Radiolaria: Sinking population,standing stock,and production rate

A method is presented for estimating sinking population, rate of production, and residence time in the living zone for Radiolaria. This method employs vertical flux measurements from PARFLUX sediment traps and laboratory sinking speed measurements of the radiolarian skeletons.The estimated population sinking through the oceanic water column is approximately equal to the standing stock at several hundred meters depth reported from direct measurements by other workers. The rate of production of total Radiolaria was estimated to be approximately 80 shells m^?3 day^?1 in the western equatorial Atlantic (E) and central Pacific (P₁) stations and 230 shells m^?3 day^?1 in the Panama Basin (PB). The production of Nassellaria is greater than that of the other suborders. The average residence time for Radiolaria in the living zone (0–200 m) was estimated to be between 16 and 42 days.     

Cenomanian Cephalopods of Bellezma-Aures mountains,NE Algeria: Taxonomy and biostratigraphy

The Cenomanian Smail Marl Formation in the Bellezma and Aures mountains of northeastern Algeria is well exposed and rich in macroinvertebrates, including cephalopods. Twenty-five ammonite species and two nautiloid species from the Thénièt El Manchar, Djebel Metrassi and Djebel Bouarif sections are described and seven assemblage zones proposed as provisional working units: Mantelliceras mantelli–Sharpeiceras laticlavium Assemblage Zone (lower Cenomanian), Mantelliceras dixoni Assemblage Zone (uppermost lower Cenomanian), Cunningtoniceras inerme Assemblage Zone (lower middle Cenomanian), Acanthoceras rhotomagense and Acanthoceras cf. rhotomagense Assemblage Zone (middle middle Cenomanian), Acanthoceras amphibolum Assemblage Zone (upper middle Cenomanian), Acanthoceras jukesbrownei Assemblage Zone (uppermost middle Cenomanian), and Neolobites vibrayeanus Assemblage Zone (lower upper Cenomanian). The lower Cenomanian Mantelliceras mantelli–Sharpeiceras laticlavium Zone is subdivided into the Submantelliceras aumalense, Sharpeiceras schlueteri and Mantelliceras saxbii subzones. The base of the middle Cenomanian is marked by the disappearance of species of Mantelliceras and the appearance of the scleractinian coral Aspidiscus cristatus (Lamarck, 1801), associated with Cunningtoniceras inerme (Pervinquière, 1907). The middle Cenomanian contains abundant A. cristatus and species of Acanthoceras, i.e., A. cf. rhotomagense (Defrance in Brongniart, 1822), A. jukesbrownei (Spath, 1926) and A. amphibolum Morrow, 1935. An ammonite zonal scheme is then applied to the Cenomanian exposed in the Bellezma-Aures mountains located on the southern Tethys margin in Algeria.     

Vertical migration of Karenia brevis in the northeastern Gulf of Mexico observed from glider measurements

The toxic marine dinoflagellate, Karenia brevis (the species responsible for most of red tides or harmful algal blooms in the Gulf of Mexico), is known to be able to swim vertically to adapt to the light and nutrient environments, nearly all such observations have been made through controlled experiments using cultures. Here, using continuous 3-dimensional measurements by an ocean glider across a K. brevis bloom in the northeastern Gulf of Mexico between 1 and 8 August 2014, we show the vertical migration behavior of K. brevis. Within the bloom where K. brevis concentration is between 100,000 and 1,000,000 cells L⁻¹, the stratified water shows a two-layer system with the depth of pycnocline ranging between 14–20 m and salinity and temperature in the surface layer being <34.8 and >28 °C, respectively. The bottom layer shows the salinity of >36 and temperature of <26 °C. The low salinity is apparently due to coastal runoff, as the top layer also shows high amount of colored dissolved organic matter (CDOM). Within the top layer, chlorophyll-a fluorescence shows clear diel changes in the vertical structure, an indication of K. brevis vertical migration at a mean speed of 0.5–1 m h⁻¹. The upward migration appears to start at sunrise at a depth of 8–10 m, while the downward migration appears to start at sunset (or when surface light approaches 0) at a depth of ∼2 m. These vertical migrations are believed to be a result of the need of K. brevis cells for light and nutrients in a stable, stratified, and CDOM-rich environment.     

