Project

Fundamentals for kick-starting flat oyster rehabilitation in the North Sea; (epi)genomic considerations and SeaCrete basis

Motivation:

My PhD project focusses on the (epi)genetics of the European flat oyster (Ostrea edulis). This is a native species to the North Sea where it was once very abundant. It is considered a keystone species because it provides foraging and reproduction grounds with the reefs it builds with its shells. Several disease outbreaks, overfishing, and habitat degradation have decimated populations and made the flat oyster to become functionally extinct in the Netherlands. Restoration projects aim at restoring populations by translocation of adult flat oysters from other locations. The effects of such translocations on the genetic diversity of Dutch oyster populations remains unknown. In addition to translocating oysters, juvenile oysters are produced in hatcheries and released into the wild to replenish or kick-start wild populations. Hatchery production potentially poses a risk of inbreeding due to a small breeding stock. Inbreeding can result lower resilience of a population. To sustain flat oyster restoration and maintain genetic diversity it is imperative that we take into account the genetic background of Dutch flat oyster populations.

Flat oysters are sequential hermaphrodites that can change their sex throughout their lives. As they show no sexual dimorphism, the sex of flat oysters is currently determined using either in vivo magnetic resonance or through microscopic histology, both of which are labour intensive, expensive, and in most cases lethal to the oyster. An alternative for identifying flat oyster sex is through studying epigenetics. DNA methylation, along with other types of epigenetic processes, is known to influence gene expression. Correlations between DNA methylation and sex change have been documented for several oyster invertebrates. In this part of my research I am focussing on characterizing differences in DNA methylation between male and female oysters to allocate potential epigenetic markers that can be used for a non-lethal way of flat oyster sex identification.

The flat oyster is a larviparous and protandrous species where female oysters brood eggs and release them as pelagic larvae. After a pelagic stage of 7 to 10 days the larvae, now called pediveliger, search for suitable hard substratum to settle. In nature, flat oyster reefs can become self-sustaining when oyster larvae settle upon older individuals. It is also shown that flat oyster larvae are actively attracted towards shell material. To stimulate the recovery of self-sustaining oyster beds, utilization of shell material should therefore be included when designing artificial substrates. The sandcastle worm, Phragmatopoma californica, produces an underwater adhesive to create strong biogenic reefs with sand grains and shell material . In this research, we will compare larval settlement on this adhesive compared to more classical substrates used for reef rehabilitation, like concrete or limestone.