VARIABILITY OF THE BREAKAGE-INDUCED REPAIR RATE AMONG MARINE GASTROPODS AND ITS IMPLICATIONS FOR THE FOSSIL RECORD OF PREDATION

Predation is an important evolutionary agent that shaped marine communities through time. Repair scars in molluscs, generally produced after a failed durophagous (shell-crushing) attack, are one of the few preserved marks of predation commonly available in the fossil record. Consequently, frequency of repair scars has classically been used as a proxy for predation intensity. However, the reliability of this matrix has been questioned when employed for multiple species with different physiological attributes. Here we tested the variability of repair rate among and across species that may potentially alter repair scar frequency at the same level of predation intensity.

Using three different species of marine gastropods (Nassarius stolatus, Paratectonatica tigrina, Pirenella cingulata) in a synthetic salt-water aquarium over a period of three months, we evaluated the variation in repair rate in response to shell breakage of different amount, location, and recurrence. Our results show that the rate of repair decreases significantly across species with increasing recurrence. The repair rate is higher for larger amount of breakage; for a small amount of non-apertural breakage, the repair rates are often close to zero. Drilled holes in the experimental setup are never repaired and the gastropods are found to survive without repairing the damaged shell. This observation perhaps explains the rarity of healed drill holes in comparison to the abundance of repaired shell-crushing attacks. These observations hold true for both the species of non-predatory gastropods. The repair rate in the predatory gastropod, Paratectonatica tigrina, is primarily guided by the availability of food; in the absence of its natural prey, the repair rate decreases significantly.

Our results highlight the effect of physiological controls, apart from the predator abundance, influencing the repair rate in marine gastropods. Each benthic habitat may have characteristic composition of durophagous predators with varying behavioural traits such as preferred location of breakage, amount of breakage and may result in a specific repair rate. Spatially distant habitats may also have varying prey abundance – a factor that influences repair rate of predatory gastropods. Because the repair rate influences the inferred predation intensity, repair scar frequency across habitats with different ecological setting therefore, may not be comparable.