Intertidal Gracilaria farming in southern Chile: differences of the algal proveniance
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Aquatic Botany, 42 (1992) 327-337 327 Elsevier Science Publishers B.V., Amsterdam
Intertidal Gracilaria farming in southern Chile: differences of the algal proveniance
Alejandro H. Buschmann, Felix A. Kuschel, Pedro A. Vergara and Jacqueline Schulz
Instituto Profesional de Osorno, Departamento de Acuicultura y l~ecursos Acudticos, Casilla 933, Osorno, Chile
(Accepted 25 November 1991 )
Buschmann, A.H., Kuschel, EA., Vergara, P.A. and Schulz, J., 1992. Intertidal Gracilaria farming in southern Chile: differences of the algal proveniance. Aquat. Bot., 42: 327-337.
The transplantation of Gracilaria for the establishment of cultivation centres has been a common practice in Chile, but so far differences in the initial transplants and their eventual morphologies have not been noted. Subtidal populations of Gracilaria obtained in the Maullin area ( 41 34' S, 73 39' W) were initially morphologically different from intertidal Gracilaria populations collected in the Quil- laipe area ( 41 33' S, 72 45' w). Both populations were grown under the same experimental intertidal conditions in Metri Bay (41 36'S, 7242'W). After several months of cultivation, the morphological differences still existed. Significant differences in the yield and gel strength ofagar, and susceptibility to epiphytism, were found. However, no differences were detected in the productivity of each initially different population. This evidence indicates that the success of Gracilaria farming will depend on the origin of the initial Gracilaria inoculum.
Intraspecific variations in the morphological and functional characteristics o f benthic algae may be a reflection o f differences in habitat (Norton et al., 1981; Lobban et al., 1985; Chapman, 1986). Hanisak et al. (1988) found that the morphological intrapopulation differences o f Gracilaria tikvahiae Mc- Lachlan are reflected in different functional responses o f the plant. F rom a productive point o f view, these differences could determine the success o f a new culture (Santelices and Doty, 1989; Hanisak et al., 1990).
The cultivation o f Gracilaria in Chile has experienced rapid development during the last 5 years (Ponce, 1989), A traditional practice for the establish- ment of new cultivation centres involves the transplantation of Gracilaria from
Correspondence to: A.H. Buscbmann, lnstituto Profesional de Osomo, Departamento de Acui- cultura y Recursos AcmRicos, Casilla 933, Osorno, Chile.
1992 Elsevier Science Publishers B.V. All rights reserved 0304-3770/92/$05.00
328 A.H. BUSCHMANN ET AL.
different localities on the Chilean coastline (Santelices, 1989). This has not only created difficulties in the reliable identification of the Chilean Gracilaria species (Bird et al., 1986), but further difficulties arise when ar'dficial com- mercial Gracilaria beds are installed without taking eventual ecological inter- population differences into consideration (Santelices, 1989; Santelices and Dory, 1989). Using tank and laboratory experiments, Santelices and Ugarte (1990) demonstrated that subtidal Gracilaria populations from northern, central and southern Chile show some ecological differences that might affect the success of their cultivation. The different environmental systems used for the Gracilaria mariculture activities, such as wave-sheltered bays, estuaries and intertidal flats (Santelices and Doty, 1989), can increase the risks when initiating aquaculture activities using algae with different ecological charac- teristics with respect to abiotic factors (e.g. irradiance, temperature, sand abrasion and sand burial) and biological factors (e.g. resistance to epiphy- tism and herbivory).
In southern Chile, algae from two environmental systems have been used for the cultivation of Gracilaria, namely subtidal sheltered estuaries and in- tertidal mud flats. The cultivation in intertidal mud flats occupies approxi- mately 1000 ha, representing about 30% of the ste.te area licensed for Graci- laria cultivation in southern Chile (Ponce, 1989). These mud flats possess specific environmental characteristics suitable for testing a contrasting set of conditions shown by a subtidal estuarine habitat on given populations of Gra- cilaria. For these reasons, it is important from a productive point of view to establish whether the different Gracilaria populations used for planting com- mercial intertidal farms respond in a different or the same way. We tested the hypothesis that the response of subtidal Gracilaria estuarine populations will differ from that of the intertidal populations when they are cultivated in in- tertidal flats. Growth responses were measured in terms of changes in mor- phology, biomass production, agar yield and gel strength, epiphyte load and grazing resistance.
