INTERTIDAL VEGETATION AND ITS COMMERCIAL POTENTIAL ON THE SHORES OF GALICIA (NW IBERIAN PENINSULA)

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1 Thalassas, 2004, 20 (2): An International Journal of Marine Sciences INTERTIDAL VEGETATION AND ITS COMMERCIAL POTENTIAL ON THE SHORES OF GALICIA (NW IBERIAN PENINSULA) J. CREMADES (1,2), I. BÁRBARA (1) & A. J. VEIGA (1) Keywords: Spain, Atlantic ocean, marine vegetation, marine resources, seaweeds, wave exposure. ABSTRACT This paper presents a study of the marine benthic flora at 185 locations distributed all along the 1200 km of Galician coastline. At each location the presence/absence of 42 previously selected floristic variables was analysed. Parallel to this analysis, at each location a study was conducted on the standing stock per meter of coastline of the alginophytes: Ascophyllum nodosum, Bifurcaria bifurcata, Fucus spp., Himanthalia elongata and Pelvetia canaliculata; the carrageenophytes: Chondrus crispus, Gigartina pistillata and Mastocarpus stellatus and the agarophyte Gelidium sesquipedale. By means of classification techniques 5 broad types of shores were identified based on floristic similarity, which were deisgnated, in classical terms of wave-exposure gradient, as: "Estuaric shore", "Sheltered shore", "Semisheltered shore", "Semiexposed shore" and "Exposed shore". In addition to the floristic study, each (1) Departamento de Bioloxía Animal, Bioloxía Vexetal e Ecoloxía. Facultade de Ciencias. Campus da Zapateira s/n. Universidade da Coruña A Coruña. Spain. (2) Fax: creuga@udc.es type of shore was examined to determine the richness in the different intertidal seaweeds of commercial interest, as indicated above. This was done by calculating the mean biomass (kg m -2 ) of each resource and measuring the widths of the zones occupied by each one at all the locations sampled. After conducting a statistical analysis, it was possible to confirm that the 5 floristic shore types also showed significant differences on both a qualitative and quantitative level, in terms of the richness of exploitable resources. INTRODUCTION Many of the works carried out in the field of intertidal benthic seaweeds on the Northwest coast of the Iberian Peninsula have focussed primarily on the study of the specific richness of particular sections of the coastline (Ardré et al., 1958; Niell, 1977 a; Granja et al., 1992; Bárbara and Cremades 1996; Calvo et al. 1999), analysing the differences found in the floristic composition of each of the locations under study and, in some cases, reflecting on how certain ecological factors may affect this composition and the intertidal zonation patterns, such as wave-exposure (Donze, 1968; Pérez Cirera and Maldonado, 1982 Gallardo et al., 1984, Pérez Cirera and Pacheco, 1985 Bárbara et al., 1995). The aim of this study, however, is not to present a biological scale of wave-exposure in the 69

2 J. Cremades, I. Bárbara & A. J. Veiga study zone, but rather we intend to analyse the floristic composition and to try and define homogeneous groups related to this. We also aim to demonstrate that these groups have both qualitative and quantitative differences in terms of their richness in intertidal seaweeds of commercial interest that will enable us to carry out an overall assessment of the richness and distribution of the intertidal resources having commercial interest on the Galician coast. STUDY AREA The study area is located in Galicia (Northwest Iberian Peninsula) and covers the section of coastline found between parallels 41º52' and 43º48' North latitude and meridians 7º00' and 9º19' West longitude (Fig. 1). This zone is characterised by its extremely rugged coastline with a myriad of inlets and outlets, making the section under study come to a total length of shoreline of over 1200 km. The most important morphological units of this coastline are what are known as the "Rías" (Vidal Romaní, 1984) although, owing to the interaction of hard and soft materials, we also find large sections of the coast occupied by beaches and coastal sandy areas with dunes and littoral marshes. The main oceanographic characteristic of the Galician coast is determined by upwelling episodes that take place here. This phenomenon of upwelling should not be considered as an isolated process, rather it is included in the general upwelling caused by the North Atlantic anticyclonic rotation which extends from Galicia to the Cape Verdi Islands, its intensity coinciding in Galicia with the annual latitudinal