Diplodus Annularis Research Articles

Changing Isotopic Food Webs of Two Economically Important Fish in Mediterranean Coastal Lakes with Different Trophic Status

Transitional waters are highly productive ecosystems, providing essential goods and services to the biosphere and human population. Human influence in coastal areas exposes these ecosystems to continuous internal and external disturbance. Nitrogen-loads can affect the composition of the resident community and the trophic relationships between and within species, including fish. Based on carbon (δ13C) and nitrogen (δ15N) stable isotope analyses of individuals, we explored the feeding behaviour of two ecologically and economically important omnivorous fish, the eel Anguilla anguilla and the seabream Diplodus annularis, in three neighbouring lakes characterised by different trophic conditions. We found that A. anguilla showed greater generalism in the eutrophic lake due to the increased contribution of basal resources and invertebrates to its diet. By contrast, the diet of D. annularis, which was mainly based on invertebrate species, became more specialised, focusing especially on polychaetes. Our results suggest that changes in macroinvertebrate and fish community composition, coupled with anthropogenic pressure, affect the trophic strategies of high trophic level consumers such as A. anguilla and D. annularis. Detailed food web descriptions based on the feeding choices of isotopic trophospecies (here Isotopic Trophic Units, ITUs) enable identification of the prey taxa crucial for the persistence of omnivorous fish stocks, thus providing useful information for their management and habitat conservation.

Daily Age and Growth Rates of Larval and Juvenile Annular Seabream, Diplodus annularis Inhabiting the Gökçeada Shallow Waters

Bu çalışma Haziran 2013 – Haziran 2014 tarihleri arasında Gökçeada sığ sularında (0 - 20 m) gerçekleştirilmiştir. Gökçeada çevresinde plankton kepçesi ve ığrıp ile yapılan avcılık operasyonları sonucunda toplam boyları 2.01 mm ile 10 mm TL arasında olan toplam 190 adet larva ile toplam boyları 11 – 140 mm TL arasında olan 923 adet juvenil isparoz yakalanmıştır. Elde edilen bireylerin boy-ağırlık ilişkileri W = 8E-06TL3.1029 (R2 = 0.975) olarak hesaplanmıştır. Yapılan yaş tayinleri sonucunda larvaların 2 ile 19 gün, juvenillerin ise 18 ile 296 gün arasında oldukları tespit edilmiştir. Larvaların ortalama günlük büyüme oranlarının tespit edilmesi için yapılan boy-yaş regresyon analizi sonucunda günlük büyüme oranları 0.398 mm gün, juvenillerin ise 0.371 mm gün olarak hesaplanmıştır. Gökçeada çevresinde yakalanan isparoz larvalarının otolitlerinden yapılan günlük yaş tayinleri sonucunda yumurtadan çıkma zamanları Nisan-Eylül dönemi boyunca devam ettiği ve Haziran ayında maksimum seviyeye ulaştığı, juvenillerin ise Şubat-Eylül dönemi boyunca devam ettiği ve Mayıs ayında maksimum seviyeye ulaştığı tespit edilmiştir. İsparoz larvalarının günlük ölüm oranları (DM) 0.231027 ve günlük ölüm oranı yüzdeleri (%DM) %23.1 olarak, juvenillerin ise DM 0.02984 ve %DM ise %2.98 olarak hesaplanmıştır. Günlük yaşama oranları ise larvalarda 0.769 ve juvenillerde 0.9701 olarak bulunmuştur.