The effects of light intensity on the growth of Japanese Gambierdiscus spp. (Dinophyceae)

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R > 0.92 (p < 0.01) using regression analysis and photosynthesis-light intensity (P-L) model. Based on this equation, the optimum light intensity (L_max) and the semi-optimum light intensity range (L_s-opt) that resulted in the maximum growth rate (μ_max) and ≥80% μ _max values of the four species/phylotypes, respectively, were as follows: (1) the L_max and L_s-opt of G. australes were 208 μmol photons m⁻² s⁻¹ and 91–422 μmol photons m⁻² s⁻¹, respectively; (2) those of G. scabrosus were 252 and 120–421 μmol photons m⁻² s⁻¹, respectively; (3) those of Gambierdiscus sp. type 2 were 192 and 75–430 μmol photons m⁻² s⁻¹, respectively; and (4) those of Gambierdiscus sp. type 3 were ≥427 and 73–427 μmol photons m⁻² s⁻¹, respectively. All four Gambierdiscus species/phylotypes required approximately 10 μmol photons m⁻² s⁻¹ to maintain growth. The light intensities in coastal waters at a site in Tosa Bay were measured vertically at 1 m intervals once per season. The relationships between the observed light intensity and depth were formulated using Beer’s Law. Based on these equations, the range of the attenuation coefficients at Tosa Bay site was determined to be 0.058–0.119 m⁻¹. The values 1700 μmol photons m⁻² s⁻¹, 500 μmol photons m⁻² s⁻¹, and 200 μmol photons m⁻² s⁻¹ were substituted into the equations to estimate the vertical profiles of light intensity at sunny midday, cloudy midday and rainy midday, respectively. Based on the regression equations coupled with the empirically determined attenuation coefficients for each of the four seasons, the ranges of the projected depths of L_max and L_s-opt for the four Gambierdiscus species/phylotypes under sunny midday conditions, cloudy midday conditions, and rainy midday conditions were 12–38 m and 12–54 m, 1–16 m and 1–33 m, and 0 m and 0–16 m, respectively. These results suggest that light intensity plays an important role in the bloom dynamics and vertical distribution of Gambierdiscus species/phylotypes in Japanese coastal waters.     

Length–weight relationships of three fish species from Bohai Sea,China

Length–weight relationships were determined for three fish species (Cynoglossus macrolepidotus (Bleeker, 1851), Liparis tanakae (Gilbert & Burke, 1912), Zoarces elongatus (Kner, 1868)) from Bohai Sea (38°38′–40°28′N; 119°42′–121°10′E), China. Fish specimens were sampled monthly between May 1982 to May 1983 using pair bottom trawlers (150.5 × 96.5 m, mesh size: 30–200 mm) with a cod end (mesh size: 30 mm), which were towed at a ship's speed of two knots for 1 hr at a maximum depth of about 80 m. Relationships between length and weight were fitted very well for all species (all R² > .90).     

Fine‐scale vertical and horizontal movements of juvenile yellowfin tuna (Thunnus albacares) associated with a subsurface fish aggregating device (FAD) off southwestern Taiwan

An increase in yellowfin tuna (Thunnus albacares) catch by danish seine fisheries around the subsurface fish aggregating devices (FADs) in southern Taiwan waters has been a concern of local government and environmental groups. However, the attraction mechanism of aggregating tunas at the subsurface FADs is still poorly understood. The objective of this study is to examine the fine‐scale vertical and horizontal movements of juvenile yellowfin tunas around a subsurface FAD. In total, 53 tunas (35–81 cm fork length) were tagged with ultrasonic telemetry tags and released at a subsurface FAD in the waters off Shiao‐Liu‐Chiu Island, southwestern Taiwan from October 2008 to December 2009. These tunas stayed at the subsurface FAD for up to 31 days, with daytime vertical movement depths averaging 60–80 m at a maximum depth of 250 m. At night, the tuna gathered at a shallow depth of 40 m. The mean depth of vertical movement in the daytime is significantly different from that of the nighttime (P < 0.05). The maximum detectable distance of horizontal movement was 1.6 km, with 80% of the long horizontal movements occurring in the daytime. It is likely that the purpose of these vertical and horizontal movements was for feeding or avoiding predators. Moreover, the tagged tunas did not depart from the subsurface FAD simultaneously, suggesting distinct behaviors in their movements.     

