Just T. Bayle-Sempere

Marine reserves: size and age do matter

Marine reserves are widely used throughout the world to prevent overfishing and conserve biodiversity, but uncertainties remain about their optimal design. The effects of marine reserves are heterogeneous. Despite theoretical findings, empirical studies have previously found no effect of size on the effectiveness of marine reserves in protecting commercial fish stocks. Using 58 datasets from 19 European marine reserves, we show that reserve size and age do matter: Increasing the size of the no-take zone increases the density of commercial fishes within the reserve compared with outside; whereas the size of the buffer zone has the opposite effect. Moreover, positive effects of marine reserve on commercial fish species and species richness are linked to the time elapsed since the establishment of the protection scheme. The reserve size-dependency of the response to protection has strong implications for the spatial management of coastal areas because marine reserves are used for spatial zoning.

Extensive aggregations of wild fish at coastal sea-cage fish farms

We present evidence of a largely undocumented environmental effect of coastal sea-cage fish farms on wild fish. We estimated the total abundance and biomass of wild fish aggregated in the immediate vicinity of nine fish farms in the Mediterranean Sea and one farm off the east coast of Australia. Estimates of wild fish aggregations ranged from 2000 to 86000 individuals and from 100 kg to 38.5 tons of fish per farm and were always greater than control locations. Particularly large aggregations (>30000 fish, > 12 tons) occurred at half of the farms. Aggregations were temporally stable for weeks to months and most wild fish associated with farms (88%) were of adult size. Potential effects of such large aggregations of wild fish in the immediate vicinity of fish farms include increased vulnerability to fishing and pathogen transfer between caged and wild fish. We suggest specific legislation should be enacted wherever large aggregations of wild fish occur around fish farms to enhance the positive and reduce the negative effects of association.

Changes in amphipod (Crustacea) assemblages associated with shallow-water algal habitats invaded by Caulerpa racemosa var. cylindracea in the western Mediterranean Sea.

The effects of the invasive species Caulerpa racemosa var. cylindracea (hereafter C. racemosa) on amphipod assemblages associated with shallow-water rocky habitats were studied. Two habitats located along the SE Iberian Peninsula were compared; invaded and non-invaded. The results showed that growth of C. racemosa affects habitat structure, influencing the species composition and biomass of macroalgae, and detritus accumulation. In turn, such changes in habitat features affected the associated amphipod assemblages with different ecological requirements. However, the species richness of amphipods was relatively high in both habitats, while the species composition of amphipods changed completely. For example, some species such as Ampithoe ramondi and Hyale schmidti did not colonize invaded habitats, while others such as Apocorophium acutum were favoured by the spread of C. racemosa. Habitat invasion by C. racemosa can have an important influence on biotic assemblages, modifying both habitat structure and the associated fauna, with unknown effects on the overall ecosystem.

Proxy measures of fitness suggest coastal fish farms can act as population sources and not ecological traps for wild gadoid fish.

Background Ecological traps form when artificial structures are added to natural habitats and induce mismatches between habitat preferences and fitness consequences. Their existence in terrestrial systems has been documented, yet little evidence suggests they occur in marine environments. Coastal fish farms are widespread artificial structures in coastal ecosystems and are highly attractive to wild fish. Methodology/Principal Findings To investigate if coastal salmon farms act as ecological traps for wild Atlantic cod (Gadus morhua) and saithe (Pollachius virens), we compared proxy measures of fitness between farm-associated fish and control fish caught distant from farms in nine locations throughout coastal Norway, the largest coastal fish farming industry in the world. Farms modified wild fish diets in both quality and quantity, thereby providing farm-associated wild fish with a strong trophic subsidy. This translated to greater somatic (saithe: 1.06–1.12 times; cod: 1.06–1.11 times) and liver condition indices (saithe: 1.4–1.8 times; cod: 2.0–2.8 times) than control fish caught distant from farms. Parasite loads of farm-associated wild fish were modified from control fish, with increased external and decreased internal parasites, however the strong effect of the trophic subsidy overrode any effects of altered loads upon condition. Conclusions and Significance Proxy measures of fitness provided no evidence that salmon farms function as ecological traps for wild fish. We suggest fish farms may act as population sources for wild fish, provided they are protected from fishing while resident at farms to allow their increased condition to manifest as greater reproductive output.

Coastal fish farms are settlement sites for juvenile fish.

Two south-west Mediterranean fish farms were monitored over a period of 22 months to test if sea-cage fish farms act as settlement habitats for juvenile fish. Twenty juvenile fish species were found to settle at farms throughout the year. Fish assemblage composition varied markedly over time and was dependent on the spawning period for each species. The most abundant species were Obladamelanura, Atherina sp., Diplodussargus, Boopsboops and Lizaaurata. Up to 3783+/-1730 individuals/cage were found closely associated with the cages. Highest densities were observed during the warmer summer and autumn months. Zooplankton sampling and stomach content analyses of the most abundant species were done to assess prey availability, selectivity and diet overlap among species. Copepods were the main prey item for all juvenile fish species, irrespective of fish size. Ivlevs Index indicated that food was not a limiting factor for juvenile fish at farms. Furthermore, food pellets from the farm affected the food chain by modifying the fatty acid profiles of farm-associated zooplankton and juveniles of L. aurata and O. melanura. These results show that aquaculture can directly influence the body composition of juvenile fish that recruit to sea-cage fish farms.

