The silencing of the seas: how our oceans are going quiet

Ivan Nagelkerken, University of Adelaide; Sean Connell, University of Adelaide, and Tullio Rossi, University of Adelaide

Despite appearances, the oceans are far from silent places. If you dunk your head underwater you’ll hear a cacophony of sounds from wildlife great and small, crashing waves, and even rain. And it’s louder still for creatures attuned to these sounds.

However, humans are changing these ocean soundscapes. Our recent research showed that changes caused by people, from ocean acidification to pollution, are silencing the seas’ natural noises. (We’re also filling the oceans with human noise).

This is bad news for the species that depend on these noises to find their way.

Ocean soundscapes

All over the world you can hear a lively crackling sound made by thousands of snapping shrimp that live along coastlines.

These common shrimp, often referred to as pistol shrimp, have a large claw that they can close with such force that a cavitation bubble is formed. As this bubble implodes on itself a loud snap is created – like a pistol shot – which can be heard over long distances.

In fact, snapping shrimp are the loudest marine invertebrates, and second only to the noisest marine animals, which are sperm whales! Snapping shrimp are found all over the world, including in coral reefs, kelp forests, seagrass beds and mangroves.

Other types of animals create ocean noise too. Urchins and parrotfish make clearly audible chomping sounds as they scrape algae off rocks. Many fish are frequent and loud talkers and make an array of sounds such as chirps, burps, whistles, knocks and so on. They use these to mark out their territory, during fights and to locate mates.

These biological sounds, together with those from rain, crashing waves and seismic activities, form the so-called underwater soundscape.

Learn more about marine soundscapes watching this video.

Sounds that are emitted from temperate and tropical reefs are loud and quite constant. As such these sounds form a reliable source of information for animals, particularly for navigation.

Most animals in the sea let go of their fertilised eggs without providing any parental care. As these eggs hatch, small babies (larvae) are dispersed by ocean currents. Growing up away from coastal areas provides a safer place with fewer predators.

However, after growing for a few weeks or months in the open ocean, it is time for these young animals to return to the coast to find a home. How do they find their way in the vast and uniform open ocean? Sounds and odours from coastal habitats are key cues that allow marine animals to find their new homes and replenish adult populations.

Going quiet

Humans are increasingly dominating the physical and chemical environment. We are altering the carbon cycle through the burning of fossil fuels and the nitrogen cycle by extracting vast amounts of nitrogen for food production and releasing it as waste. Large amounts of this carbon and nitrogen liberation end up in the ocean.

About one-third of the carbon dioxide that humans emit into the atmosphere dissolves in the ocean, leading to increased seawater acidity (or ocean acidification). This is an obvious problem for animals that produce a calcium carbonate shell or skeleton (such as corals, some plankton, and snails). Remarkably, ocean acidification also alters the behaviour of many animals by messing up their brain functioning.

Earlier studies (see also here) have shown that ocean acidification can change the response of fish larvae to settlement habitat sounds by deterring them rather than attracting them.

Learn more about the effects of ocean acidification on fish behaviour watching this animation video.

Two of our recent studies (see also here) showed that ocean acidification not only affects sound reception, but also the sounds that ocean ecosystems produce. If we don’t reduce greenhouse gas emissions, rocky reefs could be much quieter in 2100 than now. And snapping shrimps are the reason.

Coastal discharge of nutrients from sewage plants and catchment runoff also degrades kelp forests and seagrass beds. These coasts are more silent than their healthy counterparts.

In many parts of the world, kelp forests, seagrass beds and coral reefs have been replaced by carpets of turf-forming or mat-forming algae. These weedy types of algae have much lower diversity of species and provide less shelter and feeding opportunities for shrimps and other noisy animals.

Degraded habitat means fewer animals, which means less noise. For larvae that use sound as a navigational cue, this means that fewer larvae will be able to successfully locate their home. And fewer returning larvae means less replenishment of fish stocks.

The effects of ocean acidification on fish orientation and soundscapes.
Dr Tullio Rossi

Options for restoration

Climate change and ocean acidification act at global scales and are difficult to stop in the short term. In contrast, nutrient pollution is a local stressor, which makes it more manageable.

Various options exist for local communities to reduce nutrient pollution of coastal areas. These include improved sewage treatment, restoration of coastal vegetation (such as mangroves) and swamps that extract sediment and nutrients from stormwater runoff, and decreasing the use of rivers as outlets for polluted waters.

Reducing the impacts of nutrient pollution on coastal ecosystems makes these systems more robust and provides them with increased resilience to cope with the impacts of ocean warming and acidification.

The Conversation

Ivan Nagelkerken, Associate Professor, Marine Biology, University of Adelaide; Sean Connell, Professor, University of Adelaide, and Tullio Rossi, PhD student, University of Adelaide

This article was originally published on The Conversation. Read the original article.


