Abundance patterns of macrofauna associated to marine macroalgae along the Iberian Peninsula

Zool. baetica, 22: 3-17, 2011 Abundance patterns of macrofauna associated to marine macroalgae along the Iberian Peninsula Patrones de abundancia de la macrofauna asociada a macroalgas marinas a largo de la Península Ibérica J. M. GUERRA-GARCÍA, M. P. CABEZAS, E. BAEZA-ROJANO, D. IZQUIERDO, J. CORZO, M. ROS, J. A. SÁNCHEZ, A. DUGO-COTA, A. M. FLORES-LEÓN & M. M. SOLER-HURTADO Laboratorio de Biología Marina, Dpto. de Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, 41012 Sevilla (Spain) Fax: 0034 954233480; E-mail: jmguer[email protected] Recibido el 6 de agosto de 2010. Aceptado el 3 de octubre de 2010. ISSN: 1130-4251 (2011), vol. 22, 3-17 Key words: Macrofauna, distribution, biogeography, Spain, Portugal. Palabras clave: Macrofauna, distribución, biogeografía, España, Portugal. ABSTRACT The distribution and abundance patterns of the macrofauna associated to macroalgae were studied on a spatial scale along the Iberian Peninsula. Nineteen stations and four dominant algae were selected (intertidal zone: Corallina elongata and Asparagopsis armata; subtidal zone: Stypocaulon scoparium and Cladostephus spongiosus). Five environmental factors were also considered (seawater temperature, conductivity, dissolved oxygen, turbidity and pH). The Atlantic coast was characterized by lower temperature and conductivity as well as higher values of oxygen and turbidity than the Mediterranean coast. A total of 106274 macrofaunal specimens were sorted and examined (68% arthropods, 27% molluscs, 4% annelids and 1% echinoderms). Crustaceans were the dominant group in all the macroalgae (ca. 80% in C. elongata and A. armata, ca. 50% in S. scoparium and C. spongiosus) followed by molluscs, which were more abundant in the subtidal algae (ca. 40%) than in intertidal ones (ca.10%). Abundance patterns of macrofauna along the Iberian Peninsula were similar in the four studied algae. Most of crustaceans belonged to the order Amphipoda, which showed high densities (>1000 ind/1000 ml algae) along the whole Peninsula; isopods showed the highest abundances in the Atlantic, while tanaids, cumaceans and decapods were more abundant in the Mediterranean. Among molluscs, gasteropods showed highest abundances along the Atlantic coasts, whereas bivalves showed higher densities along the Mediterranean. Taking into Zool. baetica, 22: 3-17, 2011 J. M. GUERRA-GARCÍA, et al. 4 account that all selected stations were characterised by absence of anthropogenic influence, the abundance patterns obtained for macrofauna could be explained on the basis of natural differences in water temperature, oxygen, conductivity and turbidity between Mediterranean and Atlantic, existing a transitional gradient between warm-water (from north Africa and Mediterranean Sea) and cold-water taxa (from the North Sea and the Arctic). RESUMEN Se llevó a cabo un estudio espacial de los patrones de abundancia y distribución de la macrofauna asociada a macroalgas a lo largo de la Península Ibérica. Se seleccionaron 19 estaciones y 4 algas dominantes (zona intermareal: Corallina elongata y Asparagopsis armata; zona submareal: Stypocaulon scoparium y Cladostephus spongiosus). Se consideraron también cinco variables ambientales (temperatura del agua, conductividad, oxígeno disuelto, turbidez y pH). La costa atlántica se caracterizó por valores más bajos de temperatura y conductividad, y más altos de oxígeno y turbidez. Se examinaron 106274 individuos de la macrofauna (68% artrópodos, 27% moluscos, 4% anélidos y 1% equinodermos). Los crustáceos fueron dominantes en todas las macroalgas (alrededor del 80% en C. elongata y A. armata, y en torno al 50% en S. scoparium y C. spongiosus), seguidos por los moluscos, que fueron más abundantes en el submareal (40%) que en el intermareal (10%). Los patrones de abundancia de la macrofauna