What does it look like?
The Asian date mussel reaches a maximum length of 30mm, but is more commonly only 10-25mm in length, and 12mm in width. It has a smooth olive-green to greenish-brown shell, with straight or zig-zag stripy markings and a protective cocoon of threads. It burrows vertically in to sediment and filters food particles from the water using a short siphon. The Asian date mussel produces a thick cocoon of byssus threads around itself to protect its shell in at mussel densities of over 1500/m2 these cocoons combine to form a continuous mat on the surface of the sediment.
The Asian date mussel is an opportunistic species that can live in intertidal and subtidal areas down to depths of up to 20m. It can tolerate low salinity and low oxygen levels. It prefers to settle onto soft sediments and seagrass but can also be found on hard surfaces.
Why is it a problem?
Asian date mussels can reach very high densities in soft sediments. For example in Auckland Harbour it has been recorded at densities of 16,000/m2 with peak densities of over 150,000/m2. When densities are high in soft sediments, the protective cocoons will fuse to form carpets which may exclude native shellfish and impact on the growth of eelgrass. Its high rate of reproduction and long, free-swimming larval stage mean the mussel is a successful invader.
The Asian date mussel is a prolific breeder with a fast growth rate and a short life span, the adults mature at 9 months of age and have an expected lifespan of 18-24 months. Male and female mussels release eggs and sperm into the water column at the same time. The larvae remain free-swimming for up to 55 days and during this time it can disperse over large distances.
You can help prevent the spread of marine pests by:
• Regularly cleaning your boat’s hull – ideally keep fouling growth to no more than a light slime layer.
• Applying good thorough coatings of antifouling paint and keep it in good condition
• Ensuring your hull is clean and free of fouling before you go travel to a new region
• Cleaning and drying any marine equipment (e.g. ropes, lines, pots) before using in a new location.
• Inspecting areas on your boat that retain water in case they’re harbouring marine life.
• Checking anchors, trailers and other equipment for tangled weeds.