The Indian Ocean hydrothermal vent is a region where a new oceanic crust is formed by magma at the interface of the deep-sea bed over 2000 m in depth. Here we examined for the first time the exoskeleton structure and mechanical properties of Austinograea rodriguez crabs living in hydrothermal vents. Scanning electron microscope (SEM) and energy dispersive x-ray (EDX) were used for structural analysis, and a nanoindentation system was used for mechanical analysis. The exoskeleton was divided into four layers: epicuticle, exocuticle, endocuticle, and membrane. The thickness of each layer was different from that of other crustaceans previously reported. Additionally, the number of constituent elements, composition ratio, and hardness of each layer were unique among previously studied crabs. This observation indicates that those characteristics might have evolved for creatures with a hard exoskeleton living in the deep-sea hydrothermal vent.
This article investigates the response of the Manila clam Venerupis philippinarum to possible temperature and salinity changes in a holding facility. First, clams are exposed to four temperatures for 15 days. Valve closure and survival of clams exposed to seawater at 18 °C are higher than those exposed to seawater at 24 °C. Second, clams are exposed to six salinities for 15 days. Survival of clams exposed to two salinity fluctuation conditions (24–30 and 27–24 psu) is lower than that of clams exposed to constant 30 psu conditions. Valve closures of clams exposed to constant low salinity conditions (24 psu) and two salinity fluctuation conditions (24–30 and 27–24 psu) are higher than those exposed to constant 30 psu conditions. Lastly, clams are exposed to two different temperatures and three different salinities conditions for eight days. Valve closure and survival decreased significantly under the combination of 24 °C and 18 psu. These results suggest that an increase in temperature or a wider range of salinity fluctuations are detrimental to the survival of the Manila clam. The synergistic effect of temperature and salinity stressors may decrease the survival period of clams compared to the effect of a single stressor.
Animals living in extreme environments, such as hydrothermal vents, would be expected to have evolved protective shells or exoskeletons to maintain homeostasis. The outer part of the exoskeleton of vent crabs (Austinograea sp.) in the Indian Ocean hydrothermal vent was one of the hardest (approximately 7 GPa) biological materials ever reported. To explore the exoskeletal characteristics of vent crabs which enable them to adapt to severe environments, a comparative analysis was conducted with the Asian paddle crab (Charybdis japonica) living in coastal areas. Nanoindentation, thermogravimetric analysis, scanning electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy were used to analyze the mechanical properties, thermal stability, structure, surface components, and the composition of compounds, respectively. Though both species have four-layered exoskeletons, the outermost layer of the vent crab, a nano-granular structure, was much thicker than that of the coastal crab. The proportions of aluminum and sulfur that constitute the epicuticle of the exoskeleton were higher in the vent crab than in the coastal crab. There was a lack of water or volatile substances, lots of CaCO3, and no carotenoid-based compounds in the exoskeleton of the vent crab. These might have improved the mechanical properties and thermal stability of the hydrothermal species.
We investigated the response of the Manila clam Venerupis philippinarum to possible temperature and salinity changes in a holding facility. First, clams were exposed to four temperatures for 15 days. Valve closure and survival of clams exposed to seawater at 18℃ were higher than that of those exposed to seawater at 24℃. Second, clams were exposed to six salinities for 15 days. Survival of clams exposed to two salinity fluctuation conditions (24–30 and 27–24 psu) was lower than that of clams exposed to constant 30 psu conditions. Valve closures of clams exposed to constant low salinity conditions (24 psu) and two salinity fluctuation conditions (24–30 and 27–24 psu) were higher than of those exposed to constant 30 psu conditions. Lastly, clams were exposed to two different temperatures and three different salinities conditions for 8 days. Valve closure and survival decreased significantly under the combination of 24℃ and 18 psu. These results suggest that an increase in temperature or a wider range of salinity fluctuations are detrimental to the survival of the Manila clam. The synergistic effect of temperature and salinity stressors may decrease the survival period of clams compared to the effect of a single stressor.
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