Factors affecting RPSI in imposex monitoring studies using Nucella lapillus (L.) as bioindicator

Abstract

Nucella lapillus (L.) is a marine gastropod mollusc widely used as a bioindicator of TBT pollution in the North Atlantic coastlines. The species reproductive cycle and the male penis length seasonal/spatial variation were studied at a single site at Aveiro seashore (NW Portugal) between December 2005 and June 2007. The main objective of this work is to assess if the "Relative Penis Size Index" (RPSI)--an important imposex assessment index--varies seasonally and spatially in the same sampling site and how this can affect results obtained in imposex monitoring programmes. Animals able to reproduce were found every month but a seasonal pattern in N. lapillus reproductive cycle was evident. Female gametogenic maturation varied seasonally and a decrease in capsule gland volume and condition factor occurred in late summer/early autumn. The gametogenesis in males did not show a significant seasonal variation as in females but the condition factor, penis length, amount of sperm and prostate volume also diminished in late summer/early autumn. On the other hand, males that were close to egg capsules clusters had larger penises than those far away from clusters. The temporal and spatial male penis length variation introduces a bias on imposex assessment results when using RPSI and the magnitude of the error involved is evaluated for different TBT pollution levels scenarios. We consider that RPSI provides interesting and complementary information that should not be excluded from monitoring programmes, but temporal or spatial comparisons of imposex should be based on other more reliable imposex indices like the VDSI.

Size matters: importance of penis length variation on reproduction studies and imposex monitoring in Bolinus brandaris (Gastropoda: Muricidae)

“…Seasonal variation in male PL (or even penis shedding at the end of breeding season) has been described in several marine gastropods. Besides B. brandaris, PL variation has been reported to occur in Haustrum scobina (Smith & McVeagh, 1991), Hexaplex trunculus (Vasconcelos et al, 2006), Littorina littorea (Grahame, 1969;Fretter & Graham, 1994;Davies & Minchin, 2002;Barroso et al, 2007;Van den Broeck et al, 2007, L. saxatilis (Berry, 1961), Nassarius incrassatus (Stroben et al, 1996), N. obsoletus (Jenner & Chamberlain, 1955;Jenner, 1979;Bryan et al, 1989;Oberdörster et al, 2005;Hotchkiss et al, 2008), N. reticulatus (Stroben et al, , 1996Barroso & Moreira, 1998), Nucella lapillus (Gibbs et al, 1987;Oehlmann et al, 1991;Stroben et al, 1996;Davies et al, 1997;Gibbs, 1999;Galante-Oliveira et al, 2010), Ocenebra erinacea (Stroben et al, , 1996, Thais clavigera (Li, 2005;Chan et al, 2008) and Trivia arctica (Stroben et al, 1996).…”

Nucella lapillus L. imposex levels after legislation prohibiting TBT antifoulants: temporal trends from 2003 to 2008 along the Portuguese coast

“…14, 20 The current study shows that the VDS stage (and consequently the VDSI) is also dependent on animal size (SH), (see the 'SH' coefficient and respective p-value column in Table 3). This can be problematic, since imposex assessment at a given site is generally carried out using adult animals that rarely have uniform sizes.…”

“…Three slides with 4 gonad sections each were made by specimen, stained with haematoxylin-eosin and mounted in DPX resin for light microscopy observation, in order to determine individual gametogenesis stage. Gametogenesis classification for prosobranch gastropods was proposed by Barroso and Moreira 24 and was applied to study the N. lapillus reproductive cycle by Galante-Oliveira et al 20 being therefore fully described for this species. Animals at stages I, II and III were grouped and classified as having gonad maturation GonadsMat 0 -'immature', while specimens at gametogenesis stages IV, V and VI were classified as GonadsMat 1 -'mature'.…”

“…The other objective is to create an imposex level baseline at the moment when the IMO TBT-based AF paints global ban came into force. As some factors have been described to induce variation in imposex assessment indices, [17][18][19][20][21] which might result in less reliable results, new monitoring and data analysis procedures are described.…”

“…A large sample of animals of all sizes (from juveniles to adults) was collected in 1A). Sampling was carried out right before the main spawning period described for the population at that site, 20 a moment when all the adults are expected to be sexually mature.…”