Underwater video reveals culprits behind disappearance of NSW kelp forests

Underwater video reveals culprits behind disappearance of NSW kelp forests
A frenzy of rabbitfish feeding on kelp transplanted by a UNSW-led team of researchers off the coast of NSW in eastern Australia. Credit: Adriana Verges

Seaweed-eating fish are becoming increasingly voracious as the ocean warms due to climate change and are responsible for the recent destruction of kelp forests off the NSW north coast near Coffs Harbour, research shows.

The study includes an analysis of underwater video covering a 10 year period between 2002 and 2012 during which the water warmed by 0.6 degrees.

"Kelp forests provide vital habitat for hundreds of marine species, including , lobster and abalone" says study first author Dr Adriana Vergés of UNSW and the Sydney Institute of Marine Science.

"As a result of climate change, warm-water fish species are shifting their range and invading temperate areas. Our results show that over-grazing by these fish can have a profound impact, leading to kelp deforestation and barren reefs.

"This is the first study demonstrating that the effects of warming in kelp forests are two-fold: higher temperatures not only have a direct impact on seaweeds, they also have an indirect impact by increasing the appetite of fish consumers, which can devour these seaweeds to the point of completely denuding the ocean floor.

"Increases in the number of plant-eating fish because of warming poses a significant threat to kelp-dependent ecosystems both in Australia and around the globe," she says.

The study is published in the journal Proceedings of the National Academy of Sciences.

The team recorded around August-time each year at 12 sites along a 25 kilometre stretch of coast adjacent to the Solitary Island Marine Park off northern NSW.

During this period, kelp disappeared completely from all study sites where it was initially present. At the same time the proportion of tropical and sub-tropical seaweed-eating fish swimming in these areas more than tripled. Grazing also intensified, with the proportion of kelp with obvious feeding marks on it increasing by a factor of seven during the decade.

"We also carried out an experiment where we transplanted kelp onto the sea floor. We found that two warm-water species - rabbitfish and drummer fish - were the most voracious, eating fronds within hours at an average rate of 300 bites per hour" says Dr Vergés.

"The number of fish that consumed the smaller algae growing on rock surfaces also increased, and they cleared the algae faster when there was no kelp present. This suggests the fish may help prevent kelp regrowing as well, by removing the tiny new plants."

In Australia, kelp forests support a range of commercial fisheries, tourism ventures, and recreation activities worth more than $10 billion per year.

"The decline of kelp in temperate areas could have major economic and management impacts," says Dr Vergés.

The video footage used in the study from 2002 onwards was originally collected for a very different research project - to measure fish populations inside and outside sanctuary zones in a . But the team realised it could also be used to determine whether was present in the background or not.

This unplanned use of an historic dataset is a good example of the value of collecting long-term data in the field, especially if it includes video or photos for permanent records.


Explore further

A marine heatwave has wiped out a swathe of WA's undersea kelp forest

More information: Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1610725113
Citation: Underwater video reveals culprits behind disappearance of NSW kelp forests (2016, November 14) retrieved 19 June 2019 from https://phys.org/news/2016-11-underwater-video-reveals-culprits-nsw.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
232 shares

Feedback to editors

User comments

Nov 14, 2016
Ahh, Global Warming.... is there any eco 'disaster' it isn't responsible for?

Nov 14, 2016
Ahh, conservative thought...is there no collective problem that can't be ignored.

Nov 14, 2016
Ahh, the Pathological Lies of the AGW Cult and their Pathological "science". Billions squandered on lies err...excuse me "science" just to propagate their dogma and desire for doom and gloom.

Nov 14, 2016
Ahh, anti... cut and paste much?

Nov 14, 2016
Changes in kelp abundance showed no direct relationship to seawater temperatures over the decade and were also unrelated to other measured abiotic factors


So we have a biotic shift and increased pressure on the kelp. These herbivore fishes are opportunists and I suspect they move on to the next hot spot.
My issue is that in our ecological world, it is never just one factor that is causing change, there are many dynamic variables.

For instance, you could argue for a increase of herbivores and lack of predators due to human pressures on the fisheries. DOI: 10.1126/science.1059199
Or you could argue that it's a combination of all factors, even add in newer models that incorporate complex ecological, biophysical, and chemical changes. Interesting read:
DOI: 10.1007/s10021-016-9998-6


Nov 14, 2016
Or you could consider the effects of low oxygen closer to home. For some unknown reason the American public was sold a bill of goods in installing the new hi-eff furnaces that exhaust/intake thru the basement wall. Why the intake is adjacent the exhaust makes no sense to me. And it makes it difficult for the CO2 to diffuse thru the air locked close to the ground. If you complain about high co2 levels, you are sold on yet another scan, installing another cut in the house envelope for 'air.'
Sometimes I imagine we are being eliminated thru this CO to CO2. Low oxygen means less capability. In all areas.
You would think ,if any corporate interests were actually concerned about CO2 levels, they would throw money at the gasoline car engine with abandon. 10% efficiency is a disgrace but NO, what they are doing is 'creating new markets' by changing the existing use to make it different but not better. Welcome to capitalism.

Nov 14, 2016
>Why the intake is adjacent the exhaust makes no sense to me.

Because it is much cheaper to make one hole in a wall or roof than two: easier to make watertight, less labor cost, less trouble routing it in tight spaces.

> And it makes it difficult for the CO2 to diffuse thru the air locked close to the ground.

No worse than any other furnace. You can now do a direct-vent through the wall because the exhaust gasses from a modern, high efficiency gas furnace are much safer: not nearly as hot, no carbon monoxide.

> 10% efficiency is a disgrace but NO, what they are doing is ...

Modern automobiles are around 25% efficient, thermally.

>Low oxygen means less capability. In all areas.

So, you're saying that you support a low-carbon economy? Carbon dioxide is the primary means by which oxygen is depleted in cities.

Nov 14, 2016
>Why the intake is adjacent the exhaust makes no sense to me.

Because it is much cheaper to make one hole in a wall or roof than two: easier to make watertight, less labor cost, less trouble routing it in tight spaces.

Mine is 90%. Intake is ambient air around the furnace. Exhaust is a pvc pipe thru wall.
And why is this conversation part of the subject of the article, again?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more