12 months on at Ōkahu Bay

This kaupapa is long-term and intergenerational, and for that reason, milestones defined simply by the passing of time can seem a little arbitrary. But, time itself can also be a marker of progress. Although it’s early days, we were excited to reach the 12-month anniversary of the Ōkahu Bay mussel reefs. I will confess to wondering if the anniversary warranted cake. However, like a baby that cannot yet fend for itself at 12 months old, the mussel reefs at Ōkahu Bay are still at a very early stage.

Here are the highlights on how the reefs are doing.

After one year on the seafloor, the density of the mussel reefs was substantially lower than when they initially went in. This initial change is to be expected and was observed in the one-month survey and could be for a range of reasons including the mussels spreading out. However, there was little to no change in mussel densities from the previous (seven-month) surveys suggesting densities, and possibly mussel losses, have leveled out and are remaining consistent. Most mussels were generally oriented upright – in a vertical position.

The mussel size (growth) changed very little over the first year on the seafloor. Our team suggests that in general mussels have slower growth rates when they’re already adult in size, and also the environmental conditions at Ōkahu Bay are sub-optimal for mussel growth so we do not expect to see fast growth rates in the short-term. 

Similar to the 7-month survey, we observed epibiota in the mussel reefs. Epibiota are organisms that live on other organisms – so in this case, we’re talking about the organisms that attach to mussels. The team observed small amounts of kelp, several sea stars, sponges, and encrusting ascidians (more commonly known as sea squirts) during their survey.

Two unwanted organisms, the Mediterranean fanworm, and the clubbed tunicate were observed in the reefs, but do not appear to be spreading extensively and are found elsewhere in the area off the mussel reefs as well.

For those following this project closely, you’ll know that half of the mussels were placed on a shell base, and the other half were placed directly onto the seafloor (mud). At this early stage, there’s little discernible difference in the results between the two sites.

Although this research is still in its infancy, these reefs provide a valuable test case for learning and knowledge building. We’ll collectively hold our breath over the summer with the forecast warm water temperatures and look forward to sharing further updates with you throughout 2023.

Nga mihi nuinui to Dr. Al Alder and Sophie Roberts for the monitoring report. Fieldwork was conducted with the assistance of Dr. Jen Hillman, Dr. Carina Sim-Smith, Eliana Ferretti, and Dr. Paul Caiger. And, of course, ngā mihi nui to project partner Ngati Whatua Ōrakei for their leadership and kaitiaki over this kaupapa.

Visit the Ōkahu Bay project page