Substrate Selection in Early Developmental Stages of Swimming Crab (Portunus trituberculatus)

Substratum preference is shown to be the most important factor influencing crab distribution. Characterizing habitat selection of the swimming crab Portunus trituberculatus provides crucial information for the successful management of this commercially important fishery in China. To clarify the preference for substrate at early development stages of P. trituberculatus, this study compared four different substrates (mud, muddy sand, medium sand (0.5–1.0 mm), and fine sand (0.2–0.5 mm)) by analyzing behavior of juvenile and subadult crabs under controlled laboratory conditions. Group experiments revealed that juvenile crabs exhibited the strongest preference for muddy-sand substrates, followed by fine sand, whereas subadult crabs preferred fine sand, followed by medium sand. Results from individual experiments demonstrated that subadult crabs spent significantly more time on fine-sand and medium-sand substrates compared to muddy-sand and mud substrates. Diurnal and nocturnal observations showed significant differences in substrate selection for both subadult crabs and juvenile crabs between day and night. Specifically, subadult crabs displayed significant differences in selecting medium-sand and fine-sand substrates across the two periods (p< 0.05), while juveniles showed a significant day–night difference in preference for fine sand (p < 0.05). In terms of resting behavior, subadult crabs predominantly buried themselves in muddy-sand and fine-sand substrates, whereas juveniles exhibited a markedly lower resting rate. These results indicate pronounced ontogenetic variation in substrate selection during the early developmental stages of P. trituberculatus, providing important insights for habitat restoration and resource conservation.