Pablo Sanchez-Jerez

Marine reserves: fish life history and ecological traits matter.

Marine reserves are assumed to protect a wide range of species from deleterious effects stemming from exploitation. However, some species, due to their ecological characteristics, may not respond positively to protection. Very little is known about the effects of life history and ecological traits (e.g., mobility, growth, and habitat) on responses of fish species to marine reserves. Using 40 data sets from 12 European marine reserves, we show that there is significant variation in the response of different species of fish to protection and that this heterogeneity can be explained, in part, by differences in their traits. Densities of targeted size-classes of commercial species were greater in protected than unprotected areas. This effect of protection increased as the maximum body size of the targeted species increased, and it was greater for species that were not obligate schoolers. However, contrary to previous theoretical findings, even mobile species with wide home ranges benefited from protection: the effect of protection was at least as strong for mobile species as it was for sedentary ones. Noncommercial bycatch and unexploited species rarely responded to protection, and when they did (in the case of unexploited bentho-pelagic species), they exhibited the opposite response: their densities were lower inside reserves. The use of marine reserves for marine conservation and fisheries management implies that they should ensure protection for a wide range of species with different life-history and ecological traits. Our results suggest this is not the case, and instead that effects vary with economic value, body size, habitat, depth range, and schooling behavior.

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.

Comparison of the epifauna spatial distribution in Posidonia oceanica, Cymodocea nodosa and unvegetated bottoms : Importance of meadow edges

In order to detect the influence of seagrass, the most important habitats of shallow soft-bottom along the Mediterranean coast, on spatial distribution of epifauna, four different types of habitat were sampled: Posidonia oceanica, Cymodocea nodosa, edge of Posidonia meadow and sandy bottoms. Sampling was carried out, using the hand net method, in various random sites and at different times (April 95, August 95 and February 96) on the Alicante coast (SE Spain). A double taxonomic approach was used in order to detect spatial and temporal changes in the abundance of the main taxonomic groups and amphipod species. The differences among habitats were detected by non-parametric multidimensional scaling (MDS) for community structure and by analysis of variance for groups and amphipod populations. The community structure defined by the abundance of taxonomic groups was not significantly modified by the habitats. Single abundance of taxonomic groups also had no significant preference for the type of habitat except in the case of Acari, a group linked to Posidonia. However, certain trends of preference, such as mysids on Posidonia edge and isopods on Cymodocea, were detectable. On other hand, the amphipod assemblage showed important differences among habitats. Some species changed significantly in abundance depending on the habitat considered, e.g. Dexamine spiniventris and Perioculodes longimanus. It was possible to conclude that there is an important influence of Posidonia and Cymodocea on epifauna distribution by diversification of habitat structure on sandy bottoms, but it was more important at the species level than when considering taxonomic groups. Furthermore, sandy bottoms and the meadow edges had a relatively high importance on fauna distribution, depending on taxa and the period of the year.

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.

Spatial variation in the structural parameters of Cymodocea nodosa seagrass meadows in the Canary Islands: a multiscaled approach

Abstract Meadows of the seagrass Cymodocea nodosa (legislated as an endangered species) are the dominant vegetated communities in shallow soft bottoms throughout the Canary Islands (central east Atlantic Ocean). We provide baseline ecological information for this key species for the whole Canarian Archipelago by describing the spatial distribution patterns of structural parameters (percent coverage and shoot density) at different hierarchical spatial scales (from tens of meters to hundreds of kilometers). The coverage values varied between 42.5 and 100% (mean±SE=76.7±2.5%, N=80) and the mean shoot density per location ranged between 164 and 710 shoots m−2 (mean±SE=403.6±17.0 shoots m−2, N=160). We observed a strong variability at small- to medium-spatial scales (locations within islands separated by tens of kilometres and sites hundreds of meters apart within locations) in contrast to a lack of inter-island variability. Additionally, the structural parameters respond differentially to different sets of ecological and physical processes operating at these scales.

Can one species determine the structure of the benthic community on a temperate rocky reef? The case of the long-spined sea-urchin Diadema antillarum (Echinodermata: Echinoidea) in the eastern Atlantic

We sampled 36 coastal rocky reefs throughout the overall Canarian Archipelago and consider (1) the daily macroalgal consumption of the long-spined sea urchin Diadema antillarum and (2) the daily net production of macroalgae along temperate rocky-substrates, to provide evidence that Diadema antillarum plays an important role in the structure of the shallow benthic environment of the eastern Atlantic. D. antillarum was found to be the main key-herbivore species, as it controls by its own the algal assemblages, with negligible contribution of other grazing species.

Detecting the degree of establishment of a non-indigenous species in coastal ecosystems: sea bass Dicentrarchus labrax escapes from sea cages in Canary Islands (Northeastern Central Atlantic)

This article gives an insight into the degree of establishment and potential impact of escaped sea bass in shallow coastal habitats of Tenerife. We studied spatial distribution, abundance, size frequency and use of habitat by visual census. Stomach contents and gonadal maturity of escaped sea bass were analysed. Results show that abundance of escaped sea bass is related to distance from to the nearest fish farm and to the habitat complexity. The most frequent size found in the wild corresponds to that of first marketing size. Stomach contents indicate that escaped sea bass were able to exploit natural resources, especially fish. The presence of a female with mature gonads indicates that conditions for successful maturation exist. However, further studies are needed to ensure whether or not escaped sea bass are able to establish self-reproducing populations. Thus, we can conclude that sea bass seem to be already established in shallow coastal habitats of Tenerife, but the population may depend mainly on escapees. As a result of being an opportunistic piscivore, sea bass could be predating on and competing with other native species that are economically important. These results are useful to develop a risk assessment based on quantitative data to predict negative effects. Moreover, management policies such as communication of massive escapes or mitigation measures are needed to prevent future impact on the marine environment.

Daily vertical migrations in the epifauna associated with Posidonia oceanica meadows

To estimate the importance of the vertical daily migrations in the structure of the community of the epifauna associated with the leaf stratum of Posidonia oceanica , we compared to the vagil epifauna abundance in respect to the period of the day and the height of the sediment. The study was developed in the P. oceanica meadow of El Campello (Alicante, south-east Spain), during May of 1996, to a depth of 12 m, repeating the samplings in four sites to obtain a correct spatial interpretation. Three main behaviours were detected. Decapods, amphipods, isopods, mysids, ostracods and polychaetes showed a nocturnal increase in the leaf stratum of P. oceanica. By contrast, copepods showed a nocturnal decrease in the leaves and gastropods did not show any temporal change. Chaetognaths and acari did not show statistical differences because of the considerable spatial heterogeneity. These vertical migrations have an extreme importance in the configuration of the structure of the epifauna associated to P. oceanica , in addition to the diverse response of the different taxa.