Abundance of the introduced seastar, Asterias amurensis, and spatial variability in soft sediment assemblages in SE Tasmania: Clear correlations but complex interpretation

The northern Pacific seastar, Asterias amurensis, was first collected in southeast Tasmania in 1986. Mistaken for the endemic asteroid Uniophora granifera, its true identity was not realised until 1992. It is now a conspicuous predator in soft sediment habitats in this region, and is considered a major threat to native assemblages and commercial species. We examined the structure of soft sediment assemblages at different spatial scales in southeast Tasmania, and correlated spatial variation in community composition with seastar abundances. We found that the structure of soft sediment assemblages is highly variable at a range of spatial scales from metres to tens of kilometres. Clear differences in the composition of assemblages and abundances of major taxa were detected between areas with and without seastars and between areas with low and high seastar densities. However, the nature of these patterns suggests that they are more likely due to differences in sediment characteristics than due to impacts of the seastar. Thus, spatial differences in soft sediment assemblages might have been erroneously attributed to seastars without detailed information on important physical factors such as sediment characteristics. A second survey, using larger sampling units (1 m²) but across a more limited spatial extent, targeted bivalves and heart urchins that were identified as important prey of the seastar in observations of feeding and in experimental studies. Large-scale patterns of abundance and size structure were consistent with seastar effects anticipated from small-scale experimental and feeding studies for some, but not all, species. While the field survey ultimately provided evidence about the presence or absence of seastar impacts at large-scales, the identification of key ecological variables in experimental and feeding studies proved crucial to both the design and interpretation of patterns observed in the large-scale surveys. Overall, this work highlighted the necessity to consider multiple lines of evidence rather than relying on a single ‘inferential’ test, in the absence of pre-impact data.     

Optimum Sample Size to Detect Perturbation Effects: The Importance of Statistical Power Analysis – A Critique

Abstract. The current article describes statistical power analysis as an efficient strategy for the estimation of the optimum sample size. The principle aim is constructively to criticise and enrich the results presented by Mouillot et al. (1999) , who estimate the optimum sample size for evaluating possible perturbations. The authors did not make any reference to statistical power analysis, even though their objective clearly went beyond a simple stock evaluation to assess management strategies in a particular marine ecosystem. Surprisingly, they proposed (a priori) an ANOVA design to test a hypothesis considering both space and temporal scales. However, the authors did not cover important topics related with power analysis and the precautionary principle, both used into environment impact assessment programmes for marine ecosystems. Based on their results and on statistical power analysis, it is demonstrated that the variability (dispersion statistics), a key factor they used to estimate the sample size, is less relevant than the magnitude of perturbation (effect size). Therefore, a greater effort must be devoted to estimate the effect size of a particular phenomenon rather than a desired variability.     

Surface circulation of the Levantine Basin: Comparison of model results with observations

The eastern Mediterranean (Levantine Basin) hydrography and circulation are investigated by comparing the results of a high-resolution primitive equation model with observations. After a 10-year integration, the model is able to reproduce the major water masses and the circulation patterns of the eastern Mediterranean. Comparisons with the POEM hydrographical observations show good agreement. The vertical distribution of the water masses matches that of the observations quite well in terms of monthly mean. The model surface circulation is in agreement with circulation schemes derived from recent observations. Some well-known mesoscale features of the upper thermocline circulation are also realistically reproduced. In agreement with satellite observations, the model shows that high-energy mesoscale eddies dominate the upper thermocline circulation in the southern and the central parts of the Levantine Basin. Most of the Atlantic Water follows the north African coast and forms a strong coastal jet near the Libyan coast rather than forming the Mid-Mediterranean Jet described by several authors. The sub-basin circulation shows a strong seasonal signal. A strong and stable current flows along the isobaths in winter, becoming weaker and with more meanders in summer. The mesoscale eddies throughout the whole basin are more energetic in summer than in winter.     

Three‐dimensional simulation of tsunami run‐up around conical island

At the circular Babi Island in the Flores tsunami (1992) and pear shaped island in the Okushiri event (1993), unexpectedly large tsunami run‐up heights in the lee of conic islands were observed. The flume and basin physical model studies were conducted in the Coastal Hydraulic Laboratory, Engineering Research and Development Center, U.S. Army Corps of Engineers to provide a better understanding of the physical phenomena and verify numerical models used in predicting tsunami wave run‐up on beaches, islands, and vertical walls. Reasonably accurate comparison of run‐up height of solitary waves on a circular island has been obtained between laboratory experimental results and two‐dimensional computation model results. In this study we apply three‐dimensional RANS model to simulate wave run‐up on conical island. In the run‐up computation we obtain that 3D calculations are in very good comparison with laboratory and 2D numerical results. A close examination of the three‐dimensional velocity distribution around conical island to compare with depth‐integrated model is performed. It is shown that the velocity distribution along the vertical coordinate is not uniform: and velocity field is weaker in the bottom layer and higher on the sea surface. The maximum difference (about 40%) appears at the time when solitary wave reached the circular island.     

