Biochemical responses and physiological status in the crab Hemigrapsus crenulatus (Crustacea, Varunidae) from high anthropogenically-impacted estuary (Lenga, south-central Chile)

Intraspecific variation in reproductive traits and embryo elemental composition of the crab Hemigrapsus crenulatus (Milne Edwards, 1837) across fluctuating coastal environments along Chilean coasts

The estuarine crab Hemigrapsus crenulatus has a wide distribution range along the coast of the South Pacific Ocean (from 20 °S to 53 S°). This decapod is abundant in these coastal and estuarine habitats and plays a key ecological role as prey of the snook fish (Eleginops maclovinus) and kelp gull (Larus dominicanus). Its diet consists of detritus, dead fish, and crustaceans, and the macroalgae Ulva sp. In response to contrasting environmental conditions and anthropogenic impacts along the Chilean coast, H. crenulatus may present intraspecific variations in its reproductive traits and changes in the elemental composition of its embryos, directly affecting its biological fitness. Along the Chilean coast, female individuals were collected during late spring 2019 and early summer 2020 (from November 2019 to February 2020) in six areas of Chile (north: Tongoy (30°S); south-central: Lenga (36°S), Tubul (37°S); south austral: Calbuco (41°S), Castro (42°S), Quellón (43°S). The environmental conditions (i.e. sea surface temperature, precipitation and chlorophyll α) present during each sampling event were also recorded. We evaluated the reproductive parameters of females (fecundity, reproductive output (RO)) as well as their body size (carapace width and dry weight), volume, water content, dry weight, elemental composition (carbon, hydrogen, nitrogen: CHN), and finally the energy content of their embryos. Our results indicated that the environmental conditions of the sea water temperature, precipitation (proxy of water salinity) and chlorophyll α (proxy of food availability) have direct effects on the reproductive parameters of females and the characteristics of their embryos. We observed a low fecundity and high RO in Calbuco and Quellón, where precipitation was high (i.e. diluted salinity) and temperatures and productivity was low. For embryo traits, the highest values of volume and water content were observed in female crabs from the estuarine areas (i.e. Tongoy, Lenga, Tubul), values much higher than those found in the internal sea of Chile (i.e. Calbuco, Castro, Quellón). For the elemental composition, we observed high nitrogen levels and a low C:N proportion in embryos from female crabs from Lenga (a nitrogen enriched area). Fluctuating environmental variables among localities proved to modulate intraspecific variations in females and embryos of H. crenulatus, revealing different reproductive strategies, particularly in the quality and energy investment per embryo, which subsequently influenced successful embryogenesis and larval survival.

Slow and steady hurts the crab: Effects of chronic and acute microplastic exposures on a filter feeder crab

Microplastics are a widespread environmental contaminant. Although detrimental effects on aquatic organisms are well documented, little is known about the long-term effects of microplastic exposure to filter-feeding organisms at ecologically realistic levels. This study investigates the effects of environmentally relevant concentrations of polyethylene micro beads ranging in size from 3 to 30 μm, on the physiology and energetics of a coastal filter-feeding crab Petrolisthes laevigatus. We evaluated the impact of microplastics by exposing P. laevigatus to two different concentrations and exposure times: i) a chronic exposure for five months at 250 particles L^-1, and ii) an acute exposure for 48 h at 20,800 particles L^-1, ~80 times higher than the chronic exposure. The results showed that only chronic exposures elicited negative effects on the coastal crab in both, metabolic and physiological parameters. Our findings demonstrate a strong correlation between the ingestion rate and weight loss, even at low concentrations, the crabs exhibited severe nutritional damage as a result of long-term microplastic exposure. By contrast, acute exposure revealed no significant effects to the crabs, a possible explanation for this being short-term compensatory responses. These results suggest that environmentally relevant concentrations of microplastics are harmful to marine organisms, and they should be evaluated during realistic temporal scales, as their effects strongly dependent on the exposure time. Our results also suggest that the effects of microplastics have been likely underestimated to date, due to the dominance of short-term exposures (acute) reported in the current literature.