Plankton community of trafficked ports as a baseline reference for Non Indigenous Species arrivals. Case study of the Port of Bar (South Adriatic Sea)

Plankton (ichthyo, zoo and phyto) communities were studied in the temperate shallow waters of the Port of Bar, one of the main cargo ports on the south-eastern Adriatic coast. Sampling was undertaken in February, April, June and October 2015 at 12 stations using the BALMAS Port Baseline Survey protocol. The research was conducted to determine the presence of invasive and potentially toxic plankton species in the port.The most dominant species of ichthyoplankton were eggs and larvae of families Engraulidae, Bothidae and Sparidae with a dominance of Engraulis encrasicolus, Arnoglossus laterna and Diplodus annularis. In addition to ichthyoplankton, sampling of phyto and zooplankton was performed to estimate the abundance and diversity of species.The most numerous zooplankton species throughout investigated period were Penilia avirostris, Euterpina acutifrons, Oithona nana, Acartia clausi, Centropages kroyeri, Paracalanus parvus, Oncaeidae and larvae of Bivalvia. One very unusual occurrence was the spawning of parrotfish Sparisoma cretense (Linnaeus, 1758), a species with Atlantic origin and tropical affinities, whose presence throughout the Mediterranean has shown an increasing trend over the last decade. The most dominant species of phytoplankton were the diatoms Chaetoceros affinis and Chaetoceros spp., Asterionellopsis glacialis, Pseudo-nitzschia spp., Thalassionema nitzschioides, and dinoflagellates Gymnodinium spp. and Prorocentrum triestinum. The potentially toxic species from genus Pseudo- nitzschia reached an abundance of 104 cells L-1. Toxic dinoflagellates Prorocentrum cordatum and P. micans reached values of 103 cells L-1.Although there were no HAOP species found during the survey, presence of several potentially toxic and toxic phytoplankton species whose impact is not sufficiently known indicates the necessity of introduction of regular monitoring activities and definition of preventive protection measures.

-Identification of a novel intestinal phospholipase A2 from annular seabream: Insights into its catalytic mechanism and its role in biological processes

Phospholipase A2 (PLA2) is responsible for the lipid hydrolysis process. Fish PLA2 have warranted renewed interest due to their excellent properties in phospholipid digestion. We report for the first time the catalytic properties of a PLA2 secreted from the intestine of the annular seabream Diplodus annularis (IDaPLA2). The refolded IDaPLA2 was purified to homogeneity and showed a molecular mass of around 15 kDa attested by SDS-PAGE and MALDI-TOF analyses. Interestingly, IDaPLA2 revealed higher thermostability compared to mammal pancreatic sPLA2 as it was active and stable at 55 °C with specific activity of 290 U mg−1 on phosphatidylcholine (PC) as a substrate. Using the lipid monolayer technique, the activity of IDaPLA2 was found to be 21.68, 6.88 and 5.66 mol cm−2 min−1 mM−1 using phosphatidylglycerol (PG), PC and phosphatidylethanolamine (PE) monolayers, respectively, at surface pressures from 20−30 mN m−1. Interestingly, the interfacial activity of IDaPLA2 measured at higher surface pressures may highlight its ability to penetrate into phospholipid monolayers suggesting its involvement in cell lipid membrane degradation which can explain the cytotoxicity potential towards macrophage. The docking simulation data provided insights into the involvement of some key amino-acids in substrate binding and selectivity. The dynamic simulation proved the high stability of IDaPLA2. Overall, these results provide original evidence on the involvement of IDaPLA2 into the lipid hydrolysis suggesting it as a potential target in biotechnological applications.

Incidence of morphometry variation, growth alteration, and reproduction performance of the annular sea bream (Diplodus annularis) as effective tools to assess marine contamination: how useful is a multi-biotimarkers approach?

A wide variety of contaminants in the aquatic environment causes several deleterious effects on aquatic organism traits ranging from molecular to individual and population levels. This in situ study investigated morphometry, growth performance, and reproduction success of a teleost fish, Diplodus annularis, from a polluted site "Sayada" and a reference site "Salakta" in the eastern Tunisian coastline. Morphometric indexes, generalized Procruste analysis, thin plate, and otolith contour methods were used to assess the pollution effects on morphological traits. The growth performance of fish from contaminated and control sites were studied using the Von Bertalanffy equation. Gonadosomatic (GSI) and Hepatosomatic (HSI) Indexes and absolute and relative fecundity were used to assess the impact of pollution on the reproduction success of this species. The obtained results showed that the fish of the contaminated zone had significant alteration of the morphology, slower growth, significant increase in the HSI, significant decrease in female GSI, and a decrease in absolute and relative fecundity compared to specimens from the unpolluted zone. Based on these results, the biological traits of Diplodus annularis can be used as biological biomarkers in the monitoring and protection programs of the marine contamination in the Mediterranean Sea.