MATERIALS AND METHODS
Study site, algal provenance and experimental 4esign
The Gracilaria populations were collected in two localities in Chile: Maullin (41 34'S, 7339'W) and Quillaipe (41 33'S, 7245'W) (Fig. 1A). The first locality is a wave-protected subtidal estuarine habitat and the Gra- cilaria beds extend between 1 and 3 m on a sand bottom, with temperatures and salinities ranging between 9 and 16C and 18 and 32%0, respectively (Westermeier et al., 1984, 1988). The Quillaipe area represents an intertidal flat created as a consequence of the high tidal amplitudes found in this area,
INTERTIDAL GI~4CILARIA FARMING IN SOUTHERN CHILE
Pac nt ina
I I IMlol 101 l O:Ou i l la ipe ; M:Mau l l in
Fig. 1. A, Map showing the provenance of the algae and the culture site in southern Chile and B, the treatntent arrangement of the three experimental plots.
which vary between 6 and 8 m. The Gracilaria beds are also situated on sand beaches with temperatures and salinities varing between 9 and 20C and 26 and 30%o during an annual cycle (A.H. Buschmann, unpublished data, 1988- 1989). As both populations are at approximately the same latitude with sim- ilar water temperatures and salinities, the most obvious environmental dif- ference is the periodic exposure to air (lunar semidiumal tides, with exposure during spring tides) of the Quillaipe population.
The Gracilaria beds in Chile are frequently infertile, therefore the field ex-
330 A.H. BUSCHMANN ET AL.
periments were performed without establishing the specific identity of the plants used. However, it is known that the Maullin algae correspond mainly to Gracilaria chilensis Bird, McLachlan & Oliveira. Observations on Quil- laipe Gracilaria indicate that it corresponds to Gracilaria chilensis, but a more detailed study must be carried out. Both populations differ morphologically: the Quillaipe algae have thinner thalli (Mann Whitney U-test; U=85; P
INTERTIDAL GRACTLARIA FARMING IN SOUTHERN CHILE :3:31
described by Canting and Orellana (1987), and the percent dry weight was calculated. The gel strength was obtained by measuring a 1.5% agar solution prepared in I00 ml distilled water and gelled at room temperature (16C) for 12 h. The gel strength measurement was carried out utilizing a 'Marine Colloidal Gel Tester'. A total of five measurements was taken for each replicate.
Before installing the experimental plots, the algae from Manllin and Quil- laipe were cleaned by hand. The Maullln algae showed a very small load of epiphytes (mainly Ceramiales), but the algae collected in Quillaipe had a higher epiphyte load (up to 30% Ceramiales; wet weight). The clean algae were then planted in the experimental plots as described earlier and, after 3 months of culture, between October and November when the epiphyte load owing to the filamentous brown alga Giffordia sp. is highest (Buschmann ct al., 1990; Kuschel and Buschmann, 1991 ), three subsamples (0.50.5 m) were taken from each replicate plot and the epiphytes were removed by hand in the laboratory. The Gracilaria and the epiphytes (Giffordia) were then weighed on a Sartorius balance ( __.0.01 g accuracy). The epiphyte load was then expressed as the weight of epiphytes divided by the total algal weight (~0).
During May 1990, samples of Maullin and Quillaipe algae were collected from the experimental plots in Metri (22 month acclimatized algae). Maullin algae which had not been acclimatized were also brought to Metri. All the algae were transported to the laboratory and epiphytes removed. Using the algae collected, six bundles of I00 g (wet weight) ofthe acclimatized Maullfn Gracilaria were prepared, six of the non-acclimatized Manllin and six of the QuiUaipe algae. A bundle of each ofthe three different types ofalgae was fixed to short polyethylene tubes (30 em long).
The snail Te~la atra Lesson is the most common ~'azer in the intertidal fiats in southern Chile, reaching over 30 individuals m -= (A.H. Buschmann, unpublished results, 1990). Experimental cages were used to maintain a fixed number of snails for food preference experiments in the field. The cages (50 cm X 50 cm X 50 cm) were anchored in the sand bottom and algal offerings placed inside them (Maullln and Quillaipe algae), as previously described. Thirty individuals of T. atra were added to each ofthe three cages. Consump- tion rates were calculated after 30 days based on weight differences of the algae measured on a balance ( +_ 1 g accuracy), and after making corrections for weight changes which occurred in three other unf~.ed controls. Con- sumption rates were then standardized by dividing the fresh weight of the
332 A.H. BUSCHMANN El" AL.
algae consumed by the fresh weight of the snails, multiplied by the number of experimental days.
