Macrofaunal communities of threatened subtidal maërl seabeds on Tenerife (Canary Islands, north-east Atlantic Ocean) in summer

This study contributes with the first data on physical and taxonomical structure of macrofaunal assemblages of ma¨erl beds from the Canary Islands. Ma¨erl beds and Cymodocea nodosa meadows of the Canary Islands are considered biodiversity hot-spots in terms of taxonomic and functional biodiversity with a broad geographical and depth ranges. The authors have studied the structure of the macrofaunal assemblages on different habitat types (Cymodocea, Caulerpa, sabellid field, garden eel and ma¨erl beds). Samples were taken at a range of depths between 14 and 46 m. Correlations were performed among abiotic variables (granulometry, organic matter, nitrogen and phosphates) and the most abundant taxa. Similarity analysis was performed to explore the patchiness of seabeds at a local scale. Significant differences were found in macrofaunal assemblages among seabed types, with highest abundances and lowest biodiversity in sabellid fields, where the sabellid Bispira viola dominated. The polychaetes Aponuphis bilineata and Chone filicauda and the mollusc Turritella brochii were the most abundant taxa on ma¨erl beds. The mosaic of granulometric conditions would explain the associated macroinfaunal community structure and contribute to the creation of diversity on these relatively well preserved seabeds at a local scale.     

Paleoearthquake evidence in Tenerife (Canary Islands) and possible seismotectonic sources

A series of clastic dikes and tubular vents were identified in southern Tenerife (Canary Islands). These features are the result of seismic liquefaction of a Holocene sand deposit, as the consequence of a high intensity paleoearthquake. The peak ground acceleration (pga) and magnitude of the paleoearthquake generating these liquefaction features were estimated by back calculation analysis. A representative value of 0.30 ± 0.05 g was obtained for the pga. From this, an earthquake intensity of IX was estimated for the liquefaction site. Magnitude bound methods and energy based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M = 6.8. The zone in which the liquefaction structures are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing Holocene materials. Dating of the uplifted sand formation indicates an age of 10,081 ± 933 years, the liquefaction features ranging from this age to 3490 ± 473 years BP. This paleoearthquake was of much greater magnitude than those known historically. Faults with neotectonic activity are significant features that should be borne in mind when assessing the seismic hazards of the Canary Islands, presently considered as low and mainly of volcanic origin.     

Conspicuous sediment structures in fossil beach deposits (southern Tenerife, Canary Islands, Spain): paleoliquefaction features versus biogenic origin

Tubular-shaped concretions and concretionary dykes occur in Holocene fossil beach deposits between the township of El Médano and Punta Roja in southern Tenerife, Canary Islands. These sediment structures have been interpreted either as the result of (a) the interaction between hot ignimbrites that overflowed wet beaches; (b) fast accumulation of beach sands on hot and degassing ignimbrites; (c) paleoliquefaction caused by an earthquake (seismites). Based on the interpretation as seismites, an intense paleoearthquake with a moment magnitude of M = 6.8 was proposed to be responsible for the generation of the paleoliquefaction structures. However, we here reinterpret the sedimentary structures in question using the general criteria diagnostic for rhizocretions and root tubules with respect to their orientation, size, branching system, and style of cementation and, thus, consider them, to be of biogenic origin.     

Response of benthic opportunistic polychaetes and amphipods index to different perturbations in coastal oligotrophic areas (Canary archipelago,North East Atlantic Ocean)

Oligotrophic areas harbour low macrofaunal abundance and patchy distribution. In these areas it is necessary to test the reliability of biological indicators, especially those based on taxonomic sufficiency where the level of identification is balanced against the need for ecological information and could affect the efficiency of bioindicators. The BOPA (benthic opportunistic polychaetes and amphipods) index was applied in five coastal areas subjected to different perturbations (aquaculture, harbour, brine, sewage, and thermal pollution) in the Canary archipelago, an oligotrophic area of the Atlantic Ocean. Significant differences in the BOPA index between impact and control sites were only found in the area affected by a harbour. Perturbations such as aquaculture, brine or sewage discharge produce only a weak response of the BOPA index, whereas no effects were observed at thermal pollution‐impacted locations. The BOPA index should be used with caution to establish the ecological status of coastal water bodies in the Canary Islands, since it was only reliable in strongly impacted regions (enlargement harbour works), but did not respond clearly to other man‐induced perturbations.     