Changes in the juvenile fish assemblage of a Mediterranean shallow Posidonia oceanica seagrass nursery area after half century

The within-year dynamics of the juvenile fish community over a shallow nursery seagrass-dominated habitat (Posidonia oceanica) in a Mediterranean Bay was compared between two surveys separated 50 years (1960 and 2012-2013). A nocturnal survey over depths ranging from 2 to 10 m over patched seagrass meadows was conducted for one year (2012-2013) through 72 epibenthic tows spread fortnightly in 4 close-by stations, mimicking a survey, conducted in 1960, in terms of sampling intensity, sampling zone, temporal coverage and sampling gear. Although a large proportion of fish species was similar among surveys, remarkable and statistically significant differences were detected. A striking feature was that one of the most common and abundant sparidae species nowadays, Diplodus annularis, did not appear in 1960. Other strong differences included the disappearance of European eel Anguilla anguilla in the recent survey. Further, one of the most valuable species for artisanal fisheries in the area, the black scorpionfish Scorpaena porcus, was almost 10 times less abundant in 1960. A finer-scale study of the 2012-2013 survey allowed a quantitative analysis between species composition and potential environmental drivers through Redundancy Analysis that described well the current pattern of time-dependent recruitment pulses in nearshore meadows from the area through a year, with marked effects of surface temperature and photoperiod. The comparison between surveys suggests that some strong differences between surveys are unlikely attributable to interannual stochasticity in recruitment or environmental variability but may be related with i) unaccounted for habitat transformation and/or ii) the strong decrease of juvenile fishing mortality in this shallow nursery area since the enforcement of bans on littoral epibenthic trawling activities characteristic of this area.

STUDY OF ECOSYSTEM OF THE SUKHUM BAY WITH EMPHASIS ANTHROPOGENIC IMPACT, ABKHAZIAN BLACK SEA COAST

For the first time in thirty years, baseline comprehensive studies plankton and zoobenthos of the Sukhum Bay were conducted and an assessment of its current environmental status was given. The summer phytoplankton abundance of the port of Sukhum was represented mainly by coccolithophorids Emiliania huxleyi and diatoms algae, among the latter, the common species in polluted or eutrophic brackish waters were recorded. The presence of euglenic algae and cyanobacteria indicates a higher nutrient status, pollution and desalination of the sea area. The alien species Peridinium quinquecorne Abé (Dinophyceae) was recorded in the Abkhazian coastal waters for the first time. Totally, 7 species of tintinnids belonging to 3 genera Favella, Tintinnopsis, Eutintinnus were established from the Sukhum Bay. Among them, the non-indigenous species Eutintinnus tubulosus and E. apertus were noticed. Tintinnid ciliates accounted for ca. 5% of total ciliates abundance. The values of the abundance of aloricated ciliates were comparable to the values obtained from offshore of bays and ports of the northeastern Black Sea. As the pressure of predators is reduced the well-pronounced peaks of holo- and meroplankton biomass were recorded in the last summer – early autumn. A significant part of total holoplankton biomass – 66.5 % (up to 1.1 g/m3) was composed of cladocerans Penilia avirostris. The meroplankton was dominated by larvae of bivalve mollusks Mytilaster lineatus, polychaetes Polydora cornuta and cirripede barnacle Amphibalanus improvisus. The number of meroplankton in the open Sukhum port was 10–15 times lower above than a level of values obtained for ports and bays of the northeastern Black Sea. Among ichthyoplankton, the dominant species were Mullus barbatus ponticus, Diplodus annularis, Trachurus mediterraneus, Engraulis encrasicholus and Sciena umbra. Mean abundance of ichthyoplankton in vertical catches was 5–10 times lower than in offshore of Anapa and Gelendzhik of the northeastern Black Sea. And the proportion of dead eggs was 2 – 3 times higher than areas of these resort cities. The composition of macrozoobenthos was drastically depleted and resembled that of the polluted port complexes of the northeastern Black Sea. Heteromastus association dominated in mud bottom sediments. Among spionid polychaetes, the worst invaders Streblospio gynobranchiata and Polydora cornuta have been recorded in soft bottom communities. Depletion of benthic communities, loss from the structure of the trophic web of the macrophyte community and appearance of cyanobacteria and a new alien species in the planktonic and benthic communities leads inevitably to imbalance of the structure of the Sukhum port ecosystem.

