Spatio-temporal variation in the structure of a deep water Posidonia oceanica meadow assessed using non-destructive techniques

The Malta-Comino Channel (Maltese islands, central Mediterranean), supports extensive meadows of the seagrass Posidonia oceanica that in some places extend to a depth of around 43 m, which is rare for this seagrass. To assess spatial and temporal variation in the state of the deeper parts of the P. oceanica meadow with time, data on the structural characteristics of the seagrass meadow at its lower bathymetric limit were collected during the summers of 2001, 2003 and 2004 from four stations (two stations within each of two sites) located at a similar depth, over a spatial extent of 500 m. Shoot density was estimated in situ, while data on plant architecture (number of leaves, mean leaf length, and epiphyte load) were successfully obtained using an underwater photographic technique that was specifically designed to avoid destructive sampling of the seagrass. Results indicated that P. oceanica shoot density was lower than that recorded from the same meadow during a study undertaken in 1995; the observed decrease was attributed to the activities of an offshore aquaculture farm that operated during the period 1995–2000 in the vicinity of the meadow. ANOVA indicated significant spatial and temporal variations in meadow structural attributes at both sites during the 3-year study; for example, shoot density values increased overall with time at site A; a indication of potential recovery of the meadow following cessation of the aquaculture operations. Lower shoot density values recorded from site B (compared with site A) were attributed to higher epiphyte loads on the seagrass, relative to those at site A. The findings, which include new data on the structural characteristics of P. oceanica occurring at depths >40 m, are discussed with reference to the use of the nondestructive photographic technique to monitor the state of health of deep water seagrass meadows.peer-reviewe

Structural changes in a Posidonia oceanica meadow exposed to a pollution gradient from a marine fish-farm in Malta (Central Mediterranean)

Posidonia oceanica morphological parameters where measured at increasing distance from a marine fish-farm that has been operational for 7 years. Most parameters changed significantly with increasing distance from the cages, the greatest change occurring in the first 50 m.peer-reviewe

The effects of a marine fish-farm on the species richness and abundance of molluscs, decapods and echinoderms associated with a "Posidonia oceanica" meadow in Malta (Central Mediterranean)

The composition of the echinoderm, mollusc and decapod assemblages associated with a Posidonia oceanica meadow located close to a fish-farm varied with distance from the cages Three ecological zones were identified. The intermediate zone II (40-160m from the cages) had a higher species richness and abundance than either zones I (nearest the cages) and III (320m from the cages), probably due to the higher production resulting from a moderate level of nutrient enrichment at intermediate distances from the source of pollution.peer-reviewe

Baseline marine benthic surveys in the Maltese Islands (Central Mediterranean)

Extract from: MEDCOAST 97 : Proceedings of the Third International Conference on the Mediterranean Coastal Environment, Qawra, Malta / E. Ozhan (editor), (1997)During the period 1991 to 1997, extensive baseline studies of the submarine geomorphology, infralittoral habitats, macrobenthic assemblages, and demersal fish fauna, were carried out in 14 different sites around the Maltese Islands, using conventional SCUBA diving techniques. These were made as part of assessments of the environmental impact of existing or proposed projects, or in order to produce an inventory of coastal resources. In total, these surveys covered a sea-bed area of ca. 7.55Km² and a coastline length of ca 24 km, and represent the most extensive biological surveys of the marine environment carried out to date in the Maltese Islands. The results of these surveys have been presented as maps showing the type, location, and spatial extent of these physical and biological features. The Peres & Picard (1964) scheme, as adapted by Pen~s (1967; 1982) was used to classify and characterize the benthic assemblages recorded during the surveys. Our results show that, in tenus of spatial extent, the most important macrobenthic assemblages are the communities of photophilic 'algae on hard substrata, meadows of the sea-grass Posidonia oceanica and communities of bare well-sorted sand. For all these, many subtypes and facies exist, depending on the light intensity, hydrodynamic conditions, microtopography, sediment granulometry and other edaphic factors, and anthropic influences, including pollution. Other assemblages with a limited spatial distribution include meadows of the sea-grass (vmodocea nodosa and of the Lessepsian immigrant Halophila stipu/acea on sandy bottoms, the assemblages of boulder fields which are complexes of photophilic and sciaphilic communities, and those of marine caves. Our maps are supplemented by descriptions of the different habitats and macrobenthjc assemblages, species lists, and semi-quantitative data on percentage cover for the dominant macroalgae, shoot density counts for sea-grass meadows, and population density counts for the main macrofaunal species. These maps and data-sets are intended to be used (i) for assessing the status of habitats, species assemblages, and individual species, around the Maltese Islands in order to recommend appropriate measures for their conservation, including inclusion in red data lists; (ii) for designation of marine protected areas; and (iii) as baselines against which future monitoring studies and surveys can be compared.peer-reviewe

