<
https://theconversation.com/sediment-runoff-from-the-land-is-killing-nzs-seas-its-time-to-take-action-221966>
"The fishers at Separation Point, between Golden Bay and Tasman Bay in New
Zealand’s northwest South Island, used to be cautious. Something they called
“hard coral” would tear their nets. If you dived down about 30 metres, you
could see why: extensive reefs.
These reefs were constructed by bryozoans, tiny polyp-like creatures that
cooperate to build large, branching colonies. They are similar to corals but
live in deeper and cooler water.
The reefs at Separation Point were gorgeous and biodiverse. They provided
shelter for small animals such as oysters and young fish. In 1980, the world’s
first bryozoan-based fishing exclusion area was created to protect them: 146
square kilometres of seafloor was closed to most fishing, from the coastline to
a depth of about 50 metres.
It went well at first. A 1983 study from the National Institute of Water and
Atmospheric Research (NIWA) of just one reef found 37 species of bryozoans and
another 39 invertebrate species, plus numerous fish. In 2008, a study comparing
fished and unfished areas off Separation Point found more biodiversity where
fishing had been limited.
Alas, subsequent developments have not been so kind. Land clearance for
agriculture and forestry since human occupation has resulted in a ten-fold
increase in sediment runoff in the area.
Thick beds of mud and silt have built up, destroying and burying the reefs. A
survey of the same area in 2021 found flat mud deposits, with the occasional
small, dead bryozoan sticking up. No fish remained in this marine ghost town."
Cheers,
*** Xanni ***
--
mailto:xanni@xanadu.net Andrew Pam
http://xanadu.com.au/ Chief Scientist, Xanadu
https://glasswings.com.au/ Partner, Glass Wings
https://sericyb.com.au/ Manager, Serious Cybernetics