Distribution and biomass assessment of macroalgae from Moroccan Strait of Gibraltar.

The taxonomic richness, population structure, biomass assessment, and geographic distribution of macroalgae were studied between May 2017 and July 2018 from the Moroccan strait of Gibraltar. The study was based on the economic, ecological and environmental interests of macroalgae on a national scale. Samples were harvested by Scuba diving. Sixty-seven species, including one recently introduced in the Strait, have been identified. They were distributed over four classes: Bangiophyceae (2 species), Florideophyceae (36 species), Phaeophyceae (17 species), and Ulvophyceae (12 species). The distribution map of the most abundant agarophytes, Gelidium attenuatum and Pterocladia capillacea, was constructed from GPS and field data using System Information Geographic software. G. attenuatum stands extended from 1 to 7 m depth, with maximum biomass at 1 m. The population analysis revealed thalli up to 15.8 cm long, with the length class 11–13 cm mostly represented. As for the population of P. capillacea, it was located from 0 to 1.50 m depth, with highest biomass at 0–0.50 m depth. Unlike Gelidium, P. capillacea stands were distributed from 5 to 12 cm, with 85% measuring between 7 and 11 cm long. The estimated total biomass of G. attenuatum and P. capillacea was 7.77 ± 3.57 t of fresh weight and distributed on two sectors: Mrisat (66.66%) and Oued-Alian (33.34%). This Finding indicates a relatively low biomass in the strait.     

Bathymetric distribution of benthic foraminifera on the Australian-Irian Jaya continental margin,eastern Indonesia

We identified 164 taxa of benthic foraminifera in 35 selected box-core top samples collected on the Australian-Irian Jaya continental margin in waterdepths between 60 and 2119 m, along three systematically sampled transects across the Banda Arc. The bathymetric distribution pattern of the benthic foraminiferal faunas is related to the oceanographic situation of this area, where the watermasses of the Indian Ocean collide with the watermasses of the Pacific Ocean. With the results of cluster analyses and empirical depth-ranges of “isobathyal” taxa, four faunal depth-zones and four subzones can be distinguished:

• 1.(A) The Outer Shelf Biofacies (60–150 m), corresponding to the photic oxycline-zone of the Indonesian Surface Waters, and inhabited by a benthic foraminiferal association dominated by Amphistegina lessonii, Operculina ammonoides, Heterolepa dutemplei and various miliolids.
• 2.(B) The Upper Bathyal Biofacies (150–400 m), reflecting the aphotic, deeper Indonesian Surface Waters, dominated by Bolivina robusta, Heterolepa mediocris, Hanzawaia nipponica and Lenticulina spp. A major faunal break is situated at the lower boundary of this depth-zone.
• 3.(C) The Middle Bathyal Biofacies (400–1500 m), representing the Indonesian Intermediate Waters with minimum oxygen-contents, dominated by Bolivina robusta, Cassidulina carinata, Gavelinopsis lobatulus and Sphaeroidina bulloides. In this depth-zone many taxa occur with only limited depth-ranges, on which four subzones (C1–4) could be identified, allowing for a local (paleo)bathymetric resolution of a few hundred meters.
• 4.(D) The Lower Bathyal Biofacies (1500–2120 m) corresponds with the Indonesian Deep Waters. It is dominated by Pullenia bulloides and other cosmopolitan deep water indicators, such as Epistominella exigua, Laticarinina pauperata, Oridorsalis umbonatus and Planulina wuellerstorfi.

The sample fraction > 250 μm can be used to readily delineate the major faunal trends. Paleobathymetric resolution improves when the sample portion > 125 μm is used.     

