Two-banded Seabream Diplodus Vulgaris Research Articles

Population Structures of the Two Banded Seabream, Diplodus vulgaris and the White Seabream, Diplodus sargus Reveal New Records in Maximal Age

The common two-banded seabream Diplodus vulgaris and Diplodus sargus were sampled from
 non-commercial fishing catches around the Maltese Islands between July 2012 and December
 2017. A total of 1550 (D. vulgaris N=1204, D. sargus N=346) specimens were collected. In this
 study, age, growth, length-weight relationship (LWR), condition factor (K) and relative condition
 factor (Kn) were investigated. Ages ranged from 0 to 17 years for D. sargus and 0 to 16 years for
 D. vulgaris. A positive allometric growth was observed for D. sargus while growth in D. vulgaris
 was isometric. Average Kn was found to be 0.99 and 1.01 in D. vulgaris and 0.97 and 1.00 in D.
 sargus for males and females respectively. The growth parameters of the von Bertalanffy equation
 were: L∞=26.71 and 30.86 cm, K= 0.275 and 0.286 year-1
 and tₒ = -2.27 and -1.61 year for all
 individuals of D. vulgaris and D. sargus respectively. This study is the first reference on the LWR
 equation parameters, Kn, K and Age for these species around the Maltese Islands and establishes
 a new maximum age for D. vulgaris of 16 years.

Modelling long-term fisheries data to resolve the attraction versus production dilemma of artificial reefs

The main role of artificial reefs (ARs) is to enhance the productivity and sustainability of coastal fisheries by creating new fish biomass. From a modelling point of view, the creation of new fish biomass would be realized by a shift to a state of higher carrying capacity of the environment (K) for aquatic populations and communities. However, it has not been possible to demonstrate unequivocally rising K as a result of AR deployment because of the difficulty in disentangling enhancements due to simple distributional changes (the attraction hypothesis) versus total abundance rise (the production hypothesis). Here we develop a modelling framework based on simple, inexpensive fisheries data to quantify the impact of ARs, disentangling attraction from production by assessing the rise in regional K. The rationale is that if attraction to ARs from the wider region was the main driver of increased abundance in the ARs then regional K would have remained constant before, during and after deployment of the ARs. Therefore an increase in regional K disproves the hypothesis of attraction. The study case is the fishery for the two-banded seabream Diplodus vulgaris in southern Portugal. Monthly time series of 27 years of landings, 20 years of fishing effort, were available from three small-scale fleets: one was the artisanal fleet operating on the ARs and the other two were semi-industrial fleets operating on the wider continental shelf. The model that we developed and applied incorporated the data from all fleets so it evaluated the change in regional K. We show that regional K for D. vulgaris increased by 35% after final deployment of the ARs and it did so in linear fashion during four years. From a fisheries perspective the result was more nuanced because although the deployment succeeded in raising regional K, stock biomass and thereby enhancing the artisanal fishery, it also led to a substantial rise in total fishing mortality and exploitation rate because the semi-industrial fleets operating offshore increased their harvest rate nearly 3-fold. Our modelling framework has wide applicability in other regions due to the elementary nature of the necessary fishing monitoring data.

Patterns of Fish Connectivity between a Marine Protected Area and Surrounding Fished Areas.

Patterns of connectivity and self-recruitment are recognized as key factors shaping the dynamics of marine populations. Connectivity is also essential for maintaining and restoring natural ecological processes with genetic diversity contributing to the adaptation and persistence of any species in the face of global disturbances. Estimates of connectivity are crucial to inform the design of both marine protected areas (MPAs) and MPA networks. Among several approaches, genetic structure is frequently used as a proxy for patterns of connectivity. Using 8 microsatellite loci, we investigated genetic structure of the two-banded sea bream Diplodus vulgaris, a coastal fish that is both commercially and ecologically important. Adults were sampled in 7 locations (stretches of coastline approximately 8 km long) and juveniles in 14 sites (~100 to 200 m of coastline) along 200 km of the Apulian Adriatic coast (SW Adriatic Sea), within and outside an MPA (Torre Guaceto MPA, Italy). Our study found similar genetic diversity indices for both the MPA and the surrounding fished areas. An overall lack of genetic structure among samples suggests high gene flow (i.e. connectivity) across a scale of at least 200 km. However, some local genetic divergences found in two locations demonstrate some heterogeneity in processes renewing the population along the Apulian Adriatic coast. Furthermore, two sites appeared genetically divergent, reinforcing our observations within the genetic makeup of adults and confirming heterogeneity in early stage genetics that can come from either different supply populations or from chaotic genetic patchiness occurring under temporal variation in recruitment and in the reproductive success. While the specific role of the MPA is not entirely known in this case, these results confirm the presence of regional processes and the key role of connectivity in maintaining the local population supply.

