Montserrat Ramón

Rising seawater temperatures and increasingly frequent marine heatwaves are posing major challenges for mussel aquaculture worldwide. Developing reliable indicators of sublethal thermal stress is therefore essential to assess population vulnerability and support adaptive management. Here, we evaluated the response of the Mediterranean mussel (Mytilus galloprovincialis) to temperature stress using histopathological conditions (HCs) as potential environmental indicators. Mussels from Atlantic and Mediterranean aquaculture sites were exposed to controlled temperature treatments (16.4-30.8°C), and complementary field surveys were conducted under contrasting natural thermal regimes. HCs affecting several tissues were quantified individually and integrated into a composite histopathological index.Most individual HCs increased significantly with temperature, including hemocyte infiltration, tissue degeneration, and gonadal atresia. However, the composite index provided a stronger and more consistent signal of thermal stress than individual lesions alone. In laboratory experiments, cumulative HCs increased with temperature in both populations, but the shape of the response differed between sites. Atlantic mussels exhibited a linear increase in tissue damage across the thermal gradient, whereas Mediterranean mussels maintained low levels of damage until temperatures exceeded approximately 25°C, after which HCs increased rapidly. Importantly, the same temperature-damage relationships were observed under field conditions despite greater environmental variability.Our results demonstrate that a composite histopathological index is a sensitive and transferable indicator of sublethal thermal stress in M. galloprovincialis. By integrating multiple tissue-level responses into a single metric, this approach captures population-specific vulnerability to warming and provides an operational early-warning tool for monitoring mussel health.

Holothurians provide important ecosystem services by enhancing sediment health through bioturbation. The sea cucumber Parastichopus regalis has a wide distribution in the Mediterranean Sea. Even though it is a commercially exploited species, little is known about its ecological traits and there is no information on the bioturbation potential resulting from its feeding activity. To address these knowledge gaps, the population density, demographic structure, musculature and evisceration of P. regalis were investigated on Arenys de Mar, NW Mediterranean. Food assimilation efficiency, and feeding and bioturbation rates were assessed through field and laboratory experiments. The exploited population exhibited a healthy distribution of sizes/ages, and the density values were similar to or greater than those described in other Mediterranean areas. This species did not show seasonal evisceration, and seasonal patterns in muscle weight depended on year and body size. The field results indicated that P. regalis selected organic matter from the sediment as food. The average individual feeding rate was 8.6 g wet sediment d⁻¹. The bioturbation role of the P. regalis population in the studied area was especially important at depths between 81 m and 124 m, where it consumed between 7.6 and 13.8 t of wet sediment y⁻¹ km⁻². These results highlight the important role that this species play in deep habitats as sediment bioturbator, controlling the accumulation of dead organic matter.

The Ebre Delta (NW Mediterranean), which is considered a highly vulnerable ecosystem, is one of the most important European wetlands and belongs to the Natura 2000 network. The present study aims to characterize the benthic megainvertebrate communities inhabiting the Ebre Delta soft-bottom infralittoral to acquire faunistic and biological knowledge for two periods of time, 23 years apart. Experimental trawls were conducted during the two periods (1992–1993 and 2016–2017) in three depth strata, between 5 and 25 m. A total of 139 and 170 taxa were collected at each period, respectively. Our results showed that community species composition and structure varied between periods and among depth strata. Overall, a large decrease in density and biomass was detected for most species in all three depth strata examined (0–5, 15–20, and 20–25 m) in 2016–2017, especially in the shallowest stratum. Species richness was higher in 2016–2017 than in 1992–1993, and the lowest values were found at the shallowest stratum in both periods. The significant biomass losses herein reported highlight the need to increase, in time and effort, the monitoring of large marine invertebrates in coastal areas, where many taxa provide important ecosystem functions and services.

Seamounts are globally important and essential ecosystems for supporting and maintaining marine biodiversity. In the Mallorca Channel, three prominent seamounts are present: Ausias March, Ses Olives and Emile Baudot. Currently, this area is being evaluated for inclusion in the Natura 2000 network. For this objective three surveys were conducted in the seamounts of the Mallorca Channel during July 2018 and July 2020. Samples of macro-invertebrates obtained in the deep sea revealed a rich fauna of Mollusca (68 species belonging to 40 families). New Mollusca occurrences included: four species of Gastropoda: Colus jeffreysianus, Cantrainea peloritana, Fusiturris similis, Gymnobela abyssorum, and seven species of Bivalvia: Pododesmus squama, Allogramma formosa, Asperarca nodulosa, Cetomya neaeroides, Spondylus gussonii, Haliris granulata and Policordia gemma. Where possible, the identification of these species was confirmed using the DNA barcoding method (sequencing of the cytochrome c oxidase subunit I). This study contributes towards filling the gap in knowledge of deep-sea mollusc fauna of the north-western Mediterranean.

Small crabs belonging to the family Pinnotheridae are characterized by living inside mainly bivalves. In European waters the recently-described pea crab Pinnotheres bicristatus increased to five the known number of pinnotherid species. The know distribution of the recently-described pea crab Pinnotheres bicristatus encompassed the area between the Gulf of Cádiz (NE Atlantic) and the western Alboran Sea (SW Mediterranean). The species was so far reported to occur in the pallial cavity of the common saddle oyster, Anomia ephippium, between 11 and 52 m depth. During two years, a total of 43 specimens of Pinnotheres bicristatus were collected in two different projects/surveys along the Mediterranean coasts of the Iberian Peninsula, thus enlarging its known occurrence to the eastern Alboran Sea and the NW Mediterranean, at depths between 37 and 71 m. We also report a new bivalve host for the species, the flat oyster Ostrea edulis, and population structure information of these new records. As a conclusion, this study considerably extends both in latitude and longitude, as well as in depth, the known geographical distribution of P. bicristatus.