Estudos em macroalgas carragenófitas (Gigartinales, Rhodophyceae) da costa portuguesa: aspectos ecológicos, bioquímicos e citológicos

Abstract

Oito carragenófitas, da costa portuguesa, representando sete géneros e quatro famílias das Gigartinales, foram estudadas na baía de Buarcos durante cerca de um ano (estudo da variações sazonais) e em quinze estações costeiras (estudo das variações geográficas), localizadas entre o Baleal (Peniche) e Moledo. Em geral, o comprimento e a biomassa das carragenófitas estudadas apresentam variações sazonais, com um incremento no início da Primavera (Abril), um aumento acentuado no início do Verão (Junho/Julho) e valores reduzidos no final do Verão, Outono e Inverno. O maior conteúdo médio em carragenana foi registado numa amostra de Chondracanthus acicularis (40.1 %), seguido dos valores registados nas amostras de Gigartina pistillata (38.7 %) e Chondracanthus teedei var. lusitanicus (34.9 %). As carragenófitas com maior cobertura e biomassa foram as seguintes: Chondrus crispus (3.75 % - 570 g m-2); C. acicularis (3.45 % - 99 g m-2); C. teedei var. lusitanicus (2.51 % - 208 g m-2); Mastocarpus stellatus (2.02 % - 520 g m-2). Para a caracterização dos diferentes tipos de carragenana foram usadas as técnicas espectroscópicas: FTIR-ATR, FT-Raman, 1H e 13C-RMN. Com base nestas técnicas, nomeadamente em FTIR-ATR e FT-Raman, foram desenvolvidas metodologias inovadoras que nos permitiram a correcta identificação das diversas fracções de carragenana, em particular das variantes da família lambda (carragenana lambda, ksi e theta) e dos precursores biológicos (mu e nu) das carragenanas gelificantes (kappa e iota, respectivamente). Visto que as amostras foram sujeitas a uma manipulação mínima (as algas são simplesmente secas e moídas), a composição determinada representa, o mais fielmente possível, a composição natural dos ficocolóides. A espectroscopia de ressonância magnética nuclear do protão e do carbono 13 foi usada na caracterização e quantificação dos diferentes componentes das carragenanas extraídas.

Eight carrageenophytes from the Central and Northern coast of Portugal, representing seven genera and four families of Gigartinales, were studied for a period of one year (seasonal variation studies) in the Buarcos bay and in fifteen other different coastal stations (geographic variation studies) from Baleal (Peniche), in the Central zone, to Moledo, in the Northern zone. The reproductive status, dry weight and carrageenan content have been followed by monthly random sampling. In general, the plant size and the biomass shows a seasonal increase in early Spring (April), a marked increase in early Summer (June/July) and low values in late Summer, Autumn and Winter. The low colloid content in Winter (December) and the high colloid content in Summer (July) can be related to high and low nutrient (N and P, mainly) contents of the water, respectively. The highest average carrageenan yield was found in Chondracanthus acicularis (40.1 %), Gigartina pistillata (38.7 %) and Chondracanthus teedei var. lusitanicus (34.9 %). The haphazard sampling method (with quadrates) was used to determine the biomass and the continuous sampling method, applied along a perpendicular transept to the shoreline, was used to calculate the carrageenophytes cover in two periods: Autumn/Winter and Spring/Summer. The following results must be enhanced: the highest cover and biomass was found in Chondrus crispus (3.75 % - 570 g m-2), Chondracanthus acicularis (3.45 % - 99 g m-2), Chondracanthus teedei var. lusitanicus (2.51 % - 208 g m-2) and Mastocarpus stellatus (2.02 % - 520 g m-2). In order to characterize the different carrageenan types, vibrational (Infrared and Raman) and resonance (1H and 13C-NMR) spectroscopy has been used to show detailed information concerning the properties and structure of these polysaccharides at molecular level. In this work some techniques of analysis based on the FTIR-ATR and FT-Raman spectroscopy have been developed in order to obtain an accurate identification of the diverse carrageenan fractions, with particular relief for the variants of lambda-family (lambda, ksi and theta) and for the biological precursors (mu and nu) of the gelling carrageenans (kappa and iota, respectively). Because the samples are minimally treated (dried ground algal material), the determined composition represents, as accurately as possible, the natural composition of the colloids. The spectra of both commercial carrageenan samples and common carrageenophytes were used as reference. The NMR (1H and 13C) spectroscopy was used in order to characterize and quantify the different carrageenan fractions in the extracted phycocolloids (water and alkali extractions). A new set of 13C and 1H-NMR chemical shifts of most common carrageenan types is given relative to DSS as the internal standard according to the IUPAC recommendations. Moreover, the chemical shifts of characteristic signal for pyruvate acetal and floridean starch are reported. Relatively to the carrageenan types, the following results are to be enhanced: female gametophytes and non-fertile thalli samples of C. crispus, M. stellatus, C. teedei var. lusitanicus, G. pistillata, C. acicularis and Gymnogongrus crenulatus, show a significant degree of kappa-iota hybrid carrageenan (copolymers of kappa-iota carrageenan). Relative amounts of the different gelling carrageenan fractions were determined with 1H-NMR. The carrageenans extracted from Ahnfeltiopsis devoniensis are mainly constituted by iota-carrageenan, but seasonal variations in the nature of carrageenans are present. Lambda-family carrageenans were found in tetrasporophytes of C. cripus (lambda carrageenan), M. stellatus (lambda carrageenan), C. teedei var. lusitanicus (hybrid ksi-theta carrageenan), C. aciculais (hybrid ksi-theta carrageenan) and G. pistillata (hybrid ksi-lambda carrageenan). Calliblepharis jubata presents carrageenans of iota-type in all reproductive stages. Considering these results, based on FTIR-ATR, FT-Raman and 1H-NMR techniques, more sensible than 13C-NMR, we can conclude that the carragenana kappa and iota have distinct biological precursors, mu and nu respectively. The “soft” alkaline extraction method, used in this work, makes possible the carrageenan extraction with low degradation and high molecular weight. Taking in consideration the high available biomass and the phycocolloid content of the Chondracanthus species and Gigartina pistillata they are a potentially important source of copolymers of kappa-iota carrageenan, in addition to the traditionally harvested carrageenophytes (M. stellatus and C. crispus). However, collection of seaweeds from rocky shore has its limitations, as it always contains the risk of overcollection and subsequent loss of the population. The next step, in the near future, will be to develop further studies in order to introduce these carrageenophytes in the aquaculture integrated systems. In this work, fronds of G. pistillata exhibiting both tetrasporangial sori and cystocarps, i.e., tetraspores and carpospores (heterosporic thalli), were found in several costal stations. In order to clarify the nature and function of these reproductive structures, it’s morphological, cytological and biochemical study was carried out. Other morphological, citochemical and ultrastructural studies were performed in selected carrageenophytes in order to study both the carpospore/tetraspore formation (C. teedei var. lusitanicus) and polysaccharide distribution (cellulose and carrageenan) in the thalli and cell walls (G. crenulatus, A. devoniensis and G. pistillata).