Reproductive pattern and egg development of the deep-sea crab Paromola cuvieri (Brachyura,Homolidae) around the Canary Islands (NE Atlantic)

This work investigated the biology of Paromola cuvieri in the Atlantic Ocean, including reproductive patterns, sex structure, depth distribution and egg development. Females were more abundant than males, mainly at depths greater than 600 m. Males were dominant in size classes larger than 110 mm carapace width (CW), especially over 120 mm, for which only males were observed. The mean length of both sexes decreased with depth. P. cuvieri appears to have continuous reproduction throughout the year. Large females tend to spawn mainly between summer and winter, but smaller females spawn during the summer. Four maturity categories were identified based on the ovary colour, and these categories were histologically validated. Three categories of testes were identified according to their colour and morphology. Sexual maturity was estimated at sizes between 71.6 and 74.0 mm CW for females and at 91.0 mm CW for males. The relative growth showed changes along the ontogeny, at 73.6 mm CW (females) and 91.3–92.2 mm CW (males). Egg development appears to not be completely synchronous, and two colour patterns can be observed simultaneously. Four stages of egg development were found: eggs undivided and fully filled with yolk in orange egg masses; eggs with a free region of yolk visible in orange or red egg masses; embryos with slightly pigmented, crescent-shaped eyes in brown egg masses; and embryos with visible pigmented structures, enlarged eyes, segmented appendages and abdomen in brown egg masses. The mean number of external eggs carried by females in stage I was estimated to be 315,753±19,267. Three species of barnacle were observed on the exoskeleton: Poecilasma aurantia, Poecilasma crassa and Heteralepas microstoma (Cirripedia, Thoracica).     

Recent (post-1930) changes in the extent of subtidal seagrass (Zostera muelleri) beds of the eastern Bay of Islands,New Zealand

The surface areas of 12 subtidal seagrass Zostera muelleri beds at the islands and adjacent mainland shores of the eastern Bay of Islands (35° 12′ S, 174° 10′ E), New Zealand were estimated from aerial images. It appears that little subtidal seagrass existed until after the early-1950s, so significant beds here may be a relatively recent biome. Possible explanations for recent emergence of subtidal seagrass include that debilitating periods of turbid water and pulses of sedimentation associated with the land clearances of the late 1800s had worked through the marine ecosystem. An overall peak in seagrass-cover in the 1960s to 1980s was followed by declines in several beds in the 1990s to 2000s, with recovery since. The temporal presence of seagrass was well-correlated among the three mainland beds, and moderately well among the south-facing beds on the islands, consistent with mechanisms driving seagrass establishment and persistence operating at reasonably broad scales.     

Changes in subtidal assemblages in a scenario of warming: Proliferations of ephemeral benthic algae in the Canary Islands (eastern Atlantic Ocean)

The present work analysed the main changes in subtidal algal assemblages in the last decade in an oceanic archipelago (Canary Islands – eastern Atlantic Ocean). Changes result from increases in cover of ephemeral benthic algae, such as the non-native chlorophyte Pseudotetraspora marina and the native cyanophytes Blennothrix lyngbyacea, Schizothrix calcicola and Schizothrix mexicana. Ephemeral algae overgrow subtidal assemblages which are extensively dominated by Lobophora variegata, but competitively do not exclude other species. Increases in the abundance of species coincided with a warming of about 2 °C in surface seawater temperature (SST) linked to the weakening of the Cold Canary Current and the Northwestern African upwelling. Shifts in the distribution and cover of ephemeral species follow the SST gradient from warmer waters in the western islands to colder waters in the eastern ones. While in the warmest western islands, species have spread quickly colonizing all type of substrates in just a few years (2005–2008), the occurrence of ephemerals towards the coldest eastern islands is yet inconspicuous.     

