Sandspit “Seasnot” Degenerating for the Winter

It looks like the sea snot, or Australian droplet tunicate, is slowly degenerating for the winter, but there are large numbers of juveniles which may stay in a dormant state until the spring.

The Australian droplet tunicate is still abundant at Sandspit, but appears to be degenerating with the onset of winter and cooler temperatures.  Photo: 1 May 2014.

The Australian droplet tunicate is still abundant at Sandspit, but appears to be degenerating with the onset of winter and cooler temperatures. Photo: 1 May 2014.

[Read more…]

Sediment Accumulation in Sandspit Traps on Target for >300mm per Year, Again!

Mud near a Whangateau sediment trap

Mud near a Whangateau sediment trap

At the start of the year I installed an additional sediment trap at both the Sandspit and Whangateau sites, with a view to increasing the precision of the estimates of sediment accumulation in a theoretical hole dug in the estuaries.

Not surprisingly, this has made no difference to the interpretation of the annual rate of sediment accumulation. The Sandspit traps are accumulating sediment at an annual rate of a little over 300mm, which is the same as last year.

The updated spread sheet is attached, showing the results for this year with the three traps at each site. The Whangateau traps continue to accumulate sediment at a rate a little over half of that at Sandspit.

[Read more…]

More Concerns About Spread of Marine Invasive Species from Sandspit During Marina Construction

Jon Nicholson from the Sandspit Yacht Club Marina Society has assured us that the various marine invasive species found at Sandspit within the proposed marina footprint will not be spread by dumping the dredged spoil at sea because of the technique they intend to use for dealing with the dredged material (Mahurangi Matters, 19 March 2014, page 7).

Figure 1.  Large quantities of highly invasive Australian droplet tunicate festoon the low tide and shallow sandstone reef in the Sandspit estuary, including the footprint of the proposed marina.  Although tunicates may be killed in the stockpiling and draining process before dredgings are shipped to Great Barrier island, there is still a huge risk of larvae settling on the bottom of the barges themselves while being loaded at Sandspit.  Tunicates attached to the barges would then release larvae all the way across the Hauraki Gulf to the dump site and return. (Photo: 8 April 2014).

Figure 1. Large quantities of highly invasive Australian droplet tunicate festoon the low tide and shallow sandstone reef in the Sandspit estuary, including the footprint of the proposed marina. Although tunicates may be killed in the stockpiling and draining process before dredgings are shipped to Great Barrier island, there is still a huge risk of larvae settling on the bottom of the barges themselves while being loaded at Sandspit. Tunicates attached to the barges would then release larvae all the way across the Hauraki Gulf to the dump site and return. (Photo: 8 April 2014).

[Read more…]

A New Start for the Sediment Traps at Sandspit and Whangateau

Mud near a Whangateau sediment trap

Mud near a Whangateau sediment trap

A full year of results from the sediment traps at Whangateau and in the footprint of the proposed marina at Sandspit indicated a likely filling rate for the marina of 329.3mm in one year. This is far in excess of the estimate of only 30mm from the marina proposers. There was no experimental verification or ground truthing of that theoretical estimate, despite the SYCMS having ample time to do so.

[Read more…]

Risk of Spreading Marine Pests from Sandspit by Dredge Spoil Dumping at Sea

NZ Hydrographic Chart number NZ531

NZ Hydrographic Chart number NZ531

It is understood that dumping of most dredgings from the proposed Sandspit marina is likely to be at the eastern Great Barrier Island site designated for disposal of marina maintenance dredgings from various Auckland marinas.

I am not in possession of the actual coordinates for the disposal site, but I understand it is east of Great Barrier Island and north of Cuvier Island, in a clear “indentation” in the boundary line for the 12-nautical-mile outer limit of the Territorial Sea in this area (see chart NZ531). This is the closest point of “open sea” to Auckland, where many rules and regulations of the Territorial Sea do not apply.

[Read more…]

Marine Pest Species at Sandspit, Northern New Zealand

The invasive Asian paddle crab Charybdis japonica brandishes its nippers in a defiant stance in front of the Sandspit Yacht Club.  This aggressive crab has the potential to alter the ecology of natural shallow reefs in sheltered areas by competing with native species and changing the trophic balance.  It is now established at Auckland, Sandspit, Mahurangi and Whangarei harbours.

The invasive Asian paddle crab Charybdis japonica brandishes its nippers in a defiant stance in front of the Sandspit Yacht Club. This aggressive crab has the potential to alter the ecology of natural shallow reefs in sheltered areas by competing with native species and changing the trophic balance. It is now established at Auckland, Sandspit, Mahurangi and Whangarei harbours.

By Roger Grace Ph.D.
Independent Marine Biologist
gracer@xtra.co.nz
January 2014

Contents

  1. Summary
  2. Introduction
  3. Non-indigenous marine species recorded at Sandspit
  4. Observations and recent surveys
  5. Discussion of each non-indigenous species
    1. Parchment worm (Chaetopterus sp.)
    2. Asian date mussel (Musculista senhousia)
    3. Pacific oyster (Crassostrea gigas)
    4. Asian paddle crab (Charybdis japonica)
    5.  Clubbed tunicate (Styela clava)
    6. Australian droplet tunicate (Eudistoma elongatum)
  6. Biosecurity risk for marina development plans
    1.  Biosecurity Management Plan
    2. Dumping Permit
    3. NZ Coastal Policy Statement
  7. Conclusions
  8. References

[Read more…]