Oxygen consumption in trilobite larvae of the mangrove horseshoe crab (Carcinoscorpius rotundicauda; Latreille, 1802): effect of temperature, salinity, pH, and light–dark cycle

Abstract

<em>Carcinoscorpius rotundicauda</em> is one of the four extant species of horseshoe crab, occurring only in Asia: around India, Indonesia, Malaysia, Philippines, Singapore, Thailand and Hong Kong. Virtually nothing is known about the physiology of this Asian species. In the present study, the respiratory physiology in terms of oxygen consumption rate of the trilobite larvae of <em>C. rotundicauda</em> was evaluated under laboratory conditions. The trilobite larvae were exposed to different levels of temperature (10, 20, 30 and 40 °C), salinity (10, 20, 30 and 40 ppt), pH (5, 6, 7, 8 and 9) and dark–light conditions for a period of 12 h. Effect of temperature on oxygen consumption in trilobite larvae was not so significant among all the temperatures tested. However, both 10 and 40 °C temperature showed comparatively high rate of oxygen consumption at the initial 4 h of experiment. More or less consistent oxygen consumption pattern observed at 20 and 30 °C temperature suggested 20–30 °C as the best temperature range for rearing trilobite larvae. Trilobite larvae revealed enormous tolerance to temperature and indicated that the temperature is not critical in terms of respiration. The trend in oxygen consumption was more or less uniform at all salinities tested indicating the insignificant influence of salinity on respiration. Though not significant, the oxygen consumption trend was more consistent at 20 ppt as compared to other salinities and thus could be considered as the most suitable salinity for rearing trilobite larvae. There was a positive relationship between oxygen consumption rate and the various seawater water pH tested with trilobite larvae. Maximum oxygen consumption was recorded between pH 7 and 9 at the initial hours of the experiment and the overall trend suggests that the larvae preferred slightly acidic conditions. Although the larvae showed higher oxygen consumption under light, in the overall analysis of the data the light–dark condition did not have a statistically significant influence. However, more consistent oxygen consumption pattern and swimming activity in the dark condition as compared to light condition during the 12 h of experiment revealed that the larvae have active nocturnal behaviour.