Analyses of the non-target catch from the Egyptian Mediterranean trawlers, off Port Said

The present study aimed to analyze the non-target catch in the Egyptian Mediterranean waters, off Port Said, during the period from spring 2017 to winter 2018. The analysis revealed that from 75 non-target species, fish constituted about 69.4% of the total catch weight, whereas invertebrates reached about 30.6%. For non-target fish, 51 fishes were identified (50 bony fishes and one elasmobranch), of which 17 lessepsian species were found. The high percentage of fish (82.67%) was with an average length between 4.0 and <9.0 cm. The highly represented fish species by numbers were: Engraulis encrasicolus (25.608%), Herklotsichthys punctatus (23.711%), Terapon puta (9.572%), Equulites klunzingeri (9.342%), Gobius niger (7.177%), Argyrosomus regius (6.280%), Alepes djedaba (4.155%), Gobius paganellus (3.397%), Sardinella aurita (2.525%), Ariosoma balearicum (1.093%) and Diplodus annularis (0.803%). Total analysis, seasonal analysis and an index of diversity (H′) for the non-target catch species were provided. On the other hand, length-weight relationship, condition factor and age composition were described for the most dominant species. For non-target invertebrates, 24 species were identified among which 13 lessepsian species were found. Shrimps and mantis shrimp Erugosquilla massavensis were the main constituents during the period of study. The authors propose to change the cod end mesh size from 2.5 cm to 4.0 cm to minimize the high percentage of non-target catch and preserve recruits of valuable species from over fishing along the Egyptian coast of the Mediterranean Sea while doing experiments to ensure the best results. Further, continuous monitoring and managements of trawlers must be put into consideration.

Spatial and temporal variation in the distribution and abundance of pelagic fish eggs and larvae off Giresun, south-eastern Black Sea, Turkey

Background. Giresun Bay is an important spawning ground of many migratory fish species and hence it has been a major fishing area of pelagic fishes in the Turkish territorial waters of the Black Sea. However, this area has not been evaluated thoroughly for the abundance and distribution of pelagic fish eggs and larvae, which are prerequisite for understanding the dynamics of fluctuating fish populations. The presently-reported study aimed to fill this gap in the existing knowledge of spatial and temporal variation in the distribution and abundance of ichthyoplankton in the south-eastern Black Sea. Materials and methods. Bimonthly surveys were carried out from January through November 2009 at inshore and offshore sites (&gt;38&deg;E, &gt;40&deg;N). The samples were collected by horizontal tows with Manta nets. The mouth of the net was equipped with flowmeters to measure the amount of water passing through the net during each tow. Results. The horizontal tows returned a total of 13 556 eggs and 1304 larvae representing 26 species (from 22 families): Engraulis encrasicolus, Sprattus sprattus, Merlangius merlangus, Gaidropsarus mediterraneus, Atherina boyeri, Scorpaena porcus, Chelidonichthys lucerna, Dicentrarchus labrax, Trachurus mediterraneus, Diplodus annularis, Sciaena umbra, Mullus barbatus, Gymnammodytes cicerelus, Ctenolabrus rupestris, Symphodus ocellatus, Trachinus draco, Uranoscopus scaber, Parablennius sanguinolentus, Parablennius tentacularis, Blennius sp., Ophidion rochei, Callionymus pusillus, Gobius sp., Arnoglossus kessleri, Buglossidium luteum, Pegusa lascaris. Overall, the dominant species were E. encrasicolus with 89.8% of all collected eggs, followed by G. mediterraneus (7.0%). Similarly, 47.4% of the total larvae were represented by E. encrasicolus, followed by P. sanguinolentus (22.8%) and S. sprattus (13.2%). The colder months (January, March, and November) presented a total of four species: S. sprattus, B. luteum, Gymnammodytes cicerelus, and Gaidropsarus mediterraneus. The warmer months had a greater variety of different species than colder months. Of these, E. encrasicolus was the most dominant species, providing the maximum abundance of fish eggs and larvae in September. The abundance of E. encrasicolus eggs and larvae decreased from offshore toward inshore sites highlighting the preference of this species to deeper waters for spawning as well as for nursery purposes in Giresun Bay. Conclusion. The results of this study suggest that the length of the closed fishing season in the Black Sea should be reconsidered. We suggest that it should be extended to include also the last week of September in order to provide more time for pelagic fish (e.g., E. encrasicolus) to complete their spawning period. This could result in a healthier and more sustainable stock of E. encrasicolus in the Black Sea.

