Published: 16 July 2012

More reserves, less seaweed for coral reef health

New research based on DNA-fingerprinting provides conclusive evidence that no-take protected areas can help restock exploited fish populations on neighbouring reefs. The findings were revealed at the recent’s International Coral Reef Symposium in Cairns.

More proof has emerged that even small areas of coral reef reserves can protect fish stocks.

Credit: Geroge Roff/CoECRS

The research is expected to help resolve a long-running debate worldwide about whether areas closed to all forms of fishing help replenish fish numbers outside marine protected areas (MPAs).

‘Using DNA fingerprinting technology, we now can clearly show that the benefits of MPAs spread beyond reserve boundaries, providing a “baby bonus” to fisheries,’ said Dr Geoff Jones, from the ARC Centre of Excellence for Coral Reef Studies (CoECRS) and James Cook University, who was behind the study, published in Current Biology.

Research was carried out in the Keppel Island group on Australia’s Great Barrier Reef by scientists from the ARC Centre of Excellence for Coral Reef Studies (CoECRS), in conjunction with other leading research institutions.

‘The implications for local fishing communities around the world are huge,’ said Dr Leanne Fernandes from Earth to Ocean, Australia. ‘Fishermen need to know for sure it will work.’

Dr Fernandes said that finding that MPAs can be effective on small scales has implications worldwide. For many communities, particularly in the developing world that depend on small areas of reef for food and income, there are limited options for closing areas to fishing.

‘The MPAs weren’t tens of kilometres across. Some were about two kilometres cross or even 800 metres across, and still worked,’ she said.

‘This is great news for local fishing communities around the world because protecting areas about this size might be possible for them; protecting really big areas is just too hard.’

Using DNA samples, the team of scientists tracked dispersal pathways of juvenile coral trout and stripey snappers larvae from MPAs in the Keppel island group. They found that six marine reserves, which cover only 28 per cent of the total reef area of the Keppels, generated 50 per cent of the total juvenile fish, both inside and outside of the reserves.

In other research announced at the conference, Dr George Roff and Professor Peter Mumby from CoECRS and the University of Queensland found that coral reefs in the Indo-Pacific region, including the Great Barrier Reef, recover faster from major stresses than their Caribbean counterparts.

‘The main reason that Indo-Pacific reefs are more resilient is they have less seaweed than the Caribbean Sea,’ Dr Roff says.

‘Seaweed and corals are age-old competitors in the battle for space. When seaweed growth rates are lower, such as the Indo-Pacific region, the reefs recover faster from setbacks. This provides coral with a competitive advantage over seaweed, and our study suggests that these reefs would have to be heavily degraded for seaweeds to take over.

‘This doesn’t mean that we can be complacent – reefs around the world are still heavily threatened by climate change and human activities,’ he says. ‘What it indicates is Indo-Pacific reefs will respond better to protection, and steps we take to keep them healthy have a better chance of succeeding.’

The study, published in Trends in Ecology and Evolution includes survey data from the Indo-Pacific region and Caribbean reefs from 1965 to 2010.

The researchers also found that seaweeds in Indo-Pacific region bloom four times more slowly than those in the Caribbean.

‘We’re not sure why this happens, but a plausible theory is that Caribbean waters are highly enriched in iron,’ they say. ‘For thousands of years, the Caribbean Sea has received dusts that blow across the Atlantic from the Sahara, and the dust contains iron – an essential element for algae to grow.

‘Another factor that protects these reefs is the abundance of herbivorous fish, such as surgeon and parrotfish that treat seaweed as a delicacy. The Indo-Pacific region has a lot of these fishes.

Source: CoECRS

Published: 25 November 2014

Things warm up as the East Australian Current heads south

Jaci Brown

Occasional erratic bursts southward of the East Australian Current (EAC) are thought to have moderated the weather of south-east Australia this autumn and winter and they continue to introduce tropical and sub-tropical marine species to Tasmanian waters.

Tasmania’s east coast: tropical and sub-tropical marine species normally found off NSW are finding their way further south, thanks to changes in the East Australian Current.

Credit: spelio/flickr under CC BY-NC-SA 2.0

Ocean monitoring by Australia’s Integrated Marine Observing System is providing scientists with significant new insights into the changing structure of the EAC. Over the past 50 years sporadic warm bursts have become more common as the EAC moves further south. With global warming, the warm burst we’ve seen this year may also become the norm.

