1,721,054 research outputs found
The effect of protection on fish populations in the Ses Negres Marine Reserve (NW Mediterranean, Spain)
Full text linkThis work is the result of a 3-year monitoring programme for assessing the effect that the Ses Negres marine reserve has had on fish populations. Species richness (based on fish species that are considered to be reserve effect indicators), and the size structure of 4 species vulnerable to angling and spear fishing were studied by visual censuses conducted both inside and outside the marine reserve. Analysis of fish populations inside the reserve showed a reserve effect (larger sizes, higher abundance and richer fish assemblages) when compared to the non-reserve sites, especially by the end of the study period. The results highlight the importance of marine reserves for the recovery of fish populations. Future management plans are discussed for this marine reserve
Ascidian introductions through the Suez Canal: the case study of an Indo-Pacific species
No full textAlthough marine biological invasions via the Suez Canal have been extensively documented, little is known about the introduction of non-indigenous ascidians (Chordata, Ascidiacea), a group containing particularly aggressive invasive species. Here, we used a multidisciplinary approach to study the introduction of the ascidian Herdmania momus into the Mediterranean Sea. We reviewed its taxonomy and global distribution, and analyzed how genetic variation is partitioned between sides of the Suez Canal. The taxonomic revision showed that H. momus currently has a wide Indo-Pacific distribution. Genetic data indicated two well-differentiated colonization histories across the eastern Mediterranean. Our findings suggest that the range expansion of H. momus has been greatly facilitated by the combined effect of human-mediated transport and the species' ability to adapt to different environments. The integrative approach presented here is critical to attain a holistic understanding of marine biological invasions, especially when studying groups with a poorly resolved taxonomy
How important is intraspecific genetic admixture to the success of colonising populations?
No full textGenetic admixture of divergent intraspecific lineages is increasingly suspected to have an important role in the success of colonising populations. However, admixture is not a universally beneficial genetic phenomenon. Selection is typically expected to favour locally adapted genotypes and can act against admixed individuals, suggesting that there are some conditions under which admixture will have negative impacts on population fitness. Therefore, it remains unclear how often admixture acts as a true driver of colonisation success. Here, we review the population consequences of admixture and discuss its costs and benefits across a broad spectrum of ecological contexts. We critically evaluate the evidence for a causal role of admixture in successful colonisation, and consider that role more generally in driving population range expansion
A revision of the Pyura stolonifera species complex (Tunicata, Ascidiacea), with a description of a new species from Australia
No full textPyura stolonifera is a large solitary ascidian found in Africa, Australasia and South America. The taxonomic status of different populations of this species is disputed, especially since there is evidence for several distinct morphological and genetic units that point towards the existence of multiple cryptic species. While some researchers still recognize P. stolonifera as a single species, others treat the different populations as distinct species. Here, we present a revision of the P. stolonifera species complex based on the examination of samples from all regions where there are reliable reports of this taxon. We recognize four species that are both morphologically and genetically distinct, one of which is new to science and is formally described here. This species is morphologically distinct from the other three members of the species complex in terms of the colour and texture of the tunic, the arrangement of the gonads within the gut and the shape of the dorsal tubercle, among other characters. We name the new species Pyura dalbyi after Dr. J.E. Dalby Jr., whose research on its ecology and distribution provided the incentive for examining this species more closely
Human harvesting of Mytilus galloprovincialis Lamarck, 1819, on the central coast of Portugal