The morphological data were analysed using the non-parametric U-test (Sokal and Rohlf, 1979) because some of the data did not meet the homoge- neity of variance and normality requirements. All other data were compared using univariate statistical analysis (t-test and ANOVA) throughout (Sokal and Rohlf, 1979).
After 8 months of culture, the initial morphological differences observed between the Maullin and Quillaipe Gracilaria populations remained. The to- tal weight of the 15 cm long thalli was not significantly different in the two algal populations (Table 1 ). However, the number of ramifications was sig- nificantly higher (Mann-Whitney U test; U= 83; P< 0.01 ) in the Quillaipe algae than in the Maullin algae (Table 1 ). The weight of the central axis was significantly higher (Mann-Whitney U test; U=I00; P
INTERTIDAL GRACILARIA FARMING IN SOUTHERN CHILE 333
During the growth period (spring and summer), there was no significant difference in the amount of biomass obtained from each population studied (Fig. 2). The algal production during this period varied between 550 and 800 g m -2 month- i.
The Maullin algae showed significantly (t = 5.43; P< 0.01 ) higher agar yields than the Quillaipe algae (Table 2). However, the Quillaipe algae produced an agar with a significantly higher (t=3.00; P
334 A,H. BUSCHMANN ET AL,
Epiphytism susceptibility ( (g epiphytes/g algae) i 00) of Gracilaria from Maullln (M) and Quil- laip (Q) populations
Gracilaria population Epiphytism load (%) (mean+- 1 SE)
SE, standard error. *P
INTERTIDAL ORACILARIA FARMING IN SOUTHERN CHILE ~35
(1980), Gracilaria with a higher surface-volume ratio had higher production capacities (Hanisak ct al., 1988, 1990). Following this argument, it would be expected that the Quillaipe algae with a higher surface-volume ratio would also have higher biomass production rates. However, in the field it was Found that this potential was not realized. This evidence suuests that both algae could be equally productive, but several other aspects must be considered be/ore transplanting Gracilaria to an intertidal cultivation centre.
The agar yield and gel strength of the Maullin algae differed from that of the QuiUaipe algae. The Maullfn algae had common yield values (20%), but the Quillaipe algae had low yields (below 15%) compared with previous re. sults (McLachlan and Bird, 1986). Several Factors could account for these differences. The results regarding the gel strength also varied between the populations studied. It is known that both agar characteristics of yield and gel strength are independent variables (McLachlan and Bird, 1986). As different algal clones can show differences in the chemical constituents of the agar (Craigie and Wen, 1984), it is not surprising that the gel strength varied be- tween the Maullfn and Quillaipe area. Again, the reasons for these differences are still unknown. However, from a production point of view, the quantity and quality or'the final product will vary depending on the source of the algae used for the initial planting.
Epiphytism could be a major problem for the establishment of cultivation areas in southern Chile. The results obtained in this study show the same pattern as that reported previously by Kuschel and Buschmann (I 991 ). The Maullfn algae were more susceptible to epiphytism by Giffordia. The initial epiphyte load could not account for these differences because the Quillaipe (more resistant population) had the highest initial epiphyte load. Further- more, if epiphytism were to depend on the surface area available, it would be expected that the morphology of the Quillaipe algae (higher surface-volume ratio) could enhance epiphytism by Giffordia. However, we Found that the Quillaipe algae had the lower epiphyte level. Santelices and Ugarte (1990) also Found in their experiments that the Maullfn population showed recruit- ment of the brown alga Ectocarp~ sp. ( = Giffordia). As Giffordia can signif- icantly suppress Gracilaria production in intertidal systems (Kuschel and Buschmann, 1991 ), it is a very important variable which must be considered in the establishment of commercial intertidal beds.
No differences were Found between the subtidal algae (Maullfn) which had been acclimatized to intertidal environmental conditions (r~=::: stressful conditions) and subtidal algae which had not been acclimatiz~ :' ]~ naud et al. (1990) have shown that desiccation can modify the susceptibility of G. tikvahiae to sea urchin grazing. We have not Found such differences between the acclimatized and non-acclimatized Maullfn algae, and our results do not confirm those of Renaud et al. (1990). Our results also indicate that no dif- Ferences exist between the algae from the Maullfn area and those from the Quillaipe area.
336 A.H. BUSCHMANN ET AL.
Considering that in Chile propagation is carried out through fragmentation of the thai!i, it is probable that the mariculture practices have already shown some sort of selection, diminishing the natural variability both within and between populations. However, the results obtained in this study indicate that some differences exist when algae of different provenience,...