shift of this system (Fraga, 1981 Fraga et al. 1982). The tides in the study area are semidiurnal with an average range of around 3 m, although during the tide stage of minimum range (neap tides), this value is around 1.2 m, while during the period of greatest range (spring tides) it exceeds 3.5 m (Rey Salgado, 1993). MATERIAL AND METHODS The samplings were carried out between October, 1996 and March, 1999 at a total of 170 coastal locations distributed all along the shores of Galicia. At each location we analysed the presence/absence of a series of floristic variables as well as the richness in exploitable resources of commercial seaweeds. Sampling locations were selected by means of cartographic information available on the study area, ruling out zones that presented, a priori, an inappropriate substrate for the settlement of populations of intertidal seaweeds or a composition of flora that had been severely altered by human intervention. When choosing the locations, we set out to ensure that they were relatively equidistant from each other, in an attempt to avoid, where possible, leaving long stretches of the shoreline unprospected and we also tried to select sampling locations that would encompass the entire wave-exposure spectrum. Floristic study Figure 1. Geographic location of the study area. As a preliminary step prior to the floristic characterisation of the shore types, a series of floristic taxa (variables) were selected based on the following criteria: In order to avoid errors caused by seasonal changes, following the classification of life-forms as introduced by Feldmann (1966) and Garbary (1976), we omitted the seasonal eclipsophyceae, hypnophyceae and ephemerophyceae, and considered as possible candidates the perennial species (mainly phanerophyceae, chamaephyceae and hemiphanerophyceae) as well as the ephemerophyceae which from the standpoint of population, may be found all year round. 70

3 Intertidal Vegetation and Explotaible Resources on Galician Coasts which for biogeographic reasons, had an irregular distribution in the study area or which were only found under specific conditions at a location. Bearing in mind that we may consider the intertidal zone to be a mosaic-cycle of different seaweed communities (Remmert, 1991; Little and Kitching, 1996), it was necessary to select a large number of species in order to minimise, where possible, erroneous characterisations due to the presence or absence of a certain species at a specific point in time. We tried to make sure that the species selected as floristic variables formed clear bands of vegetation that were easy to identify, thus cutting down on the sampling efforts and the subsequent data analysis. In view of the above considerations the following 42 floristic variables were selected: Figure 2.. Resulting cluster of the relationships between the 170 transects carried out that shows 5 clearly defined conglomerates (I-V) or floristic shore types: "Estuaric", "Sheltered", "Semisheltered", "Semiexposed" and "Exposed", following a zonation that goes from the least to the maximum degree of wave-exposure. The floristic variables had to be preferably stenoic as opposed to wave-exposure related, as this is precisely one of the most important ecological factors in the distribution of coastal organisms (Lewis, 1964; Lubchenco, 1980). The presence or absence of any floristic variable had to be attributable only to the general environmental conditions of the place where it was found. In keeping with this, we ruled out species, Ascophyllum nodosum (Linnaeus) Le Jolis Bifurcaria bifurcata Ross Boergeseniella thuyoides (Harvey) Kylin Bostrychia scorpioides (Hudson) Kützing Catenella caespitosa (Withering) Irvine Caulacanthus ustulatus (Turner) Kützing Ceramium gaditanum (Clemente) Cremades Ceramium shuttleworthianum (Kützing) Rabenhorst Cladostephus spongiosus (Hudson) C. Agardh Corallina elongata Ellis and Solander Cystoseira baccata (Gmelin) P. Silva Cystoseira nodicaulis (Withering) Roberts Cystoseira tamariscifolia (Hudson) Papenfuss Chondracanthus spp.: include C. acicularis (Roth) Fredericq and C. teedii (Roth) Kützing Chondrus crispus Stackhouse Fucus ceranoides Linnaeus Fucus spiralis Linnaeus Fucus spp.: include F. vesiculosus Linnaeus and F. serratus Linnaeus Gelidium attenuatum (Turner) Thuret Gelidium pusillum var. pulvinatum (C. Agardh) J. Feldmann Gelidium sesquipedale (Clemente) Thuret Gelidium spinosum (Gmelin) Silva Gigartina pistillata (Gmelin) Stackhouse Gracilaria gracilis (Stackhouse) Steentoft, Irvine and Farnham 71

