The importance of seaweed

File picture

I’m glad to be able to give Shannon Dowsing an ‘A’ for his position on the issue of beach cast seaweed. Beach seaweed, or ‘drift weed’ is a critical component of inshore ecosystems. Starting at its most landward resting place, the foreshore dunes, it helps build these areas physically, by entrapping otherwise mobile sand, and providing nutrients and organic matter for colonising and erosion-inhibiting plants such as pingao and spinifex (which is referred to as ‘soft engineering’ hazard protection).

As the weed lies along the zone at, or below high water, this body of material (and the more the better) provides habitat for vast colonies of small crustacea (eg sand hoppers and other small water bugs). As the incoming tides engulf this body of apparently lifeless weed, lifting and moving it around, who should be waiting for the veritable feast of arthropods, but juvenile predatory fish species, particularly kahawai, that are too young to actively hunt for swimming fish.

But wait, what are the herons and other birds doing assembling at remarkably even distances along the foreshore as the tide begins to rise? Well if you stay and watch for long enough, you’ll see that they are there to get their share of the fish abundance, thus nicely fulfilling the cycle of drift weed, coastal invertebrate, juvenile fish, and migratory bird life. If you get the chance, after a good swell has brought a body of drift ashore, Te Tapuwae o Rongokako Marine Reserve is an excellent place to observe this process.

Many in our community are aware of the role organic matter and waste products perform providing nutrients and other important elements for plant and animal growth. And it’s the same in the ocean. Current research indicates that drift weed provides approximately 25 percent of the energy available to inshore coastal ecosystems out to 1km to 2km, dependant on a range of factors. In short, the nutrients and detritus available from these weed beds help fuel the productivity of our local coastal ecosystems and food resources. Indeed the drift weed is itself consumed by inshore species, in particular kina, but possibly also paua and other gastropods.

It gets better though. Some of the drift weed that enters the wider coastal marine environment is effectively used by other juvenile pelagic fish (notably hapuka) who shelter beneath these floating weed rafts, and feed on the array of invertebrates and small fish they attract.

The weed is definitely a resource for any gardeners who need some nutrient rich organic matter and are happy to person-handle this away, but also for the local seaweed gatherers from Agrisea NZ, operating in the area who demonstrate best practice by only hand harvesting one target species, Eklonia radiata, and leaving at least 20 percent of that species on the beach.

Humble as it may be, and for some apparently a minor nuisance, the presence of the body of drift weed that at times cloaks our foreshore is a good example of the often complex nature of the ecology of the coastal area, and its importance to the overall well being of our communities.

I’m glad to be able to give Shannon Dowsing an ‘A’ for his position on the issue of beach cast seaweed. Beach seaweed, or ‘drift weed’ is a critical component of inshore ecosystems. Starting at its most landward resting place, the foreshore dunes, it helps build these areas physically, by entrapping otherwise mobile sand, and providing nutrients and organic matter for colonising and erosion-inhibiting plants such as pingao and spinifex (which is referred to as ‘soft engineering’ hazard protection).

As the weed lies along the zone at, or below high water, this body of material (and the more the better) provides habitat for vast colonies of small crustacea (eg sand hoppers and other small water bugs). As the incoming tides engulf this body of apparently lifeless weed, lifting and moving it around, who should be waiting for the veritable feast of arthropods, but juvenile predatory fish species, particularly kahawai, that are too young to actively hunt for swimming fish.

But wait, what are the herons and other birds doing assembling at remarkably even distances along the foreshore as the tide begins to rise? Well if you stay and watch for long enough, you’ll see that they are there to get their share of the fish abundance, thus nicely fulfilling the cycle of drift weed, coastal invertebrate, juvenile fish, and migratory bird life. If you get the chance, after a good swell has brought a body of drift ashore, Te Tapuwae o Rongokako Marine Reserve is an excellent place to observe this process.

Many in our community are aware of the role organic matter and waste products perform providing nutrients and other important elements for plant and animal growth. And it’s the same in the ocean. Current research indicates that drift weed provides approximately 25 percent of the energy available to inshore coastal ecosystems out to 1km to 2km, dependant on a range of factors. In short, the nutrients and detritus available from these weed beds help fuel the productivity of our local coastal ecosystems and food resources. Indeed the drift weed is itself consumed by inshore species, in particular kina, but possibly also paua and other gastropods.

It gets better though. Some of the drift weed that enters the wider coastal marine environment is effectively used by other juvenile pelagic fish (notably hapuka) who shelter beneath these floating weed rafts, and feed on the array of invertebrates and small fish they attract.

The weed is definitely a resource for any gardeners who need some nutrient rich organic matter and are happy to person-handle this away, but also for the local seaweed gatherers from Agrisea NZ, operating in the area who demonstrate best practice by only hand harvesting one target species, Eklonia radiata, and leaving at least 20 percent of that species on the beach.

Humble as it may be, and for some apparently a minor nuisance, the presence of the body of drift weed that at times cloaks our foreshore is a good example of the often complex nature of the ecology of the coastal area, and its importance to the overall well being of our communities.

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