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

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

Living deep-water Lophelia and Madrepora corals in Maltese waters (Strait of Sicily, Mediterranean Sea)

The occurrence of living deep-water corals, Lophelia pertusa and Madrepora oculata, from stations 21-42 km off the southern and south-western coast of Malta is reported. Fragments of living colonies of both species, as well as some large pieces of Lophelia frameworks were recovered from depths of 390-617 m together with the solitary coral Desmophyllum dianthus (= cristagalli). The accompanying biota included the barnacle Pachylasma giganteum, the gastropod Coralliophila richardi, the bivalves Asperarca nodulosa and Spondylus gussonii, and the polychaete Eunice norvegicus, all of which are frequently associated with deep-water corals. The occurrence of the Lophelia-Madrepora- Desmophyllum triad, the large pieces of coral frameworks consisting predominantly of live, healthy polyps, and the associated biota, suggest that coral patches may be present in at least some of the investigated localities, rather than just fragmented remains or isolated colonies.peer-reviewe

Marine litter from circalittoral and deeper bottoms off the Maltese Islands (Central Mediterranean)

During the 2005 leg of the MEDITS trawl survey, benthic anthropogenic debris around the Maltese Islands (central Mediterranean) was quantified for the first time, with the aim of studying its abundance and distribution in the area. 357 items were sampled from 3.5 km2 of swept area. Each item was recorded, measured and its planar and surface areas were estimated. Plastic (47%), metal and glass (13% each) were the most prevalent types of litter in terms of number. Limestone slabs, sacks and fabric were the items with the highest planar and surface area per item. This suggests that it is also important to consider the size of debris items as well as numerical abundance in assessing impact of litter on benthic organisms. An attempt was made to correlate anthropogenic and environmental variables, including fishing activities and wave parameters, to litter abundance and distribution but no interpretable correlations were found, implying that litter abundance and distribution depends on factors other than those considered.peer-reviewe

Age, growth and reproduction of Coryphaena hippurus (Linnaeus, 1758) in Maltese waters, Central Mediterranean

Age, growth and reproduction of the dolphinfish Coryphaena hippurus Linnaeus, 1758 collected from the Central Mediterranean in the period 2004-2010 by the traditional Maltese fish aggregating devices (FAD) and surface longline fisheries were studied. The a and b parameters of the length-weight relationship for fish 11-142 cm fork length (FL) (n = 4042) were determined as a = 0.018 and 0.022 with b = 2.85 and 2.79, for males and females respectively. The counting of annual increments from dorsal spines of >65 cm FL dolphinfish at X25 magnification (n = 47) permitting an age reading resolution in years, and the counting of daily increments from sagittal otoliths of <65 cm FL dolphinfish at X400 magnification (n = 583) permitting an age reading resolution in days, were estimated; the von Bertalanffy growth model applied to these fish gave the following parameters: L∞ = 107.8 cm FL and 120.2 cm FL, and K = 1.9 yr-1 and 1.56 yr-1, for males and females respectively. The maximum age observed was 2 years. Size at 50% maturity for fish 10-131 cm FL (n = 1376) was 58.9 cm FL and 62.5 cm FL for males and females, respectively. The sex ratio for the fish sampled from the FAD fishery (10.5-131 cm FL) was 1:1.54 (M:F) and for dolphinfish sampled from the surface longline fishery (91-130 cm FL) was 1:0.76 (M:F). Back-calculated hatch dates from age-0 dolphinfish (n = 518) suggested that spawning occurs from June to September with the highest levels in June. This study is the first to use dorsal spines to determine the age of adult dolphinfishpeer-reviewe

Motile macroinvertebrate assemblages associated with submerged Posidonia oceanica litter accumulations

In the Mediterranean, seagrass leaf litter derived from Posidonia oceanica beds constitutes an important source of detritus. Large areas with P. oceanica leaf litter are ubiquitous in the infralittoral, but data on the species assemblages characterising this habitat are lacking. Samples of leaf litter were collected in December 2001 from 8 stations in each of two bays on the northern coast of Malta, using a suction sampler. A total of 4794 motile macroinvertebrates comprising 43 species were recorded. Overall, diversity and evenness values were low, however, abundance values were very high. Detritivorous crustaceans were the most abundant taxon (>97 %), with amphipods having the highest abundance (81.8 %). Our results indicate that P. oceanica leaf litter is a distinct habitat that supports characteristic motile macroinvertebrate assemblages dominated by gammarid amphipods. Mediterranean marine Gammarus spp. are typically found in brackish habitats, and only infrequently occur in fully marine waters. However, no sources of brackish water were present in the vicinity of our study sites, which seems to indicate that the occurrence of Gammarus spp. in P. oceanica leaf litter accumulations may be widespread. We suggest that the P. oceanica leaf litter habitat supports unique macroinvertebrate assemblages composed mostly of motile detritivores and which may constitute an important link in transferring production from P. oceanica leaves to higher trophic levels.peer-reviewe

