Disrupting tropical seaweed farming with offshore submersible cages

Former CEO of Catalina Sea Ranch Phil Cruver is developing a submersible cage system to take tropical seaweed farming offshore and into a new era. In addition to providing higher yields, the cages should also protect from predators, storms and ice-ice disease.

Submersible cage concept study – image courtesy of KZO Sea Farms

In 2010, KZO Sea Farms developed a submersible cage for fish farming, together with collaborators at the University of New Hampshire and ISCO Industries. Later, the company secured the first permit for offshore aquaculture in U.S. Federal waters. This paved the way for its successor Catalina Sea Ranch to pioneer the cultivation of mussels and giant kelp 6 miles offshore of Huntington Beach, California.

As the founder and CEO of Catalina Sea Ranch from 2012 to 2019, Phil Cruver stood at the cradle of offshore mariculture in the US. Seeing no future in the United States due to over-regulation by NOAA and the FDA, a consulting project for the Inter-American Development Bank instead turned his attention to tropical seaweeds.

Protecting crops from predators and ice-ice disease

A chance discovery of the work of Professor Kasim of the Halu Oleo University of Sulawesi led Cruver to revisit the fish cage idea that started it all and to revive the collaboration with UNH and ISCO Industries to adapt it to seaweed aquaculture.

“I was astounded to learn that this multi-billion industry has relied upon primitive production methods requiring tedious hand-tying seedlings to lines for planting and untying for harvesting”, Cruver says. “I then discovered recent research that provided an overview of floating cage technology for seaplant cultivation in Indonesia. Using cages suspended from PVC floating rafts with multifilament netting produced a 54.9% increase in Eucheuma growth in 40 days compared to traditional long line cultivation.”

The paper also documents how bleaching and ice-ice disease, two major problems for tropical seaweed cultivators, are avoided by submerging the cages just below the surface, thus avoiding the fluctuations in surface salinity and temperatures that cause it. On top of that, the cage protects the seaweed from predators like fish and sea turtles, accounting for the higher crop yields.

Eucheuma growth rates on long line vs cage culture – Ma’ruf Kasim, Abdul Muis Balubi, Ahmad Mustafa, Rahman Nurdin, Rahmad Sofyan Patadjai and Wardha Jalil (June 10th 2020). Floating Cage: A New Innovation of Seaweed Culture

Going offshore

The chief innovation of KZO Sea Farms design lies in its improved submersible properties. While the Indonesian cages are deployed nearshore and remain vulnerable to storms and typhoons, Cruver envisions taking his structures offshore. Built from High Density Polyethylene (HDPE), the cage pipes would be filled with seawater to lower the structure into the sea. Once a storm has passed, air from scuba tanks would then discharge the water to resurface the cage. Monitoring sensors provide traceability while recording sunlight, current, salinity, and temperature.

Cruver sees going offshore as the best option for scaling tropical mariculture in a world of warmer, more acidic seas.

“Research shows that ocean depth significantly affects abiotic factors of temperature, sunlight, salinity, and nutrients which are critical factors for seaplant survivability and growth. The submersible capability allows the structure to make use of the ocean water vertical column’s optimum cultivation characteristics to produce significantly higher crop yields.

Crops cultivated in shallow, near-shore farms are increasingly impacted by higher seawater temperatures, acidification, and increased salinity because of climate change. Expansion of the industry will require moving farms further offshore to cooler and more nutrient-rich offshore waters not conflicting with Marine Protected Areas, tourism, and vessel shipping lanes.”

Questioned on how small-scale, low-income farmers fit into this vision, he thinks that artisanal techniques cannot scale to attract the necessary private sector capital. Cruver: “Only companies with the requisite capital and management resources can expand and transform the industry. Moreover, these companies will be able to pay higher wages for skilled “Blue Economy” workers to meet the future demand of this rapidly growing multi-billion dollar industry.”

Final question: you came up with the idea while consulting on a project in Belize. What do you see happening in Belize over the next 5-10 years?

“I have drafted a business plan for raising public and private sector capital to launch a seaplant industry in Belize and the ROI is encouraging over the next five years. However, I have been emphatic that a pilot project must first be conducted to demonstrate the efficacy of the submersible technology and to prove the increased yields of cage culture over traditional long line farming.

Without a submersible structure, public and private sector investment is an illusion because of the increased intensity and frequency of hurricanes attributed to climate change.”

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