Live and dead benthic foraminiferal assemblages from coastal environments of the Aegean Sea (Greece): Distribution and diversity

Benthic foraminiferal composition assemblages and their temporal changes, ecological indices and foraminiferal densities are used to compare three coastal environments with different physicogeographical features in the Aegean Sea (coastal environment of Avdira–Vistonikos Gulf and Kitros–Thermaikos Gulf and open lagoonal environment of Vravron–South Evoikos Gulf). Three main foraminiferal assemblages have been recognized: a) “Assemblage A”; high degree of similarity between living and dead foraminiferal species, dominated by Ammonia beccarii, Elphidium spp. and relatively abundant and diverse miliolids, b) “Assemblage B1”; intermediate degree of similarity between live and dead assemblages, characterized by highly-abundant and well-diversified foraminiferal assemblages including the algal symbiont bearing Peneroplis pertusus together with Ammonia tepida and several small epiphytic rotaliids and miliolids, and c) “Assemblage B2”; absence of living individuals, strongly dominated by the opportunistic species A. tepida. Our results suggest a good comparison between living and dead assemblages from different coastal environments in the Aegean Sea, however the prevailing environmental conditions (vegetation cover, hydrodynamics, fresh water influx) have a strong impact on the taphonomic processes.     

New Mesozoic and early Cenozoic spicular Nassellaria and Nassellaria-like Radiolaria

This paper continues a former study (Rev. Española Micropaleontol. 14 (1982b) 401), where the author described spicular nassellarian and entactinarian Radiolaria found in the Middle Triassic samples available at that time. Based on the study of new samples bearing well preserved radiolarians collected during the 20 years that followed the former publication, samples coming from Triassic, Jurassic, Cretaceous, and Paleogene deposits, the author found that spicular Nassellaria are extremely rare in the post-Fassanian radiolarian faunas. Their fossil record is punctuated, their occurrences being separated by very long gaps. And even so, when they occur their number is usually reduced to one, two, or several specimens of a single species. Spicular Nassellaria are rare or very rare in the upper Spathian and Anisian, frequent in the upper Anisian-lower Ladinian, practically absent in the upper Ladinian and the whole upper Triassic and pre-Toarcian Lower Jurassic, rare in lower Toarcian, very rare in the Bajocian, rare in the lower Tithonian. No specimens were recorded in the other stages of the middle and upper Jurassic and in the whole Cretaceous, except for one in the Coniacian. In the Paleogene only five species belonging to four genera have been recorded in the upper Paleocene-middle Eocene. In the Neogene the only genus known so far is Neosemantis that occurs sporadically since the lower Miocene. A wider diversity is recorded in the living plankton or Recent sediments that comprise all genera and species described in the literature before 1970. It is suggested that this scarcity reflects their real scarcity in the tropical or subtropical seas of the past, but this scarcity was probably magnified by selective preservation. The idea of origination of spicular Nassellaria once or several times from shell-bearing Nassellaria by the reduction of shell during some environmental crises of the Mesozoic and Cenozoic or by hybridization is rejected because the group is rather unitary in its spicular structure and it shows a certain evolution from taxa with massive spines to taxa with three-bladed spines. Nassellarian-like spicular Radiolaria range within the boundaries of the Triassic; they seem to have disappeared by the end on the Norian.In order to give a complete inventory of these radiolarians all taxa known in the Mesozoic and lower Cenozoic are described, discussed, or just mentioned. They comprise 44 species of which 20 are new, 14 genera of which six are new (Palaeosemantis, Molzaxis, Daniplagia, Verticiplagia, Jeanpierria and Nandartia), three subfamilies of which one (Zaldacriinae) is new, and two families (Plagiacanthidae and Archaeosemantidae).     

Treatment of high-strength wastewater in tropical vertical flow constructed wetlands planted with Typha angustifolia and Cyperus involucratus

The ability of vertical flow (VF) constructed wetland systems to treat high-strength (ca. 300 mg L^?1 of COD and ca. 300 mg L^?1 total-nitrogen) wastewater under tropical climatic conditions was studied during a 5-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d^?1. Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d^?1 were 17.8, 15.4 and 0.69 g m^?2 d^?1. The first-order removal rate constants at a HLR of 80 mm d^?1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 m year^?1, respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m^?2 d^?1 in the planted systems as opposed to ca. 60 g m^?2 d^?1 in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphorus, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium.     

