**4. Growth**

#### **4.1 Production technologies**

Technological designs must ensure specimens have the best access to food and water flow during the growth phase in suspended barnacle cultures. Similarly, space availability must be sufficient to maintain animals up to the harvest stage. As is the case in spat collection systems from the wild, materials used must be innocuous. Weight must also be compatible with suspension from rafts or long-lines, ensuring easy manipulation and costs that are compatible with a commercial activity.

There are two types of production technologies for the growth phase of the "giant barnacle": "Cultch" systems - corresponding to technologies that maintain the specimens over the period from spat collection, during growth, through to the harvest stage. Substrates used have included plates and 900 cm2 to 2,200 cm2 polythene tubes, suspended vertically in groups of three units. One advantage is that harvesting of spat is not necessary and this system can be more effective, because specimens are less exposed to mechanical manipulation, and, therefore, suffer fewer mortalities. In the "cultchless" system, two different production technologies are used, one for obtaining spat from the wild and another for growth. Spat harvest occurs approximately four months post-larval settlement. Subsequently, individuals are transferred to a growth system where they remain until the harvest stage. The surfaces used as artificial collectors must permit the innocuous extraction of juveniles. Since specimens are cemented to the collector substrate, a surface must be used that avoids damaging the calcareous structures, particularly of the basal zone, when the specimens are detached. Expanded polystyrene and felts ("bidin") covered with tar have been used as substrates, with an area of 900 cm2 to 1,600 cm2. For subsequent growth, trays can be used or specimens can be attached with adhesive to a new surface. The best results have been obtained with the "cultch" systems. Both the "cultch" and "cultchless" systems are located on floating structures (long-lines or rafts) suspended from surface levels to a depth of 8 m, in shallow wave-protected or semiprotected bays. Maintenance and cleaning of the systems is necessary during the growth phase eliminating, periodically, the accumulation of sediment and fouling (mainly mytilids, ascidians and other species of barnacles), in order to avoid mortalities by suffocation and overgrowth by other species.

#### **4.2 Spatial and temporal variability: Results in the "giant barnacle"**

In balanomorph barnacles, a density-independent estimator of growth is the carino-rostral length or opercular length, corresponding to the maximum rectilinear distance between the carinal plate and the rostral plate (López et al., 2007b). Other growth estimators, such as mural plate height or basal diameter, are inadequate growth indicators, because they are modified by growth density.

Average commercial size of the "giant barnacle" in Chile is 3.5 cm ± 0.6 carino-rostral length (approximately 10 cm height). Specimens of around 2 cm carino-rostral length can be found in local markets,. Nevertheless, specimens from natural banks can reach sizes in excess of 6 cm carino-rostral length and more than 30 cm height. Shell height depends on the degree of aggregation during growth, due to the development of a modified base generated in the hummocks (López et al., 2007b).

Growth rate varies according to depth. Twenty months after larval settlement, average carino-rostral length of "giant barnacle" specimens growing at depths of between 4 and 6 m, was 3.4 ± 0.17 cm, while the average size of individuals growing at depths of between 1 and 2 m, was 2.92 ± 0.14 cm (López et al., 2008a).

If minimum commercial size on the Chilean market is considered (2.1 cm carino-rostral length), the culture period, from larval settlement up to harvest, can be 7-8 months. Nevertheless, recent studies in the northern zone of Chile show a relative increase in growth in comparison to the results obtained in the southern zone, probably associated with the differences in water temperature. In the north, specimens of a commercial size (> 2 cm carino-rostral length) have been obtained over a period of only 4-6 months (Fig. 4).

over the period from spat collection, during growth, through to the harvest stage. Substrates used have included plates and 900 cm2 to 2,200 cm2 polythene tubes, suspended vertically in groups of three units. One advantage is that harvesting of spat is not necessary and this system can be more effective, because specimens are less exposed to mechanical manipulation, and, therefore, suffer fewer mortalities. In the "cultchless" system, two different production technologies are used, one for obtaining spat from the wild and another for growth. Spat harvest occurs approximately four months post-larval settlement. Subsequently, individuals are transferred to a growth system where they remain until the harvest stage. The surfaces used as artificial collectors must permit the innocuous extraction of juveniles. Since specimens are cemented to the collector substrate, a surface must be used that avoids damaging the calcareous structures, particularly of the basal zone, when the specimens are detached. Expanded polystyrene and felts ("bidin") covered with tar have been used as substrates, with an area of 900 cm2 to 1,600 cm2. For subsequent growth, trays can be used or specimens can be attached with adhesive to a new surface. The best results have been obtained with the "cultch" systems. Both the "cultch" and "cultchless" systems are located on floating structures (long-lines or rafts) suspended from surface levels to a depth of 8 m, in shallow wave-protected or semiprotected bays. Maintenance and cleaning of the systems is necessary during the growth phase eliminating, periodically, the accumulation of sediment and fouling (mainly mytilids, ascidians and other species of barnacles), in order to avoid mortalities by

suffocation and overgrowth by other species.

modified by growth density.

hummocks (López et al., 2007b).

