Some seaweeds recover
Knowledge of New Zealand’s almost 1000 seaweed species is desperately thin, a major new report has found. But encouraging news from the Kaiko¯ ura region, where seaweeds were badly affected by the 2016 earthquake, shows some appear to be recovering.
The new report assessed 938 macroalgae, 874 of them for the first time.
A whopping 609 are considered ‘‘data deficient’’, which means they are ‘‘very poorly understood’’.
‘‘The data deficient list may include some of the most threatened species in New Zealand,’’ wrote the authors, who included some of the county’s most eminent seaweed scientists, led by Dr Wendy Nelson of the University of Auckland and Niwa.
The report, produced for the Department of Conservation and called Conservation Status of New Zealand Macroalgae, 2019 assessed the conservation status of almost all macroalgae in the country.
But this effort was ‘‘strongly constrained by the state of knowledge’’, the ‘‘extent of collections available’’, and the ‘‘limited funding for systematic research,’’ the authors wrote.
Of the 609 data deficient seaweeds, for example, 11 are known from one location.
About 45 per cent are known from fewer than six specimens, Nelson said in an interview.
Six are listed as nationally critical, one as nationally endangered, five are in decline, and 166 are not threatened.
None are listed as extinct because the evidence for such a definitive conclusion is not available, she said.
But the authors have grave concerns for two incredibly rare species.
Prasionema heeschiae has been collected once from subantarctic Campbell Island. It was found on a wooden wharf that has since been demolished.
Another, Dione arcuata, was collected on two occasions from sites about five kilometres apart on the Kaiko¯ ura coast.
One of the sites was completely buried in the 2016 earthquake and the other was affected by uplift.
The species, also known as eyelash seaweed for its shape and length, has not been found since.
Meanwhile, some seaweeds might be recovering from the destructive consequences of the earthquake.
Otago University zoologist Jon Waters found Neptune’s necklace (Hormosira) was recolonising uplifted coast at Ward Beach, 78km north of Kaiko¯ ura.
Ceridwen Fraser and colleagues have been tracking kelp since days after the November 2016 disaster and they were on the shoreline again in September.
‘‘Slowly, slowly, with many false starts, bull kelp is colonising the new intertidal at Waipapa Bay where the 2016 earthquake uplifted the rocks by about 6m,’’ she tweeted.
Bull kelps have been arriving from the subantarctic islands, Fiordland and elsewhere, she said in an interview.
If they happen to arrive in the winter breeding season, they can release millions of gametes and some will grow into adults.
But she has colloquially observed that uplifted boulders once covered in a coralline algae seem to be breaking down.
Coralline acted like cement on shore rocks and provided strength. But the coralline has gone and what seemed like ‘‘strong rocks a year or two ago are now soft and silty’’, she wrote.
Some kelps – but not many – are surviving on the eroding rock, she said.
Wendy Nelson, the report first author, was worried that marine heatwaves of recent years were hurting bull kelps.
The species are treasured by Kiwis and taonga for Ma¯ ori, but the status of two has been downgraded from ‘‘not threatened’’ to ‘‘at risk – declining’’. Two other bull kelps are listed as ‘‘at risk – naturally uncommon’’.
At least another 150 seaweeds are known but their data was not peer reviewed in time for the report.