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).

The process will be explained in the Construction Management Plan to be submitted to Auckland Council for approval. A high level platform will be built from the first dredgings on part of the marina footprint. This will allow subsequent dredgings to be stockpiled above the tide level so they can drain most of their water content over a period of several weeks, before being loaded on to barges for transport to the disposal site. Apparently this will also dry out and kill the invasive species such as sea squirts (Figure 1) and paddle crabs.

I doubt there have been experiments done to check just how long this drying period needs to be to kill sea squirts and their propagules, but if the process leaves the material to dry for several weeks as stated this is probably sufficient. Experiments to confirm the time needed would be desirable.

So it would appear that the process is likely to prevent spread of invasive marine species via dumping of the processed dredgings at the specified site off the back of Great Barrier Island, the site having been confirmed by Jon Nicholson in the Mahurangi Matters article previously cited. The risk of potential spread of invasive species in untreated dredgings was outlined in Grace, (2014b).

There remains, however, another problem which could also lead to spread of the two undesirable species of sea squirt now common at Sandspit.

Biosecurity Management Plan.

In the Biosecurity Management Plan required under Marina Structures and Dredging Permit 41065 there is provision to prevent the introduction of unwanted or risk species to the Sandspit estuary via vessels and equipment brought to Sandspit for the construction of the marina.

The objectives of the Plan are listed in Section 23.3, which includes clause iv) To ensure effective treatment of all the equipment used in association with the marina construction to ensure it does not become a vector for the spread of any unwanted or risk species, including but not limited to Undaria. Vessels and barges brought to Sandspit have to be certified “clean” of unwanted organisms such as the seaweed Undaria , the clubbed tunicate Styela clava, and the Meditterranean fan worm Sabella spallanzanii.

Risk of invasives attaching to barges at Sandspit.

That is all good and fine, but.………… the barges and tugs will be stationed at and working out of Sandspit for quite a long time. Although a small amount of material will be accommodated in shore reclamations and another land site, there are more than 100,000 cubic metres of spoil to be carried to the ocean dump site.

Depending on the size of barges used, there will be hundreds of barge loads to be transported to the dump site. Even with two barges working, that is looking like many months of barge movements from Sandspit, across the Hauraki Gulf to the dump site and return.

My question is how frequently will the barges themselves be inspected for invasive species which have attached to their hulls while working at Sandspit? My earlier report on marine invasive species at Sandspit (Grace, 2014a) indicated two non-indigenous sea squirt species were present at Sandspit, one of which is classed as an unwanted organism (clubbed tunicate, Styela clava) and cannot knowingly be moved without a permit, and another which is clearly a “risk” species (Australian droplet tunicate, Eudistoma elongatum) and should also not be moved knowingly. Both of these species will have ample opportunity to infect the hulls of tugs and barges while stationed at Sandspit.

Part of Condition 23.1 under Biosecurity states:

. The Consent Holder shall not allow the use of any vessel under its control or direction, or otherwise associated with the construction of the marina:
. (i) That is not certified as having been treated and inspected as required by this condition, or
. (ii) That is showing any indication of being infected with any unwanted or risk species, including but not limited to Undaria.
So it would appear that there is a requirement for frequent inspection of the barges and tugs being used in the operation in order to comply with condition 23.1 (ii), as presumably that condition remains in force during the time the vessels are in use on the job.

There can be no assumption that the vessels will remain “clean” during their time working at Sandspit. Indeed it must be assumed to be inevitable that the Australian droplet tunicate (Eudistoma) will readily settle as larvae on the barges, unless they are newly antifouled and frequently inspected and cleaned.

During my most recent snorkel inspection in Sandspit estuary on 17 February 2014, I noted several Styela occurrences (Table 1) on a swing mooring rope, a yacht hull, and on two mooring poles. I also noted, significantly, a large infestation of Eudistoma on the bottom of a small barge temporarily moored to poles near the low tide boat launching site near the end of the spit. This barge frequently carries heavy equipment and timber to Kawau Island.

TABLE 1.  Recent significant observations of non-indigenous marine species at Sandspit

TABLE 1. Recent significant observations of non-indigenous marine species at Sandspit

With very large numbers of Eudistoma widespread in the Sandspit estuary, releasing enormous numbers of larvae throughout the summer months, newly settled larvae forming tiny new colonies are common on the sandstone reef along the edge of the proposed marina footprint and elsewhere, as shown in Figure 2.

Figure 2.  Tiny newly settled colonies of Eudistoma elongatum show as a cluster of small white dots 1 to 2mm across in the middle of this picture, as well as more tiny colonies scattered over the sandstone, toward low tide in the proposed marina footprint.  The larger colonies will be releasing larvae daily.  (Photo: 2 March 2014).

Figure 2. Tiny newly settled colonies of Eudistoma elongatum show as a cluster of small white dots 1 to 2mm across in the middle of this picture, as well as more tiny colonies scattered over the sandstone, toward low tide in the proposed marina footprint. The larger colonies will be releasing larvae daily. (Photo: 2 March 2014).

Such tiny colonies appear at only one or two millimetres across, but will soon grow to release larvae of their own. Within just a few weeks barges could be infected with breeding colonies of Eudistoma, which would then release their larvae all the way across the Hauraki Gulf, around the south end of Great Barrier and to the dump site, and then again on the return journey.

With a huge population of breeding Eudistoma in the Sandspit estuary and a larval life of only 24 hours, there will be daily opportunity for larvae to settle on the bottom of the barges.

There is every possibility that during hundreds of crossings of the Gulf to dump spoil outside Great Barrier Island that larvae of Eudistoma, and probably Styela, will be released from infestations on the bottom of the barges and possibly the tugs towing them.

Conclusion.

To ensure the barges do not become a vector in spreading Eudistoma and possibly Styela clava around the Hauraki Gulf, extraordinary diligence will be required to frequently and thoroughly inspect the hulls of the barges and tugs working on the marina project, and to carry out whatever maintenance and cleaning is required to prevent colonies from establishing on the hulls.

References.

Grace, R.V. 2014a Marine pest species at Sandspit, Northern New Zealand. Report by Roger Grace, published on Whangateau HarbourCare website, 5 February 2014.

Grace, R.V. 2014b Risk of spreading marine pests from Sandspit by dredge spoil dumping at sea. Report by Roger Grace, published on Whangateau HarbourCare website, 24 February 2014.

Mahurangi Matters 2014 Marina construction imminent. MM 19 March 2014, p7.

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