Production rates of neon xenon isotopes by energetic neutrons

As a first step in an experimental program to study the behavior of noble gases produced in situ in minerals, a suite of minerals and pure chemicals were irradiated with 14.5 MeV neutrons at LLNL's Rotating Target Neutron Source (RTNS-II) and production rates for noble gases were determined. While neutron effects in meteorites and lunar samples are dominated by low-energy neutron capture, more energetic cosmic-ray secondary neutrons can provide significant depth-dependent contributions to production of cosmogenic nuclides through endothermic reactions such as (n,2n), (n,np), (n,d) and (n,alpha). Production rates for nuclides produced by cosmic-ray secondary neutrons are therefore useful in interpreting shielding histories from the relative abundances of cosmogenic nuclides. Absolute production cross sections were calculated from isotope dilution analyses of NaCl, Mg, CsCl, and Ba(NO3)2 samples, assuming purity, stoichiometry, and quantitative noble gas retention and extraction. Relative production cross sections determined from neon isotopic ratios in the mineral samples were also considered in evaluating the neon production cross sections. Results are presented

Mean first passage time analysis reveals rate-limiting steps, parallel pathways and dead ends in a simple model of protein folding

We have analyzed dynamics on the complex free energy landscape of protein folding in the FOLD-X model, by calculating for each state of the system the mean first passage time to the folded state. The resulting kinetic map of the folding process shows that it proceeds in jumps between well-defined, local free energy minima. Closer analysis of the different local minima allows us to reveal secondary, parallel pathways as well as dead ends.Comment: 7 page

The state of Posidonia oceanica (L.) Delile meadow in the Maltese Islands (Central Mediterranean)

We have assessed the state of local Posidonica oceanica meadows by considering spatial and bathymetric distribution, general health and plant morphological characteristics. Our results show that dense and healthy meadows cover large areas off bottom of the Maltese coasts and extend to considerable depths, in places down to 43 meters.peer-reviewe

Preliminary data on the occurrence and distribution of shallow water marine sponges (Porifera) around Maltese coasts

Data on the ecology of the Maltese Porifera is lacking altogether. Even documented basic information on the occurrence of commercial sponge species in Maltese coastal waters is unavailable. This study presents the results of a four-year diving survey aimed at studying the occurrence and distribution of shallow water sponges around the Maltese Islands.peer-reviewe

Alignment of marine habitat data of the Maltese Islands to conform to the requirements of the EU habitats directive (Council Directive 92/43/EEC)

In 1992 the European Union (henceforth referred to as the EU) adopted a Council Directive on the conservation of natural habitats and wild fauna and flora that became known as the ‘Habitats Directive’. This Directive contains a range of measures aimed at the protection of species and habitats of EU interest. One of these measures requires each Member State to forward to the European Commission a list of sites proposed for inclusion in a EU-wide network of protected areas known as NATURA 2000. Sites adopted at Community level will be designated by Member States as Special Areas of Conservation (SACs).peer-reviewe

Preliminary data on bathymetric and temporal changes in the morphology of a Maltese Posidonia oceanica (L.) Delile meadow

Preliminary data on the morphology of a local Posidonia oceanica meadow were obtained as part of an ongoing study on the community structure and composition of the vagile fauna associated with this seagrass. The values for Shoot Density, Leaf Standing Crop and Leaf Area Index obtained appear to be higher than those reported for meadows of this seagrass in other parts of the Mediterranean.peer-reviewe