Salinity shapes the stress responses and energy reserves of marine polychaetes exposed to warming: From molecular to functional phenotypes

Combined Use of Fatty Acid Profiles and Elemental Fingerprints to Trace the Geographic Origin of Live Baits for Sports Fishing: The Solitary Tube Worm (Diopatra neapolitana, Annelida, Onuphidae) as a Case Study

Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is one of the most exploited polychaete species in European waters, particularly in Ria de Aveiro, a coastal lagoon in mainland Portugal, where the overexploitation of this resource has led to a generalized decline of local populations. In an attempt to reduce the impact of harvesting, several management actions were implemented, but illegal poaching still fuels a parallel economy that threatens the sustainable use of this marine resource. The present study evaluated the combination of fatty acid profiles and elemental fingerprints of the whole body and jaws, respectively, of D. neapolitana collected from four harvesting locations within Ria de Aveiro in order to determine if their geographic origin could be correctly assigned post-harvesting. Results showed that both fatty acid profiles and elemental fingerprints differ significantly among locations, discriminating the geographic origin with higher accuracy when combining these two natural barcodes than when employing each individually. The present work can, therefore, contribute to the implementation of an effective management plan for the sustainable use of this marine resource, making it possible to detect if D. neapolitana was sourced from no-take zones and if it was collected from the place of origin claimed by live bait traders.

Effect of an environmental microplastic mixture from the Seine River and one of the main associated plasticizers, dibutylphthalate, on the sentinel species Hediste diversicolor

The aim of this study was to explore the adverse effects of a microplastic (MP) mixture obtained from litter accumulated in the Seine River (France) compared to those of their major co-plasticizer, dibutylphthalate (DBP), on the sentinel species Hediste diversicolor. A suite of biomarkers has been investigated to study the impacts of MPs (100 mg kg-1 sediment), DBP (38 μg kg-1 sediment) on worms compared to non-exposed individuals after 4 and 21 days. The antioxidant response, immunity, neurotoxicity and energy and respiratory metabolism were investigated using biomarkers. After 21 days, worms exposed to MPs showed an increasing aerobic metabolism, an enhancement of both antioxidant and neuroimmune responses. Energy-related biomarkers demonstrated that the energy reallocated to the defence system may come from proteins. A similar impact was depicted after DBP exposure, except for neurotoxicity. Our results provide a better understanding of the ecotoxicological effects of environmental MPs and their associated-contaminants on H. diversicolor.

Thermal tolerance limits and physiological traits as indicators of Hediste diversicolor's acclimation capacity to global and local change drivers

Global projections predict significant increases in ocean temperature and changes in ocean chemistry, including salinity variations by 2100. This has led to a substantial interest in the study of thermal ecophysiology, as temperature is a major factor shaping marine ectotherm communities. However, responses to temperature may be influenced by other factors such as salinity, highlighting the relevance of multiple stressor studies. In the present work, we experimentally evaluated the thermal tolerance of the marine ragworm Hediste diversicolor under predicted global change scenarios. Organisms were subjected to an experimental trial under control (24 °C), and two temperature treatment scenarios (ocean warming +3 °C - (27 °C) and heat wave +6 °C - (30 °C)), combined with salinity variations (20 and 30) in a full factorial design for 29 days. Environmental data from the field were collected during 2019 and 2020. At day 30 post exposure, upper thermal limits (Critical Thermal Maximum - CTMax), thermal safety margins (TSM) and acclimation capacity were measured. Higher acclimation temperatures led to higher thermal tolerance limits, confirming that H. diversicolor features some physiological plasticity, acclimation capacity and a positive thermal safety margin. This margin was greater considering in situ temperature data from 2019 than maximum temperatures for 2020 (CTMax > maximum habitat temperature-MHT). Moreover, smaller organisms displayed higher upper thermal limits suggesting that thermal tolerance is size dependent. Ragworms subjected to higher salinity also showed a higher CTMax than those acclimated to lower salinity. However, temperature and salinity showed an additive effect on CTMax, as no significant interaction was detected. We conclude that H. diversicolor can easily acclimate to increased water temperature, independently of salinity variations. Given the key role of ragworms in food webs in estuaries and coastal lagoons, substrate bioturbation and aquaculture, this information is relevant to support conservation actions, optimize culture protocols and identify thermal resistant strains.

