As our use of the world’s oceans increases, so too does our need to assess and monitor our impacts accurately.

It’s a challenge we face globally, not least of all, here in Australia. As part of an initiative by the Victorian Department of Environment, Land, Water and Planning (DELWP), the team at Fathom Pacific Pty Ltd has been carrying out studies in Port Phillip Bay, in southern Victoria.

Port Phillip Bay is home to a host of marine life, from the iconic seadragon (Victoria’s marine State emblem) to brightly coloured nudibranch molluscs and fishes. It’s also one of the most diverse places on the planet for seaweeds and reef systems that support a diverse array of sponges and other invertebrates. Port Phillip Bay is also shadowed by the city of Melbourne which has a growing population of nearly 5 million people.

To protect the Bay, DELWP is implementing the Port Phillip Bay Environmental Management Plan 2017-2027 (EMP). That’s where we come in, providing models and maps and monitoring the bay’s marine biotopes – i.e. areas of the bay that provide habitats for specific species – to support decisions about how to manage the bay.

Firsthand ecological research and environmental monitoring are key building blocks of these models and maps, so the data we gather has to be quantitative and accurately geo-referenced. But we have to gather it in increasingly cost-efficient ways. That means we need easily available and affordable monitoring systems that we can deploy from small craft and track their whereabouts with a reasonable level of confidence. What’s more, the tech we work with has to be able to work in Port Phillip Bay’s challenging conditions, which has a large embayment exposed to strong winds and periods of low underwater visibility.

BlueROV2 + Micro-Ranger 2

The setup we’ve gone for is a BlueROV2 remotely operated vehicle (ROV) from Blue Robotics and a Micro-Ranger 2 USBL from Sonardyne. The HD camera onboard the ROV captures incredible detail whilst the USBL tell us where it was when we recorded it. If we have divers and other assets in the water, it can track them as well.

We’ve found Micro-Ranger 2 to be extremely portable and easy to mobilise; it’s the ideal solution for our small-boat coastal operations.  

The MRT – the part of the system that communicates with transponders fitted to underwater targets – is so small and light, we’ve been able to mount it to the bottom of our stern diver ladder. For something the size of a small flower pot, we’ve been really impressed with its range and coverage.

The Nano transponders are also perfect for our work. They are strapped to the frame of our ROV or diver’s tank without affecting balance or freedom of movement. They’re rechargeable and last for a full day of operations.

First time out, the whole system was simple to install and calibrate, helped by the instructional videos on YouTube.  Once the software was set up and tested on our laptop, we put it straight to work supporting surveys throughout our last winter and spring, often mobilising it at very short notice due to the unpredictable weather windows we had.

Accurate results

The results from Micro-Ranger 2 have been impressive. The system has accurately and consistently tracked our ROV in the bay’s shallow waters, even when it has been transecting some 50-100 m from the [MRT] transceiver. This is important for our assessment of the bay’s biotopes during which we image the key structural and functional components of temperate reef and sediment biotopes using the ROV.

We fly ROV transects in two modes. The first is a ‘video inspection mode’, detailing the canopy, sub-canopy, lower strata and turfing components and identifying the associated macrofaunal biodiversity. The second is a ‘still image mosaicking mode’, where fixed-altitude planar stills are taken to create biotope mosaics.

Using Micro-Ranger 2, we were also able to place our analyses of reef biodiversity and biotopes into a spatial context by corelating our imagery data with real world coordinates. This means we can now provide ground-truth data for biotope modelling, while also establishing biotope condition and informing ecosystem models. And we can go back to exactly the same locations for future surveys.

Quite simply, our investment in Sonardyne’s USBL technology is paying enormous dividends. We’re better able to monitor – and therefore react to – issues like the spread of marine pests, loss of canopy-forming algae to urchin grazing, biodiversity loss, eutrophication, litter and impacts from marine industries, which are just some of the threats facing our marine systems. 

The work continues

DELWP’s program involves the selection of suitable indicators and methods for monitoring. As we move forward, an important consideration for future monitoring will be the selection of robust indicators at multiple levels of the ecosystem and the application of methods that are repeatable, auditable and affordable.

This, along with increasing appropriately-gauged citizen science contributions to monitoring programs, will require linking imaging systems and other science sensors with affordable and adaptable subsea positioning systems.

Micro-Ranger 2 provides this capability. In fact, we’re using the system again shortly to survey unique bryozoan reefs in Western Port, also in Victoria. There, georeferenced image mosaics will be used to monitor the extent and condition of these delicate reefs.  The system will also be used to ground-truth remote sensing products including multibeam bathymetry.

With Micro-Ranger 2, we have an important addition to our operational versatility and responsiveness.  We can now deploy to the field with minimal fuss, achieve excellent positioning and deliver high quality outcomes.

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