Dispersal of larval and juvenile seabream: Implications for Mediterranean marine protected areas

In the marine context, information about dispersal is essential for the design of networks of marine protected areas (MPAs). Generally, most of the dispersal of demersal fishes is thought to be driven by the transport of eggs and larvae in currents, with the potential contribution of dispersal in later life stages relatively minimal.Using otolith chemistry analyses, we estimate dispersal patterns across a spatial scale of approximately 180km at both propagule (i.e. eggs and larvae) and juvenile (i.e. between settlement and recruitment) stages of a Mediterranean coastal fishery species, the two-banded seabream Diplodus vulgaris. We detected three major natal sources of propagules replenishing local populations in the entire study area, suggesting that propagule dispersal distance extends to at least 90km. For the juvenile stage, we detected dispersal of up to 165km. Our work highlights the surprising and significant role of dispersal during the juvenile life stages as an important mechanism connecting populations. Such new insights are crucial for creating effective management strategies (e.g. MPAs and MPA networks) and to gain support from policymakers and stakeholders, highlighting that MPA benefits can extend well beyond MPA borders, and not only via dispersal of eggs and larvae, but also through movement by juveniles.

New and rare coastal fishes in the Azores islands: occasional events or tropicalization process?

Seven coastal fish species are newly reported for the remote north Atlantic archipelago of the Azores: Mediterranean sand eel Gymnammodytes cicerelus, bar jack Caranx ruber, two-banded seabream Diplodus vulgaris, bastard grunt Pomadasys incisus, unicorn leatherjacket filefish Aluterus scriptus and longspined porcupinefish Diodon holacanthus. The occurrence is also confirmed for 19 species that had been hitherto cited occasionally for the region, totalling a list of two elasmobranchs and 23 teleosts. Diplodus vulgaris, which appears to have recently colonized the islands, as well as roughtail stingray Dasyatis centroura and golden grey mullet Liza aurata, re-cited based on new records, are frequent or common coastal species in the Azores. The remaining 22 species, exceptional or rare in the region, are of tropical or subtropical affinity and find their northernmost distribution limit within the central and north-east Atlantic Ocean precisely in the Azores. This biogeographical pattern contrasts with that of the Azorean coastal fish community and suggests a tropicalization process in the region in line with previous findings of similar patterns across the north-east Atlantic Ocean and the Mediterranean Sea. These novel data from the most isolated archipelago of the North Atlantic Ocean, located in a biogeographic boundary area where colonization opportunities are reduced, reinforce the need for long-term monitoring programmes of coastal fish communities and, in particular, of indicator species groups to improve understanding of the effects of climate change on marine communities.

Patterns of variability in early life traits of a Mediterranean coastal fish

Spawning dates and pelagic larval duration (PLD) are early life traits (ELT) crucial for understanding life cycles, properly assessing patterns of connectivity and gathering indications about patchiness or homogeneity of larval pools. Considering that little attention has been paid to spatial variability in these traits, we investigated variability of ELT from the analysis of otolith microstructure in the common two-banded sea bream Diplodus vulgaris. In the southwestern Adriatic Sea, along ~200 km of coast (~1° in latitude, 41.2° to 40.2°N), variability of ELT was assessed at multiple spatial scales. Overall, PLD (ranging from 25 to 61 d) and spawning dates (October 2009 to February 2010) showed significant variability at small scales (i.e. <6 km), but not at larger scales. These outcomes suggest patchiness of the larval pool at small spatial scales. Mul- tiple causal processes underlying the observed variability are discussed, along with the need to properly consider spatial variability in ELT, for example when delineating patterns of connectivity.