Effect of biological and anthropogenic habitat sounds on oxidative stress biomarkers and behavior in a key crab species

Soundscapes are characterized by a combination of natural and anthropogenic sounds. This study evaluated the stress effect of biological and anthropogenic sounds characterizing a Man and Biosphere UNESCO wetland, by assessing the protein content, oxidative biomarkers, and behavior of a key crab species (Neohelice granulata), through a tank-laboratory experiment. Biological sounds corresponded to predators of N. granulata (fish and crustacean stimuli), while anthropogenic ones belonged to motorboat passages (boat stimulus). Biochemical results showed differences depending on the sound stimuli used and the crab tissue analyzed. Protein content was higher in hemolymph when crabs were exposed to fish and boat stimuli, and in gills when exposed to boat stimulus. The enzymatic activity in hemolymph showed a decreased GST (fish stimulus) and CAT (fish and boat stimuli) activity, in hepatopancreas a higher GST (crustacean stimulus) and CAT (crustacean and boat stimuli) activity was found, and in gills a higher CAT activity was also observed (crustacean and boat stimuli). Lipid peroxidation was higher only in hemolymph (fish and crustacean stimuli). Protein oxidation was higher in gills (fish stimulus) and hepatopancreas (crustacean stimulus). Behavioral analysis demonstrated that the crab locomotion activity diminished when exposed to diverse sound stimuli. Thus, both sound sources caused physiological and behavioral stress in this species. The results contribute important data to be used in the development of management plans considering the habitat importance in terms of biodiversity, the ecosystem services provided and the role of the studied species.

Seasonal effect on biomarker responses in sentinel species: innovation in mangrove conservation status assessment

We evaluated the environmental quality in mangrove areas of the Western Atlantic with different levels and history of contamination, considering biomarkers for the crab Ucides cordatus. For this purpose, specimens were collected in two climatic seasons (rainy and dry seasons) and assays of genotoxicity (MN, micronucleus), cytotoxicity (NRRT, neutral red retention time) and biochemical (MT, metallothionein; and LPO, lipoperoxidation) were conducted. In the most impacted mangroves, there was an increase in the mean of micronucleus (frequency of MN/1000), which was associated with a shorter retention time (minutes of NRRT). In contrast, the most pristine areas showed MN < 3 and NRRT < 100 min, with no seasonal effect, indicating a lower effect of degenerative processes by xenobiotics. The rainy season was more harmful, especially regarding cytogenotoxicity. The use of bioindicator species for environmental monitoring should be guided by an analysis of biomarkers considering the season, because during the period of highest rainfall, biomarkers values can change.

Comparison of lipids and fatty acids among tissues of two semiterrestrial crabs reveals ecophysiological adaptations in changing coastal environments

Decapods have successfully colonized changing coastal habitats throughout the world by adapting their behavior, physiology, and biochemistry. Biochemical reserves, such as lipids and fatty acids (FAs), play fundamental roles in this adaptation process. These energy reserves are key for the development of decapods and their composition mainly depends on the type and quality of food available in their habitats. This study evaluated the lipid content and FA composition of three tissues (hepatopancreas, gills, and muscle) in two widely distributed, semi-terrestrial coastal crab species in Chile, Cyclograpsus cinereus from the upper intertidal and Hemigrapsus crenulatus from estuaries. This evaluation aimed to assess the physiological role of the bioenergetic reserves of these crabs, which tolerate fluctuating environmental conditions. Our results showed that both species had a higher lipid content in the hepatopancreas and a lower lipid content in its gills and muscle. All three of the evaluated tissues in C. cinereus showed high contents of saturated fatty acids (SFAs), and its hepatopancreas displayed the highest contents of monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs). In turn, H. crenulatus had the highest contents of MUFAs and PUFAs in its gills and muscle tissues, including an important amount of eicosapentaenoic acid (EPA). The FA content of C. cinereus may indicate an adaptive physiological response aimed at maintaining its cellular fluid balance during periods of desiccation in the upper intertidal zone. In contrast, the FAs found in H. crenulatus may be linked to the high activity of the sodium‑potassium pump in its gills, in order to maintain osmoregulation in estuaries.