Levels, distribution, and ecological risk of organochlorines in red mullet (Mullus barbatus) and annular sea bream (Diplodus annularis) from the Gulf of Izmir, Eastern Aegean, in 2009-2012.

Organochlorine (OCs) concentrations were measured in two fish species, Mullus barbatus and Diplodus annularis, collected from Izmir Gulf during 2009-2012 in order to explain the status of these contaminants in edible fish. No data is available on the levels of organochlorines in marine organism from Izmir Gulf. In both fish species from the study area, Aroclors were determined in higher concentrations than organochlorine pesticides (OCPs). Maximum concentrations of OCPs and PCBs measured in the edible part of D. annularis were 45-165 and 530-1591ngg-1 lipid weight (lw), respectively. DDTs (sum of DDT and metabolites) and cyclodienes ranged from 4-56 to 16-110ngg-1 lw, respectively. The levels of DDTs measured in the present study were generally comparable or lower than those found in studies from other Mediterranean and non-Mediterranean regions. The potential risks for fish consumers were assessed. Although the estimated daily intake (EDI) for DDTs, heptachlor, and drins through the sampled fish species by Izmir inhabitants was quite lower than the ADI (acceptable daily intake) established by the FAO/WHO, EDI for Aroclor 1254 was close to the ADI value of 20ngg-1 recommended by the IPCS (2000).

Heterologous Expression and Functional Characterization of Sparidae Fish Digestive Phospholipase A2.

In this study, we have produced for the first time a fish phospholipase (PLA2) in heterologous system (E. coli). The Diplodus annularis PLA2 (DaPLA2) was then refolded from inclusion bodies and purified by Ni-affinity chromatography. We used the pH-stat method (with emulsified phosphatidylcholine as substrate) and the monomolecular film technique (using various glycerophospholipids substrates spread in the form of monomolecular films at the air-water interface) to access the biochemical and kinetic properties of the recombinant DaPLA2. The DaPLA2 was found to be active and stable at higher temperatures (37-50°C) than expected. Interestingly, DaPLA2 hydrolyzes efficiently both purified phosphatidylglycerol and phosphatidylethanolamine at 20mN/m. These analytical results corroborate with the fact that the catalytic activity of DaPLA2, measured with the pH-stat using egg yolk as substrate, is mainly due to the hydrolysis of the PE fraction present in egg yolk, whereas the phosphatidylglycerol is a hallmark substrate for the most secreted PLA2-IB.