a lo largo de la Península Ibérica fueron similares en las cuatro algas estudiadas. La mayoría de los crustáceos pertenecieron al orden Amphipoda, que mostró densidades muy altas (>1000 ind/1000 ml alga) en toda la Península; los isópodos mostraron las mayores densidades en el Atlántico, mientras que los tanaidáceos, cumáceos y decápodos fueron más abundantes en el Mediterráneo. Entre los moluscos, los gasterópodos mostraron abundancias mayores en el Atlántico, mientras que los bivalvos dominaron en el Mediterráneo. Teniendo en cuenta que todas las estaciones seleccionadas no tenían influencia antrópica importante, los patrones de abundancia obtenidos podrían explicarse en base a diferencias naturales en la temperatura del agua, oxígeno, conductividad y turbidez, existiendo un gradiente transicional entre taxones de aguas más cálidas (del norte de Africa y del Mediterráneo) y taxones de aguas más frías (del Mar del Norte y el Ártico). INTRODUCTION Studies dealing with marine macrofauna associated to macroalgae are very scarce, probably due to the considerable time and efforts required to sort and identify all the material. However, faunistic information obtained from this kind of studies is essential, not only as baseline for future ecological and biogeographical studies, but also as bioindicator tool in marine monitoring programmes (e.g. Sánchez-Moyano & García-Gómez, 1998; Dauvin & Ruellet, 2007; Guerra-García et al., 2009a). Zool. baetica, 22: 3-17, 2011 ABUNDANCE PATTERNS OF MACROFAUNA ASSOCIATED TO ALGAE 5 The presence of vegetation allows a greater species diversity and abundance of individuals than unvegetated habitats (Sánchez-Moyano et al., 2007) providing suitable microhabitats, nutritional resources and protection from predators. Marine algae are known to provide habitats for a wide range of animal species (Williams & Seed, 1992). Crustaceans, molluscs and polychaetes are the major animal taxa associated with macrophytes (Taylor & Cole, 1994), and information about their spatial and temporal patterns of abundance is necessary to properly understand marine ecosystems. Nevertheless, few attempts have been made to investigate the relation between geographical changes in algae composition and patterns of macroinvertebrate diversity and abundance (Russo, 1997; Pereira et al., 2006). The Iberian Peninsula is especially interesting from the biogeographical point of view. It is located in the southwest of Europe, being the westernmost of the three major southern European peninsulas. Its coasts are washed by the Mediterranean on the eastern side and Atlantic on the northern and western side, converging at the Strait of Gibraltar. In spite of its privileged location, studies focused on invertebrates associated to marine macroalgae are scarce and the majority of contributions have been conducted in the Strait of Gibraltar: molluscs (Sánchez-Moyano et al., 2000), annelids (Sánchez- Moyano et al., 2002; Sánchez-Moyano & García-Asencio, 2009) and crustaceans (Sánchez-Moyano & García-Gómez, 1998; Sánchez-Moyano et al., 2007; Guerra-García et al., 2009b,c). Although a variety of studies have dealt with macrofauna associated to algae in different areas of the Iberian Peninsula (e.g. Jimeno & Turón, 1995; Viejo, 1999; Pereira et al., 2006; Vázquez-Luis et al., 2008), these studies have been focused in particular groups or are restricted to specific sites. The main objective of the present study was to explore the abundance patterns of the main groups of macrofauna along the Iberian Peninsula, comparing the data obtained in four dominant algae along the coasts of Spain and Portugal: Corallina elongata J. Ellis & Solander, Stypocaulon scoparium (L.) Kützing, Cladostepus spongiosus (Hudson) Agardh and the invasive Asparagopsis armata Harvey. MATERIAL AND METHODS Nineteen stations were selected along the Atlantic and Mediterranean coasts, including