Mussel reefs are crucial for marine ecosystems, providing homes for various species and supporting biodiversity. A recent study conducted by the University of Auckland in Kenepuru Sound explored the obstacles hindering the restoration of mussel reefs. The research focused on understanding the factors affecting the settlement and establishment of young mussels, known as spat.

Kenepuru Sound, like the Hauraki Gulf Marine Park, was once teeming with green-lipped mussel reefs. However, extensive commercial dredging and harvesting in the past severely depleted these reefs. Despite the halt in harvesting activities, the reefs have not recovered. 

The experiment

The study employed various methods to assess the state of mussel settlement. Researchers examined samples of wild seaweed from both the seabed and floating docks. They gathered data on the abundance of spat and their preferred substrates. Additionally, they conducted transplantation experiments to understand settlement patterns on different surfaces. The team also measured sediment accumulation and turbidity to determine their potential impact on mussel settlement.

What was learned?

The results of the study unveiled the challenges facing mussel reef recovery. Surprisingly, very few spat were found on the seabed, while significantly higher numbers were observed on seaweed attached to floating docks. This raised concerns about the suitability of natural substrates for mussel settlement near the seabed. 

Turbidity measurements indicated that there was significantly higher turbidity near the seabed compared to near the water surface. Researchers suspect that factors like increased turbidity near the seabed might hinder the successful settlement and survival of young mussels.

The transplantation experiments provided further insights into the preferences of spat. It was discovered that a specific type of brown seaweed called Cystophora retroflexa attracted the most settlers compared to other substrates, including artificial options. 

Larger spat displayed different settlement preferences, indicating that their choices may change as they grow in size.

Implications for mussel reef restoration

The study underscores the importance of considering the entire life cycle of mussel species when planning restoration efforts. It reveals that the current process of natural recovery is not functioning properly. To ensure successful restoration, it is crucial to identify and address obstacles that arise throughout the entire life cycle, particularly those affecting young mussels.

Understanding the substrate preferences of young mussels is essential for designing effective artificial substrates in restoration projects. By mimicking the characteristics of seaweed that attract these spat, restoration efforts can create substrates that promote settlement and establishment.

The study also highlights the challenging implications of sediment for mussel reef restoration. The lack of spat settling on natural substrates near the seabed emphasises the need to address sediment influx, as sediment accumulation can hinder the survival and growth of young mussels. To facilitate the recovery of mussel reefs, it is crucial to tackle the issues associated with sediment and reduce its impact on restoration areas.

By understanding substrate preferences and addressing sediment issues, restoration projects can enhance the chances of successful mussel reef recovery. These findings provide valuable insights for restoring and preserving these vital marine ecosystems.

This news article has been adapted from a publication in the academic journal Aquatic Conservation: Marine and Freshwater Ecosystems by authors Trevyn A. Toone, Jenny R. Hillman, Paul M. South, Emilee D. Benjamin, Sean Handley and Andrew G. Jeffs.