Development of a protocol for imposex measures on tropical neogastropod molluscs
Date
1991
Authors
Pattisina, Limy Agan
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Abstract
Tributyltin (TBT) used in antifouling paints 1s toxic to many non-target organisms. A known sublethal effect of TBT to marine organisms is neogastropod imposex, i.e., the imposition of male sexual characters on functionally gonochoristic females. This anatomical abnormality was rare before the 1960s, but has now been reported from many parts of the world, mostly from temperate regions, with the same prominent feature: association with boating or shipping activity. There is very little information available on such abnormality from developing countries. The importance of this research lies in showing that even a tropical area that is remote from major shipping routes, i.e., Ambon, Indonesia, showed the presence of the TBT biological indicator. Therefore, it appears to be at risk from the environmental impact of TBT-antifouling paints.
A reconnaissance survey was conducted m 1988 to determine whether
neogastropod imposex occurred in Ambon Bay. As the abnormality was found there, follow-up field research was undertaken in 1989 to confirm the 1988 results. In both field studies, the sampling sites were selected based on their levels of marine activity; harbours and ferry docks were considered to be the Test Sites, while "clean" shores were treated as the Reference Sites. Specimens were collected as they were seen, in harbour areas by snorkeling divers and on shores by hand.
Species selection was based on specimen size, availability and accessibility in the field. Imposex was determined by the presence of a penis behind the right tentacle of females. Females were particularly distinguished from males by the presence of a sperm-ingesting gland. The diameter of a recurved penis was recorded as the penis length by using a 1 mm scale. Imposex incidence was expressed by the Relative Frequency 'of Imposex (RFI), i.e. the relative ratio of imposex females to the total number of females. Imposex intensity was calculated by the Relative Penis Size (RPS) index, i.e. (mean length of female penis/mean length of male penis )3 X 100%.
Thais luteostoma, an intertidal neogastropod mollusc, showed widespread imposex in Ambon Bay, Indonesia. All sites showed some imposex, but the higher levels of occurrence were recorded at the two harbours in the bay serving oceanĀ going traffic (RFI = 90-100% and RPS = 20 - 90% ). A number of sites with low levels of incidence and intensity were spread around the harbours. An imported TBT-antifouling paint is available at a ship slipway, but is rarely used due to relatively high cost. Accordingly, the causative agent is suspected as TBT leaching from antifouling paints used by deep-sea vessels.
Thais luteostoma is the most suitable bioindicator for imposex study in Ambon Bay as a moderately large (2-3 cm shell length), moderately abundant and readily accessible species. It occurs from mid-tide into shallow water, on rocky shores, concrete and wooden pilings.
The investigation protocols developed allow for confirmation of the presence of neogastropod imposex in a laboratory without histological sectioning facilities, and also allow graphical intersite comparisons of imposex occurrence where small samples preclude rigorous statistical significance tests.