the Strait of Gibraltar (Fig. 1). We chose relatively undisturbed enclaves with low human pressures to avoid the effect of anthropogenic influence on the natural biogeographical and ecological patterns of species. Zool. baetica, 22: 3-17, 2011 J. M. GUERRA-GARCÍA, et al. 6 Sampling was conducted in summer 2008 (from 5th June to 5th August). The following environmental parameters were measured “in situ” at each sampling site: water temperature, pH, conductivity, dissolved oxygen and turbidity. Five measurements were made for each parameter and mean values and standard deviation were calculated. Conductivity and pH were measured using a conductivimeter-pHmeter CRISON MM40, temperature and oxygen concentration with an oxymeter CRISON OXI 45P, and turbidity in nephelometric turbidy units (ntu) using a turbidimeter WTW 335 IR. The algae Corallina elongata, Stypocaulon scoparium, Cladostephus spongiosus and Asparagopsis armata were selected as substrates since they Fig. 1.—Study area showing the sampling stations. Ogella (1), Oyambre (2), Cetarea (3), Baleo (4), Cabo Silleiro (5), Labruge (6), Playa Azul (7), Vale dos Homens (8), Castelo (9), Bolonia (10), Isla de Tarifa (11), Torreguadiaro (12), Cerro Gordo-Herradura (13), Cabo de Gata (14), Cala del tío Ximo (15), Benicassim-Oropesa (16), Torrent del Pi (17), Cala de Sant Françesc (18), L’Estartit (19). Fig. 1.—Área de estudio mostrando las estaciones de muestreo. Ogella (1), Oyambre (2), Cetarea (3), Baleo (4), Cabo Silleiro (5), Labruge (6), Playa Azul (7), Vale dos Homens (8), Castelo (9), Bolonia (10), Isla de Tarifa (11), Torreguadiaro (12), Cerro Gordo-Herradura (13), Cabo de Gata (14), Cala del tío Ximo (15), Benicassim-Oropesa (16), Torrent del Pi (17), Cala de Sant Françesc (18), L’Estartit (19). Zool. baetica, 22: 3-17, 2011 ABUNDANCE PATTERNS OF MACROFAUNA ASSOCIATED TO ALGAE 7 are among the dominant algae along the whole Iberian Peninsula (pers. observ.). Corallina elongata was present in all stations (19) whereas S. scoparium was present in 14 stations, A. armata in 11 and C. spongiosus in 9. Corallina elongata and A. armata were collected from the low zone of the intertidal area, whereas S. scoparium and C. spongiosus were taken by snorkeling from shallow waters (0-5 m deep) along the subtidal. Hence, two algae were selected to characterise the intertidal zone and other two to explore the macrofaunal patterns in the shallow subtidal. At each station, macroalgae were collected by hand from different rocks to avoid effect of patchiness and to adequately sample macrofaunal diversity, until a volumen of approximately 200 ml of each algae was completed (see Thiel et al., 2003; Guerra-García et al., 2009b,c). The samples were preserved in ethanol 70-80%, brought to laboratory and sieved using a mesh size of 0.5 mm. All macrofauna were sorted and separated to general groups: arthropods (including Crustacea, Pycnogonida and Chironomida), Molluscs, Annelids and Echinoderms. Crustaceans were also separated in Amphipoda, Isopoda, Tanaidacea, Decapoda and Cumacea, and molluscs in Gastropoda, Bivalvia and Polyplacophora. Abundance of each faunal group was expressed as number of individuals/1000 ml and maps of distribution were elaborated per groups and algae. To estimate the cover of each algal species in each locality, we used five random quadrats of 50 x 50 cm subdivided into 25 square units of 10 x 10 cm with thick fishing line. The presence/absence of the species was recorded for each unit and data were expressed as cover percentage (mean ± SD of the 5 replicates). RESULTS AND DISCUSSION The Mediterranean stations showed higher values of temperature and conductivity, as well as lower values of oxygen concentration and turbidity than the stations along the Atlantic coast (Fig. 2). Oppositely, pH maintained similar values amongst the surveyed sites, with an average of 8.16, ranging from 8 (station 6) to 8.33 (station 10). Temperature was negatively correlated with oxygen (r=-0.69, p<0.01) and turbidity (r=-0.54, p<0.05) and positively with conductivity (r=0.73, p<0.01). Station 6 showed abnormal characteristics when compared with the rest of the stations, with the maximum value of turbidity and minimum value of conductivity and temperature, probably due to river influence. When focusing on the abundance patterns of macroalgae, cover of the four species showed lower values in Mediterranean stations than in the Atlantic Zool. baetica, 22: 3-17, 2011 J. M. GUERRA-GARCÍA, et al. 8 Fig. 2.—Abiotic variables measured in each station (Mean ± SD) Fig. 2.—Variables abióticas medidas en cada estación (Media ± DE) (Fig. 3). This pattern was more evident in the intertidal Corallina elongata and Asparagopsis armata (in fact this algae was absent in Mediterranean stations) while it was not so clear in the subtidal Stypocaulon scoparium and Cladostephus spongiosus. Lower algal abundances in Mediterranean stations can be probably explained by higher seawater and air temperatures. Other factors could also affect this distribution, such as tides, which affects the Atlantic coast; in Atlantic coast some species are adapted to grow up with specific conditions, while in the Mediterranean Sea, the competition among species for substrate is very high due to the lack of tidal effect. In general terms, the most important species in terms of cover was C. elongata, Zool. baetica, 22: 3-17, 2011 ABUNDANCE PATTERNS OF MACROFAUNA ASSOCIATED TO ALGAE 9 followed by S. scoparium. Cover of C. spongiosus was lower than 20% in all the stations. Concerning the fauna, a total of 106274 specimens were sorted and examined, out of which 68% were arthropods (mainly crustaceans), 27% molluscs, 4% annelids and 1% echinoderms. Arthropods (basically crustaceans) were the dominant phyla in the four algae. In fact, in the intertidal algae C. elongata and A. armata, arthropods represented more than 80%. In the subtidal algae S. scoparium and C. spongiosus, arthropods were also dominant, but molluscs were also significantly represented (Fig. 4). This general pattern is normally maintained in all the sampled stations (Fig. 5). Crustaceans were the dominant group in C. elongata and A. armata in all the sites. In the case of S. scoparium and C. spongiosus, crustaceans were Fig. 3.—Cover percentage of the four algae studied (Media ± SD) in each station. Fig. 3.—Cobertura en porcentaje de las cuatro algas estudiadas (Media ± DE) en cada estación. Zool. baetica, 22: 3-17, 2011 J. M. GUERRA-GARCÍA, et al. 10 also dominant in most stations, except for stations 7 and 8 (S. scoparium) and stations 1 and 15 (C. spongiosus), where molluscs represented more than 70% of the total abundance. Annelids and echinoderms were always the less important group in terms of abundance. Sánchez-Moyano (1996) studied the macrofauna associated to S. scoparium in 13 stations of Algeciras Bay, Southern Spain (3-10 m deep); in this case, arthropods were also the dominant group, followed by annelids, which were more abundant in Algeciras Bay (20-50%) than in the stations sampled during the present study (<10%). This could be probably due to the degree of anthropogenic influence in Algeciras Bay, which favoured polychaetes in comparison with Fig. 4.—Total abundance percentages of arthropods, molluscs, annelids and echinoderms measured in each algal species Fig. 4.—Porcentajes de abundancia total de artrópodos, moluscos, anélidos y equinodermos medidos en cada especie de alga. Zool. baetica, 22: 3-17, 2011 ABUNDANCE PATTERNS OF MACROFAUNA ASSOCIATED TO ALGAE 11 Fig. 5.—Abundance percentages of arthropods, molluscs, annelids and echinoderms in each station for the four algae sampled. Fig. 5.—Porcentajes de abundancia de artrópodos, moluscos, anélidos y equinodermos en cada estación para las cuatro algas muestreadas.