Evasion from predation : the perilous life of planktonic copepods throughout development
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As one of the most abundant metazoan groups on the planet, copepods are found in virtually all marine environments. They provide a key link in marine food webs between photosynthetic algae and higher trophic levels. Subsequently, copepods are preyed upon by a wide variety of organisms throughout their life history. As a result copepods have evolved a powerful escape behavior at all stages of development, in response to hydrodynamic stimuli created by an approaching predator. Typically copepods exhibit 6 naupliar stages and 5 copepodite stages before becoming adults. This work focuses on quantifying the effectiveness of the escape behavior during key periods of development. The earliest developmental stage of copepod (nauplius N1) experiences the greatest amount of viscous forces and may be at a disadvantage when exposed to larger predators at cold temperatures. The results show that the nauplius exhibits a compensatory mechanism to maximize escape performance across its thermal range. Later in development, the nauplius (N6 stage) molts into a copepodite (C1 stage) which resembles the body form of an adult copepod. Here, there is a significant morphological change with little change in mass. Escape capabilities are investigated for key stages in response to feeding strikes from natural fish predators. The results demonstrate that the improvement in escape capability of the C1 stage is effective only against certain modes of predation. Finally, successfully escaping from predation has evolutionary fitness implications and adults (post C5) are the only reproductive stage. Some species have developed unique mechanisms to avoid predation such as breaking the water surface and making aerial escapes to avoid predators while in other cases, the predator has developed unique morphology in order to reduce the amount of hydrodynamic disturbance in the water which improves capture success of copepods. By investigating copepod behavior and their ability to avoid predation at various stages of development, we can begin to understand which stages copepods are most susceptible to different types of predators and how the escape response changes as development progresses. This can help in understanding localized abundances or deficiencies of both predator and prey in the marine food web.