did not affect them; live samples were subject to gradients in light and pressure, while fixed samples were not.The main objective of this study was to characterize the bacterial associates of Lophelia pertusa from two sites in the northern Gulf of Mexico. Comparing multiple individual colonies from two geographic locations in the Gulf to each other and to bacterial data from Lophelia samples on the eastern side of the Atlantic will clarify whether Lophelia has a species-specific bacterial community, as has been described for shallow-water corals (49, 55). The results of this study will also better define the total microbial diversity associated with this cold-water coral. A specialized sampling device (see Fig. S1 in the supplemental material) was designed to minimize contamination and thermal shock and to allow the introduction of preservative at depth to determine if environmental gradients were affecting microbial diversity during sampling.     

Effects of Elevated CO2 and Simulated Seasonal Changes in Temperature on the Species Composition and Growth Rates of Pasture Turves

Large turves from a ryegrass/white clover based pasture wereexposed to 350 or 700 µl l^-1 CO₂ for a period of 217 din controlled environment rooms. The temperature was increasedduring the experiment from 10/4 °C day/night to 16/10 °Cand finally to 22/16 °C. The turves were cut to a heightof 2 cm at intervals and growth rates calculated from the regrowth. Growth rates over the duration of the experiment were 8% higherat elevated CO₂; the difference between CO₂ treatments beingstatistically significant only at the highest temperature. Speciescomposition of the turves at 350 µl l^-1 CO₂ showed seasonalchanges similar to those measured in the field. The effect ofCO₂ was to exaggerate the normal decline of ryegrass at warmertemperatures and increase the proportion of white clover. About30% of the total growth rate was from other species (notablyBromus hordeaceus L. and Poa trivialis L.) and this fractionwas similar between CO₂ levels. Root mass was measured at theend of the experiment and was 50% higher at elevated CO₂. The modest above-ground response to CO₂ was a result of CO₂stimulation occurring only at the higher temperature. Becauseof the CO₂ x temperature interaction, the effect of CO₂ in temperateregions will be seasonal. When this is matched with seasonalgrowth patterns of herbage species, a complex response of pasturecommunities to CO₂ is possible. In our case, white clover wasgrowing most strongly during the period of greatest CO₂ stimulationand consequently its growth was enhanced more than that of ryegrass;however, the cooler season growth of ryegrass gives it a temporalniche which is little affected by CO₂ and this may be importantfor ryegrass stability if it is an inherently poor responderto CO₂. The results indicate that for temperate species theeffects of competition at elevated CO₂ cannot be easily determinedfrom experiments conducted at a single temperature.Copyright1994, 1999 Academic Press CO₂ enrichment, seasonal growth, species composition, turves, Trifolium repens L., Lolium perenne L., climate change     

Effects of the oxygen minimum zone on squat lobster distributions in the Gulf of California, Mexico

Distribution of squat lobsters of the genera Gastropthychus (one species), Uroptychus (1), Janetogalathea (1), Galacantha (1), Munidopsis (8), and Munida (7) in the Gulf of California, Mexico, was plotted vs. the localization of the Oxygen Minimum Zone (OMZ) using bottom projections of the 0.50, 0.25, 0.10, and 0.05 ml l^?1 oxylines. Four fringes where oxygen concentrations were equal or lower than these concentrations were obtained, extending from the southern Gulf to about 28°–28°30′N. A total of 172 sampling locations with squat lobsters were plotted on four maps, one for each fringe, noting that with decreasing values of bottom oxygen (i.e., from 0.50 to 0.05 ml l^?1) the number of locations with species included between the upper and lower boundaries of these fringes decreases as follows: 34% for 0.50, 25% for 0.25, 12% for 0.10, and 5% for 0.05 ml l^?1. The upper and lower limits of the 0.05 ml l^?1 fringe are recognised as threshold frontiers, acting as barriers between shallow and deep communities of squat lobsters in the area. The distribution of the localities where species have been collected with respect to the upper and lower boundaries of the 0.05 ml l^?1 fringe clearly indicates a segregation pattern. Eight species of Munida (except M. perlata), and one each of Janetogalathea and Gastropthychus inhabit the shallow area, just above the OMZ core, with species of Munida generally found a rather long distance from this fringe. By contrast, species of Munidopsis, G. diomedeae and U. pubescens correspond to the deep area, i.e., below the OMZ core. It is suggested that the core of the OMZ in the Gulf of California serves as a vertical and latitudinal distribution filter, preventing species from freely migrating up and down or south and north.