Novel flotation model for the experimental culture of macroalgae Kappaphycus alvarezii in Florianópolis , Brazil

A new flotation model for the experimental culture of macroalgae Kappaphycus alvarezii (Doty) Doty ex P.C. Silva is described and illustrated. The ellipsis-shaped 90L apparatus is made of medium density virgin polyethylene, measuring 2000mm long x 300mm wide x 200mm high, and weighing 9kg. The device has been successfully tested in the littoral region of the state of Santa Catarina, Brazil, throughout the experimental period. Contrastingly to traditional models available on the market, with their instability in strong sea currents, current model is an alternative to enhance algae-mollusks integrated culture, by providing stability to culture structures. It may also serve as a spacer and support for mooring of double long lines.

Macroalgae Kappaphycus alvarezii (Doty) Doty ex P.C. Silva is a worldacknowledged sea commodity.It is the main source for the extraction of carrageenan, the mucilaginous substance on the cell wall, with high economic value due to its vast application as thickener and stabilizer used in the food, cosmetic and pharmaceutical industries (BIXLER & PORSE, 2011;FAO, 2014).
During the last decades, several countries have developed its commercial culture, whilst others, Brazil in particular, have focused on experiments.Due to its exotic status, the introduction of the macroalgae occurred experimentally in Ubatuba, in the state of São Paulo, Brazil, in 1995, warranted by the Brazilian Institute for the Environment and Renewable Natural Resources (IBAMA) (OLIVEIRA et al., 2009).In 2008, IBAMA also authorized the introduction of the species in the Sambaqui beach, Florianópolis, Santa Catarina (HAYASHI et al., 2011) and, more recently, further warrants have been provided to other municipalities, such as Penha and Governador Celso Ramos, in the state of Santa Catarina, in 2017.
These activities have triggered the production of data on the capacity of the culture and its adaptation to local environmental conditions such as environmental safety of sea culture (HAYASHI et al., 2011;CASTELAR et al., 2015;CARVALHO et al., 2015) and the seasonality of production (culture occurs between September and May exclusively, due to high temperatures; low water temperature kills the tropical species) (HAYASHI et al., 2011).
However, great progress occurred in culture technologies.At first, 100mm-PVC tube cylindrical rafts were employed for the culture of K. alvarezii (Figure 1A).However, they proved to be unsatisfactorily throughout the culture cycle since the device could not resist the strong maritime currents of the Santa Catarina littoral (HAYASHI & SANTOS, 2010;HAYASHI et al., 2011).
PVC-tube rafts were than replaced by other flotation devices, round-shaped, 20cm diameter, and manufactured of recyclable polyethylene material (3mm thick injectable plastic) (Figure 1B).Its field performance was equally unsatisfactorily since it did not provide proper stability to culture structures, with excessive mobility due to the waves´ hydrodynamic force, rupture of cables and moorings and an increase in maintenance and managements events.
Further, wooden spacers coupled to a round-shaped flotation device were also tested (Figure 2A) to keep distance between the two culture cables.The latter were heavily colonized by Teredo sp., popularly known as "shipworms", and replaced every six months, with more liabilities (Figure 2B).
Since 2012, several studies were conducted for the development of a flotation device adapted to sea conditions on the littoral of the state of Santa Catarina, Brazil.Current study described a novel flotation model for the integrated culture of mollusks and K. alvarezii, featuring three functions: spacer and support of double long line increase in productivity, greater stability to culture structures on the surface to cope with local environmental conditions.
The flotation device was manufactured in medium density virgin polyethylene, with a 5mm-thick wall, with a 2.000mm long x 300mm wide x 200mm high, at a cost of US$ 73.It was treated with UVA/UVB to increase durability, estimated between 8 and 10 years.The prototype had an elliptical shape to reduce attrition against sea waves and to accommodate 5 culture cables fixed to grooves placed 370mm one from another to prevent the lateral drag of the cables (Figure 3).
The prototype counter-mold, made of wood and fiber, was then cast in aluminum.The device later received holes for cables and moorings.Parts were manufactured by auto-molding employing micronized polyethylene powder of medium linear density.Linear molecule structure provided the required malleability and resistance against breakage.It may crumple in certain cases but it would not crack or break.The mold was then placed in an oven at approximately 200ºC, rotated in two directions on axis X (12rpm) and axis Y (3rpm).During rotation, the powder polyethylene melted and adhered to the mold.After 30 min in the oven, the structure was removed and cool rotation started for 15 min until the solidification of the material.After cooling, the structure was smoothed and breather sealed with a PVC buffer, screwed and glued with silicone (Figure 4).
First field tests with the prototype were performed between April and May 2017 in the sea of Sambaqui beach, featuring monoculture system,  with great success throughout the assay period.The apparatus´s elliptical device was less affected by waves since they passed over it, with a reduction of hydrodynamic force (Figure 5).Current studies on the novel flotation elliptical device developed by EPAGRI in joint partnership with the Federal University of Santa Catarina (UFSC) have so far only focused on the algae monoculture in Sambaqui beach, Brazil (Figure 5A).It is believed, however, that it may be a useful tool for integrated culture with K. alvarezii, oyster and mussel.
The pre-experimental phase of the project "Assessment of commercial cultivation of Kappaphycus alvarezii in the littoral of Santa Catarina" occurred in October 2017, identifying the best technology in product mechanization for algae culture and evaluating the integration of such technology with mollusk cultivation (ranging between oyster Crassostrea gigas and mussel Perna perna).The preexperimental phase comprises the formation of biomass (Figure 5B    of the technical, environmental and financial performance will be assessed for its commercial viability.

Figure 4 .
Figure 4. Prototype of flotation device in wood and fiber, with grooves for mooring cables for the cultivation of algae and holes for moorings to the long line.

Figure 5 .
Figure 5. Field tests with the new elliptical flotation model.(A) Culture rafts spaced 5 m, with double long lines; (B) Planting of Kappaphycus alvarezii for biomass formation.