Reproductive and energetic costs of injury in the mangrove tree crab

Abstract

Nonlethal injury is a common and ubiquitous feature of marine systems and can result in altered growth and survival rates. Ecological theory predicts that injured animals should face an energetic tradeoff between investing in recovery vs. investing in reproduction. Possible impacts on reproduction may range in magnitude from very strong (elimination of reproduction), to intermediate (reduced number of offspring), to weak (reduced investment in each offspring). While this tradeoff is well established in terrestrial systems, it has received little attention in the marine environment, particularly in a way that quantitatively relates the degree of injury to the degree of reproductive impact. We examined injury via limb loss across 4 sites in the mangrove tree crab Aratus pisonii. We found that limb loss was highest at the site that was closest to roads and had the highest level of human presence, and conversely, injury was lowest at the site furthest from the road and with the lowest level of human presence. We found evidence that the quality of consumed food likely decreases with the number of limbs lost, but found no influence of limb loss on amount of food consumed or on energy storage. We show that limb loss reduced the number of eggs produced and that the mass of the ovary declined with the number of regenerating limbs, providing direct evidence for a tradeoff between reproduction and injury recovery. Further, our study therefore suggests that these impacts may increase with the level of human disturbance.

Morphometric correlations between dietary and reproductive traits of two brachyuran crabs, Hemigrapsus sanguineus and Aratus pisonii

“…We rotated sampling between the four sites across sampling dates to avoid depleting any one population. The samples were originally collected for a study that explored reproduction [ 23 ], so they were collected before each spring tide from March-October in order to encompass the time leading up to and during their reproductive season. During sampling, the first 20 female crabs encountered during each sampling date were collected by hand and immediately frozen with dry ice and stored at -80° C until dissection.…”

“…Our study considers two brachyuran crab species, the Asian shore crab Hemigrapsus sanguineus and the mangrove tree crab Aratus pisonii . Both species are primarily herbivorous [ 22 , 23 ]. Hemigrapsus sanguineus has an omnivorous diet that can include macroalgae and detritus, as well as amphipods, polychaetes, and juvenile shelled prey, such as barnacles, bivalves, and gastropods [ 24 ].…”

Dietary and Reproductive Traits of Two Brachyuran Crab Species

“…We rotated sampling between the four sites across sampling dates to avoid depleting any one population. The samples were originally collected for a study that explored reproduction (Griffen et al, 2020b), so they were collected before each spring tide from March-October in order to encompass the time leading up to and during their reproductive season. During sampling, the first 20 female crabs encountered during each sampling date were collected by hand and immediately frozen with dry ice and stored at −80° C until dissection.…”

“…Our study considers two brachyuran crab species, the Asian shore crab Hemigrapsus sanguineus and the mangrove tree crab Aratus pisonii . Both species are primarily herbivorous (Griffen et al, 2020a; Griffen et al, 2020b). H. sanguineus has an omnivorous diet that can include macroalgae and detritus, as well as amphipods, polychaetes, and juvenile shelled prey, such as barnacles, bivalves, and gastropods (Brousseau & Goldberg, 2007).…”

Evidence for use of both capital and income breeding strategies in the mangrove tree crab, Aratus pisonii

“…Additionally, if stored energy becomes limiting, then reproductive effort should decrease as the reproductive season progresses and stored capital becomes exhausted. Exhausted energy stores may be expressed as smaller clutches (fewer eggs) or reduced per-propagule investment (smaller individual egg masses) 33 , 34 as the reproductive season progresses. Alternatively, if reproduction relies substantially on income breeding, then a clear shift in reproductive effort or energy storage is not expected over the duration of the reproductive period.…”