An estimate of Atlantic Ocean thermal energy conversion (OTEC) resources

An interhemispheric box model of the Atlantic thermohaline circulation (THC) is modified by replacing the tropical box with two vertically resolved sub-domains. Seawater flows from large-scale ocean thermal energy conversion (OTEC) are allowed in one of the tropical sub-domains. Under present conditions and standardized OTEC operations, steady-state net power production density would reach a maximum of about 80 kW/km² (corresponding to 1.8 TW) with a cold seawater withdrawal per unit area of about 14 m/yr. This maximum reflects the impact of large OTEC flows on the oceanic thermal structure, although the THC would not be significantly affected. It is larger than a recently suggested worldwide value of the order of 30 kW/km² because of the relative strength of the Atlantic THC. Under asymmetric high-latitude warming scenarios potentially representative of current climatic trends, a substantial weakening or a reversal of the THC are possible. In the former case, recoverable OTEC resources could practically vanish. In the latter case, the emergence of a stronger reverse THC eventually could boost OTEC resources. Such events are hypothetical and would unfold over centuries, but the mere possibility of their occurrence challenges the accepted notion that OTEC resources are forever renewable.     

Batch fecundity and spawning frequency of southern blue whiting (Micromesistius australis) in the southwest Atlantic Ocean

The reproductive biology of southern blue whiting (Micromesistius australis) inhabiting waters of the southwest Atlantic Ocean (52°‐53°S and 57°‐62°W) was studied through histological analysis of the ovaries. During 2003, the spawning peak occurred at the beginning of September south of the Malvinas Islands. Batch fecundity of this species ranged from 35 000 (41 cm total length, TL) to 245 000 (62 cm TL) oocytes and relative batch fecundity was 122 ± 43 (Mean ± SD, n = 24) oocytes per gram somatic weight. The average proportion of mature females with stage‐0 post‐ovulatory follicles was 0.25 for September 2003, which indicated a spawning frequency of 4 days during the peak of the season. Large females produced more egg batches than small spawners during the same period, but no significant relationship was found between oocyte dry weight and female size of southern blue whiting.     

Temporal Variations in the Dissolved Nutrient Stocks in the Surface Water of the Western North Atlantic Ocean

Changes in patterns of undetectability and molar ratios of dissolved nutrients in the euphotic zone of the oligotrophic western North Atlantic Ocean were investigated utilizing the Bermuda Atlantic Time-series Study (BATS) data set of the US Joint Global Ocean Flux Study (JGOFS). Our aim was to examine the temporal dynamics of nutrient stocks over a decade (1989∼1998) and to gain insight into the interactions between the different biotic and abiotic factors underlying BATS. Patterns of nutrient undetectability clearly revealed the depleted nature of the nutrients in surface water at the BATS location, particularly phosphorous. The N:P ratio was consistently far above the nominal Redfield ratio (mean, 38.5) but was significantly lower during the 1993∼1994 period (22.1). Over the same period the proportion of samples depleted in N only increased while the proportion of samples depleted in P only decreased. This indicates an overall reduction of N relative to P in the surface water at BATS during the 1993∼1994 period, the reasons for this anomaly, though, are not clear. The correlation analysis between the biotic and abiotic variables at BATS has indicated some interesting relationships that can help understand some of the parameters affecting nutrient stocks in the euphotic zone and their consequent impacts on marine biota. Although nutrient stocks in the oligotrophic environment are limited, they might be subject to interannual variation that may become anomalous in some cases. These variations might underlay significant feedback mechanisms by affecting marine productivity, the prime factor controlling the sequestration of atmospheric CO₂ by the oceans. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diversity and large-scale biogeography of Paramesochridae (Copepoda, Harpacticoida) in South Atlantic Abyssal Plains and the deep Southern Ocean

