Substrate selectivity in the byssal attachment behavior of Ruditapes philippinarum (Bivalvia: Veneridae)

Abstract

Ruditapes philippinarum is an infaunal adult-byssate bivalve. In byssal attachment behavior, R. philippinarum clams can use various types (e.g., shell debris, mineral grain, and metallic, glass, ceramic, and plastic pieces) and sizes (e.g., sand grain, granule, pebble, and cobble) of substrates as objects for adhesion. Substrate selectivity in byssal attachment behavior has been well studied in mytilid bivalves, whereas it remains undescribed for R. philippinarum. This study aimed to test the hypothesis that R. philippinarum clams select substrates for byssal attachment, like mytilid bivalves. For this purpose, a combination of a field survey and laboratory experiments was conducted. The field survey was conducted at three intertidal sedimentary sites with different ratios of shell debris and mineral grain, and the proportional availability and use of the two substrate types were compared. A similar comparison was made in the laboratory experiments using substrates of three different sizes (i.e., sand grain, small pebble, and large pebble), whose availability was evaluated based on the total surface area. Our results indicated that substrate selectivity for byssal attachment of R. philippinarum was confirmed only for the size of substrate and that the type of substrate was not significant. In this selectivity, clams preferentially selected substrates larger than a threshold grain size that varied with given clam size and substrate availability. In addition, the position and inclination of substrates also seemed important. Suitable substrates for byssal attachment are often rapidly buried by sedimentation in nature, to deeper sediment layers that are inaccessible for juvenile clams. Therefore, a steady supply of riverine gravel and/or continuous dead-shell deposition from dense adult populations into surficial sediments is considered to be essential natural components to facilitate clam recruitment.