Potential fishing-related effects on fish life history revealed by otolith microchemistry

Abstract Although inferring habitat selection and movement in wild fishes using otolith microchemistry has been the subject of much debate, experimental results suggest that complex environmental vs. life history interactions affect the incorporation of certain chemical elements into otoliths. We hypothesized that under relatively homogeneous hydrographic conditions, individual life history trait strategies should dominate signals of geochemical signatures. We tested our hypothesis by analyzing individual chronologies of otolith signals of strontium to calcium (Sr:Ca) and barium to calcium (Ba:Ca) ratios in a sedentary coastal fish (Diplodus annularis). Two areas from the same northwest Mediterranean region with different levels of fishing pressure were sampled: (1) a no-take marine protected area where the “bigger-is-better” strategy should prevail (energy allocation is biased toward growth to compensate for high natural mortality at small sizes) and (2) a highly exploited population where the “smaller-is-better” strategy should dominate (energy allocation is biased toward reproduction to compensate for high fishing mortality at large sizes). Significant differences in reproduction vs. growth trade-offs were observed between the sub-populations. Sr:Ca and Ba:Ca chronologies were compared between back-calculated ontogenetic stages (larvae, juveniles and adults) and sub-populations/life histories using a general linear mixed model. The Sr:Ca chronology successfully reproduced the allocation of energy for growth or reproduction according to the life history strategy of the individual, whereas correlation between ontogeny and otolith microchemistry was less obvious for Ba:Ca. We contend that the direct and/or indirect (e.g., the removal of large predators) effects of fishing pressure on microchemical signals should receive more attention in field studies, as trade-offs between mortality and growth/reproduction might alter microchemical patterns under a given a set of conditions.

Diet of bottlenose dolphins (Tursiops truncatus) from the Gulf of Cadiz: Insights from stomach content and stable isotope analyses.

The ecological role of species can vary among populations depending on local and regional differences in diet. This is particularly true for top predators such as the bottlenose dolphin (Tursiops truncatus), which exhibits a highly varied diet throughout its distribution range. Local dietary assessments are therefore critical to fully understand the role of this species within marine ecosystems, as well as its interaction with important ecosystem services such as fisheries. Here, we combined stomach content analyses (SCA) and stable isotope analyses (SIA) to describe bottlenose dolphins diet in the Gulf of Cadiz (North Atlantic Ocean). Prey items identified using SCA included European conger (Conger conger) and European hake (Merluccius merluccius) as the most important ingested prey. However, mass-balance isotopic mixing model (MixSIAR), using δ13C and δ15N, indicated that the assimilated diet consisted mainly on Sparidae species (e.g. seabream, Diplodus annularis and D. bellottii, rubberlip grunt, Plectorhinchus mediterraneus, and common pandora, Pagellus erythrinus) and a mixture of other species including European hake, mackerels (Scomber colias, S. japonicus and S. scombrus), European conger, red bandfish (Cepola macrophthalma) and European pilchard (Sardina pilchardus). These contrasting results highlight differences in the temporal and taxonomic resolution of each approach, but also point to potential differences between ingested (SCA) and assimilated (SIA) diets. Both approaches provide different insights, e.g. determination of consumed fish biomass for the management of fish stocks (SCA) or identification of important assimilated prey species to the consumer (SIA).

Swimming speeds of Mediterranean settlement‐stage fish larvae nuance Hjort's aberrant drift hypothesis

AbstractHistorically, the mortality of early‐life stages of marine fishes was supposed to be mostly caused by poor feeding during a critical period and aberrant drifting away from favorable recruitment areas. While fish larvae may display remarkable swimming abilities, Hjort's aberrant drift hypothesis has rarely been tested. In this study, we measured critical swimming speed (Ucrit) of settlement‐stage larvae of six coastal, warm temperate Mediterranean fish species, for which no data were previously available (Sparidae: Boops boops, Diplodus annularis, Spicara smaris, Spondyliosoma cantharus; Pomacentridae: Chromis chromis; Mugilidae sp.). Their swimming speeds were comparable with those of other temperate species, but also with the speeds of tropical species, which are considered as very fast swimmers. Mugilidae were the fastest (29.2 cm s−1), followed by Pomacentridae (22.8 cm s−1) and Sparidae (11.6 cm s−1). Most larvae swam in an inertial regime (Reynolds number &gt; 1000). Those swimming speeds were then implemented in a Lagrangian model of the competency period of these species, set in the same area (the Ligurian Sea) and at the same time (June 2014) as the observations. In this modeling experiment, directional swimming strongly increased the proportion of successful settlers, independent of mesoscale hydrological structures. Fish larvae could settle on the coast from as far as tens of kilometers offshore, in just 4 d. These findings suggest that aberrant drift is unlikely to occur for strong swimming temperate larvae and show that larval behavior should be considered on equal footing with ocean currents when assessing larval fish dispersal.

