Seaweeds play a crucial role in the marine environment. Their increasing threats from humans could have catastrophic effects to the wider marine ecosystem.
Seaweeds represent a very large and diverse group of marine organisms. There are over 35,000 different species of red, brown, and seaweeds located in higher intertidal to deeper subtidal zone and in estuarine to true marine environments. New Zealand is home to over 850 species of which one - third are endemic and unique to Aotearoa.
Seaweeds have many important roles in the marine environment. As primary producers they contain photosynthetic pigments which harness light energy from sunlight to convert carbon dioxide (C02) and water into living biomass and oxygen. They are important for the sequestration of nutrients and for providing a food source, habitat, and refuge to other marine species. Detached seaweed that washes up on coastlines (beach-cast) following storm events then continues to host important ecological functions in sand dune formation and terrestrial food webs.
SANZ has worked hard for many years to educate groups and individuals on the risk of an unsustainably managed seaweed industry. At present the majority of seaweed in New Zealand cannot be harvested from the wild in an attached state. There is however increasing threat that this will change after seven species were earmarked for inclusion into the Quota Management System (QMS) in 2005. SANZ argue there is not enough ecological understanding on seaweed to implement a volume - based management framework such as the QMS. We advocate an advocate area-based management with researched and site specific harvest plans is the only way to ensure an ecologically sound and economically viable industry.
New Zealand represents 0.2% of the worlds landmass and yet produces 1% of sediment entering the marine environment. Increased water turbidity from sedimentation reduces the amount of available light for photosynthetic organisms and increases disturbance to benthic marine habitats. For many New Zealand seaweeds this increases the risk of reduced depth-distribution, decreased recruitment rates, and increased mortality from sedimentation.
New Zealand harbours a rich marine biodiversity in temperatures ranging 8 to 23°C. Predicated increases in sea surface temperatures over the next century will impact both upper and lower distribution limits for many seaweeds. Recent examples from Western Australia have demonstrated climate change can have severe impacts on seaweed ecosystems. This occurred when a heatwave which caused sea temperatures 2 - 4°C higher than normal resulted in decimation of the native brown seaweed Scytothalia dorycarpa at its northernmost limit. Cases like this remain unreported in New Zealand, however there is anecdotal evidence to suggest warmer than average temperatures along the Northeastern coastline has resulted in canopy disturbance (dieback) of the brown kelp Ecklonia radiata.
Approximately 23 of the 850 seaweeds inhabiting New Zealand’s marine waters have been introduced. Of these the invasive brown laminarian kelp Undaria pinnatifida poses the biggest threat. Undaria was first discovered in New Zealand at Wellington Harbour in 1987 and was likely to have arrived in the ballast water of a ship from Japan or Australia. It has broad environmental tolerances, can widely colonise, be easily spread and transported, and grow rapidly (1 cm per day). Dense stands of Undaria can alter the structure of native New Zealand seaweed communities by reducing the presence and diversity of smaller benthic species and out-compet slower growing canopy forming species. It can also shift of the natural macrofaunal assemblage through an increased abundance of grazers (gastropods, urchins, crabs, fish).
Undaria is now widespread throughout New Zealand. A recent compliance patrol carried out in Fiordland in April 2017 identified six mature individuals on a mooring line, resulting an extensive programme to eradicate it from the previously pest - free area.