Changes in the structure of a Posidonia oceanica meadow and in the diversity of associated decapod, mollusc and echinoderm assemblages, resulting from inputs of waste from a marine fish farm (Malta, Central Mediterranean)

Nutrient inputs resulting from fish farming activities located in the vicinity of seagrass meadows can potentially alter the structure and affect the functioning of these ecosystems, however, few studies have addressed this problem. The impact of waste generated by an offshore fish farm in Malta (Central Mediterranean) on the structure of a meadow of the seagrass Posidonia oceanica and on the associated decapod, echinoderm and mollusc assemblages was studied by collecting samples from stations located at distances of 10 m, 30 m, 50 m, 90 m, 170 m and 330 m away from the farm. Meadow morphology and leaf epiphyte load changed with distance from the fish cages, as did the species richness and abundance of macroinvertebrates associated with the seagrass. However, while shoot morphometric measures increased significantly in value over the whole length of the transect (330 m), macroinvertebrate species richness and abundance peaked at an intermediate distance (40–160 m) from the cages. These results suggest that while waste generated from fish farms can severely alter the structure of a seagrass meadow over a large area, nutrient enrichment could increase productivity in certain parts of the same meadow, leading to a localized increase in species richness and abundance of associated macroinvertebrates. These changes result in different 'ecological zones' round the source of nutrient input.peer-reviewe

Litter as a source of habitat islands on deepwater muddy bottoms

Certain types of marine litter, usually considered as pollutants, may also be a resource, serving as artificial reefs on sedimentary bottoms. In order to study this aspect, marine debris was collected by bottom trawl from muddy bottoms (depths of 45-700m) in the waters around the Maltese islands, during July 2005. The associated fauna was identified and quantified. Litter was found to support a higher abundance of organisms than the surrounding sediment, but a lower species richness. However, the suite of epifaunal species on the debris was different from the infauna of the surrounding substratum. Thus litter was found to increase the overall biodiversity of particular areas.peer-reviewe

Commercial and non-target species of deep water trawled muddy habitats on the Maltese continental shelf

Prior to joining the European Union, Malta operated a 25nm Exclusive Fishing Zone that was retained as a Fisheries Conservation Zone (FCZ) following EU membership. The present study was conducted in this FCZ as part of the ongoing MEDITS trawl survey programme. Otter trawl samples were collected from muddy bottoms at depths of 100-300m. The catch from each haul was sorted into commercial and non-commercial components, and fauna were identified and counted. Samples for analyses of infauna and sediment characteristics were collected using a 0.0625m² capacity box-corer. Macrofaunal abundance data for the stations were analysed using ordination techniques (nMDS) and relationships between environmental variables and faunal assemblages were explored by superimposing individual variables on the two-dimensional nMDS plots. The analyses clearly separated the commercial species into two distinct groups of assemblages that seemed to be defined principally by depth: those from inshore and south-eastern stations (depth range 100-250m) and those from north-western stations (depth range 250-300m). The non-commercial species showed a similar pattern with assemblages from inshore stations grouping together; however, the offshore stations had a greater variability in non-target species composition, especially for infauna. For the offshore stations, geographical position seemed to be important since stations off the north-western coast of the Maltese islands grouped separately from those off south-eastern Malta.peer-reviewe

Feeding habits of the small-spotted catshark Scyliorhinus Canicula (l., 1758) in the Central Mediterranean

The catshark Scyliorhinus canicula is a common demersal elasmobranch in the Mediterranean. It has a wide geographical and bathymetric distribution and is found primarily over sandy, muddy or gravelly bottoms. Studies on the feeding habits have been made in various regions, but not in the Central Mediterranean. The present study addresses this gap by presenting information on the diet of the species for this region, for the first time.peer-reviewe