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Forest & Bird » Marine and Coastal

1. Greg Jenks
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   Beneficial Effects of Beach-cast Seaweed for Natural Dune Growth

   1. Beach-cast seaweed is delivered to beaches by natural storm-surge processes.

   2. This valuable source of natural nutrients has largely been unimportant on beaches with degraded dunes (i.e. dunes dominated by adventive plants – like marram, kikuyu, lupins etc). All these plants are sensitive to salt water inundation, and so are unable to survive wave run-up and inundation, a critical factor for natural dune function.

   3. Degraded beaches simply do not possess the suitable plants and naturally-induced gentle morphology to be able to take advantage of beach-cast seaweed deposition.

   4. However it has been found that where dune systems are successfully restored, these dunes (now dominated by indigenous salt-tolerant and functional species) have greatly improved and gentle-sloping morphology for more natural dune function.

   5. Dunes in this condition can more readily utilise the nutrients supplied through beach-cast seaweed deposition.

   6. This is achieved by seaweed now being naturally deposited at the dune-toe during storm events.

   7. The next effect to occur is burial of the seaweed by sand (seaweed possesses effective but rather limited sand-trapping abilities). Most of the seaweed volume soon disappears beneath the accumulated sand through this process.

   8. It has been observed that a host of beach invertebrates then congregate amongst the buried seaweed, consuming the mass and recycling the contained nutrients in their excretions, often staining surrounding sand brown with these exudates.

   9. It is known that the indigenous salt-tolerant pioneer dune plants (especially spinifex and pingao) have roots that colonise the barren beach ahead of plant top-growth and the incipient dune. It is considered that these roots utilise the supplied rich nutrients for creation of the observed lush growth of foredune areas in this otherwise nutrient-poor substrate, maintaining plant vigour & the buffering ability of indigenous dune systems.

   10. Therefore wholesale removal of all beach-cast seaweed can have unforeseen consequences on the natural integrity and resilience of retsored beaches and dunes.

   Greg Jenks
   Coastal Management Specialist
   Tauranga
   gregj@slingshot.co.nz

   Posted 2 years ago #

2. Kim
   User Profile

   Hi Greg,

   I never knew that seaweed played such an important role - interesting stuff. I just didn't understand your third point however -

   Degraded beaches simply do not possess the suitable plants and naturally-induced gentle morphology to be able to take advantage of beach-cast seaweed deposition - what does that mean?

   Cheers,

   Kim

   Posted 2 years ago #

3. Kirstie
   User Profile

   Awesome post Greg!

   Here's the low down re. Forest & Bird's position:

   CONCERNS
   - Potential fundamental change to the ecology of some of our beaches
   - Knock on consequences for a wide variety of marine life
   Which in turn may not only affect marine life abundance and diversity, but also our fisheries and our economy.

   WHERE?
   - This decision actually decreases the number of areas that are currently protected
   - Where once there was a moratorium on seaweed harvesting, the recent decision by the Mintser of fisheries to open up more areas marks another green light for removal of this important resource.
   - It appears the only reason that more areas weren't opened up is because the seaweed industry didn't ask for them.

   WHO Wants to harvest seaweed commercially?
   There are lots of uses of seaweed which support a commercial market for it:
   - Aquaculture industry use it to collect mussel spat and as a feed for farmed paua;
   - Used as a fertiliser for agricultural purposes;
   - Also used for medicinal and pharmaceutical products (including cosmetics)

   WHY is it important - isn't it just dead and lying there?
   NO!
   As Greg have pointed out very clearly, it has a wide rale of important roles:
   - food
   - shelter / home (e.g. to bacteria, sand hoppers, flies - a whole range of beasties that provide food for shore birds and other marine life)
   - nest material
   - dune formation
   - fertliser (sea's own natural source of nutrients!)
   - dispersal of larval (juvenile) marine life
   Not only is beach cast seaweed an important habitat and natural part of some beach systems, it also plays a vital role in supporting our fisheries. E.g. moki, yellow-eyed mullet, flounder and baitfish - all connected with seaweed

   WHAT NOW?
   - Urgently need an environmental risk assessment to be completed
   - Work out some no-go areas (areas of ecological importance, but also cultural and social importance where commercial scale harvesting would be inappropriate).
   - Identify aeas that may be suitable, but would require strict management
   -Add seaweeds to the quota management system - thereby require information collection and strict management procedures.

   Our position in relation to the Minister's recent decision is also spelt out in our media release:

   http://forestandbird.colo.onesquared.net/what-we-do/publications/media-releases/-forest-bird-warning-over-commercial-seaweed-harvest

   Posted 2 years ago #

4. Kirstie
   User Profile

   Also, .. here's my wee map of the areas open to commercial harvesting.

   Where:

   Red/Pink = CLOSED under the 2002 Fisheries Notice
   White = Open under the 2002 Fisheries Notice
   Green = new areas that have been opened up

   

   Attachments

   1. SeaweedHarvestingAreas_RedclosedGreenO.jpg (27.8 KB, 0 downloads) 2 years old

   Posted 2 years ago #

5. Kirstie
   User Profile

   Hmmm.... not easy to see.

   New Areas opened:

   Northland-Auckland region:
   - Coastal area between North Cape and Blackney Point, Rangaunu Bay
   - Coastal area between eastern end of Coopers Beach (Doubtless Bay)and Marsden Point )Whangarei)
   - Coastal Area between Pakiri River and Orere Point (Auckland)
   Coastal area surrounding Great Barrier Island (Auckland)

   East Coast North Island:
   - coastal Area between Mahia and Mataikona River

   West Coast North Island:
   - Coastal area between Patea River and the Tirua Point (Taranaki)

   In other words.... much of the North Island is now open to commercial harvesting of seaweed (along with their diggers).

   :(

   Posted 2 years ago #

6. Kirstie
   User Profile

   Nice to know we're not alone of the issue of mis-management of our seaweed - check out US (Maine) based group facing similar struggles:

   http://www.rockweedcoalition.org/

   Some very useful information.

   Posted 2 years ago #

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