4 J. Cremades, I. Bárbara & A. J. Veiga Gracilaria multipartita (Clemente) Harvey Haliptilon squamatum (Linnaeus) Johansen, Irvine and Webester Himanthalia elongata (Linnaeus) Gray Laminaria saccharina (Linnaeus) Lamouroux Laminaria spp.: include L. ochroleuca Pylaie and L. hyperborea (Gunnerus) Foslie Lithophyllum incrunstans Philippi Lithophyllum byssoides (Lamouroux) Foslie Mastocarpus stellatus (Stackhouse) Guiry Mesophyllum lichenoides (Ellis) Lemoine Monostroma oxyspermum (Kützing) Doty Pelvetia canaliculata (Linnaeus) Decaisne and Thuret Polysiphonia atlantica Kapraun and Norris Polysiphonia polyspora (C. Agardh) J. Agardh Pterosiphonia complanata (Clemente) Falkenberg Rhizoclonium tortuosum (Dillwyn) Kützing Stypocaulon scoparium (Linnaeus) Kützing Ulva intestinalis Linnaeus Zostera noltii Horneman Based on the data obtained after the completion of the field work, we drew up a matrix of the presence and absence of the variables in the transects. In order to create the matrix of the distances between the transects, we used the Lance and Williams distance and the UPGMA as the grouping method to arrive at the resulting cluster (Fig. 2). Productive study In order to perform this study there was a previous selection of the species which had been subjected to, or, in the future, might be subjected to some form of harvesting in the study area, therefore prompting us to focus on the analysis of the following 11 productive variables: Ascophyllum nodosum Bifurcaria bifurcata Chondrus crispus Fucus ceranoides Fucus spiralis Fucus spp. (F. vesiculosus and F. serratus) Gelidium sesquipedale Gigartina pistillata Himanthalia elongata Mastocarpus stellatus Pelvetia canaliculata A "resource" was considered to be both an individual species as well as groups of species that tend to be harvested jointly for a common purpose. For this reason, when we refer to "alginophytes" we take into consideration only the sum of the production of Ascophyllum nodosum, Fucus spiralis and Fucus spp. (including Fucus vesiculosus and F. serratus). When we refer to "carrageenophytes" we are considering the sum of the productions of Chondrus crispus, Mastocarpus stellatus and Gigartina pistillata, whereas references to "agarophytes" include only the production of Gelidium sesquipedale. A study of the richness of resources of the different shore types was carried out for each species, calculating the mean biomass (kg m -2 ), an intrinsic characteristic of each resource (Levitt et al., 1995), and the mean zone width occupied by said species on each type of shore on which it appears. A study of the mean biomass (kg m -2 ) of the different resources was performed by scraping off 2500 cm 2 samples (Niell, 1977 b; Fernández and Anadón, 1989) of all the species present in each transect. The zone width occupied by each species was measured perpendicular to the coastline. These samples and data were collected over the course of different times of the year to be able to reflect seasonal variations. In the case of Himanthalia elongata, for instance, which is a resource with strong seasonal variations, the subsequent analyses only took into account values corresponding to the summer period, which is the season when this resource is harvested. Fresh weight for each resource was calculated by weighing the clean, drained samples on a scale with an accuracy of 1 gr. Dry weight was determined by reserving an aliquot (15-25% of the fresh mass) which was dried at 110 ºC for 24 hours. The dry mass was weighed using a scale having an accuracy of 0.01 gr. These data were used to calculate the mean biomass (kg m -2 ) of each resource and its 95% confidence interval (De Wreede, 1985), in both fresh and dry weight. The standing stock of each resource per meter of coastline for each type of shore was estimated as the product of its mean biomass (kg m -2 ) and the mean width of the band of vegetation that forms there. 72

5 Intertidal Vegetation and Explotaible Resources on Galician Coasts Figure 3. Distribution of the floristic variables throughout shore types, taking into account the number of subgroups identified on each type of shore 73