No full textThe Mediterranean mussel, Mytilus galloprovincialis Lamarck, 1819, has traditionally been removed from the shore by humans in coastal areas to supplement diet, for commerce or for bait. On exposed rocky shores of the central coast of Portugal, humans are an important intertidal predator, especially of mussels and of the pedunculate barnacle Pollicipes pollicipes (Gmelin, 1789). Four rocky shore sites near Cabo Raso with different levels of accessibility were compared in terms of harvesting pressure, substratum cover, density and size structure of M. galloprovincialis. Sampling surveys were conducted from March to September 2002. For substratum cover determinations a 50 cm x 50 cm square was used, while density and size structure were estimated based on scrapings performed on a 10 cm x 10 cm area. A log-linear model was used to evaluate human harvesting according to several factors. Significant differences in the harvesting intensity were related to accessibility, type of day (weekday, weekend or holiday), period of the day, weather and tidal amplitude. The differences relative to zone were not significant. The least accessible site (0.30 person day-1) showed the highest values of substratum cover, and a negative correlation was found between number of harvesters and substratum cover by mussels. Size distribution also varied considerably according to site. The major difference that was noticed was that less accessible sites showed a higher number of large individuals than more accessible areas. Density in the most accessible location showed a clear decline, above all after summer holidays. Over the study period, in the more accessible sites biomass decreased while in the other locations it increased. Long-term studies are necessary to determine the real magnitude and effects of human disturbances in intertidal communitie
Wave action and competitive interaction between the invasive mussel Mytilus galloprovincialis and the indigenous Perna perna in South Africa
No full textOn the south coast of South Africa, the invasive alien mussel Mytilus galloprovincialis shows partial habitat segregation with the indigenous mussel Perna perna. P. perna predominates in the lower mussel zone and M. galloprovincialis in the upper zone, with mixed beds where the two overlap. We examined competitive interactions between these species by translocating mussels into small plots at high densities. Treatments involved different combinations of species and densities placed in each zone. Mortality was monitored regularly and at the end of each experiment, growth and condition index were measured. The experiment was attempted three times. The first two attempts were disrupted by wave action, especially winter storms, but provided information on species-specific effects of wave action. In experiment one, wave induced mortality decreased from a mean for both species of approximately 90% on the low shore to ca. 50% on the high shore, and was 15–30% lower for P. perna than M. galloprovincialis in each zone. In experiment two, M. galloprovincialis mortality was not affected by zone (Kruskal–Wallis test, P > 0.05), but was higher than P. perna mortality in the low zone (P < 0.05). P. perna survival was significantly (P < 0.05) lower on the high than mid and low zones, apparently due to the effects of greater emersion. Condition index showed a similar pattern, being lowest in the low zone for M. galloprovincialis and in the high zone for P. perna (3-way ANOVA, P < 0.05). Growth rates were fastest for both species in the low zone (Kruskal–Wallis, P < 0.05 in both cases). The third experiment was run for 12 months in the low zone only and provided evidence of intraspecific competition for P. perna and of interspecific competition. Condition was significantly greater for P. perna in all treatments (2-way ANOVA), as was growth (Kruskal–Wallis P < 0.05). Significant treatment effects indicated that P. perna had a negative effect on M. galloprovincialis survival (Kruskal–Wallis, P < 0.05). Again wave action was important; by the end of the experiment all mussels had been removed from plots stocked only with M. galloprovincialis. Thus P. perna improves survival of M. galloprovincialis on the low shore in the short term, by providing protection against wave action, but excludes it competitively in the longer term. The results show that partial habitat segregation is likely to be a permanent feature on the south coast, with M. galloprovincialis unable to dominate the low shore due to the effects of waves and competitive exclusion by P. perna. This study is the first attempt to examine the mechanisms of interaction between invasive and indigenous marine mussel species and provides evidence of the importance of environmental conditions in the mediation of this interaction
Facilitation and competition between invasive and indigenous mussels over a gradient of physical stress
