Relative growth of pereiopods of the megalopa and early juveniles of Portunus trituberculatus (Miers, 1876) (Brachyura: Portunidae)

Abstract

We examined relative growth of the pereiopods in megalopae and first to fifth crab stages of Portunus trituberculatus (Miers, 1876) reared in the laboratory. Relative growth of the body parts in relation to a reference dimension (carapace length) was analyzed by the log-transformed allometric growth equation lny＝lna＋blnx. Body proportions differed between the megalopae and juvenile crabs. In juveniles, the chela size showed isometric growth (b＝1); the second to fourth pereiopods (walking legs) showed mainly negative growth (b＜1) in length, and isometric growth (b＝1) in width; and the width and length of the fifth pereiopod showed positive allometric growth (b＞1). Portunus trituberculatus cling to drifting seaweeds using their chelae and pereiopods before undertaking a benthic life after the fourth or fifth crab stages; the chelipeds and fifth pereiopods are utilized mainly in the burying behavior of juveniles after settlement. Accordingly, the negative allometric growth in length of the walking legs likely represents an adaptation for a lifestyle shift from drifting seaweeds to benthos, whereas the isometric or positive allometric growth of the chelae and fifth pereiopods would be advantageous for the burying behavior of the crabs post-settlement.