Response of Rocky Reef Top Predators (Serranidae: Epinephelinae) in and Around Marine Protected Areas in the Western Mediterranean Sea

Groupers species are extremely vulnerable to overfishing and many species are threatened worldwide. In recent decades, Mediterranean groupers experienced dramatic population declines. Marine protected areas (MPAs) can protect populations inside their boundaries and provide individuals to adjacent fishing areas through the process of spillover and larval export. This study aims to evaluate the effectiveness of six marine reserves in the Western Mediterranean Sea to protect the populations of three species of grouper, Epinephelus marginatus, Epinephelus costae and Mycteroperca rubra, and to understand in which circumstances MPAs are able to export biomass to neighbouring areas. All the studied MPAs, except one where no grouper was observed, were able to maintain high abundance, biomass and mean weight of groupers. Size classes were more evenly distributed inside than outside MPAs. In two reserves, biomass gradients could be detected through the boundaries of the reserve as an indication of spillover. In some cases, habitat structure appeared to exert a great influence on grouper abundance, biomass and mean individual weight, influencing the gradient shape. Because groupers are generally sedentary animals with a small home range, we suggest that biomass gradients could only occur where groupers attain sufficient abundance inside MPA limits, indicating a strongly density-dependent process.

Caprellid assemblages (Crustacea: Amphipoda) in shallow waters invaded by Caulerpa racemosa var. cylindracea from southeastern Spain

Growth of the invasive algae Caulerpa racemosa var. cylindracea in shallow habitats may influence the faunal assemblage composition. We studied its effects on caprellid assemblages associated with shallow-water habitats of hard and soft bottoms from the SE Iberian Peninsula (native rocky-bottom algae, C. racemosa from hard and soft bottoms, and Caulerpa prolifera, Cymodocea nodosa and Posidonia oceanica from soft bottoms). Samples were taken in two different sampling periods (September 2004 and March 2005). A total of seven caprellid species were identified, with important differences in their distribution in different habitats. Total abundance of caprellids was very high in March on native algae on hard bottoms, and on C. racemosa on both soft and hard bottoms. On both hard and soft bottoms, abundances of Caprella hirsuta recorded from C. racemosa were low. On the other hand, a higher abundance of other species, namely C. acanthifera, C. santosrosai, Phtisica marina and Pseudoprotella phasma, was recorded from C. racemosa. The results indicate that C. racemosa may have a positive influence on some caprellid species, while seasonal changes are also evident. It is concluded that introduced C. racemosa may serve as a new habitat, promoting and maintaining caprellid populations in shallow Mediterranean habitats.

Morphological differences between wild and farmed Mediterranean fish

Gilthead seabream (Sparus aurata L.) and European seabass (Dicentrarchus labrax L.) are important commercial marine fish species both for aquaculture and fisheries in the Mediterranean. It is known that farmed individuals escape from farm facilities, but the extent of escape events is not easy to report and estimate because of the difficulty to distinguish between wild and farmed individuals. In this study, significant differences provided through morphometry evidence that the cranial and body regions of seabream and seabass are different regarding their farm or wild origin at different scales. Morphological variations have been shown to be a valuable tool for describing changes in shape features. Therefore, the biomass contribution of escapees to local habitats could be determined by identifying escaped individuals from fisheries landings as a first step to assess the potential negative effects of fish farm escapees on the environment, and their influence on wild stocks and local fisheries.

Discriminating farmed gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax from wild stocks through scales and otoliths.

The study of mass and standard length (L(S) ) relationships showed that farmed individuals had higher values than wild fishes for both gilthead sea bream Sparus aurata and European sea bass Dicentrarchus labrax. Such differences were more pronounced in larger individuals than smaller ones and were more noticeable in S. aurata than in D. labrax. Additionally, differences in external characteristics of scales were detected between origins. A high proportion of farmed S. aurata had a regenerated nucleus (98%) and scale malformations (73%), and there were no annual rings in the farmed D. labrax (100%). Variation in otolith morphology was examined through shape descriptors such as area, perimeter, circularity, roundness, mass, height and length relationship and elliptic Fourier descriptors (EFDs). Important differences were found within geographical origins according to each shape descriptor separately, but no clear patterns distinguished wild and farmed fish. Discriminant analysis with either all shape descriptors together or EFDs was able to classify with high accuracy both S. aurata (89·5-95·7%) and D. labrax (93·2-95·2%) according to their origin. Hence, this study suggests the use of scale characteristics as the easiest and quickest way to distinguish farmed or escaped fishes, and secondly, the usefulness of EFDs or shape descriptors to improve such separation.

Does the invasion of Caulerpa racemosa var. cylindracea affect the feeding habits of amphipods (Crustacea: Amphipoda)?

maite va’ zquez-luis, pablo sanchezQ1 jerez and just t. bayle-sempere I.E.O., Centre Oceanogràfic de les Balears, Moll de Ponent s/n, 07015 Palma de Mallorca, Spain, Centro de Investigación Marina de Santa Pola (CIMAR), Ayto. de Santa Pola y Universidad de Alicante, Torre d’Enmig s/n, Cabo de Santa Pola, Alicante, Spain, Departamento de Ciencias del Mar y Biologı́a Aplicada. Edificio Ciencias V. Universidad de Alicante, POB. 99, E-03080 Alicante, Spain