The effects of temperature on aspects of respiratory physiology of the semi-terrestrial crabs, Uca inversa (Hoffmann) and Metopograpsus messor (Forskål) from the Red Sea

Effects of temperature increase on the physiology and behavior of fiddler crabs

Intertidal organisms rely on physiological and behavioral adjustments to maintain homeostasis under warm exposure. We examined the effects of the temperature increase related to climate warming on the physiology and behavior of two fiddler crab species: Leptuca uruguayensis, which inhabits mostly vegetated areas, and Leptuca leptodactyla, that inhabits unvegetated areas. We hypothesized that L. uruguayensis would be more sensitive to warming than L. leptodactyla. Crabs were exposed to different temperatures: 27 °C (control), 31 and 33 °C (+4 and +6 °C, respectively) for 15 days to evaluate their physiological responses (oxygen consumption, Q₁₀, ammonia excretion and hepatosomatic index) and for 2 days to observe their behavioral responses (feeding rate and duration of burrow retreat). We also tested in situ the effect of air, surface, and body temperatures on the claw-waving display of both species. We found that species were affected differently by increasing temperature. Leptuca uruguayensis showed adaptation limit (Q₁₀ <1), increasing oxygen consumption. Also, in comparison with control, L. uruguayensis decreased the ammonia excretion at 31 °C, but not at 33 °C, indicating a compensatory mechanism to cope with thermal stress. In contrast, L. leptodactyla was able to adjust its metabolic rate to temperature rise (Q₁₀ ~3) and reduce ammonia excretion, suggesting changes in the energetic substrate and amino acid catabolism. Higher temperatures reduce the hepatosomatic index of both species, indicating increased use of energy reserve (although only the L. uruguayensis feeding rate was reduced). Furthermore, warmer temperatures increase the duration of burrow retreat in both species, potentially impacting social interactions, such as mating. Temperature increase did not affect the claw-waving display frequency, suggesting that other factors may affect this behavior, e.g., the presence of females and competitors. Specific behavioral (e.g., microhabitat selection) and morphological attributes (e.g., larger major claw) might benefit the thermoregulation of each crab species since no differences in body temperature were found between them in situ. Therefore, fiddler crabs that inhabit vegetated areas are more vulnerable to higher temperatures and may change its geographic range as a result of climate warming, while fiddler crabs that inhabit unvegetated areas are more tolerant to temperature rise and may have a competitive advantage under a temperature increase scenario.

Limited impact of several years of pretreated wastewater discharge on fauna and vegetation in a mangrove ecosystem

It was hypothesized that mangroves, tropical wetlands, could be used for the finishing treatment of domestic wastewaters. Our aim was to determine if a nutrient-stressed mangrove could tolerate long-term discharges of pretreated wastewater (PW). Since 2008, in an in situ experimental system set up in Mayotte Island (Indian Ocean), domestic PW are discharged into two impacted areas (675 m²) dominated by different species of mangrove trees. Anthropogenic inputs during > 4.5 years led to an increase in vegetation growth associated with an increase in leaf pigment content, leaf surface and tree productivity. A marked increase in tree mortality was observed. There was no effect on crabs and meiofauna densities, but significant modifications of community structures. These effects may be directly linked to PW inputs, or indirectly to the modifications of the environment associated with higher tree growth. However, our results indicate that there was no major dysfunction the ecosystem.

Effect of food availability on the growth and thermal physiology of juvenile Dungeness crabs (Metacarcinus magister)

Juvenile Dungeness crabs spend ~1 year in the San Francisco Estuary, where they undergo considerable growth before returning to the coastal ocean. Previous studies suggest that competition, food scarcity and avoidance of conspecifics may cause some juvenile Dungeness crabs in the San Francisco Estuary to become food limited. Food limitation may force these crabs to forage in higher temperature intertidal environments in the estuary, exposing them to stressful conditions in order to sustain growth and, potentially, necessitating physiological trade-offs in energy allocation between growth and stress tolerance. To investigate the effects of food limitation on aerobic metabolism and physiological performance of crabs, we assessed growth, moulting frequency, metabolic rate, citrate synthase and malate dehydrogenase enzyme activity and cardiac performance, as an index of temperature sensitivity and upper temperature tolerance. Summer- and winter-caught crabs were acclimated to either a high- or a low-food ration for 5 weeks. Overall, our results demonstrated that while food limitation had a negative effect on growth of juvenile Dungeness crabs in both the summer and the winter feeding trials, crabs in the low-food group maintained both metabolic rate at ambient San Francisco Estuary temperatures (15°C; summer trial only) and upper temperature tolerance as determined by failure of cardiac function when compared with crabs in the high-food group (summer and winter trials). Therefore, the ability to maintain stress tolerance when food is limited appears to come as a physiological trade-off to growth. Food-limited crabs were unable to increase their metabolic rate to the same level as that achieved by well-fed crabs; therefore, if exposure to elevated temperatures persists and requires more energy than can be met by crabs in their food-limited state, physiological performance may be compromised.