6 J. Cremades, I. Bárbara & A. J. Veiga All calculations and analyses were performed using the SPSS statistics pack for Microsoft Windows ver RESULTS Floristic characterisation In the cluster diagram shown in Fig. 2 the relationships between the 170 transects carried out are depicted. In this cluster there are 5 clearly defined conglomerates or floristic shore types following a zonation that goes from the least to the maximum degree of wave-exposure. Within these 5 main groups, it is also possible to pinpoint several subgroups. Fig. 3 shows the distribution of the floristic variables throughout these conglomerates, taking into account the number of subgroups identified on each type of shore. The first group, named "Estuaric shore" (Fig. 3: 1), is characterised by the constant presence of Fucus ceranoides, Ulva intestinalis Linnaeus, Monostroma oxyspermum and Rhizoclonium tortuosum and on rare occasions, Bostrichya scorpioides, Zostera noltii and Fucus spiralis, which are species typically found on the "Sheltered shore". This type of shoreline is more homogeneous and shows less diversity in its floristic composition. The second group corresponds to the "Sheltered shore" (Fig. 3: 2), where bands of Ascophyllum nodosum, Catenella caespitosa and Gracilaria gracilis are found almost exclusively. Other species, which are very characteristic, but may also appear occasionally on other types of shores are: Pelvetia canaliculata, Fucus spiralis, Fucus spp. (F. vesiculosus/f. serratus) and Zostera noltii; in addition to Bostrychia scorpioides, Gelidium pussillum var. pulvinatum and Ceramium gaditanum, which form caespitose communities underneath the covering of different intertidal fucaceae. On the "Sheltered shore" three floristic subgroups can be distinguished. In the first (Fig. 3: 2A), it is common to observe the presence, although in small amounts, of species that are characteristic of the "Estuaric shore". The second subgroup (Fig. 3: 2B) is the most characteristic and stands out because of its great abundance in Ascophyllum nodosum; while the third, (Fig. 3: 2C), is in a transitional stage with the "Semisheltered shore". The latter species becomes scarce, as do many of the caespitose species mentioned above, while a lot of the species typical of the "Semisheltered shore" begin to make their appearance. The third group pertains to the "Semisheltered shore" (Fig. 3: 3), characterised mainly by the large bands of Fucus spp. (F. vesiculosus/f. serratus) and Himanthalia elongata, caespitose communities of Caulacanthus ustulatus, Chondracanthus spp. (C. acicularis/c. teedii) and communities of the large brown sublittoral seaweeds Cystoseira baccata and Laminaria saccharina. On this type of shore two floristic subgroups can be differentiated. In the first (Fig. 3: 3A), which is closer to the "Sheltered shore", Gelidium spinosum, Gracilaria multipartita and Cystoseira nodicaulis are frequently found. The second (Fig. 3: 3B), which is closer to the "Semiexposed shore", commonly includes bands of Bifurcaria bifurcata and, on rare occasions species such as Cladostephus spongiosus, Stypocaulon scoparium, Mastocarpus stellatus and Laminaria spp. (L. ochroleuca/hyperborean) start to appear. The fourth group identified is the one we call the "Semiexposed shore" (Fig. 3: 4), which has an enormous species richness and is characterised by its bands of Mastocarpus stellatus, Bifurcaria bifurcata and Laminaria spp. (L. ochroleuca/l. hyperborea). Other species which are typical of this type of shore are: Cladostephus spongiosus, Stypocaulon scoparium, Gelidium attenuatum and Gigartina pistillata. On this shore two floristic subgroups can be distinguished. In the first, (Fig. 3: 4A), which is closer to the "Semisheltered shore", the following species are common: Fucus spp. (F. vesiculosus/f. serratus), Chondracanthus spp. (C. acicularis/c. teedii), Caulacanthus ustulatus, Himanthalia elongata and Cystoseira baccata. The second (Fig. 3: 4B), which is closer to the "Exposed shore", frequently includes bands of Boergeseniella thuyoides, Cystoseira tamariscifolia, Gelidium sesquipedale, Mesophyllum lichenoides and Chondrus crispus. The last conglomerate identified is known as the "Exposed shore" (Fig. 3: 5). Its main floristic characteristic is the frequent and abundant occurrence of populations of Chondrus crispus, Ceramium 74