Settlement of bivalve spat on artificial collectors in Eyjafjordur, North Iceland

The seasonal pattern of bivalve spat settlement in Eyjafjordur, North Iceland, was investigated using artificial collectors of monofilament netting over 14 months (March 1998–January 2000) at 5, 10 and 15 m depth. SCUBA divers replaced the collectors at 4-weekly intervals. Twelve bivalve species settled on the collectors but only Mytilus edulis and Hiatella arctica were present throughout the year; they were the most abundant bivalve taxa. Of the remaining species, only Chlamys islandica, Heteranomia spp., Arctica islandica, Serripes groenlandicus and Mya spp. were sufficiently abundant to enable statistical analysis. All settled in late summer and autumn. Peak settlement of M. edulis, in September, consisted mainly of primary settlers (0.25–0.5 mm) although secondary settlers (>0.5 mm) were present in all samples. Mytilus edulis settled mostly at 5 m depth, especially larger individuals, possibly reflecting stronger currents at shallower depth and the proximity of mussel beds in the intertidal zone. Primary (<1 mm) and secondary H. arctica settlers (>1 mm) were present in most months, with the former being most numerous in September, 1999; settlement was equally abundant at 5 and 10 m depth. Primary settlement of C. islandica and S. groenlandicus occurred in autumn (mainly in September), and secondary settlers were very scarce and only seen in winter. Arctica islandica, Heteranomia spp. and Mya spp. settled mainly in September 1999 at 10 m depth, except for A. islandica, which was more numerous in August.     

Mesophotic communities of the insular shelf at Tutuila, American Samoa

An investigation into the insular shelf and submerged banks surrounding Tutuila, American Samoa, was conducted using a towed camera system. Surveys confirmed the presence of zooxanthellate scleractinian coral communities at mesophotic depths (30–110 m). Quantification of video data, separated into 10-m-depth intervals, yielded a vertical, landward-to-seaward and horizontal distribution of benthic assemblages. Hard substrata composed a majority of bottom cover in shallow water, whereas unconsolidated sediments dominated the deep insular shelf and outer reef slopes. Scleractinian coral cover was highest atop mid-shelf patch reefs and on the submerged bank tops in depths of 30–50 m. Macroalgal cover was highest near shore and on reef slopes approaching the bank tops at 50–60 m. Percent cover of scleractinian coral colony morphology revealed a number of trends. Encrusting corals belonging to the genus Montipora were most abundant at shallow depths with cover gradually decreasing as depth increased. Massive corals, such as Porites spp., displayed a similar trend. Percent cover values of plate-like corals formed a normal distribution, with the highest cover observed in the 60–70 m depth range. Shallow plate-like corals belonged mostly to the genus Acropora and appeared to be significantly prevalent on the northeastern and eastern banks. Deeper plate-like corals on the reef slopes were dominated by Leptoseris, Pachyseris, or Montipora genera. Branching coral cover was high in the 80–110 m depth range. Columnar and free-living corals were also occasionally observed from 40–70 m.     

Small-scale diel vertical migration of zooplankton in the High Arctic

Diel vertical migration (DVM) of zooplankton is considered less prominent at high latitudes where diel changes in irradiance are minimal during periods of midnight sun and polar night, leaving zooplankton without a temporal refuge and thus eliminating a key advantage of DVM. One of the shortcomings of previous DVM studies of zooplankton based on net sampling is that the depth resolution often has been too coarse to detect vertical migrations over short distances. We investigated DVM of zooplankton during August 2010 in drifting sea ice northeast of Svalbard (~81.5°N, ~30.5°E). Classical DVM behaviour (midnight rising, midday sinking) was observed between 20 and 80 m in young copepodite stages (CI–III) of Calanus finmarchicus and Calanus glacialis. The copepods Microcalanus spp., Pseudocalanus spp., Oithona atlantica, Oithona similis and Triconia borealis, alongside Eukrohnia hamata, Limacina helicina, and Fritillaria spp., all displayed signs of DVM. We conclude that zooplankton exhibit DVM in ice-covered waters over rather short distances to optimise food intake in the presence of predators.     

