Latitudinal and temporal variation in injury and its impacts in the invasive Asian shore crab Hemigrapsus sanguineus

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.

Figure 1

Map of the US east coast showing the five sampling sites used in 2020 along with the GPS coordinates for each sampling site. Letters on map are state abbreviations. Pie charts next to letters for each state show an increasing proportion of Hemigrapsus sanguineus that are injured at sites towards the southern end of the range (white = injured; gray = uninjured). The origins of the arrows pointing to each graph show the approximate locations of sampling sites. The x-axis on each inset graph is the number of missing limbs, and the y-axis on each inset graph is the number of limbs that were regenerating per crab. The data are jittered along the x-axis for clarity of presentation. Crabs missing no limbs are included in figures for completeness but were not included in statistical analyses to avoid zero-inflation.

Figure 2

Residual gut mass, after accounting for body mass, of individual Hemigrapsus sanguineus sampled in 2020 as a function of the number of missing limbs. Box plots show median values (solid line), first to third quartile of the data (box), 95% of the data (whiskers), and outliers that fall outside this range (circles). Numbers in parenthesis across the top show the sample size in each category.

Figure 3

Clutch mass of Hemigrapsus sanguineus sampled in 2020 as a function of the number of missing limbs that are regenerating. Part (a) shows crabs > 20 mm CW and part (b) shows crabs < 20 mm CW.

Figure 4

Ovary mass of individual gravid Hemigrapsus sanguineus of all sizes sampled in 2020 as a function of the number of missing limbs that are regenerating.

Figure 5

Changes in residual body mass (after accounting for differences with CW) of individual female (a) and male (b) Hemigrapsus sanguineus sampled in 2019 with the number of missing limbs that are regenerating.

Figure 6

Number of limbs regenerating for female (a) and male (b) Hemigrapsus sanguineus from the 2019 sampling in New Hampshire as a function of CW. Circle size shows the relative number of missing limbs, as indicated in the inset box. The dashed vertical line shows the cutoff used in the analysis to examine crabs < 20 mm or ≥ 20 mm CW.