Multicorer samples for meiofaunal study were obtained within the framework of the international project CeDAMar, at 21 stations occupied during the DIVA and ANDEEP campaigns (2000, 2002 and 2005) to the southern Atlantic Ocean (Guinea, Angola and Cape Basins) and the Southern Ocean (Weddell and Scotia Seas), respectively. A total of 311 adult Paramesochridae Lang, 1944 (Copepoda, Harpacticoida) was extracted from 437 cores obtained during 83 deployments of the corer at depths between 1107 and 5655 m. All specimens were determined to species based on morphological characteristics. They belonged to 19 species and four genera (Kliopsyllus Kunz, 1962, Leptopsyllus T. Scott, 1894, Paramesochra T. Scott, 1892 and Scottopsyllus Kunz, 1962). Eleven species were restricted to single regions, whereas the others showed a much wider distribution. For example, Kliopsyllus andeep Veit-Köhler, 2004 and Kliopsyllus diva Veit-Köhler, 2005, were both collected from Guinea, Angola and Weddell Abyssal Plains, and Kliopsyllus schminkei Veit-Köhler & Drewes, 2009 occurred in the three West-African basins. This study provides a first insight into the large-scale biogeography of deep-sea harpacticoids, represented by the Paramesochridae, and indicates that distribution ranges, at least in this family, may extend across South Atlantic and Southern Ocean Abyssal Plains.     

Trends in the solubility of iron,aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean

The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO₄²⁻, NO₃⁻) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean.     

东山湾潮下带前鳃类软体动物的生态

本文研究了东山湾潮下带前鳃类软体动物的生态。结果表明,该湾有前鳃类软体动物31科59属86种。其中,分布到黄、渤海的有18种,分布到东海的有59种,只在南海分布的有26种。广温广布种占20.93%,暖水种55.81%,热带种仅5.81%。平均生物量和栖息密度分别为125.37g/m~2和16个/m~2,数量分布不均匀并有明显的季节变化。该湾主要有三个群落:棒锥螺-浅缝骨螺-红带织纹螺群落、假(?)拟塔螺-线缝骨螺-细肋蕾螺群落、细肋蕾螺-假(?)拟塔螺-双带光螺群落。前鳃类软体动物的种类组成、数量分布和群落结构与底质环境关系密切,生物量和栖息密度在粘土质粉砂和粉砂质粘土底质中较高。     

Coral assemblages and reef growth in the Commonwealth of the Northern Mariana Islands (Western Pacific Ocean)

Reef development varies considerably around the high, raised‐limestone islands of the Commonwealth of the Northern Mariana Islands (CNMI). Here we examine the modern assemblages at 30 sites for coral composition, colony density, colony size, and fidelity. We defined four reef types and hypothesize the presence of environmentally driven ecological stasis, whereby the environment continuously selects for coral species membership, defines colony sizes, and over time creates the noted reef types. Our results show that constructional spur‐and‐groove reefs supported significantly larger coral‐colony sizes and higher coral species richness compared with high‐relief interstitial framework, low‐relief incipient, and non‐constructional coral assemblages. Non‐constructional reefs supported much smaller coral colony sizes, despite similar population densities, and were consistently found in association with high wave exposure. The distinct coral assemblages found on interstitial framework and low‐relief incipient reefs were not affiliated with any wave exposure regime, but were located adjacent to large watersheds and on islands with unique geological history. These assemblages were nested within the spur‐and‐groove species pool. Overall, modern coral cover was well predicted by bathymetric slope and watershed size, while species richness was additively influenced by two proxies of pollution, suggesting the latter is better suited for establishing management targets. In contrast with previous studies that suggested modern assemblages were biologically controlled in the CNMI, we show reef assemblages and reef development are highly influenced by long‐term environmental forcing.     

Chromium(VI) distributions in the Arctic and the Atlantic Oceans and a reassessment of the oceanic Cr cycle

Chromium(VI) concentrations ranging between 3.0 and 6.1 nmol l⁻¹ and 3.1 and 7.3 nmol l⁻¹ were found in the Arctic and Atlantic Oceans, respectively. The vertical profiles show modest depletion of chromium(VI) in surface waters, but poor overall correlations between Cr(VI) and nutrient profiles. Given that Cr(VI) is the dominant oxidation state of chromium in open-ocean waters, these data are combined with literature data to reassess the distribution of Cr in oceanic waters. It is concluded that while Cr shows some characteristics of both “recycled” and “accumulated” vertical profiles, it does not fall clearly within either group.     