7 Intertidal Vegetation and Explotaible Resources on Galician Coasts Table 1. Mean biomass values (gr m -2 ), 95% conf. int. and S.D. in both fresh an dry weight pertaining to the different resources studied. *In Himanthalia elongata we only took into account values corresponding to the summer period shuttlerwothianum, Lithophyllum incrustans, Corallina elongata, Haliptilon squamatum and Lithophyllum byssoides. Two floristic subgroups can be distinguished on this type of shore. In the first (Fig. 3: 5A), which is closer to the "Semiexposed shore", the following species are common: Boergeseniella thuyoides, Cystoseira tamariscifolia, Gelidium sesquipedale and Mesophyllum lichenoides. The second (Fig. 3: 5B), which is more exposed, frequently includes bands of Polysiphonia atlantica, P. polyspora and Pterosiphonia complanata. Productive characterisation Tables 1 and 2 provide the mean biomass values (gr m -2 ) in both fresh and dry weight pertaining to the different resources studied. Table 3 presents the mean zone widths occupied by each resource on the different shore types, and lastly, Table 4 shows the standing stock per lineal meter of coast for each resource and shore type. From the standpoint of production, the "Estuaric shore" is primarily characterised by the presence of Fucus ceranoides as the sole recourse forming major bands of vegetation, with a mean of 27.1 kg fresh mass per meter of coastline (Table 4). The "Sheltered shore" is characterised for being the richest in alginophytes, with a mean of 96.0 kg fresh mass per meter of coastline (Table 4); with Ascophyllum nodosum being the most important and exclusive resource found there. Other resources, which are not exclusive, but which reach the highest production values on this coast are Pelvetia canaliculata and Fucus spiralis. The "Sheltered shore" also has resources such as Fucus spp., Bifurcaria bifurcata and Himanthalia elongata which are virtually absent from the "Estuaric shore". These two types of shores share Fucus ceranoides and F. spiralis as common resources. Statistical tests (T-test) show that there are significant differences in the mean widths of both resources on the two types of shore, 75

8 J. Cremades, I. Bárbara & A. J. Veiga Table 2.. Himanthalia elongata. Mean biomass values (gr m -2 ), 95% conf. int. and S.D. in both fresh an dry weight pertaining to the different sampling seasons. with the "Estuaric shore" being richer in F. ceranoides (P-value = 0.000), while the "Sheltered shore" is more abundant in F. spiralis (P-value = 0.006). Moreover, the "Sheltered shore" is significantly richer in alginophytes than the "Estuaric shore" (P-value = 0.000). The "Semisheltered shore" stands out because it produces high levels of Fucus spp., Bifurcaria bifurcata and, particularly the seaweed used in the food industry, Himanthalia elongata, which attains a mean of 44.5 kg fresh mass per meter of coastline (Table 4). These three resources also commonly occur on the "Sheltered shore", however the "Semisheltered shore" is significantly more productive in terms of H. elongata (P-value = 0.015) and B. bifurcata (P-value = 0.033). There were no significant differences found as regards productions of Fucus spp. (P-value = 0.105) and alginophytes (P-value = 0.496), and the two shore types were found to be rich in both resources. Other common resources include Fucus spiralis and Pelvetia canaliculata; with the "Sheltered shore" being significantly more productive both in the former species (P-value = 0.001) as well as in the latter (P-value = 0.000). Other aspects which prompted our decision to separate the two shore types from the standpoint of production are the fact that on the "Sheltered shore" we can still find Fucus ceranoides, while on the "Semisheltered shore" resources such as Gigartina pistillata and Mastocarpus stellatus (Table 3), characteristic of more exposed shores, begin to make their appearance. The "Semiexposed shore" is characterised, above all, by its richness in carrageenophytes, with a mean of 21.1 kg fresh weightmass per meter of coastline (Table 4). This may be attributed to the fact that it is on this type of shore where the highest levels of standing stocks of Mastocarpus stellatus and Chondrus crispus are reached. On the other hand, it is also somewhat rich in Gelidium sesquipedale, Fucus spp., Bifurcaria bifurcata and Himanthalia elongata. The "Semiexposed shore" can be distinguished from the "Semisheltered shore" in that only on the former do we find productions of Chondrus crispus and Gelidium sesquipedale, while only on the latter do we observe the appearance of Pelvetia canaliculata. As regards common resources, the "Semiexposed shore" is significantly more productive in Mastocarpus stellatus (P-value = 0.000), Gigartina pistillata (P-value = 0.008) and in the standing stock of carrageenophytes (P-value = 0.000). In contrast, the "Semisheltered shore" is significantly richer in Fucus spp. (P-value = 0.008) and in the standing stock of alginophytes (Pvalue = 0.002). No significant differences were found between the two shores in terms of the production of Himanthalia elongata (P-value = 0.328) and Fucus spiralis (P-value = 0.117); although the values were higher on the "Semisheltered shore" (Table 4). The "Exposed shore" is characterised by its moderate richness in carrageenophytes and, particularly by its great richness in the agarophyte Gelidium sesquipedale (3.8 kg fresh weight per meter of coastline, Table 4). The differences between the 76

