Field Monitoring of Tritia mutabilis (Linnaeus, 1758) Egg Capsule Deposition and Intracapsular Embryonic Patterns Using Artificial Substrates and Machine Learning-Based Approaches

Paolo Cocci,Emanuele Troli,Francesco Alessandro Palermo,Mauro Angeletti

doi:10.3389/fmars.2021.661389

Abstract

Tritia mutabilis (Linnaeus, 1758) represents a marine gastropod species of ecological and economical importance especially in coastal areas of the central Adriatic Sea (Italy). T. mutabilis encloses its fertilized eggs within capsules which play a protective role in the embryo defense against adverse environmental factors. Egg capsules are attached to any hard substrates and the availability of adequate substrates for oviposition represents therefore a major determinant of reproductive output of this species. The aim of the present study was to provide the first comprehensive monitoring of T. mutabilis egg capsule deposition and intracapsular embryonic patterns using specific artificial substrates and innovative analytical approaches. Square-based pyramid structures were placed within an area subjected to small-scale fishing activity along the Italian coastal waters of the central Adriatic Sea and monitored from March to June 2019. In addition, a machine learning-based approach was developed in order to speed up and automate time-consuming counting procedures of egg capsules attached on each pyramid. Overall, egg capsules were deposited on the almost totality of the artificial substrates reaching values of the surface coverage per site ranging from 31 to 97%. These findings lead to a quantitative estimation of egg number per site included between 27,060 and 62,940 capsules. Our results demonstrate that using these artificial substrates together with monitoring of both egg capsule deposition patterns and intracapsular developmental stages may be useful to improve the T. mutabilis stock management.

Highlights

Many marine invertebrates, mostly gastropod families, enclose their fertilized eggs within capsules that play a protective role in the embryo defense against adverse environmental factors (Pechenik, 1983; Rawlings, 1994, 1999; von Dassow and Strathmann, 2005; Przeslawski and Davis, 2007)
Deposition of T. mutabilis egg capsules along the Italian coastal waters of the Central Adriatic Sea (Marche region, Italy) was monitored using artificial substrates and innovative analytical approaches
The artificial substrates employed in the present study were square pyramids covered by a high strength nylon net and anchored on the sandy seabed in order to leave available for deposition a surface of about 0.4 m2 per structure (Figure 1)

Summary

Introduction

Mostly gastropod families, enclose their fertilized eggs within capsules that play a protective role in the embryo defense against adverse environmental factors (Pechenik, 1983; Rawlings, 1994, 1999; von Dassow and Strathmann, 2005; Przeslawski and Davis, 2007). Species living in marine soft-bottom environments with limited availability of hard substrates must adopt different oviposition strategies such as attaching their egg capsules to living organisms (e.g., algae or bivalves; von Dassow and Strathmann, 2005; Carrasco and Phillips, 2014; Aguilar et al, 2017; Corte et al, 2019). Communal egg-laying is one of the most frequent behavior observed in several neogastropod species (Carrasco and Phillips, 2014) This behavior is considered a typical strategy for ensuring stable substrata for egg capsule deposition (Yokoyama and Amaral, 2011) or for providing protection against predators (Dumont et al, 2008)

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