The effect of environmental variation on the reproductive development time and output of the high-shore rockpool copepod Tigriopus brevicornis

Abstract

The extreme environmental changes observed in high-shore rockpools occupied by Tigriopus brevicornis, provide a significant physiological challenge that may have implications for the energetics and hence the life history characteristics of this species. The present study was designed to assess the effect of this environmental variation on the reproductive development time and output of T. brevicornis in terms of duration of the various stages in ovary and egg sac development and maturation as well as naupliar development time to the first copepodite stage and total numbers of copepodites produced. There was a significant difference in reproductive development time and output in the three test salinities with only successful development to copepodite I stage seen in normal seawater (35 psu). There was also a successful release of nauplii seen at the low salinity (5 psu), but no subsequent survival to the copepodite I stage, whilst there was not even a development of egg sacs in the high salinity test medium (70 psu). There was also a significant difference in reproductive development times in the three test temperatures with fastest ovary development in the high temperature (23 °C) and slowest development time in the lowest temperature (5 °C). However, it should be noted that the highest number of nauplii produced was actually in the mid temperature (12 °C), not the high temperature. Exposure to hypoxic and anoxic conditions had a significantly detrimental effect on reproductive development with slower development time through the reproductive stages and no individuals surviving to copepodite stage I from the hypoxic and anoxic test conditions, but good development from the normoxic conditions. The present study indicates that animals living in high-shore rockpools may incur a considerable energetic cost, due to the environmental changes that are characteristic of this habitat and the importance of resource allocation in these different physiological conditions is paramount to the species' survival.