Morphological and reproductive acclimations to growth of two charophyte species in shallow and deep water

We investigated the distribution of two charophyte species, Chara fibrosa var. fibrosa (A. Br.) and Nitella hyalina (DC.) Ag., in Myall Lake, a shallow lake in New South Wales, Australia, in an attempt to elucidate the factors causing their distribution patterns. The field study was carried out from July 2003 to May 2005 and charophytes were sampled together with bottom sediments at 20 sampling locations in the lake on 13 occasions. Charophyte biomass (0–321 g DW m⁻²) displayed an optimum curve with depth and maximum biomass occurred between 1 and 2.5 m depth. In deeper water, shoots were longer (i.e., around 30 cm at 1 m depth to 60–90 cm between 2 and 4 m depth). Oospore and antheridia densities were higher in shallower water with a maximum around 80 cm. Plants growing in shallow depths had shorter internodes implying a short life cycle of shoots, and nodal spacing was relatively regular in contrast to its deep water counterparts although spacing tended to increase at locations farther from the apex. The present study also reports that there is an apparent decline in sexual propagule production rates with increasing water depth, further highlighting the different morphological and reproductive acclimations of charophytes in shallow and deep water.     

Phaeodarian Radiolaria from the Upper Cretaceous beds of central Japan

Upper Cretaceous Phaeodarea (Radiolaria) were recovered from the Shoya Formation, which crops out 100 km northwest of Tokyo, central Japan. The Shoya Formation consists of about 600 m-thick marine sedimentary rocks, represented by alternating beds of sandstone and mudstone, which are overlain by about 10 m of Phaeodarian-bearing siliceous mudstone. The latter is assigned to the Upper Cretaceous (late Campanian to early Maastrichtian) based on the associated Polycystine Radiolarian fossils. In spite of the poor general preservation of nearly all Phaeodarian specimens as recrystallized quartz infillings, three new Phaeodarian species, Challengeranium cretaceum, Challengeron paleotriangulum, and Medusetta fossilis, were identified on the basis of their shape and ornamentation. Our finding, together with two other very recent reports of fossil Phaeodarians clearly document that the origin of Phaeodarian Radiolarians can be extended back to at least the Upper Cretaceous.     

Hypoxia tolerance in the copepod Calanoides carinatus and the effect of an intermediate oxygen minimum layer on copepod vertical distribution in the northern Benguela Current upwelling system and the Angola-Benguela Front

There is a growing concern that hypoxic and anoxic areas in the sea spread in extent and intensity, posing a severe risk to marine ecosystems and fisheries. Hypoxia may affect fish stocks directly or via detrimental effects on important prey species, such as zooplankton. A unique feature of the northern Benguela Current upwelling region and Angola-Benguela frontal system is a pronounced intermediate oxygen minimum layer (IOML) at 60-500 m depth with oxygen concentrations ≤ 1.4 mg O₂l^− 1 (minimum < 0.7 mg O₂l^− 1). Field studies during February-March 2002 demonstrated that the abundance of calanoid copepods and the biomass of mesozooplankton in general were severely reduced within the IOML. The dominant copepod Calanoides carinatus showed a bimodal vertical distribution with parts of the population either comprising all developmental stages concentrated in the surface layer (0-60 m), or copepodids C5 diapausing below 400 m depth apparently avoiding the IOML. Accordingly, abundances of other calanoid copepods were higher at the surface and below 300 m than in the centre of the IOML. The scarcity of planktonic life within the IOML raises the question whether this layer represents an effective barrier for zooplankton vertical migrations. Especially in C. carinatus, ontogenetic vertical migration plays a key role in the retention of the population within the productive upwelling region and for the rapid re-colonisation of plumes of newly upwelled water. To address this issue, the hypoxia tolerance of C. carinatus was determined in a series of laboratory-based, closed-bottle experiments in January 2005. Copepods were kept in gas-tight bottles and the decreasing oxygen concentrations were monitored to establish their minimum oxygen demands. Although copepodids survived apparently unharmed at surprisingly low oxygen concentrations of ca. 1.5 mg O₂l^− 1, they could not tolerate oxygen levels < 1.1 mg O₂l^− 1, implying that the core of the IOML, where O₂ concentrations are below this threshold, is uninhabitable for C. carinatus. In contrast, the IOML may represent a refuge from competition and predation for other copepod species specifically adapted to hypoxic environments.     