9 Intertidal Vegetation and Explotaible Resources on Galician Coasts Table 3. Mean zone widths, in meters, occupied by each resource on the different shore types. "Semiexposed shore" and the "Exposed shore" may be partially due to the fact that the former may still include Fucus spiralis and Bifurcaria bifurcata, although in very low quantities (Table 4). If we consider the resources common to the two shore types, we can see that the "Semiexposed shore" is significantly more abundant in Fucus spp. (P-value = 0.000), Himanthalia elongata (P-value = 0.000), Mastocarpus stellatus (P-value = 0.001) and Gigartina pistillata (P-value = 0.027). The "Exposed shore", in contrast, produces significantly higher quantities of the agarophyte Gelidium sesquipedale (P-value = 0.009). For the above reasons, the "Semiexposed shore" has a greater production of alginophytes (P-value = 0.000) and carrageenophytes (P-value = 0.013); whereas the "Exposed shore" is more abundant in agarophytes (Pvalue = 0.010). The only resource common to the two shore types that did not present significant differences was Chondrus crispus (P-value = 0,407). DISCUSSION In view of the floristic composition of the different locations under study in this work, and after considering the results obtained from the similarity analysis, we were able to classify the Galician coastline into five main types, labelled in increasing order of wave-exposure, as follows: "Estuaric shore", "Sheltered shore", "Semisheltered shore", "Semiexposed shore" and "Exposed shore". A number of previous research papers done in Galicia already reported the existence of different shore types in regard to a floristic classification of different locations. Thus Donze (1968) identified 6 shore types from the Ría de Arousa (Pontevedra), Pérez-Cirera (1976) also reported 6 types from the Ría de Corme e Laxe (A Coruña), while Pérez-Cirera and Pacheco (1985) described 5 shore types from the 77

10 J. Cremades, I. Bárbara & A. J. Veiga Ría de Lires (A Coruña) and Bárbara et al. (1995) and Bárbara and Cremades (1996) described 4 shore types from the Ría de A Coruña. These classifications have generally been carried out subjectively, in some cases based on the personal experience of the authors, and in others there has been an attempt to draw analogies between their observations and the classification done by Lewis (1964) for the shores of the British Isles. Thanks to the methodology used in this study and to the criteria followed in the selection of the floristic variables, we believe that some of the subjective aspects of the previous classifications have been substantially reduced, given that the shore types identified and their respective subgroups are real entities that are repeated biogeographically and easily identified in nature. The fact that subgroups of a small range were found on each shore type only serves to highlight the variability within the groups. This variability might be due to independent factors related to wave-exposure whose effect was not analysed in this study (orientation, substrate type, etc.) or it might be an intrinsic characteristic of the group itself, especially attributable to their degree of variability and species richness. As can be seen in the results, the shores subjected to more extreme conditions (estuaric and exposed) have the lowest degree of floristic variability, while the greatest intragroup variability is found on shores having intermediate conditions. Table 4. Mean values (I.C. 95%) and S.D. of the standing stock (in kg of fresh and dry weight) per lineal meter of coast for each resource and shore type 78