Thermal plasticity over a marine-estuarine ecocline can buffer a tropical fish from warming

Intraspecific variation in thermal tolerance can favor species persistence in a warmer ocean, but is often overlooked in fine-scale studies. Nonetheless, local drivers (e.g. salinity) interact with temperature to shape species' thermal response. Here, we acclimated juveniles of Brazilian silversides Atherinella brasiliensis captured at the limits of a marine-estuarine ecocline under reciprocal-cross conditions, to test for phenotypic plasticity in heat tolerance. We also tested whether silversides acclimated to temperatures predicted for 2100 (+3-4.5 °C). Fish in warm-brackish waters showed higher CTMax (Critical Thermal Maximum) than those in cold-marine conditions, regardless of their origin. Silversides' CTMax reached up to 40.6 °C, but it did not increase after exposure to temperatures predicted for 2100. Lack of acclimation response suggests that silversides heat tolerance has reached a "ceiling", despite thermal plasticity. Our findings show that fine-scale environmental heterogeneity can promote phenotypic plasticity for tropical species, reducing the risk of short-term extirpation.

Combined effect of marine heatwaves and light intensity on the cellular stress response and photophysiology of the leather coral Sarcophyton cf. glaucum

Marine heatwaves (MHW) are threatening tropical coral reef ecosystems, leading to mass bleaching events worldwide. The combination of heat stress with high irradiance is known to shape the health and redox status of corals, but research is biased toward scleractinian corals, while much less is known on tropical symbiotic soft corals. Here, we evaluated the cellular stress response and the photophysiological performance of the soft coral Sarcophyton cf. glaucum, popularly termed as leather coral, under different global change scenarios. Corals were exposed to different light intensities (high light, low light, ∼662 and 253 μmol photons m^-2 s^-1) for 30 days (time-point 1) and a subsequent MHW simulation was carried out for 10 days (control 26 vs 32 °C) (time-point 2). Subsequently, corals were returned to control temperature and allowed to recover for 30 days (time-point 3). Photophysiological performance (maximum quantum yield of photosystem II (Fv/Fm), a measure of photosynthetic activity; dark-level fluorescence (F₀), as a proxy of chlorophyll a content (Chl a); and zooxanthellae density) and stress biomarkers (total protein, antioxidants, lipid peroxidation, ubiquitin, and heat shock protein 70) were assessed in corals at these three time-points. Corals were especially sensitive to the combination of heat and high light stress, experiencing a decrease in their photosynthetic efficiency under these conditions. Heat stress resulted in bleaching via zooxanthellae loss while high light stress led to pigment (Chl a) loss. This species' antioxidant defenses, and protein degradation were particularly enhanced under heat stress. A recovery was clear for molecular parameters after 30 days of recovery, whereby photophysiological performance required more time to return to basal levels. We conclude that soft corals distributed along intertidal areas, where the light intensity is high, could be especially vulnerable to marine heatwave events, highlighting the need to direct conservation efforts toward these organisms.

Cellular stress response and acclimation capacity of the ditch shrimp Palaemon varians to extreme weather events - How plastic can a plastic species be?

Species from shallow marine environments are particularly vulnerable to extreme weather events (heatwaves and extreme rainfall) that can promote abrupt environmental shifts, namely in temperature and salinity (respectively). To assess how these shifts impact species' cellular stress responses (CSR), ditch shrimps Palaemon varians were exposed to a chronic (28 days) thermohaline stress experiment. Three levels of temperature (20, 23 and 26 °C) and two levels of salinity (20 and 40) were tested in a full factorial experiment, and shrimps sampled at the 7th, 14th, 21st and 28th day of exposure. Survival, wet weight (as proxy for growth), and cellular stress biomarkers associated with oxidative stress (LPO - Lipid Peroxidation, GST - Glutathione-S-Transferase, SOD - Superoxide Dismutase, TAC - Total Antioxidant Capacity and CAT - Catalase) and protein denaturation (UBI - Ubiquitin and HSP-70 - Heat Shock Protein 70 kDa) were analysed in shrimps' muscle at each sampling day. Temperature and time of exposure significantly affected biomarker levels, with shrimps exposed to 20 and 26 °C revealing more pronounced differences. No interactions were detected between temperature and salinity, suggesting that these factors display additive effects on shrimps' CSR. Antioxidant agents (CAT and TAC) increased under elevated temperature, while protein denaturation markers (UBI and HSP-70) were mostly affected by time of exposure, decreasing at 28 days. Total protein reserves increased throughout time and no effects on wet weight were observed. A negative correlation between wet weight and HSP-70 was detected, suggesting that HSP-70 levels are dependent on organism size. Peak survival (~73 %) was found under 20 °C and salinity 40 and lower survival (~30-40 %) was associated with higher temperatures (23 and 26 °C) and lower salinity (20). We conclude that P. varians displays some level of acclimation capacity but differences in survival may indicate effects on osmoregulation processes and the need for longer timeframes to fully acclimate to heat and hyposaline stress.