Cleaning up our wastewater with freshwater algae

Photo by Juan Manuel Valero Rodriguez

Wastewater from treated sewage and urban and industrial run-off has a significant environmental impact on the biological integrity of our coastal marine ecosystems. The best way to manage wastewater is before it enters marine ecosystems, by reducing both contaminant and nutrient inputs. Algal bioremediation can significantly improve the quality of wastewater by removing nutrients. However, before algal bioremediation can be applied to Melbourne’s wastewater, it’s important to identifying suitable algae based on their biomass productivity and ability to outcompete less desirable algae. As part of his PhD, Juan Manuel Valero Rodriguez compared the productivity and competitive ability of three taxa of filamentous macroalgae (Oedogonium, Stigeoclonium and Hyalotheca) under the seasonal light and temperature conditions experienced in temperate environments, including extreme heat and cold. He found that different taxa thrived under different seasonal and competitive conditions and suggests that rather than finding an optimal taxon for all four seasons, in order to maximise stable biomass production, we should either have a seasonal rotation of algae, or bi-cultures of the most dominant ones.

To read the article, click here.

Zapping lice eggs to reduce infestation pressure

Photo by Luke Barrett

In all farming systems, both researchers and farmers are always trying to find new ways to control and manage pest populations. Sea lice infestations in Atlantic salmon farms are a huge issue, causing considerable welfare problems to farmed and wild salmon. Therefore, interest in developing new methods that prevent lice infestations from occurring in the first place is gaining momentum within the industry. Researchers from the University of Melbourne and Institute of Marine Research tested if ultraviolet C light (UVC) could be used as a new preventative method that sterilises lice eggstrings in the water column. They exposed lice eggstrings to a range of UVC intensities and durations and found that cumulative doses were the most important variable in eggstring mortality. Future research will need to determine if applying UVC doses within a farm-setting is feasible, while being fish welfare and environmentally friendly.

To read the full article, click here. 

Wakame in Port Phillip Bay is not all bad

Photo by Luke Barrett

Introduced species always seem to get a bad rap – they can outcompete native species, or allow other introduced species to prosper, which can ultimately reduce native biodiversity. In coastal environments around the world, native seaweed populations have declined, with a range of non-native species taking over. With urchin barrens growing throughout Port Phillip Bay, there is less available habitat for native fishes. Dr Luke Barrett tested if fish utilised habitats formed by wakame, an introduced seaweed, as much as habitats containing local seaweeds. He found that native fishes did not distinguish between native and wakame habitats, and that fishes had similar fitness metrics in both habitat types. Compared to natural reefs that had been urchin-grazed, wakame canopies resulted in higher fish abundance and biodiversity. Therefore, despite being considered a pest species, wakame canopies can provide important habitats for endemic fish and may play a role in sustaining native fauna populations in this degraded ecosystem.

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Jumping through oil to remove lice – does it work?

Chemical use in controlling parasites in salmon aquaculture can have a variety of negative impacts, including poor fish welfare and the release of chemicals into the environment after treatment, which can affect ecosystems and the sea life living in them. With this in mind, researchers from the University of Melbourne and Institute of Marine Research teamed up to test if a floating oil layer containing a dissolved chemical could be combined with an innate salmon behaviour to remove lice. They found that the presence of an oil layer did not deter salmon from jumping through it. Also, they found that as the concentration of the chemical dissolved in the oil layer increased, lice removal also increased. This alternative chemical treatment administration method would require minimal fish handling and also allow for simple recollection after treatment, and is therefore more environmentally friendly. It’s a win-win for everyone!


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What’s the best method to collect sea urchins for aquaculture?


A diver surfacing with a bag full of urchins. Photo by Fletcher Warren-Myers.

There are millions of purple sea urchins (Heliocidaris erythrogramma) in Port Phillip Bay chomping their way through kelp forests, which are important habitats for many creatures and critters that live within the bay. In their wake, urchins leave unsightly and biologically unproductive barrens, therefore causing reduced local biodiversity. Barrens can be flipped back into kelp forests if urchins are either removed or destroyed – but both options are extremely expensive. Fortuitously, the gonads (or roe) of urchins are a Japanese delicacy, with high quality roe fetching up to $450 kg-1. However, the roe of urchins harvested from barrens are typically unappealing and inedible, and therefore fishermen tend harvest them elsewhere.

Sea urchin aquaculture is an emerging industry in Australia, with several universities working on cultivating a variety of urchin species across Australia. The SALTT lab previously identified that harvesting adult urchins directly from barrens and feeding them with quality feeds to produce marketable roe is a nifty solution that can reduce the number of urchins in barrens while simultaneously profiting from the increasing demand for roe.

However, in order to collect urchins from barrens to bring them to aquaculture facilities to fatten them up, it’s important to determine the best harvest method that does not affect their survival and external condition. Dr Fletcher Warren-Myers and researchers from the University of Melbourne and Deakin University tested if divers using a 3-pronged hook or careful hand-collection to harvest urchins affected their mortality and external condition both in the short- and long-term. Overall, they found that survival and condition was similar regardless of collection method. As divers using the hook method collected urchins twice as fast as by hand, this will become the method to harvest urchins in the future.

Click here to read the full article. 

Can ballan wrasse keep up with salmon?

Image by Geir Friestad via Flickr

Ballan wrasse are crafty fish that eat sea lice off swimming salmon. While we know they are useful cleaner fish, we don’t know much about how well they can swim in different currents and at different temperatures. If we did, we could establish better deployment strategies and predict when their welfare may be at risk. Jeffrey Yuen, an honours student from the University of Melbourne, tested the standard and maximum metabolic rate, aerobic scope, and critical swimming speed of ballan wrasse acclimated at 5, 10, 15, 20, and 25°C, to see how performance differed. The wrasse were generally inactive and had low metabolic rates at lower temperatures. They also did not swim continuously between 5 and 20°C. Only at 25°C did they swim continuously, with an average critical swimming speed of 27 cm s-1. This is a fraction of the critical swimming speed of salmon. The much weaker swimming capacity of ballan wrasse means they won’t cope well in salmon farms with moderate to strong current speeds. Further, their low metabolic rates and inactivity at 5-10°C suggests that they won’t do their lice eating job well at these temperatures, limiting them to warmer places and times. Jeffrey’s results can be used by farmers to make sure they are stocking ballan wrasse in the right times and places in order to make sure cleaner fish are doing their jobs.

To read the full article, click here.

How submerged cages affect salmon welfare and behaviour

Submerged cages are an exciting new method being tested by the salmon aquaculture industry to avoid salmon lice infestations within farms. However, salmon do not cope with long-term submergence as they need to refill their swim-bladders regularly to maintain buoyancy. Assoc. Prof. Tim Dempster together with researchers from the Institute of Marine Research, Norway tested how salmon coped in submerged cages that were lifted to the surface weekly to allow surface access. Three submerged cages were positioned at 10 m depth were deployed for 8 weeks, and measures of welfare and behaviour were compared against three standard cages. They found that submerged fish swam 1.4 to 3.4 times faster, schooled tighter, and their swim bladder volumes declined gradually from the beginning to the end of each week. When cages were lifted and the surface became available, negatively buoyant fish immediately exhibited jumping and rolling behaviour. However, they found no evidence of acute buoyancy problems during submergence, and growth rates and welfare scores were similar to standard cages. Their research suggests farming salmon in submerged cages with weekly surface access is a viable method to prevent lice infestations.


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