No abstract

Nonlethal injury is a pervasive stress on individual animals that can affect large portions of a population at any given time. Yet most studies examine snapshots of injury at a single place and time, making the implicit assumption that the impacts of nonlethal injury are constant. We sampled Asian shore crabs Hemigrapsus sanguineus throughout their invasive North American range and from the spring through fall of 2020. We then documented the prevalence of limb loss over this space and time. We further examined the impacts of limb loss and limb regeneration on food consumption, growth, reproduction, and energy storage. We show that injury differed substantially across sites and was most common towards the southern part of their invaded range on the East Coast of North America. Injury also varied idiosyncratically across sites and through time. It also had strong impacts on individuals via reduced growth and reproduction, despite increased food consumption in injured crabs. Given the high prevalence of nonlethal injury in this species, these negative impacts of injury on individual animals likely scale up to influence population level processes (e.g., population growth), and may be one factor acting against the widespread success of this invader.

Cannibalism affects the population dynamics of many marine species, but its potential for influencing population sizes of non-native species is not well understood. A series of laboratory experiments was conducted in 2016 to examine the frequency of cannibalism in the Asian shore crab (Hemigrapsus sanguineus) and the factors influencing its rates of occurrence. Predators and prey varied in size from planktonic megalopae (the last larval stage) and the first benthic crab stage to small juveniles (3-6 mm carapace width, CW), large juveniles (7-10 mm CW), and adult crabs (12-15 mm CW). Individual crabs were paired with groups of smaller prey in glass culture dishes with sand and rocks as potential shelter for the prey, both with and without an alternative food source (commercial crab pellets). Adult and large juvenile crabs consumed megalopae, first-stage crabs and small juveniles, regardless of the presence of food. Megalopae were cannibalized the most heavily, and the size difference between predator and prey was an important factor determining cannibalism rates. Cannibalism of settling megalopae and newly settled juveniles by larger conspecifics could affect recruitment to benthic populations of this non-native crab species.

Regeneration of lost appendages is a gradual process in many species, spreading energetic costs of regeneration through time. Energy allocated to the regeneration of lost appendages cannot be used for other purposes and, therefore, commonly elicits energetic trade‐offs in biological processes. We used limb loss in the Asian shore crab Hemigrapsus sanguineus to compare the strength of energetic trade‐offs resulting from historic limb losses that have been partially regenerated versus current injuries that have not yet been repaired. Consistent with previous studies, we show that limb loss and regeneration results in trade‐offs that reduce reproduction, energy storage, and growth. As may be expected, we show that trade‐offs in these metrics from historic limb losses far outweigh trade‐offs from current limb losses, and correlate directly with the degree of historic limb loss that has been regenerated. As regenerating limbs get closer to their normal size, these historical injuries get harder to detect, despite the continued allocation of additional resources to limb development. Our results demonstrate the importance of and a method for identifying historic appendage losses and of quantifying the amount of regeneration that has already occurred, as opposed to assessing only current injury, to accurately assess the strength of energetic trade‐offs in animals recovering from nonlethal injury.