Spatial distribution and biomass of aquatic rooted macrophytes and their relevance in the metabolism of a Mediterranean coastal lagoon

Abstract

SUMMARY: This work aims to characterise the current autotrophic compartment of the Albufera des Grau coastal lagoon (Menorca, Balearic Islands) and to assess the relationship between the submerged macrophytes and the limnological parameters of the lagoon. During the study period the submerged vegetation was dominated by the macrophyte Ruppia cirrhosa, which formed dense extensive meadows covering 79% of the surface. Another macrophyte species, Potamogeton pectinatus, was also observed but only forming small stands near the rushing streams. Macroalgae were only occasionally observed. Macrophyte biomass showed a clear seasonal trend, with maximum values in July. The biomass of R. cirrhosa achieved 1760 g DW m -2 , the highest biomass ever reported for this species in the literature. The seasonal production-decomposition cycle of the macrophyte meadows appears to drive the nutrient dynamics and carbon fluxes in the lagoon. Despite the significant biomass accumulation and the absence of a washout of nutrients and organic matter to the sea, the lagoon did not experience a dystrophic collapse. These results indicate that internal metabolism is more important than exchange processes in the lagoon.Keywords: coastal lagoons, macrophytes, Ruppia cirrhosa, Western Mediterranean. RESUMEN: DISTRIBUCIÓN ESPACIAL Y BIOMASA DE LOS MACRÓFITOS SUMERGIDOS Y SU RELEVANCIA EN EL METABOLISMO DEUNA LAGUNA LITORAL MEDITERRÁNEA. -El presente estudio pretende caracterizar el componente autotrófico de la laguna litoral de s'Albufera des Grau (Menorca, Islas Baleares) y determinar la relación entre los macrófitos acuáticos y la dinámica de los principales parámetros limnológicos del sistema. Durante el periodo estudiado, la vegetación sumergida estuvo dominada por el macrófito Ruppia cirrhosa, que formaba extensas praderas en toda la laguna. También se observó otra especie de macrófito, Potamogeton pectinatus, pero sólo formando pequeñas formaciones cerca de la entrada de los torrentes a la laguna. La biomasa de macrófitos mostró un claro ciclo estacional, con los valores máximos centrados en verano. La biomasa de R. cirrhosa alcanzó 1760 g DW m -2 , que supone el valor más alto de biomasa descrito para esta especie en la literatura. El ciclo estacional de producción-descomposición de las praderas de macrófitos parece ser el responsable de la diná-mica de nutrientes y de los flujos de carbono en la laguna. A pesar de las elevadas biomasas acumuladas y de la ausencia de un lavado de nutrientes y materia orgánica hacia el mar, la laguna no mostró un colapso distrófico, sugiriendo la importancia del metabolismo interno de la laguna por encima de los procesos de intercambio con el mar.Palabras clave: lagunas litorales, macrófitos, Ruppia cirrhosa, Mediterráneo Occidental.

Differences in the growth cycle ofRuppia cirrhosa(Petagna) Grande in a Mediterranean shallow system

“…Macrophyte descriptors also differ between the two groups of ponds with values higher in B than in A ponds. Biomass outcomes were comparable with values registered previously (Pérez & Camp 1986;Menéndez & Comín 1989;Calado & Duarte 2000;Menéndez 2002;Pergent et al 2006;Casagranda & Boudouresque 2007), but were higher than values reported in Ballester (1985) and lower than values reported in Obrador et al (2007) and Obrador and Pretus (2010).…”

“…Calado & Duarte 2000;Menéndez 2002;Gesti et al 2005;Mannino & Sarà 2006;Pergent et al 2006;Casagranda & Boudouresque 2007;Obrador et al 2007;Shili et al 2007;Obrador & Pretus 2010). Many studies have shown the Ruppia capacity to adopt a different growth cycle (annual or perennial) in response to the permanency of the water body (Verhoeven 1979;Brock 1982;Kantrud 1991;Gesti 2000;Malea et al 2004), suggesting a considerable plasticity in the allocation of resources to seed production or vegetative growth.…”

“…cirrhosa shows extremely high resistance to variations in environmental conditions: salinity, water turbidity, the redox status of surface sediments, light availability and water level that are considered the main factors controlling the development and abundance of this plant (Verhoeven 1979(Verhoeven , 1980Menéndez & Comín 1989;Azzoni et al 2001;Menéndez et al 2002;Obrador et al 2007;Sfriso et al 2009;Obrador & Pretus 2010;Sfriso 2010). The enrichment in nutrients may have effects on R. cirrhosa plants improving their development (Pergent et al 2006) even though Mannino and Sarà (2006) showed that R. cirrhosa cover and suspended organic matter were negatively correlated.…”

A Dynamic Model to Simulate Water Level and Salinity in a Mediterranean Coastal Lagoon

“…In these meadows, the highest biomass ever reported for this species is found (up to 1,760 g DW m −2 ; Obrador et al 2007). Intense phytoplankton peaks, which are the main drivers of turbidity dynamics in the lagoon (Obrador and Pretus 2008), are observed every year usually in relation to the entrance of nutrients from the watershed or from the decomposition of the macrophyte meadows (Obrador et al 2007).…”

“…Unusual variations in these hydrological parameters can lead the system to critical situations with important ecological consequences. These include haline stratification and consequent bottom anoxia due to the massive entrance of seawater (Pretus and Obrador 2004), mid-term salinisation, which can result in hypersalinity (Pretus 1989;Cardona 2001;Pretus 2003), and littoral desiccation, which is caused by low water levels and can lead to large-scale mortality of the dense and extensive macrophyte meadows that are found throughout the lagoon (Obrador et al 2007).…”