Using Shading to Control Algal Bio-fouling on a Floating Oyster Farm

View the project final report

Commodities

• Animals: shellfish

Practices

• Animal Production: animal protection and health, aquaculture
• Crop Production: shade cloth
• Energy: energy conservation/efficiency
• Pest Management: physical control, prevention

Colonization of oyster farming equipment by algae and invertebrates (bio-fouling) reduces crop growth rates and can increase mortality. To address this problem many shellfish farmers have adopted floating cage designs that allow for periodic air drying as a fouling control. Though highly effective for controlling soft-bodied invertebrates (such as tunicates, worms, and larval forms of shellfish), it is much less useful for controlling macroalgae, which have evolved to tolerate periodic drying at low tides. The natural distribution of macroalgae are highly light dependent, with species tied to a specific depth and light-period. This project aims to use cage-shading a means to prevent algal colonization of oyster cages by introducing dark conditions unfavorable to algal growth. If successful, this technique would provide both labor and environmental benefits. Shading is a passive and prophylactic control, and does not rely on heavy manual labor or loud, fossil-fuel burning pressure washers- thus reducing the impact on the farmer, other users of shared-waters, and sensitive wildlife. Two varieties of shading (submerged and elevated shades) will be tested against an untreated control. Results will be shared through the farm website and social media, with detailed procedures and schematics shared to Farm Hack.

This project seeks to prevent macroalgal bio-fouling on floating oyster cages using two different shading techniques. The first technique uses solid-shades elevated just above the surface of the water. The second uses submerged mesh shades fastened to the sun-facing portions of oyster cages.

Success of these techniques will be gauged by:

1) Amount (area) of algal bio-fouling on shaded cages compared to an untreated control

2) Amount of other (invertebrate, etc) bio-fouling on sun-facing surfaces

3) Species composition of fouling organisms

4) Qualitative difficulty of handling cages in each treatment

5) Durability of each treatment in the field