Ibiza Absolute Calibration Experiment: Survey and Preliminary Results

Within the framework of a project comprising part of the Spanish Space Program related to the JASON-1 CNES (Centre National d'Etudes Spatiales)/NASA (National Aeronautics and Space Administration) mission, a campaign was conducted from June 9–17, 2003, on the Absolute Calibration Site of the island of Ibiza. The objective was to determine the local marine geoid slope under the ascending (187) and descending (248) Jason-1 ground tracks, in order to allow a better extrapolation of the open-ocean altimetric data with on-shore tide gauge locations, and thereby improve the overall precision of the calibration process. For this we have used a catamaran with two GPS antennas onboard, following the Corsica/Senetosa design (Bonnefond et al. 2003a Bonnefond, P., Exertier, P., Laurain, O., Menard, Y., Orsoni, A., Jeansou, E., Haines, B., Kubitschek, D. and Born, G. 2003a. Leveling Sea Surface using a GPS catamaran. Marine Geodesy, 26(3–4): 319–334. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Five GPS reference stations were deployed in order to reduce the distance between the areas covered by the catamaran and the fixed GPS receiver used in the kinematic process. The geodetic activities (e.g., GPS, leveling) have enabled the building of a very accurate (few mm) network in a reference frame compatible with the satellite altimetry missions (ITRF 2000). The GPS kinematic data were processed using two different software programmes, allowing checking of the consistency of the solutions. If the standard deviation of the differences (3.3 cm) is close to the kinematic process precision, they exhibit some large values (up to 14 cm). These large discrepancies have been reduced using a weighting based on the crossover differences. Inasmuch as the distances between the tide gauges and the areas covered by the GPS catamaran were becoming large, we have used the MOG2D ocean model (Carrère and Lyard 2003 Carrère, L. and Lyard, F. 2003. Modelling the barotropic response of the global ocean to atmospheric wind and pressure forcing—comparisons with observations. Geophys. Res. Letters, 30(6) [Google Scholar]) to correct the sea surface from tides. In the farthest areas, the crossover differences show an improvement by a factor of two. Finally, we also present preliminary results on Jason-1 altimeter calibration using the derived marine geoid. From this analysis, the altimeter bias is estimated to be 120 ± 5 mm. The quality of this first result validates the whole GPS-based marine geoid processing, for which the accuracy is estimated to be better than 3 cm rms at crossovers.     

Submerged vegetation of the Rotorua and Waikato lakes

Five plant communities in Lake Rotoiti, North Island, New Zealand (38° 02’ S, 176° 24’ E) are described. In shallow water (0–2 m depth) partly protected from the prevailing westerly winds, some indigenous species form characteristic mounds. From 2 to 6 m depth the exotic macrophyte Lagarosiphon major (Ridley) Moss is the dominant and forms dense beds which appear to have completely replaced any native vegetation. Elodea canadensis Michx., a longer‐established exotic, may form a minor component of this zone, but may become the dominant species in water above and below the Lagarosiphon zone. Lagarosiphon appears to be primarily restricted to silty sand, but on pure silt areas it is replaced by Elodea and/or Nitella hookeri A. Braun. These zonations are probably static rather than successional. On underwater cliff faces and boulder shores a seasonal succession of algae was the major vegetation. Only filamentous cyanophytes grew within 1–2m of geothermal springs in the lake.     

Oxygen consumption in the epilimnia and hypolimnia of two eutrophic,warm‐monomictic lakes

Oxygen consumption was estimated for two eutrophic New Zealand lakes using a simple 2‐layer model, from estimates of net changes in oxygen, phytoplankton photosynthesis, inflow and outflow, diffusion, eddy diffusion, and changes in the depth of the thermocline. Of the total oxygen consumption, 75–85% occurred in the epilimnia. Epilimetic oxygen consumption per m³ and per m² in Lake Johnson were higher than in Lake Hayes, reflecting known differences in the trophic status of the lakes, but estimates for the hypolimnia of the two lakes were similar. Daily hypolimnetic areal deficits were sensitive to both the depths and time intervals chosen.

In the epilimnia, monthly oxygen production by photosynthesis averaged 1.1 and 1.8 times the initial oxygen content in Lakes Hayes and Johnson respectively. Diffusion appeared to be of similar magnitude to photosynthesis in the isothermal period, but was less important during stratification. Losses to the hypolimnia by eddy diffusion were less than 10% of photosynthesis. Photosynthesis in the hypolimnia contributed 30–40% of the oxygen consumed there and eddy diffusion supplied a further 20%.

In Lake Johnson a 3–5 m stratum of water in the metalimnion became anoxic for 2–3 months each summer while there were still up to 5.2 g.rer³ of oxygen remaining in the hypolimnion. Metalimnetic anoxia is attributed largely to oxygen consumption in situ, resulting from the highly eutrophic state of the lake and intense thermal stratification. Zooplankton respiration accounted for less than 10% of the maximum net decline in metalimnetic oxygen in 1970–71, but was more important in the other 2 years.

