Trophic, Chemo-Ecological and Sex-Specific Insights on the Relation Between Diplodus sargus (Linnaeus, 1758) and the Invasive Caulerpa cylindracea (Sonder, 1845)

Biological invasions result in negative and unpredictable impacts on oceans worldwide. Non-indigenous macrophytes often synthesize secondary metabolites for defensive purposes and increased competition efficiency: this is the case of Caulerpa cylindracea, which has entered the Mediterranean Sea in 1990 and competed against local flora and fauna since. It was demonstrated that the white seabream Diplodus sargus (i) has included the algae into its diet, (ii) is subject to the peculiar Abnormally Tough Specimen (ATS) condition post-cooking, and (iii) suffers physiological and behavioral disturbances from caulerpin, one of the three major algal secondary metabolites. This paper confirms a feeding relationship between the fish and the algae, quantifies caulerpin accumulation in the liver, suggests a possible mollusk- and echinoderm-driven biomagnification, and highlights the fact that all ATS specimens were males. Multivariate analyses on a multi-biomarker panel reveals differential correlations to key cellular processes such as oxidative stress, metabolism, neurotoxicity, and lipid peroxidation as well as to condition indexes.

Reproductive Traits and Somatic Growth of Diplodus sargus sargus (Linnaeus, 1758) in the Central Algerian Coast (Southern Mediterranean Sea)

This work provides useful knowledge on the reproductive traits and somatic growth of the white seabream (Diplodus sargus sargus Linnaeus, 1758) of the central sector of the Algerian coast. It aimed to estimate the maximum yield size of this sparid and evaluate its reproductive potential, by presenting the first results on its global fecundity. A total of 497 specimens, ranging in size from 12.4 to 40.3 cm, were monthly and randomly sampled from the artisanal fishery fleet, between January and December 2017. The obtained length-weight relationships indicated negative allometry for males (TW=0.024 TL2.842) and isometry for females (TW=0.016 TL3.013). The white seabream is a digynic protandrous hermaphrodite species. Sex reversal was observed with a large size overlap of 12 to 32 cm with a median of 23.5 cm. The reproductive season was observed from January to May and spawning occurred in spring. The size at first sexual maturity (TL50) was 20.55 cm for both sexes. Based on these results, the current legal minimum size of capture should be raised in the study area.

Importance of recreational shore angling in the archipelago of Madeira, Portugal (northeast Atlantic)

In 2017, a total of 4825 licences were issued for shore angling in Madeira. Surveys were conducted on 734 anglers, some in the government fisheries office during the licence request and others during the fishing activity. Shore angling is practised throughout the year, mostly at weekends and during day time, and with an increase in summer. More than 60% of the anglers are unemployed, have low incomes, and spend on average €254 per person per year on this activity, adding up to a total of €1.16 million per year. Shore angling average number of fishing days per year per fisher was 65.1±62.0 and the average catch per unit of effort was 0.35±0.26 kg/angler/hour. The estimated total annual catch was 520.7 t. Forty-three teleost species, 2 elasmobranchs and 6 invertebrates were identified in the catches. Despite the limitations and inaccuracies inherent to the surveys, they still provided valuable information and gave a general perception of the recreational shore fisheries in Madeira. The possible impact on the most captured species, such as the white seabream, Diplodus sargus (Linnaeus, 1758), and the parrotfish Sparisoma cretense (Linnaeus, 1758), should be analysed because high fishing pressure could affect populations and ecosystems.

Integrated multi-trophic aquaculture systems: energy transfers and food web organization in coastal earthen ponds

Three Ecopath models were built to reproduce 3 experimental treatments carried out in earthen ponds located in Olhão, southern Portugal, to understand the energy transferred and the ecosystem state in integrated multi-trophic aquaculture (IMTA). These earthen ponds behave as simplified ecosystems or mesocosms, with well-defined borders, where the relationships between trophic groups can be described through ecosystem modeling. Different combinations of species were produced in these ponds, corresponding to the 3 treatments: (1) fish, oysters and macroalgae (FOM); (2) fish and oysters (FO); and (3) fish and macroalgae (FM). The managed species were meagre Argyrosomus regius, white seabream Diplodus sargus, flathead grey mullet Mugil cephalus, Japanese oyster Crassostrea gigas and sea lettuce Ulva spp. The results showed that the total amount of energy throughput was 15 to 17 times higher when compared with an equivalent naturalized system. The high biomass and low recycling indicated an immature system with low resilience and low stability that demands high rates of water renewal and aeration to maintain good water-quality levels for finfish production. The addition of oysters and macroalgae in the FOM treatment appeared to improve the water quality, since oysters controlled the excess of phytoplankton produced in the ponds by ingesting a fair amount of the phytoplankton, while the macroalgae helped in the absorption of excess nutrients and created a habitat for periphyton and associated macroinvertebrates. Some ecosystem attributes of the FOM ponds approached the values of the naturalized model, suggesting a possible path towards more sustainable aquaculture.