Barnacle colonization of shoes: Evaluation of a novel approach to estimate the time spent in water of human remains.

Estimating the time since death (minimum Post Mortem Interval, minPMI) is a necessary part of a forensic investigation. Besides considering the typical signs of death, minPMI can be estimated using the insects and other arthropods that colonize the remains (forensic entomology). In an aquatic environment, both insects and crustaceans may provide information regarding the time spent in water of the remains (minimum Floating Interval, minFI and minimum Post Mortem Submersion Interval, minPMSI), and this can also assist in determining the minPMI. Barnacles (Crustacea: Cirripedia) are common crustaceans that colonize solid substrates in marine environments and they can be found in association with organic and inorganic remains recovered from the sea. Barnacles colonize both floating and submerged remains and their growth rate is temperature dependent. Despite their potential to be indicative of the minFI and/or minPMSI, only a few case studies have considered it for this purpose, and scant research has been conducted in this field. Assuming that the vast majority of the bodies found in the sea are clothed, this research is focused on the barnacle colonization of two different types of shoes placed in the sea, in order to (1) identify the colonizing species in the chosen environment; (2) identify the settlement preferences of the barnacles associated with the shoes; and (3) determine the factors affecting the growth rate of the barnacles associated with the shoes. In April 2016 64 sport shoes (SS) and 64 patent leather shoes (PLS) were placed in the Boston Harbor (MA-USA) at 8/10m below sea level. Four of each shoe type were collected every two weeks for seven months. Individual barnacles from each shoe were sampled and measured to determine species and age. The overall colonization density and settlement preference was statistically analyzed. Results show that (a) Amphibalanus improvisus (Darwin) (Crustacea: Cirripedia: Sessilia) colonized the vast majority of shoes; (b) colonization occurred in less than 30 days and continued throughout the research period; (c) a significant difference in colonization densities was found between the SS and PLS, with PLS seeing higher densities; (d) barnacles showed preferential colonization of specific sections on both shoe types; (e) barnacle growth was found to be significantly affected by water temperature and shoe type but not by the time spent in water; (f) time spent in water and shoe type had a highly significant effect on the total number of barnacles per shoe, whereas water temperature did not.