Inshore/offshore gradients of imposex in Bolinus brandaris (Gastropoda: Muricidae) from the Gulf of Gabes (southern Tunisia, Central Mediterranean Sea)

Abstract

The present study provides the first data available on imposex in a gastropod species caught offshore the Tunisian coast. Imposex was analysed in the purple dye murex (Bolinus brandaris) from ten collecting sites offshore the Gulf of Gabes (southern Tunisia, Central Mediterranean Sea). From a total of 584 individuals analysed, females outnumbered males, leading to a female-biased sex ratio (1 F:0.7 M). Among the 353 females analysed, 117 were affected by imposex. On the whole, these females presented low to moderate imposex incidence (I%=33.1) and severity (FPLI=0.3, RPLI=2.6 and VDSI=0.8). The study revealed that imposex is a widespread phenomenon in the Gulf of Gabes and identified a clear inshore/offshore gradient in the imposex indices of B. brandaris. Regression analysis detected highly significant negative correlations between imposex indices and the distance to the coastline and depth of the collecting sites. Principal components analysis highlighted the specific influence of the distance to the major harbours, either in number of calling vessels (commercial harbour of Sfax) or shipping tonnage (oil terminal of Skhira). This inshore/offshore gradient of imposex development in B. brandaris reflects marked spatial variation in pollution by organotin compounds associated to the shipping activity. Overall, the study provides valuable baseline data for assessing the future evolution of imposex in B. brandaris, and subsequently the spatial and temporal trends of pollution by organotin compounds offshore the Gulf of Gabes.

u radu se iznose prvi podaci o pojavi imposeksa kod puževa uhvaćenih u otvorenom moru Tunisa. imposeks je analiziran na jedinkama bodljikavog volka (Bolinus brandaris) prikupljenim na deset postaja u otvorenom moru zaljeva Gabes (južni Tunis, središnji dio sredozemnog mora). ukupno su analizirane 584 jedinke, a omjer spolova je bio u korist ženki (1 Ž: 0,7 M). od 353 analizirane ženke, 117 ih je bilo pogođeno imposeksom. općenito, učestalost imposeksa kod ženki je bila niska do osrednja (i%=33.1) i jačina (fPli=0.3, rPli=2.6 i VDsi=0.8). studija je pokazala da je pojava imposeksa raširena u zaljevu Gabes te je utvrđen jasan gradijent pojavnosti imposeksa kod B. brandaris na relaciji priobalno/otvoreno more. regresijskom analizom otkrivene su vrlo značajne negativne korelacije između pojavnosti imposeksa, udaljenosti od obalne linije te dubine na kojoj se uzorkovalo. analiza glavnih komponenti (Pca) istaknula je određeni utjecaj udaljenosti od glavnih luka, i to ovisno o broju plovila (komercijalna luka sfax) ili brodske tonaže (naftni terminal skhira). ovaj priobalno/otvoreno more gradijent razvoja imposeksa odražava značajne prostorne varijacije kod onečišćenja organskim spojevima kositra povezanih s pomorskom djelatnošću. ova studija pruža vrijedne temeljne podatke za buduću procijenu razvoja imposeksa kod vrste B. brandaris, te prostorno i vremenskih trendova onečišćenja organskim spojevima kositra u otvorenom moru zaljeva Gabes.