Oysters are fascinating creatures, both for their ability to filter water and for their crucial role in the marine ecosystem. But a little personal anecdoteA few years ago, I found myself explaining to a child how oysters change sex. The mother gave me a dumbfounded look, thinking I was joking. But this phenomenon is very real and crucial to understanding the oyster reproduction. Let's take a closer look.
Sex change in oysters
Oysters, in particular Crassostrea gigas and Ostrea edulisThey have a unique characteristic in their life cycle: they are successive hermaphrodites. They alternate between male and female from one year to the next. The alternation of sex in oysters is influenced by the water temperature. During the months of June to September, when the water temperature reaches around 20°C, the oysters go through an intensive reproduction peak.
The Crassostrea gigas usually change sex every year. An even more interesting phenomenon is that the older oysters get, the more likely they are to become female. This ability to change sex is vital to their survival, as it significantly increases the chances of reproduction. Imagine if humans had this ability, conversations and relationships would be much more interesting!
Oyster fertilisation
Oyster reproduction is based on external fertilisation. When they are ready, male oysters release sperm into the water, while females release eggs. This synchronisation is essential for successful fertilisation. Around 24 to 48 hours after fertilisation, the oyster larvae begin to develop. The Crassostrea gigas are oviparous and expel their gametes directly into the water, while the ova of the Ostrea edulis are kept in their shell cavity to be fertilised.
And did you know that nanoplastics can disrupt this process? Plastic particles in the water can reduce the mobility and fertility of oyster spermatozoa, affecting the success rate of fertilisation. This highlights the importance of maintaining clean marine environments for the well-being of these precious sea creatures.
The larval life of the oyster
Once fertilised, oyster larvae first live off their reserves before feeding on plankton. The larvae go through several stages of transformation. They secrete their shell and develop a short-lived foot that allows them to swim freely for around 15 to 25 days. During this period, sea currents play a crucial role in dispersing the larvae to prevent overpopulation of a given area.
This phase of larval life is critical. Only a small proportion of larvae reach the stage where they attach themselves to a support and become spat. These spat continue to develop by pumping and filtering the water to feed on plankton. It's a real marathon of survival as each larva struggles to find a suitable place to attach itself.
The fixed life of the oyster
Once set, the oysters begin a new phase in their lives where they grow into mature oysters. It takes around three years for an oyster to reach maturity and be ready for consumption. During this time, they continue to filter water and feed on plankton, helping to improve water quality in their environment.
Oysters matured in oyster beds, particularly those in the Marennes-Oléron basin, have a Protected Geographical Indication (PGI). These clay basins encourage the development of phytoplankton, improving the quality and flavour of the oysters. You could say that this is haute cuisine for oysters.
A summary table could help to better understand these different phases:
| Phase | Description | Duration |
|---|---|---|
| Fertilisation | Release of gametes into the water | 24-48 hours |
| Larvae | Free-swimming larvae feeding on plankton | 15-25 days |
| Fixing | Larvae attach themselves to a support, becoming spats | Variable |
| Maturation | Naissains growing up and becoming adults | 3 years |
Impact of nanoplastics on oyster reproduction
Oysters, which we talk about here with such effort and admiration, are very sensitive to their environment. Studies have shown that microplastic and nanoplastic particles can affect their reproduction. These particles can reduce the mobility and fertility of spermatozoa, which is a cause for concern for the health of oyster populations.
This is a worrying phenomenon, as it highlights the importance of a clean marine environment. Plastic particles can also be ingested by oysters, altering the quality of their flesh and their filtering capacity. As a pet shop floor manager, I urge you to make your customers aware of the importance of reducing their use of plastic and adopting more environmentally-friendly practices to protect our bivalve friends.
English 
French