Victoria University of Wellington marine biologist and research team leader Prof James Bell said the discovery of so many new species was "a huge surprise" and exceeded all expectations.
"We set out expecting we might find a few new species if we were lucky.
"We had no idea of how many different sponges the fiords hold.
"It seems crazy because we dive so much there, but we have just been swimming past all these beautiful, undescribed sponges."
He said sponges played a vital role in the marine environment, recycling nutrients and forming habitats for fish and other species.
Prof Bell said the sponges were collected during a research trip in April to investigate the distribution of these animals in Fiordland, and how it differed between the inner and outer parts of the fiords.
Earth Sciences New Zealand sponge taxonomist specialist Dr Michelle Kelly confirmed the 41 sponge species collected were "undescribed" and had yet to be named.
They added to about 1700 sponge species that were already known to live in New Zealand waters.
Dr Kelly said finding new and undescribed species was "very exciting, although not unexpected given the sheer abundance of sponges on the vertical walls of the fiords and the lack of previous formal research on Fiordland sponges".
She said identification of sponges started by creating "spicule preparations", where sponge tissues are dissolved to reveal the calcium carbonate and silica spicules — tiny parts of the sponge skeleton.
These spicules were used along with other characteristics — including shape, colour, texture, mucus production and even smell — to classify different species.
Victoria University of Wellington postdoctoral research fellow Dr Francesca Strano said identifying and describing the new species was crucial for effectively managing and conserving Fiordland’s marine ecosystems and tracking changes in the environment.
"Species identification takes a lot of time, but is really important for managing our oceans, particularly when there is still so much biodiversity we have yet to discover, often just under our noses."
The study is one of the projects of the Southern Fiordland Initiative, a research collaboration aiming to find out more about the marine environment in the fiords and how it is changing.