Reproductive biology, age and growth of the two-banded seabream Diplodus vulgaris (Pisces: Sparidae) in the Gulf of Gabès, Tunisia

Samples of common two-banded seabream Diplodus vulgaris (N = 1097), used in this study, were caught in the Gulf of Gabès (Tunisia) from March 2008 to February 2010. Total length ranged from 7 to 25 cm. Diplodus vulgaris is a protandric hermaphrodite. The overall ratio of females to males was 1:1.66. The reproductive season extended from October to February, and the peak spawning activity occurred in December–January. The total length at which 50% of the population reached maturity was 14.14 ± 0.16 cm for females and 13.57 ± 0.01 cm for males. Parameters of the length–weight relationship (TW = aTLb) for all individuals were a = 0.0185 and b = 2.9319. The youngest specimen in this study was 0+ years, whereas the oldest one was 9 years. The von Bertalanffy growth parameters for the whole sample were: L∞ = 25.4 cm, k = 0.179 and t0 = −1.631 year. The instantaneous rate of natural mortality was: M = 0.333 year−1.

Diet overlap of juvenile salema (Sarpa salpa), bogue (Boops boops) and common two-banded sea bream (Diplodus vulgaris) in the south-eastern Adriatic

The food compositions of salema Sarpa salpa, bogue Boops boops and common two-banded seabream Diplodus vulgaris in the Donji Molunat Bay (south- eastern Adriatic) were studied in order to evaluate the diet overlap among them. Fish were collected from March to July 2009 using beach seine net. Three species of crustaceans were the most common prey, the most abundant were copepods. A significant overlap in the diet calculated using Schoener's index was recorded in May when the index was 0.9266 for bogue and salema, 0.6091 for bogue and common two-banded seabream, and 0.6142 for common two-banded seabream and salema.

Spatial and temporal patterns in the movement of adult two-banded sea bream Diplodus vulgaris (Saint-Hilaire, 1817)

The patterns of spatial and temporal activity during the spawning season for an important recreational and commercial target species from the Mediterranean Sea and mid-east Atlantic, Diplodus vulgaris, were investigated using acoustic telemetry. No diel behavior was found in the detection pattern and the probability of detecting any tagged fish was independent of time. Individual fish spent 95% of their time in an area smaller than 1 km 2. The asymptotic value of home range (HR) was observed a few days after fish were tagged and released. There was high overlap in the areas used during the day and night, and individuals exhibited high site fidelity. The movements of D. vulgaris during the spawning season resembled random movement within a specific HR area (sedentary behavior) rather than directional movement (nomadic behavior) and daily migrations were discarded. The results provided here are useful for management and suggest that small protected areas can offer a promising approach to the sustainable development of this fishery.

Skoulekia meningialis n. gen., n. sp. (Digenea: Aporocotylidae Odhner, 1912) a parasite surrounding the brain of the Mediterranean common two-banded seabream Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817) (Teleostei: Sparidae): Description, molecular phylogeny, habitat and pathology

This study describes a new aporocotylid genus and species, Skoulekia meningialis n. gen., n. sp. which was detected in the ectomeningeal veins surrounding the optic lobes of the brain of the common two-banded seabream Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817) from the Gulf of Valencia (Mediterranean Sea). A detailed morphological description of S. meningialis is provided, including drawings, measurements and scanning electron microscopy images as well as a phylogenetic study of S. meningialis and closely related taxa using DNA sequence data obtained from whole ITS2 and partial 18S and 28S rDNA regions. Morphology as well as molecular phylogeny strongly support the erection of a new genus and demonstrate its close relationship with the genera Psettarium (Goto & Ozaki, 1930) and Pearsonellum Overstreet & Køie, 1989. Skoulekia is the second aporocotylid genus described in the Sparidae, a family including economical important fishes.In contrast to the majority of the aporocotylids, which inhabit the heart or the blood vessels of the gills, S. meningialis inhabits the ectomeningeal veins surrounding the optic lobes. Eggs were found trapped within the gill vessels. Normally, blood fluke pathology is almost exclusively related to the eggs. However, in the case of S. meningialis, main histopathological alterations were related to the adult blood flukes which were found to cause mild localised meningitis.