Assessment of trace metals contamination in Diplodus annularis (Linnaeus, 1758) from the south coast of Sfax, Tunisia

Contamination of trace metals in fish is regarded as a major crisis globally, with a large share in many developing countries. On the south coast of Sfax (Tunisia), concentrations of seven trace metals, i.e., cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), mercury (Hg), nickel (Ni) and zinc (Zn), were evaluated in Diplodus annularis. The sampling was conducted during December 2014. The Cd and Zn concentrations were higher than the FAO/WHO and WHO permissible limits in all tissues, while Fe and Pb concentrations were higher than the WHO permissible limits in the gills and/or liver. The levels of metal accumulation varied between tissues: liver > gills > muscle. The total target hazard quotient (THQ) through consumption of fish, calculated by adding the individual THQs, was above 1, indicating that there is significant potential health risk associated with the consumption of D. annularis. Therefore, intake of sparaillon for the general population is a matter of concern.

The three-dimensional structure of Cymodocea nodosa meadows shapes juvenile fish assemblages at Fornells Bay (Minorca Island)

The role of the meadows of the Mediterranean seagrass Cymodocea nodosa as nursery habitats for fish remains largely unknown and there are only few studies investigating the influence of their structure on juvenile assemblages. Here, we monitored juvenile fish assemblages among shallow Cymodocea nodosa meadows (0–1 m) in Minorca Island (north-western Mediterranean Sea) in both July and September 2013. To assess the influence of structural components on juvenile fish assemblages, we selected two different meadow structure types: heterogeneous with intermingled boulders and homogeneous meadows, i.e. without boulders. Juvenile fish assemblages varied significantly among these two meadow structures. Heterogeneous meadows had higher total juvenile density and species richness, where some species were only found in these portions, such as Coris julis and Serranus spp. Other species, such as Symphodus spp. and Sarpa salpa, were also more abundant within heterogeneous meadows. However, densities of some species were not increased in heterogeneous meadows demonstrating a specific response to habitat structure. For instance, Diplodus annularis displayed similar abundances in both heterogeneous and homogeneous portions of the meadow. Our study reveals that the intrinsic structural variability of seagrass meadows plays a key role for the assemblage of several fish species that are characterized by different early life history strategies.

Using stereoscopic video cameras to evaluate seagrass meadows nursery function in the Mediterranean

Seagrasses provide an important ecological value as nursery habitats, hosting higher juvenile densities than their surrounding less-structured habitats by offering shelter and food to early stages of fish. However, the quantitative evaluations of this nursery function remain elusive. Surveys assessing abundances of juvenile fish over seagrass meadows have been largely conducted by diving visual censuses, where typically only a shallow depth range is adequately covered. Within this study, we developed a low-cost stereo-baited video camera (SBRUV) with high precision and accuracy able to deliver length frequency distributions, including the smallest juvenile fraction. The capacity of the SBRUV system increased the synopticity with respect to typical surveys. We tested the system over seagrass meadows of Posidonia oceanica in a Mediterranean bay, investigating the relationship of juvenile abundance and size of the sparid Diplodus annularis with depth, time of day and protection status (i.e. inside and outside of a Marine Protected Area, MPA). We found significant effects of the depth on the length of the older size classes fraction (larger sizes at deeper stations) and an effect of time of the day on the abundance (less abundant during the evenings), and an opposite pattern was observed for early juvenile’s abundances. The MPA protection had no effect in D. annularis population structure. Interestingly, the relative abundance of D. annularis early juveniles was comparable at all depths, from 2 to 20 m, which suggests a potentially higher nursery value of P. oceanica meadows than earlier thought.

