Life Cycle of Liocarcinus arcuatus (Brachyura: Portunidae) in the Ría de Arousa (Galicia, NW Spain): Role of Beach and Mussel Raft Culture Areas

Abstract. The population biology of the portunid crab Liocarcinus arcuatus is analyzed over a yearly cycle in beach zones and mussel raft culture areas in the Ria de Arousa.
The breeding cycle of this species has two annual peaks, which result in two annual cohorts that are recruited in different areas. The growth rate is higher in the group settled in spring than in autumn, and, especially, in the culture areas compared with the beach zones. There are movements from the beach zones to the raft polygons related to reproductive and feeding behavior as well as growth. The role of mussel culture in the dynamics of this species is discussed.     

Microstructure measurements in natural waters: Methodology and applications

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding.A new analytical approximation for the 1D Panchev–Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations.Statistical analysis of eddy K_b and thermal K_θ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between K_b and K_θ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged K_b and K_θ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χ_θ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.     

Bioaccumulation and depuration of Zn and Cd in mangrove oysters (Crassostrea rhizophorae, Guilding, 1828) transplanted to and from a contaminated tropical coastal lagoon

In order to study Zn and Cd accumulation and depuration, a set of oysters, Crassostrea rhizophorae, were transplanted to a metal contaminated coastal lagoon and another one was harvested there and transplanted to a non-polluted site. C. rhizophorae oysters and Perna perna mussels native from both sites were collected in order to monitor variability of metal concentration in resident populations. After three months exposure, oysters transplanted to the polluted site accumulated fourfold Zn (307-1319 microgg(-1)) without reaching the concentration level of resident oysters (9770 microgg(-1)). Cadmium concentrations had a slight but significant decrease during the same period (1.25-0.54 microgg(-1)). Oysters transplanted to the non-polluted site, showed threefold Zn depuration (6727-2404 microgg(-1)), while Cd had no significant variation (0.90-1.45 microgg(-1)). Results showed that transplanted oysters do not reach heavy metal concentrations in indigenous populations suggesting transplanted organisms would be better used to evaluate bioavailability instead of environmental concentrations.     

Micropalaeontological record of Holocene estuarine and marine stages in the Corgo do Porto rivulet (Mira River, SW Portugal)

The Corgo do Porto is a small tributary of the Mira River, outleting 3.5 km upstream of its mouth. The valley is flat-floored due to terrigenous siltation and forms an alluvial plain reclaimed for agriculture/aquaculture. These conditions were quite distinct in the recent past because of extensive marine flooding of this area during the high-rate positive eustatism that followed the Last Glacial Maximum. The Holocene sedimentary column registers changes imposed by several forcing factors, mainly the climate-driven sea-level rise. As part of a multidisciplinary study, the sedimentological and micropalaeontological (benthic foraminifera and calcareous nannofossils) contents of a core taken from this infill were analyzed, and five different stages were distinguished within its environmental evolution: Stage A (prior to 10,000 cal yrs BP) consists of muddy, matrix-supported sand with abundant pebbles, barren of microfossils, and free of carbonates and organic matter that represents a fluvial environment contemporaneous of a low sea level. Between 10,000 and circa 4000 cal yrs BP the sediment is made of homogeneous mud, with bioclasts and organic matter. However, the assemblages of foraminifera and calcareous nannoplankton allowed the identification of several environmental stages, defining a cycle of increasing–decreasing marine influence inside the valley: brackish and brackish-marine sedimentation (Stage B), full-marine sedimentation (Stage C) and a return to brackish-marine sedimentation (Stage D). The final part of the core is barren of microfossils (Stage E) and it represents the modern sedimentation in the area with an accreting alluvial plain. This Holocene sedimentary sequence reflects an evolutionary succession that closely agrees with the palaeoenvironmental model previously presented by the authors elsewhere for the south-western Portuguese coast, where a change in the rate of sea-level rise has been recorded at around 5500 cal yrs BP when a very effective sandy barrier formed and isolated restricted brackish to fresh-water lagoonal environments from the open sea.     

Spartina anglica eradication experiment and in situ monitoring assess structuring strength of habitat complexity on marine macrofauna at high tidal level

The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure.     

Optimisation of wave energy extraction with the Archimedes Wave Swing

This paper addresses the Archimedes Wave Swing (an offshore wave energy converter, which produces electricity from sea waves). It compares the performances of latching control (a discrete, highly non-linear, intrinsically sub-optimum control strategy), of reactive control, of phase and amplitude control (two optimum control strategies that involve non-causal transfer functions, which have to be implemented with approximations, thus rending the control sub-optimum), and of feedback linearisation control (a non-linear control strategy). From extensive simulations it is concluded that the latter performs clearly better irrespective of the sea state, and leads to a significant increase of absorbed wave power.     

Timing of diagenesis and very low‐grade metamorphism in the eastern sector of the Sierra de Cameros (Iberian Range,Spain): a U–Pb SHRIMP study on monazite

The Sierra de Cameros is an intracontinental orogen and represents the north‐western part of the Iberian Range in Northern Spain. It comprises a thick sequence of syn‐rift continental sediments (mainly sandstones and carbonates) deposited during lower Cretaceous times. A unique characteristic of the Sierra de Cameros in relation to the rest of the Iberian Range is the presence of low‐grade metamorphism in certain parts of the basin, an event that predates basin inversion. This paper describes the presence, textural relationships and geochemical aspects of authigenic and/or metamorphic monazite within different lithologies from the deepest parts of the basin. Sensitive high resolution ion microprobe (SHRIMP) U–Pb dating of monazite records the presence of two age populations: the first with ²⁰⁶Pb/²³⁸U ages ranging from 122 to 116 Ma which is considered as diagenetic in origin, whilst the second is dated at 99 ± 2 Ma and postdates the metamorphic climax.     

Holocene glacier and deep water dynamics,Adélie Land region,East Antarctica

This study presents a high-resolution multi-proxy investigation of sediment core MD03-2601 and documents major glacier oscillations and deep water activity during the Holocene in the Adélie Land region, East Antarctica. A comparison with surface ocean conditions reveals synchronous changes of glaciers, sea ice and deep water formation at Milankovitch and sub-Milankovitch time scales. We report (1) a deglaciation of the Adélie Land continental shelf from 11 to 8.5 cal ka BP, which occurred in two phases of effective glacier grounding-line retreat at 10.6 and 9 cal ka BP, associated with active deep water formation; (2) a rapid glacier and sea ice readvance centred around 7.7 cal ka BP; and (3) five rapid expansions of the glacier–sea ice systems, during the Mid to Late Holocene, associated to a long-term increase of deep water formation. At Milankovich time scales, we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier–sea ice–ocean system throughout the Holocene, in the Adélie Land region. In addition, the orbitally-forced seasonality seems to control the coastal deep water formation via the sea ice–ocean coupling, which could lead to opposite patterns between north and south high latitudes during the Mid to Late Holocene. At sub-Milankovitch time scales, there are eight events of glacier–sea ice retreat and expansion that occurred during atmospheric cooling events over East Antarctica. Comparisons of our results with other peri-Antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier–sea ice–ocean interactions and their Holocene evolutions reflect a more global Antarctic Holocene pattern.