2 m, was 2.92 ± 0.14 cm (López et al., 2008a).

**4.2 Spatial and temporal variability: Results in the "giant barnacle"** 

In balanomorph barnacles, a density-independent estimator of growth is the carino-rostral length or opercular length, corresponding to the maximum rectilinear distance between the carinal plate and the rostral plate (López et al., 2007b). Other growth estimators, such as mural plate height or basal diameter, are inadequate growth indicators, because they are

Average commercial size of the "giant barnacle" in Chile is 3.5 cm ± 0.6 carino-rostral length (approximately 10 cm height). Specimens of around 2 cm carino-rostral length can be found in local markets,. Nevertheless, specimens from natural banks can reach sizes in excess of 6 cm carino-rostral length and more than 30 cm height. Shell height depends on the degree of aggregation during growth, due to the development of a modified base generated in the

Growth rate varies according to depth. Twenty months after larval settlement, average carino-rostral length of "giant barnacle" specimens growing at depths of between 4 and 6 m, was 3.4 ± 0.17 cm, while the average size of individuals growing at depths of between 1 and

If minimum commercial size on the Chilean market is considered (2.1 cm carino-rostral length), the culture period, from larval settlement up to harvest, can be 7-8 months. Nevertheless, recent studies in the northern zone of Chile show a relative increase in growth in comparison to the results obtained in the southern zone, probably associated with the differences in water temperature. In the north, specimens of a commercial size (> 2 cm

carino-rostral length) have been obtained over a period of only 4-6 months (Fig. 4).

Fig. 4. "Giant barnacle" culture growth system in northern Chile.

Instantaneous growth rates decrease with age, fluctuating from 0.03 cm/day carino-rostral length at the beginning of growth, to 0.0005 cm/day carino-rostral length after 20 months.

For the Chilean market, "giant barnacle" harvest should occur between 18 – 24 months, depending on the season the collectors are placed in the water. Prior to harvesting, the majority of specimens must have reached over 3 cm carino-rostral length. Nevertheless, the culture period can vary according to the requirements of each market. If, eventually, the "giant barnacle" were to be used as a simil of the "fujit subo" on the Japanese market, the culture period would be substantially less.

Productivity in "giant barnacle" culture systems is extremely high, taking production by extractive fisheries as a point of reference. National average gross production of this resource by small-scale local fisheries is around 200 ton/year; this could be obtained with only 20 to 30 long lines. A double, 100 m floating long-line can produce between 7 and 10 gross ton of total biomass in one season. This can signify approximately 2 ton wet weight of soft parts. Each tubular system of approximately 1 m in length, can produce, on average, 15 ± 8 kg of biomass, equivalent to an average of 100 specimens of commercial size, with a yield corresponding to 20-30 g per individual, depending on the maturity of the female gonad. The results obtained in "giant barnacle" cultures on the Chilean coast indicate that there are spatial differences in growth, both on a latitudinal and local level, as well as bathymetrically and according to the type of culture system. Inter-annual and seasonal temporal differences also exist. Thus, production planning is still subject to a high degree of unpredictability. On the other hand, the heavy weight of the shell, that can fluctuate between 70 to 85% of total weight, together with high variability in the mortality rate during the growth stage, are also limiting factors for cultures. Nevertheless, in view of its rapid growth and productivity, as well as the simple and economic production technologies used during the fattening phase, culture of the "giant barnacle", and other balanomorphs species, constitutes an interesting alternative for diversification of Aquaculture.

#### **4.3 Factors influencing growth**

Experiments conducted under controlled conditions have examined the role of environmental variables in the spatial-temporal variability of "giant barnacle" growth (López et al., 2008a). It has been reported that photoperiod and temperature can synergistically affect the metabolism, influencing molt frequency and growth in some barnacle species (Crisp & Patel, 1960; El-Komi & Kajihara, 1991). These variables change seasonally within the geographic distribution range of the "giant barnacle". Temperature and photoperiod affect the instantaneous growth rate, which is greater at 10oC than at 16oC and at photoperiods of 8h light :16 h darkness, than at 16 h light:8 h darkness. Specimens in the natural environment presented higher instantaneous growth rates at depths of between 4 and 6 m than between 1 and 2 m depth, under conditions of greater darkness and lower temperature, in accordance with the results obtained in the laboratory. In other species of barnacles, increased growth has also been reported under darkness conditions (Costlow & Bookhout, 1953; 1956). Futhermore, as occurs in other species of barnacles, growth and molting frequency are not correlated (Costlow & Bookhout, 1956). In the "giant barnacle" molt frequency was greater at 16oC than at 10oC, with no evidence of variation due to photoperiod. This can be associated with a decreasing metabolism as a result of lower temperatures, or to effects at the neuroendocrine system level. However, the inter-molt periods were longer at 10oC than at 16oC and during photoperiods 8: 16 than 16:8 (López et al., 2008a). If this information is applied to suspended "giant barnacle" cultures, the fattening phase should be undertaken at depths of over 4 m and at low temperatures.
