Intersex and oocyte atresia in a mussel population from the Biosphere’s Reserve of Urdaibai (Bay of Biscay)

Urdaibai is a Biosphere’s Reserve, containing rich bivalve populations. In the present work we aimed to characterize the reproductive cycle and to study possible disturbances in reproduction in mussel populations from Urdaibai. During an annual gametogenic cycle (January 2003–March 2004) samples of gonads were collected bimonthly and gamete development (gonad index), histopathology of mantle tissue and vitellogenin-like protein levels by alkali labile phosphate (ALP) method were measured. No significant changes were detected in ALP levels out of those related to gametogenic development in females. However, severe oocyte atresia was observed in female mussels in January and March 2003. Male mussels showed low ALP values with the exception of high ALP levels in March 2003. High prevalence of hermaphrodite/intersex mussels (26%) was detected in March 2004. Hermaphrodites/intersex and oocyte atresia were not found in mussels from the nearby Abra estuary. In conclusion, these results suggest that mussels inhabiting the Urdaibai estuary could be exposed to toxic chemicals such as endocrine disruptors.