Disruption over Macquarie Island calls for some clever Antarctic thinking

Indi Hodgson-Johnston, University of Tasmania

The fate of the Australian Antarctic Division’s research base on Macquarie Island hangs in the balance, after last week’s surprise announcement that it would close in March 2017 was followed on Friday by a suggestion that the government could yet reprieve it.

Why all the fuss over a scattering of buildings on a windswept island (admittedly a UNESCO World Heritage-listed one) perched on a tectonic ridge halfway between Australia and Antarctica?

Macquarie Island is the perfect natural laboratory for scientific research. Unique climate, geological, biological and astronomical measurements are collected year-round. The data is fed into many large-scale, international science programs and reports, including those published by the Intergovernmental Panel on Climate Change.

It is something of an anomaly in Australia’s national Antarctic program. Unlike Heard Island, Macquarie Island lies outside the areas covered by the Antarctic Treaty and the Convention on the Conservation of Antarctic Marine Living Resources. The Tasmanian government manages the island.

The buildings at the island’s north end are home to research infrastructure and accommodation for various organisations. These include the Tasmanian Parks and Wildlife Service, the Bureau of Meteorology, and the Australian Radiation Protection and Nuclear Safety Agency, which monitors the Southern Ocean for evidence of nuclear events. These buildings are increasingly exposed to ocean inundation.

Death by a thousand cuts

Collaborations of this nature are common in Antarctic science. Budgetary decisions made in one section of the community have a direct impact on the programs of others.

This sudden closure announcement followed the harrowing CSIRO job cuts announcement earlier this year. Tasmanian Premier Will Hodgman, the Tasmanian and Antarctic science community and the Australian Greens understandably responded with dismay to last Tuesday’s announcement.

While funding to Australia’s Antarctic science program seemed assured with the long-awaited Australian Antarctic Strategy and 20-Year Action Plan this year, there is a reasonable correlation between previous successive cuts to the Antarctic program and the disrepair of Australian Antarctic infrastructure. Labor Senator Lisa Singh called this a “death of a thousand cuts”.

Competing interests

Given the huge scale of Australia’s interests in Antarctica and the Southern Ocean, there will always be competing budget priorities.

Environmental contamination from long-term human habitation, for example, is an issue common to Australia’s research infrastructure throughout the Antarctic region.

Any research in the Antarctic and sub-Antarctic must be done in a way that minimises the direct impact on the surrounding environment. Australian Antarctic Division director Nick Gales has cited the footprint of this research as one reason for withdrawal from Macquarie Island.

Environmentally sensitive replacements suited to such harsh and remote conditions are expensive. The ongoing remediation work on many old Antarctic and sub-Antarctic bases continues to cause further budgetary and logistical headaches.

Macquarie Island, Heard Island and Australia’s Antarctic Territory are notoriously difficult to access, particularly for long-term, logistically demanding tasks such as major remediation and refurbishment works. Access involves battling the increasingly unpredictable sea ice and ice airstrip conditions that already disrupt delicate resupply, search and rescue, and medical evacuation operations.

Given its position deep in the Southern Ocean, there remains a strong case for a small but permanent presence on Macquarie Island. For example, resident climate scientists have collected weekly ozone measurements for 20 years. There is a place for other Commonwealth departments, the Tasmanian government, private industry and research institutions to shoulder responsibility for maintaining this presence.

A silver lining for Tasmania?

Given successive budget cuts, precariously short-term funding of Antarctic research programs, the potential domino effect of budget cuts between collaborators and the doubt created within the community by the CSIRO climate job cuts saga, Tasmania needs to continue to build its capacity to ride out the vagaries of the federal political issues that have left it reeling over the past year.

Regardless of the current station’s fate, this could be seen as an opportunity for Tasmania’s Antarctic, climate and oceans science community to collaborate and innovate with various industries to ensure that crucial climate research and observations can continue.

By leveraging from existing programs such as the Antarctic Gateway Partnership, and with world-class scientific expertise, Tasmania is perfectly poised to innovate and invest in the areas of remote and autonomous scientific instruments, technology and data handling.

Private enterprise, including smaller non-icebreaking vessels that already operate as research and tourism platforms in the sub-Antarctic, also has a chance to fill the logistical gap.

The closure of the Macquarie Island station after almost 70 years would be sad and shocking for the generations of scientists who fondly visited “Macca”.

The continuation of a presence on the island, however, is largely a Tasmanian government responsibility. With innovation and collaboration, Tasmania can lead the way in a new, stable and less environmentally damaging era of science on Macquarie Island.

The Conversation

Indi Hodgson-Johnston, Antarctic Law and Policy Researcher, Polar Research and Policy Initiative, University of Tasmania

This article was originally published on The Conversation. Read the original article.