Hepatopancreas transcriptome analysis of Chinese mitten crab (Eriocheir sinensis) with white hepatopancreas syndrome

White hepatopancreas is a syndrome that has recently emerged in aquaculture of Chinese mitten crab (Eriocheir sinensis). High lethality of the disease caused large economic loss, which drew considerable attention of fish farmers and scientific researchers. In this study, hepatopancreas reference transcriptome was de novo assembled and differential expression analysis was conducted between white hepatopancreas and normal (yellow) hepatopancreas of E. sinensis. A total of 90,687 transcripts were assembled, and 27,387 were annotated. Transcriptomic comparison revealed 69 differentially expressed genes between individuals featuring white hepatopancreas and yellow hepatopancreas. Genes associated with immune response and cell death, include thioredoxin-related transmembrane protein 1, hemocytin, methuselah-like 1, and E3 ubiquitin-protein ligase, and they were up-regulated, whereas titin and 5-formyltetrahydrofolate cyclo-ligase, which are genes related to cell proliferation, were down-regulated in E. sinensis with white hepatopancreas syndrome. Our study provides novel insights into genetic causes of formation and novel gene markers for detection of white hepatopancreas syndrome in aquaculture of E. sinensis.

First assessment of trace metal concentration in mangrove crab eggs and other tissues, SE Brazil

The mangrove crab Ucides cordatus is widespread in the Brazilian coast, which has an important role in nutrient cycling. This species reproduces in summer and females carry eggs about a month, when they maintain contact with water and sediments. It remains unclear if trace metals can be absorbed or adsorbed by the eggs during development. The present study aims to investigate, for the first time, trace metal concentrations in ovigerous female tissues and eggs of U. cordatus in two areas with different metal pollution levels in the Southeastern Brazil. Samples were collected in two different mangroves, Guanabara Bay (GB) highly polluted environment and Paraíba do Sul River (PSR). In both populations, we observed significant increase of V, Cr, and Mn concentrations along eggs maturation. The higher metals averages were found in PSR population. This trend was reported since the 1990s and lower concentrations in GB marine organisms were attributed to reducing conditions, high organic load, and the presence of sulfide ions. These conditions restrict the bioavailability of metals in the bay, with exception of Mn. No significant differences were observed in gills and muscles. In both populations of the present study, V, Zn, As, and Pb were higher in eggs of initial stage, whereas Mn, Ni, Cu, and Cd were higher in hepatopancreas. Beside this, V, Cr, Mn, As, and Pb showed an increase concerning egg development. Thus, V, As, and Pb in eggs come from two sources previous discussed: females and environment. Zinc came mainly from females due to essential function. Those new information should be considered as one of the mechanisms of trace metal transfer to the trophic chain, between benthonic and pelagic environment.

Uptake, metabolism and sub-lethal effects of BDE-47 in two estuarine invertebrates with different trophic positions

Two microcosm types -sediment-biota and biota-biota- were constructed to simulate different pathways of BDE-47 uptake, metabolism and oxidative stress effects in two key estuarine invertebrates (polychaete Laeonereis acuta and crab Cyrtograpsus angulatus). In the sediment-biota experiment, both species were exposed to spiked sediments; an environmentally reported and a high concentration of BDE-47 for 2 weeks. In the biota-biota experiment, crabs were fed with polychaetes pre-exposed to BDE-47 in the sediment-biota experiment. The sediment-biota experiment first revealed that polychaetes significantly accumulated BDE-47 (biota-sediment accumulation factor >2; p < 0.05) to a much greater extent than the crab organs (muscle, hepatopancreas, gills) at both sediment concentrations. For oxidative stress responses, polychaete and crab tissues exposed to spiked sediment showed a significant increase (p < 0.05) of only glutathione S-transferase (GST) activity with respect to controls in both BDE-47 concentrations. No lipid peroxidation (TBARS) or total antioxidant capacity (ACAP) changes were evident in the species or organs exposed to either BDE-47 sediment concentration. The biota-biota experiment showed that feeding crabs with pre-exposed polychaetes caused BDE-47 accumulation in organs as well as significant amounts of BDE-47 eliminated through feces (p < 0.05). Unlike the sediment-biota exposure, crabs fed with pre-exposed BDE-47 polychaetes showed the most conspicuous oxidative stress responses. Significant changes in GST and ACAP in both hepatopancreas and gills, in addition to enhanced TBARS levels in the hepatopancreas with respect to controls (p < 0.05), revealed that BDE-47 assimilated by invertebrates represents a potential source of toxicity to their predators. No methoxylated metabolites (MeO-PBDEs) were detected during BDE-47 metabolism in the invertebrates in either of the two different exposure types. In contrast, hydroxylated metabolites (OH-PBDEs) were detected in polychaetes and crab organs/feces in both experiments. Our results demonstrate that PBDE hydroxylation is one of the main biotransformation routes of BDE-47 in estuarine animals, which could be associated with the oxidative stress responses found.