First record of Devonian orthoceratid-bearing limestones in southern Calabria (Italy)

Lower to Middle Devonian orthoceratid-bearing nodular limestones in Calabria are described here for the first time, along the Fiumara Assi section. The succession is tectonically inverted and has been dated by conodonts. The lower beds are Lochkovian–Lower Pragian, because they provided Icriodus cf. steinachensis and Pelekysgnathus serratus, which occur in the delta-sulcatus Zones. Upwards appear Polygnathus cf. dehiscens, corresponding to the dehiscens-gronbergi Zones, and Ozarkodina cf. steinhornensis miae of the dehiscens-inversus Zones, both indicating a topmost Pragian–Lower Emsian age. The Eifelian (or younger) age for the top of the succession is demonstrated by Polygnathus linguiformis linguiformis. This succession, as well as similar coeval deposits of the southern Variscan Chain (southwestern Sardinia, eastern Pyrenees), Betic–Rifian Maláguides-Ghomarides and southern Alps, made part of a western embayment of the Palaeotethys.     

Gas exchange and low temperature resistance in two tropical high mountain tree species from the Venezuelan Andes

Temperature may determine altitudinal tree distribution in different ways: affecting survival through freezing temperatures or by a negative carbon balance produced by lower photosynthetic rates. We studied gas exchange and supercooling capacity in a timberline and a treeline species (Podocarpus oleifolius and Espeletia neriifolia, respectively) in order to determine if their altitudinal limits are related to carbon balance, freezing temperature damage, or both. Leaf gas exchange, leaf temperature-net photosynthesis curves and leaf temperature at which ice formation occurred were measured at two sites along an altitudinal gradient. Mean CO₂ assimilation rates for E. neriifolia were 3.4 and 1.3 μmol·m^–2·s^–1, at 2 400 and 3 200 m, respectively. Mean night respiration was 2.2 and 0.9 μmol·m^–2·s^–1 for this species at 2 400 and 3 200 m, respectively. Mean assimilation rates for P. oleifolius were 3.8 and 2.2 μmol·m^–2·s^–1 at 2 550 and 3 200 m, respectively. Night respiration was 0.8 μmol·m^–2·s^–1 for both altitudes. E. neriifolia showed similar optimum temperatures for photosynthesis at both altitudes, while a decrease was observed in P. oleifolius. E. neriifolia and P. oleifolius presented supercooling capacities of –6.5 and –3.0 °C, respectively. For E. neriifolia, freezing resistance mechanisms are sufficient to reach higher altitudes; however, other environmental factors such as cloudiness may be affecting its carbon balance. P. oleifolius does not reach higher elevations because it does not have the freezing resistance mechanisms.     

Testing the depth-differentiation hypothesis in a deepwater octocoral

The depth-differentiation hypothesis proposes that the bathyal region is a source of genetic diversity and an area where there is a high rate of species formation. Genetic differentiation should thus occur over relatively small vertical distances, particularly along the upper continental slope (200–1000 m) where oceanography varies greatly over small differences in depth. To test whether genetic differentiation within deepwater octocorals is greater over vertical rather than geographical distances, Callogorgia delta was targeted. This species commonly occurs throughout the northern Gulf of Mexico at depths ranging from 400 to 900 m. We found significant genetic differentiation (F_ST = 0.042) across seven sites spanning 400 km of distance and 400 m of depth. A pattern of isolation by depth emerged, but geographical distance between sites may further limit gene flow. Water mass boundaries may serve to isolate populations across depth; however, adaptive divergence with depth is also a possible scenario. Microsatellite markers also revealed significant genetic differentiation (F_ST = 0.434) between C. delta and a closely related species, Callogorgia americana, demonstrating the utility of microsatellites in species delimitation of octocorals. Results provided support for the depth-differentiation hypothesis, strengthening the notion that factors covarying with depth serve as isolation mechanisms in deep-sea populations.