Diurnal rhythm and effect of temperature on oxygen consumption in earthworms, Amynthas gracilis and Pontoscolex corethrurus

Different species of earthworms show distinct patterns of oxygen consumption pattern. Amynthas gracilis has a diurnal rhythm of oxygen consumption, consuming more oxygen at night, whether being incubated at 20, 25, or 30 degrees C. The higher oxygen consumption of A. gracilis is directly related to its behavior, as it shows higher activity at night. In contrast, Pontoscolex corethrurus showed no obvious diurnal rhythms of oxygen consumption or behavior. In addition, its oxygen demand is not related to temperature. A. gracilis has higher oxygen consumption than P. corethrurus at 20 and 30 degrees C. The difference in temperature adaptation of oxygen consumption between these two species may be a strategy by which earthworms adapt to different temperatures. This might explain why A. gracilis disperses on the soil surface at night after a rain, in contrast to P. corethrurus for which such behavior was not been observed.

Thermoregulatory behavior of the crayfish Procambarus clarki in a burrow environment

The behavioral thermoregulation of the red swamp crayfish, Procambarus clarki, was investigated in its burrow environment. In the field, air and water temperatures within crayfish burrows fluctuated less compared with surface temperatures in the Mojave Desert. However, crayfish could still experience sub-optimal temperature regimes inside burrows. In the laboratory, P. clarki heated and cooled more rapidly in water than in air. In a thermal gradient, the crayfish selected a water temperature of 22 degrees C and avoided water temperatures above 31 degrees C and below 12 degrees C. Observations of behavior in an artificial burrow showed that P. clarki displayed three main shuttling behaviors between water and air in response to temperature. The number of bilateral emersions and emigrations, as well as the amount of time spent in air (in a 24 h period), were significantly greater at 34 degrees C than at 12, 16, 22 or 28 degrees C. This reflected an increased use of the behavioral thermoregulation at temperatures approaching the critical thermal maximum of this species. Upon migrating from 34 degrees C water into 38 degrees C air, crayfish body temperature decreased significantly. These periods of emersion were interspersed with frequent dipping in the water, allowing the crayfish to gain the benefits of evaporative cooling, without the physiological costs incurred by long-term exposure to air.

Influência da temperatura sobre os tipos celulares presentes na hemolinfa de larvas e ninfas de Rhipicephalus sanguineus

Este trabalho foi realizado com o intuito de se verificar a influência de três temperaturas (18, 27 e 32°C) sobre os tipos celulares presentes na hemolinfa de larvas e ninfas de Rhipicephalus sanguineus (Latreille, 1806). Seis tipos celulares básicos foram encontrados na hemolinfa: prohemócitos (PR), plasmatócitos (PL), granulócitos (GR), esferulócitos (ES), adipohemócitos (AD) e oenocitóides (OE). Os ES foram divididos em dois subtipos (ES I e ES II), devido às variações morfológicas encontradas. O efeito da temperatura foi mais acentuado sobre o estádio de larva. Ocorreu queda acentuada de GR e aumento de ES II na temperatura de 18°C, enquanto que à 27 e 32°C, os valores foram semelhantes. GR foi o tipo celular mais abundante, indicando o seu envolvimento no metabolismo. Para ninfas este também foi o tipo celular mais abundante, porém não ocorreram variações acentuadas segundo a temperatura, indicando que cada estádio de desenvolvimento apresenta determinada necessidade metabólica que se expressa nos tipos celulares presentes na hemolinfa.

Inter- and intra-individual variation in resting oxygen consumption in post-larvae of the giant freshwater prawn, Macrobrachium rosenbergii (De Man)

In a study of the factors that influence metabolic rate in the giant freshwater prawn Macrobrachium rosenbergii, resting oxygen consumption (ROC) was measured in 90 post-larvae ranging in size from 0.1 to 2.8 g. As in many other animal species, ROC was strongly negatively related to body weight. A stressful event (anaesthesia with or without tagging) caused a sharp increase in the ROC that disappeared over a time scale of hours. As has been demonstrated for other species of crustaceans, ROC was highest in prawns in the pre-moult stage. Individual differences in ROC among prawns handled in the same way and in the same moult stage persisted over a period of hours, but not over days. It remains unclear, therefore, whether early differences in resting metabolic rate can explain the conspicuous differences in growth rate that are found in this species during the first few weeks of life and that profoundly influence subsequent life history events.