Potential risk assessment of metals in edible fish species for human consumption from the Eastern Aegean Sea

The levels of Hg, Cd, Pb, Cr, Cu and Zn were measured in the tissues of four edible fish species namely: Diplodus annularis, Pagellus erythrinus, Merluccius merluccius and Mullus barbatus, collected from the Turkish Coast of the Aegean Sea. Except for D. annularis, the levels of Cd and Pb in all fish tissues sampled in Aliaga Bay in 2009 were above the tolerable limits according to the Food and Agriculture Organization of the United Nations (FAO). Hg in P. erythrinus and M. barbatus were higher than the maximum permitted limits (FAO), while D. annularis and M. merluccius were lower than the limit for biota in the district of Aliaga. Although the Target Hazard Quotient (THQ) values for Cd, Pb, Cu, Cr, Zn in all fish samples were lower than 1.0, the THQ for Hg levels were higher than 1.0 for most of the samples. According to the THQ values, M. merluccius may be consumed in moderation from Aliaga Bay, while the consumption of M. barbatus and P. erythrinus collected from Aliaga Bay are potentially hazardous to human health due to the Hg concentrations. Fish collected from Izmir Bay can be consumed safely.

Gap analysis on the biology of Mediterranean marine fishes.

We estimated the current level of knowledge concerning several biological characteristics of the Mediterranean marine fishes by carrying out a gap analysis based on information extracted from the literature, aiming to identify research trends and future needs in the field of Mediterranean fish biology that can be used in stock assessments, ecosystem modeling and fisheries management. Based on the datasets that emerged from the literature review, there is no information on any biological characteristic for 43% (n = 310) of the Mediterranean fish species, whereas for an additional 15% (n = 109) of them there is information about just one characteristic. The gap between current and desired knowledge (defined here as having information on most biological characteristics for at least half of the Mediterranean marine fishes) is smaller in length-weight relationships, which have been studied for 43% of the species, followed by spawning (39%), diet (29%), growth (25%), maturity (24%), lifespan (19%) and fecundity (17%). The gap is larger in natural mortality for which information is very scarce (8%). European hake (Merluccius merluccius), red mullet (Mullus barbatus), annular seabream (Diplodus annularis), common pandora (Pagellus erythrinus), European anchovy (Engraulis encrasicolus), European pilchard (Sardina pilchardus) and bogue (Boops boops) were the most studied species, while sharks and rays were among the least studied ones. Only 25 species were fully studied, i.e. there was available information on all their biological characteristics. The knowledge gaps per characteristic varied among the western, central and eastern Mediterranean subregions. The number of available records per species was positively related to total landings, while no relationship emerged with its maximum reported length, trophic level and commercial value. Future research priorities that should be focused on less studied species (e.g. sharks and rays) and mortality/fecundity instead of length-weight relationships, as well as the economy of scientific sampling (using the entire catch to acquire data on as many biological characteristics as possible) are discussed.

Functional and Structural Characterization of a Thermostable Phospholipase A2 from a Sparidae Fish (Diplodus annularis).

Novel phospholipase (PLA2) genes from the Sparidae family were cloned. The sequenced PLA2 revealed an identity with pancreatic PLA2 group IB. To better understand the structure/function relationships of these enzymes and their evolution, the Diplodus annularis PLA2 (DaPLA2) was overexpressed in E. coli. The refolded enzyme was purified by Ni-affinity chromatography and has a molecular mass of 15 kDa as determined by MALDI-TOF spectrometry. Interestingly, unlike the pancreatic type, the DaPLA2 was active and stable at higher temperatures, which suggests its great potential in biotechnological applications. The 3D structure of DaPLA2 was constructed to gain insights into the functional properties of sparidae PLA2. Molecular docking and dynamic simulations were performed to explain the higher thermal stability and the substrate specificity of DaPLA2. Using the monolayer technique, the purified DaPLA2 was found to be active on various phospholipids ranging from 10 to 20 mN·m-1, which explained the absence of the hemolytic activity for DaPLA2.