Shoreline variability via empirical orthogonal function analysis: Part I temporal and spatial characteristics

Empirical orthogonal functions (EOFs) or principal components were used to extract the significant modes of shoreline variability from several data sets collected at three very different locations. Although EOFs have proven to be a valuable tool in the analysis of nearshore data, most applications have focused on the ability of the technique to describe cross-shore or profile variability. Here however, EOFs were used to help identify the dominant modes of longshore shoreline variability at Duck, North Carolina, the Gold Coast, Australia, and at several locations within the Columbia River Littoral Cell in the U.S. Pacific Northwest. In part one of this analysis, characteristic patterns of shoreline variability identified by the EOF analysis are described in detail. At each site, the dominant modes consisting of the first four eigenfunctions were found to describe nearly 95% of the total shoreline variability. At both Duck and the Gold Coast, several interesting longshore periodic features suggestive of sand waves were identified, while boundary effects related to natural headlands and navigational structures/entrances dominated the Pacific Northwest data sets.     

Water mass formation variability in the intermediate layer of the east sea

Long-term variability in the intermediate layer of the eastern Japan Basin has been investigated to understand the variability of water mass formation in the East Sea. The simultaneous decrease of temperature at shallower depths and oxygen increasing at deeper depths in the intermediate layer took place in the late 1960’s and the mid-1980’s. Records of winter sea surface temperatures and air temperatures showed that there were cold winters that persisted for several years during those periods. Therefore, it was assumed that a large amount of newly-formed water was supplied to the intermediate layer during those cold winters. Close analysis suggests that the formation of the Upper Portion of Proper Water occurred in the late 1960’s and the Central Water in the mid-1980’s.     

Velocity-Interface Structure of the Southwestern Ryukyu Subduction Zone from EW9509-1 OBS/MCS Data

A wide-angle seismic survey, combining ocean-bottom seismometers (OBS) and multi-channel seismic (MCS) profiling, was implemented in the southwestern Ryukyu subduction zone during August and September 1995. In this paper, we present the data analysis of eight OBSs and the corresponding MCS line along profile EW9509-1 from this experiment. Seismic data modeling includes identification of refracted and reflected arrivals, initial model building from velocity analysis of the MCS data, and simultaneous and layer-stripping inversions of the OBS and MCS arrivals. The velocity-interface structure constructed along profile EW9509-1 shows that the northward subduction of the Philippine Sea Plate has resulted in a northward thickening of the sediments of the Ryukyu Trench and the Yaeyama accretionary wedge north of the trench. The boundary between the subducting oceanic crust and the overriding continental crust (represented by a velocity contour of 6.75 km/s) and a sudden increase of the subducting angle (from 5 degrees to 25 degrees) are well imaged below the Nanao Basin. Furthermore, velocity undulation and interface variation are found within the upper crust of the Ryukyu Arc. Therefore, the strongest compression due to subduction and a break-off of the slab may have occurred and induced the high seismicity in the forearc region. This revised version was published online in November 2006 with corrections to the Cover Date.     

中国近海沿岸海温多时间尺度变率及影响其变化的天气气候因素

本文通过对中国近海13个海洋站1959年～2003年逐日日平均海表温度及其相关数据的处理分析,结合中国近海多年逐日天气实况,研究了中国近海水温的短时（1d）、过程、旬、月、年际变率以及海温的长期趋势变化,并在此基础上详细讨论了影响中国近海各时间尺度水温变化的天气气候因素.     

The Aleutian Low, storm tracks, and winter climate variability in the Bering Sea

Previous studies have found inconsistent results regarding how wintertime conditions in the Bering Sea relate to variations in the North Pacific climate system. This problem is addressed through analysis of data from the NCEP/NCAR Reanalysis for the period 1950–2003. Composite patterns of sea-level pressure, 500 hPa geopotential heights, storm tracks and surface air temperature are presented for four situations: periods of strong Aleutian Low, weak Aleutian Low, warm Bering Sea air temperatures, and cold Bering Sea air temperatures. Winter temperatures in the Bering Sea are only marginally related to the strength of the Aleutian Low, and are much more sensitive to the position of the Aleutian Low and to variations in storm tracks. In particular, relatively warm temperatures are associated with either an enhanced storm track off the coast of Siberia, and hence anomalous southerly low-level flow, or an enhanced storm track entering the eastern Bering Sea from the southeast. These latter storms do not systematically affect the mean meridional winds, but rather serve to transport mild air of maritime origin over the Bering Sea. The leading indices for the North Pacific, such as the NP and PNA, are more representative of the patterns of tropospheric circulation and storm track anomalies associated with the strength of the Aleutian Low than patterns associated with warm and cold wintertime conditions in the Bering Sea.