Had our little friend Nemo the clownfish been riding the EAC this year he might have found himself holidaying in Tasmania rather than admiring the Sydney Opera House. He wouldn’t have been on the trip alone, though. Sea nettles (Chrysaora spp.) have headed from their usual home in Sydney to be found for the first time ever in Tasmania and the Gippsland Lakes.

<i>Chrysaora woodbridge</i>, or sea nettle, was found in surprising numbers in Tasmania this year.

Chrysaora woodbridge, or sea nettle, was found in surprising numbers in Tasmania this year.

Credit: copyright Lisa-ann Gershwin

Waters in the EAC travel southward along the east coast of Australia, with most of it splitting from the coast near Sydney and heading for New Zealand. A small part of the current, known as the EAC Extension, works its way southward past Victoria and Tasmania.

A typical signature in this region are the large eddies, around 200 kilometres across and hundreds of metres deep. Some of the warm water is trapped here along with marine life.

The EAC starts at the Great Barrier Reef and travels south to Sydney before turning eastward to New Zealand. Some of the water can still push southward via a series of strong eddies.

Credit: Eric Oliver

This year a larger proportion of the EAC was sent southward instead of breaking away to the east. Winter ocean temperatures off Bass Strait were around 19°C, an increase of 4°C. This impacted local fishing, beach conditions and the weather.

In the video (above) the animation on the left shows the actual sea surface temperature and speed of the ocean currents. The animation on the right shows the difference in the temperature from average conditions.

Through autumn and winter, you can see two interesting changes occur. A strong warm current heads down the coast from Sydney to the coast of Victoria. At the same time, warm water peels off from the EAC and swirls around in large eddies as it meanders toward Tasmania.

An unusual catch down south

One advantage of warm eddies is the refuge they provide for tuna. They congregate in the centre of the eddy where the waters are warm and dine at the nutrient-rich edges.

Local fishers in north-east Tasmania report a remarkable year that allowed them to fish longer than usual, providing game fishers with more opportunities to catch tuna.

Last summer’s (2013–2014) warmth provided an abundance of skipjack and striped marlin, while winter brought a run of bluefin tuna.

Redmap is a website where locals can report sightings of marine species that are unusual for a given area.

Last summer a manta ray, a tropical cartilaginous fish (in a group including rays and skates), was sighted off the north-eastern coast of Tasmania. Previously the southern-most sighting of a manta ray was just south of Sydney.

<i>Manta birostris</i> spotted off north-east Tasmania on Australia Day 2014.

Manta birostris spotted off north-east Tasmania on Australia Day 2014.

Credit: Redmap/Leo Miller

It’s not just new species visiting Tassie either. Local jellyfish such as the Lion’s Mane (Cyanea) – more commonly known as ‘snotty’ – are usually quite elusive, but turned up in unprecedented numbers last summer in Tasmania.

But there’s a catch

This movement south of the EAC may have an impact on other systems, including our health. We rely on fish such as those from the Tasman Sea as a source of omega-3 fatty acids for our brain health. But the concentration of omega-3 fatty acids in the fish is likely to decrease with global warming.

Algae are the original source of fatty acids. As our waters warm, we will see more of the algae from the tropics take up residence in the south-east.

But the algae from the tropics are much smaller, which means more steps in the food chain from the algae to the fish we eat. The more steps in the food chain, the more the omega-3 fatty acids in the fish are replaced by fatty acids that are less favourable to brain health.

The warmer coastal waters also contributed to the balmy autumn and winter in south-eastern Australia this year. Afternoon sea breezes cool coastal temperatures by drawing cool oceanic air onto the coast.

Sydney’s heat wave in May this year had 19 consecutive days of 22°C or more – this is partly due to the sea breezes failing to bring in the usual cooling air.

What’s causing the EAC to move south?

Over the past 50 years the EAC Extension has stretched about 350 km further south. This extension doesn’t happen smoothly but in erratic bursts.

The southward extent of the EAC is controlled by the collective behaviour of the winds between Australia and South America. Over that same 50-year period these winds changed their pattern due to a strengthening of a climate system known as the Southern Annular Mode.

The changes to this mode have been attributed to a combination of ozone depletion and increasing atmospheric CO₂.

One of the most robust and consistent responses of the climate system to increasing CO₂ is a further strengthening of the Southern Annular Mode.

So the result will likely be a further enhancement of the EAC extension southward and even warmer waters in the Tasman Sea.

Dr Jaci Brown is a senior research scientist with the Centre for Australian Weather and Climate Research (CAWCR), a partnership between CSIRO and the Bureau of Meteorology. Her research focuses on the El Nino Southern Oscillation (ENSO) and climate change. This article was originally published on The Conversation. Read the original article.

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