11 Intertidal Vegetation and Explotaible Resources on Galician Coasts The floristic characterisation put forth here roughly coincides with the one proposed by Donze (1968) for the Ría de Arousa, although the latter classification covers a smaller range than ours, as the stretch we call "Semiexposed shore" pertains to the area that this author labels "Very exposed shores". Therefore Donze's classification (1968) does not include what we designate as "Exposed shore". Although this could be interpreted as being one of the limitations cited by Lewis (1964) for wave-exposure biological scales, under no circumstances does it invalidate the results obtained in this paper; since, rather than being a methodological limitation, it is a logical consequence of Donze's attempt to structure his scale the same way as Lewis (1964) did on the British Isles, but in a territory that lacked one of his extreme types. The research carried out by Pérez-Cirera (1976) in the Ría de Corme e Laxe is worthy of similar commentaries, as this author described the vegetation of the different shore types identified according to the classification method proposed by Donze (1964) in the Ría de Arousa. The five shore types identified in this paper differ not only in their floristic composition, but they also show significant differences in production levels of the intertidal resources having commercial interest. In this respect, there have been very few papers dealing with the assessment of these types of resources on the Galician coast and in other regions near the Northwest Peninsula. Therefore most of the results obtained here are unprecedented. In the case of Ascophyllum nodosum, we must point out that the mean width of this resource, which was found at all the locations in Galicia belonging to the sheltered shores (3.91±1.52 m; Table 3), is similar to what Niell and Soneira (1976) reported in the Ría de Vigo (4.2±0.63 m). However, if we consider the standing stock per meter of coastline, these authors obtained 128.8±12.59 kg of fresh weight, which is much higher than our value (59.16±22.97 kg. Table 4). The difference is due to the methodology used, as these authors based their calculations on data solely from locations where this resource occurred. We, however, made calculations taking into account all the transects pertaining to the sheltered shores, regardless of whether they had populations of Ascophyllum nodosum, given that in our premise we hold that the coastal strip is a zone that is constantly changing and that it behaves like a mosaic-cycle, where the absence of a particular species may be merely a temporary situation (Remmert, 1991; Little and Kitching, 1996). As regards the mean biomass (gr m -2 ) of the carrageenophyte Chondrus crispus, Anadón and Fernández (1988) reported a biomass of approximately 434 gr dry weight m -2, on the coast of the neighbouring region of Asturias, which was lower than our data for Galician populations (654,9±76,4 gr dry mass m -2, Table 1). However, in terms of the standing stock per meter of coastline, the mean value reported by Anadón and Fernández (1988) for the transects in which this carrageenophyte occurred was kg of dry weight, slightly higher than the value of 2.18±0.58 kg and 1.77±0.66 kg, that we found on the semiexposed and exposed shores of Galicia, respectively (Table 4). Similar to the case of Ascophyllum nodosum, these differences may be attributed to the fact that these authors made their calculations with data coming exclusively from locations where this resource was present, whereas, our calculation took into consideration all the locations belonging to the semiexposed and exposed shores, regardless of whether or not there were populations of Chondrus crispus. Based on this, Anadón and Fernández (1988) reported a mean zone width of 6.58 m for the Asturian coast, whereas our study for Galicia showed mean values of 3.33 y 2.72 m on semiexposed and exposed shores, respectively (Table 3). With reference to Gelidium sesquipedale, the mean biomass values (gr m -2 ) found in this work ( gr fresh weight m -2 and gr dry weight m -2, Table 1) are substantially higher than the value of 170 gr dry mass m -2 obtained by Fernández and Anadón (1989) for the intertidal zone on the Asturian coast and than the value of 1608 gr fresh mass m -2 reported by Borja (1988) on the Basque coast, although we must bear in mind that the data from the latter author come from a subtidal zone. Similarly, the standing stock per meter of coastline that Fernández and Anadón (1989) reported in other locations of Asturias where this agarophyte is present (279 gr dry weight) is lower than the values obtained in our research (Table 4), for locations pertaining to both the semiexposed and exposed shores, 340±180 and 980±420 gr dry mass, respectively. 79

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