热带大西洋大眼金枪鱼和黄鳍金枪鱼渔场温跃层的时空变化特征

采用2007 ～2011年Argo浮标剖面温度资料研究了大西洋黄鳍金枪鱼(Thunnus albacares)和大眼金枪鱼(Thunnus obesus)延绳钓主要作业渔场温跃层的时空变化特征.研究结果表明热带大西洋黄鳍金枪鱼、大眼金枪鱼延绳钓主要作业渔场温跃层的上界深度和温度存在着明显的季节性变化.温跃层上界深度呈现出冬深夏浅的季节性变化特征,大致呈纬向带状分布,12月至翌年4月份,15°N以北海域温跃层上界深度超过80 rn,同期10°S以南海域的多低于50 m;6～10月份的则相反.在赤道纬向区域温跃层上界温度在27℃以上,往南北两侧30°区域温度值依次递减至20℃及以下.温跃层下界深度和温度没有明显的季节性变化.温跃层下界深度高值区域的空间分布呈现“W”形状,深度值在220 m以上.在25°S以南,从南美洲到非洲西沿岸海域并延伸到安哥拉外海,以及10°N非洲西海岸外海,在1a中的大部分月份里,温跃层下界深度浅于150 m.在15°N以北和15°S以南区域下界温度大于15℃,在这之间的纬向区域下界温度低于14℃.全年在大西洋西部的5 °～ 15°N和5 °～15°S区域的温跃层厚度最大,在80～150 m之间,冬季和夏季呈现相反的分布特征;温跃层强度高值在5°S～ 15°N纬向区域,尤其是大西洋东部,介于0.15 ～ 0.25℃/m之间.根据文中揭示的大西洋金枪鱼延绳钓主要作业渔场区温跃层的时空变化特征,作者建议晚上大眼金枪鱼和黄鳍金枪鱼投钩深度应该在温跃层上界深度分布的附近水域;白天捕捞黄鳍金枪鱼投钩深度应该在温跃层下界深度分布的水域附近,大眼金枪鱼投钩深度要比黄鳍金枪鱼的更深.     

Midwater fishes collected in the vicinity of the Sub-Polar Front,Mid-North Atlantic Ocean,during ECOMAR pelagic sampling

The ECOMAR project was a multidisciplinary process study conducted in the mid-North Atlantic, coincident hydrodynamically with the Sub-Polar Front (SPF; 48–54°N) and topographically with Charlie-Gibbs Fracture Zone of the Mid-Atlantic Ridge, as part of the Census of Marine Life field project MAR-ECO. Midwater trawling was conducted during the 2007 and 2009 ECOMAR expeditions at 14 stations north and south of the SPF, day and night, in four discrete depth intervals from 0 to 1000 m. A total of 56 species of midwater fishes representing 44 genera and 18 families were collected, several of which are new records for the region and/or were not previously sampled during MAR-ECO sampling. An annotated species list with depth-of-capture data is provided. Three species of the genus Cyclothone (Cyclothone braueri, Cyclothone microdon and Cyclothone pallida) and the myctophid Benthosema glaciale combined to contribute ~88% of all specimens collected. This finding differs from results of previous net-based sampling in the same area, likely due to sampling scheme differences (diel sampling, upper 800 m concentration) and gear selectivity (mesh size, trawl speed). Quantitative data from ECOMAR midwater sampling and the previous 2004 G.O. Sars MAR-ECO expedition are compared. Despite differences in gear between the major MAR-ECO expeditions, abundance estimates of some dominant species were remarkably similar. Data showed that the SPF is an asymmetrical, taxon-specific biogeographic boundary for deep-pelagic fishes in the North Atlantic; the SPF is semi-permeable to some species in one direction, while a strong boundary for species in another direction. Deeper-living fish species did not appear as affected by the SPF as a boundary.