Mechanisms of intertidal substrate influence on the distribution of two species of Macrophthalminae along the north coast of Hangzhou Bay: adaptation of morphology and burrowing behaviour to substrate compaction (Decapoda: Ocypodoidea)

Abstract

Due to the building of the Yangtze River Water Conservancy Project, the study of the changing characteristics of intertidal sediments and their interaction with benthic species along the north shore of Hangzhou Bay is vital. In this study, Macrophthalmus abbreviatus and Macrophthalmus banzai were selected to compare the significance of differences in the nature of their substrates and to analyse their preferences for different substrate conditions through indoor experiments. This reveals the effect of sediment grain size on the feeding and burrowing behaviour of both. PCA and test for significance of differences in morphological parameters between the two species showed that the morphological differences between the two species were focused on the cephalothorax width-to-length and height-to-width ratios as well as the height-to-width and height-to-length ratios of the ambulatory legs, which were significant (P < 0.05), specifically, the Macrophthalmus abbreviatus had a flatter and narrower cephalothorax and sharper ambulatory legs, which were optimised for burrowing in a high- compaction substrate. Macrophthalmus banzai, on the other hand, with its broader cephalothorax and stouter ambulatory legs, was better adapted to burrowing behaviour in a low-compaction substrate. Their tilting burrowing habits and variances in burrow angle and fit to the body also reflect adaptations to the nature of the substrate in their distinct habitats. The effects of sediment particle size changes on the two species were deduced. The changes of the two species populations caused by the change of sediment particle size in the north shore of Hangzhou Bay in recent years were analyzed. This paper emphasises that substrate tightness is an important factor driving habitat selection for both crab species, and therefore long-term monitoring of estuarine sediment grain size and benthic fauna is important for assessing anthropogenic impacts on intertidal ecosystems.