No full textThe interactions between invasive exotic and indigenous species can have profound harmful effects on the recipient community; however, not all such interactions are negative. Facilitation is increasingly recognised as important in shaping natural communities and is believed to vary under different conditions. Earlier studies have shown that the indigenous intertidal mussel Perna perna initially facilitates survival of the invasive Mytilus galloprovincialis in the low mussel zone by providing protection against waves, but later excludes M. galloprovincialis through interference competition for space. Here, we examined interactions between these species in the mid and upper mussel zones, moving mussels to experimental plots in different combinations of densities and species. Mussels were left on the shore for more than a year and treatment effects on mortality, shell length and condition were compared. In the high zone, treatment had no effects and P. perna showed greater mortality than M. galloprovincialis, indicating that its exclusion from the high shore is due to emersion stress. In the mid zone, treatment had no significant effects on M. galloprovincialis, but multiple comparisons among treatments involving P. perna showed that facilitation occurred. P. perna survived better at higher densities, but survived even better when mixed with the physiologically more tolerant M. galloprovincialis. Length data indicated both inter- and intraspecific competition for P. perna in the mid zone. Whereas facilitation occurs strongly in the low zone (P. perna facilitates M. galloprovincialis) and weakly in the mid zone (M. galloprovincialis facilitates P. perna), the lack of facilitation in the high zone suggests that the probability of facilitation is not linearly linked to increasing physical stress. Instead it is likely to be hump shaped: relatively unimportant under conditions that are benign for a particular species, significant under more severe conditions, and overridden by physical stress under very harsh conditions
Population dynamics and life cycle of the introduced ascidian Microcosmus squamiger in the Mediterranean Sea
No full textMarine introductions are a serious threat for biodiversity, especially in seas where shipping is intensive. Microcosmus squamiger is a widespread marine invader that can alter native biota and it is therefore imperative to understand its biology and ecology. We studied the population dynamics and reproductive cycles of M. squamiger over a 2-year period, as well as its settlement and colonization patterns, in a north-western Mediterranean (NE Spain) locality where M. squamiger has been introduced. All biological parameters showed a strong seasonal pattern that peaked in summer with a major spawning episode at the end of summer. Size-frequency histograms indicated a 2-year cycle. Colonization experiments suggested that M. squamiger recruitment mortality is high and requires a well structured community. In addition, we monitored the abundance of the native predator Thais haemastoma, which showed a significant positive correlation with M. squamiger biomass, indicating its potential usefulness as a biological control
Isolation and characterization of eight polymorphic microsatellite loci for the Mediterranean gorgonian Paramuricea clavata
No full textThe gorgonian Paramuricea clavata is a benthic organism often included in conservation management plans since it creates complexity in the ecosystems and is extremely vulnerable to disturbances. Eight microsatellite markers isolated from an enriched genomic library were characterized in a total of 50 individuals from two north-western Mediterranean populations. All loci were polymorphic and the number of alleles per locus ranged between 2 and 14. Significant genetic differentiation was observed between populations. The polymorphic markers presently isolated will allow for the assessment of the spatial genetic structure between and within populations of this umbrella species of the Mediterranean Sea
Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters
No full textThe Mediterranean Sea is subject to an ever-increasing arrival of non-indigenous marine organisms. Microcosmus squamiger is a solitary ascidian that inhabits shallow rocky littoral habitats. It probably originated in Australia and it has shown great invasive potential in other parts of the world. In the Mediterranean, M. squamiger has only been reported at a few sites in Spain and Italy. However, the closely related species Microcosmus exasperatus has been reported in several areas of the western Mediterranean. As these species can be easily confused, we re-examined most of the material from previous studies and our personal collections. In addition, sampling was done at several sites along the western Mediterranean and Atlantic coasts. The results showed that the majority of the M. exasperatus reports correspond to M. squamiger, and that M. squamiger is common on the Atlantic shores. This suggests that M. squamiger has entered the Mediterranean through the Gibraltar Strait, while the restricted distribution in the eastern Mediterranean of M. exasperatus suggests that this species is probably a Lessepsian migrant. In the Mediterranean Sea, M. squamiger has the ability to occupy extensive areas of hard substrata and to outcompete native species. Further studies are necessary to assess what impacts this invasive species have on native communities
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