This is what Okiwi Estuary (Great Barrier Island) used to contain within the main channel close to the estuary entrance. It was the last naturally occurring soft-sediment mussel reef in the Hauraki Gulf.
Aggregations ranged from a few individuals to meters in diameter. Mussels were frequently attached to pipis, partially buried in the sandy substrate. There were an estimated 3.2 million adults. Compared to other sites Okiwi mussels had the poorest condition but highest densities of invertebrates – Ian Mcleod’s 2009 thesis on soft-sediment mussel systems in northeastern New Zealand.
Unfortunately they were nearly completely wiped out by a major storm.
I went for a swim on the outgoing tide (excuse the murky tannin stained water) to investigate 2 years later (April 2017).
Only 50 meters or so upstream I found some small regenerating clumps.
I was really pleased to see juveniles. Note the abundant red (not green) algae. Short video below.
If we left the bed alone, I wonder how many decades it would take for it to completely regenerate?