Adult Pacific Oyster (Crassostrea gigas) May Have Light Sensitivity.

Ting Guo,Yongchuan Li,Jiao Wang,Zhuang Li,Changlu Wu,Xiaotong Wang,Yanjian Yang,Donald James Colgan

doi:10.1371/journal.pone.0140149

Abstract

Light-sensitivity is an important aspect of mollusk survival as it plays a vital role in reproduction and predator avoidance. In the Pacific oyster Crassostrea gigas light sensitivity has been demonstrated in the larval stage but has not yet been conclusively demonstrated in adult oysters. In this paper we describe an experiment which was undertaken to determine if adult Pacific oysters were sensitive to light. One LED flashlight was used to shine light onto adult oysters while they were filtering seawater through their shell openings. We found that the degree of opening increased gradually during the light period but rapidly decreased when the flashlight was turned off in the treated group but not in the control group. These results suggest that adult Pacific oyster may be sensitive to light.

Highlights

Until now, four classes of mollusca (Gastropoda, Bivalvia, Polyplacophora and Cephalopoda) have been found to possess light sensitive organs [1]: chitons (Mollusca, Polyplacophora) possess ‘ocellus eyes’, with these being set dorsally in the outermost layer of the shell [2]; gastropods have a number of different eye types [3]; cephalopods possess eyes of high morphological and functional complexity [4] with excellent perception and visual acuity [5]
We obtained a number of adult Pacific oysters from aquaculture farms located in the following areas: 66 from Yantai (China); 66 from Rushan (China); and 68 from Penglai (China)
The extent of shell opening increased in some oysters when the oysters were exposed to light, and reduced when the light was turned off, The significant statistical differences between the numbers of responding oysters in the treated groups and the lack of such individuals in the controls suggests that adult Pacific oysters are sensitive to light The eyes of scallops and Ark clams are arranged along the mantle [3,19], those of some bivalves with dermal light sense were located in the skin, mantle or siphon [15]

Summary

Introduction

Four classes of mollusca (Gastropoda, Bivalvia, Polyplacophora and Cephalopoda) have been found to possess light sensitive organs [1]: chitons (Mollusca, Polyplacophora) possess ‘ocellus eyes’, with these being set dorsally in the outermost layer of the shell [2]; gastropods (snails and slugs) have a number of different eye types [3]; cephalopods (nautilus, squid and octopus) possess eyes of high morphological and functional complexity [4] with excellent perception and visual acuity [5]. In which light sensitive organs have been widely studied, have two main types: structured and non-structured. Due to the extensive studies on the visual ability of scallops (as a representatives of bivalves), many aspects of their vision are well understood, such as the identification of light-sensitive species [11], eye structure [12,13], eye function [3] and the environmental factors that impact on vision [14]. Bivalves with non-structured eyes can sense light, probably using dermal sensors [15]. Both small (< 15 mm) and large (> 15 mm) of Limnoperna fortunei show negative phototaxis and positive geotaxis when exposed to light [16].

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Conclusion