Thermal biology of the sub-polar-temperate estuarine crab Hemigrapsus crenulatus (Crustacea: Decapoda: Varunidae)

Optimum temperatures can be measured through aerobic scope, preferred temperatures or growth. A complete thermal window, including optimum, transition (Pejus) and critical temperatures (CT), can be described if preferred temperatures and CT are defined. The crustacean Hemigrapsus crenulatus was used as a model species to evaluate the effect of acclimation temperature on: (i) thermal preference and width of thermal window, (ii) respiratory metabolism, and (iii) haemolymph proteins. Dependant on acclimation temperature, preferred temperature was between 11.8°C and 25.2°C while CT was found between a minimum of 2.7°C (CTmin) and a maximum of 35.9°C (CTmax). These data and data from tropical and temperate crustaceans were compared to examine the association between environmental temperature and thermal tolerance. Temperate species have a CTmax limit around 35°C that corresponded with the low CTmax limit of tropical species (34-36°C). Tropical species showed a CTmin limit around 9°C similar to the maximum CTmin of temperate species (5-6°C). The maximum CTmin of deep sea species that occur in cold environments (2.5°C) matched the low CTmin values (3.2°C) of temperate species. Results also indicate that the energy required to activate the enzyme complex (Ei) involved in respiratory metabolism of ectotherms changes along the latitudinal gradient of temperature.

Integrated biomarker responses of an estuarine invertebrate to high abiotic stress and decreased metal contamination

An integrated chemical-biological effects monitoring was performed in 2010 and 2012 in two NW Iberian estuaries under different anthropogenic pressure. One is low impacted and the other is contaminated by metals. The aim was to verify the usefulness of a multibiomarker approach, using Carcinus maenas as bioindicator species, to reflect diminishing environmental contamination and improved health status under abiotic variation. Sampling sites were assessed for metal levels in sediments and C. maenas, water abiotic factors and biomarkers (neurotoxicity, energy metabolism, biotransformation, anti-oxidant defences, oxidative damage). High inter-annual and seasonal abiotic variation was observed. Metal levels in sediments and crab tissues were markedly higher in 2010 than in 2012 in the contaminated estuary. Biomarkers indicated differences between the study sites and seasons and an improvement of effects measured in C. maenas from the polluted estuary in 2012. Integrated Biomarker Response (IBR) index depicted sites with higher stress levels whereas Principal Component Analysis (PCA) showed associations between biomarker responses and environmental variables. The multibiomarker approach and integrated assessments proved to be useful to the early diagnosis of remediation measures in impacted sites.

Toxic effects of antiparasitic pesticides used by the salmon industry in the marine amphipod Monocorophium insidiosum

The use of antiparasitic pesticides (APs) has been widely required by the salmon industry to treat diseases. The direct emission of chemicals in the seawater has produced uncertainty about the potential effects on nontarget organisms, such as crustaceans. The aim of this study was to assess the toxicity of three APs used by the salmon farm industry, such as emamectin benzoate (EB), cypermethrin (CP), and deltamethrin (DE), in the amphipod Monocorophium insidiosum during 10 days through whole-sediment bioassay tests. Lethal concentration by 50 % (LC50-10d) and biochemical responses, such as glutathione S-transferase (GST) and thiobarbituric acid reactive substances (TBARS), were measured as exposure and effects end points, respectively. Acute assays for DE (7.8 μg kg(-1), confidence interval, CI95% 5-11) and CP (57 μg kg(-1), CI95% 41-77) showed more mortality than EB (890 μg kg(-1), CI95% 672-1,171). In this study, it was possible to observe sublethal responses in amphipods after 2 days of exposure to APs. Significant induction in GST and TBARS (p < 0.05) were measured for CP and EB. Lower DE concentrations showed no significant biochemical responses. M. insidiosum was sensitive to AP concentrations at μg kg(-1) in sediments. This information would allow considering the possible consequences of detected concentrations for APs in areas with intensive salmon farming activity.