Changes in the oxygen content of the hypolimnion indicate that Lake Hayes has become more eutrophic since 1954–55. In Lake Johnson low oxygen concentrations at the autumn overturn (<5 g.m^‐3) represent a threat to the trout population.     

Evaluation of the Variability of the Shoreline of the Tsimlyansk Reservoir and Lake Ilmen according to Space Sounding Data

Izvestiya, Atmospheric and Oceanic Physics - This article presents the results of a study of the dynamics of the shorelines of Lake Ilmen and the Tsimlyansk Reservoir to indicate the location of...     

Composition and secondary alterations of microfossils in sediments of the Ashadze-1 hydrothermal field (tropical Mid-Atlantic Ridge)

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms, as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone of Fe-Mn crusts.     

Response of juvenile lemon sharks, Negaprion brevirostris, to a magnetic barrier simulating a beach net

Beach nets are preventative devices used to minimize interactions between potentially harmful sharks and unsuspecting swimmers. Quantitative studies demonstrated that beach nets drastically reduced local elasmobranch populations, as well as caused considerable bycatch mortality. For this experiment, a beach net-like device was constructed and the behaviors of six juvenile lemon sharks (Negaprion brevirostris) were analyzed. Induced by olfactory and gustatory cues, sharks were given the choice to swim through a magnetic or control opening in the net. In the first trial, all six sharks avoided the magnetic region and significantly preferred to swim through the control region of the fence. The magnetic stimulus no longer affected the swimming behavior of three sharks retested after resting 24 h. Results from the retested sharks were correlated with those from repeated tonic immobility trials, which demonstrated a linear decrease in sensitivity to repeated magnetic stimulation. This study serves as a baseline experiment demonstrating that permanent magnets may substantially decrease elasmobranch mortality within beach nets.     

Integration of biochemical, histochemical and toxicogenomic indices for the assessment of health status of mussels from the Tamar Estuary, U.K

The aim of this study was to examine whether a combination of biochemical, histopathological and toxicogenomic data could be used as a valuable tool for the assessment of biological risk associated with pollutants within the Tamar River and Estuary, S.W. England, U.K. Accordingly, biochemical and histopathological biomarkers (protein carbonyls, lipofuscin, neutral lipids, lysosomal stability [N-acetyl-β-hexosaminidase and neutral red], lysosomal volume, ferric reducing antioxidant power [FRAP] and malonaldehyde [MDA]) and gene expression profiles were assessed in 5 sites from the Tamar River and Estuary (Neal Point, Town Quay, Wilcove, Cremyll Ferry and Whitsand; and a reference site, Trebarwith Strand, N. Cornwall). PAHs were measured in mussel tissue and sediment and metals were measured in mussel tissue only. Data from the biomarkers was integrated into a Mussel Expert System (MES) model to produce a simple assessment of mussel stress. Clear gradients of mussel toxicity were identified by the biomarkers (with the exception of neutral lipids) with the highest impacted animals found furthest up the Tamar, whilst the MES was unable to identify a gradient of effect. Gene expression profiles also indicated a gradient of stress with the greatest number of significantly up- or down- regulated genes found at the uppermost 2 sites. The MES did, however, determine that mussels from all sites, except the reference site, were highly stressed; a conclusion that could not be inferred from the biomarker data alone. It is concluded that the MES is a valuable tool that permits integration and interpretation of complex sets of biomarker data by identifying the biological meaning of biomarker changes.     

Differential reproductive strategies of two bivalves in the Dutch Wadden Sea

Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria.     

Effects of Cystoseira Sensu lato (Fucales: Phaeophyceae) on Species Richness,Composition, and Biomass of Abrau Peninsula Shelf Macrophytobenthic Communities (Black Sea)

Oceanology - Field observations were applied to study the macrophytobenthos of the Abrau Peninsula of the Black Sea and the effect of the two most common and largest species of brown algae of the...     

The way forward with ecosystem-based management in tropical contexts: Reconciling with existing management systems

This paper discusses some of the challenges and opportunities that can arise when implementing ecosystem-based management (EBM) in tropical nations. EBM creates a new series of challenges, problems, and opportunities that must be considered in light of existing governance and management frameworks in a local context. The paper presents five case studies from different parts of the tropical world, including Oceania, insular and continental Southeast Asia, East Africa, and the Caribbean, which illustrate that the implementation of EBM in watershed and marine ecosystems offers a new series of challenges and opportunities for its inclusion with existing forms of environmental governance and management. The paper suggests that EBM is best thought of as an expansion of customary management (CM) and integrated coastal management (ICM), rather than a paradigm shift, and that it has certain benefits that are worth integrating into existing systems when possible. The paper concludes that the cultural and institutional context of CM as well as the experience, technical skills, and legal basis that serve ICM programs are logical platforms from which to build EBM programs. Some guidelines for creating hybrid management regimes are suggested. In sum, declining marine species and ecosystems require urgent action, necessitating utilization of existing paradigms such as ICM and CM as a foundation for building EBM.