Assessment of long-term interaction between an opportunistic macroalga and a native seagrass in a Mediterranean coastal lagoon
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1
Oceanographic Center of Murcia, Spanish Institute of Oceanography, Spain
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2
Independent researcher, Spain
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3
Association of Naturalists of the Southeast (ANSE), Spain
Algal overgrowth has been recognized as an important potential threat to seagrass habitats in many coastal areas. Opportunistic seaweed species can quickly develop large and dense populations able to replace seagrass species due to their higher ability to compete for resources (e.g. light, nutrients). They can also modify sediment properties, generating adverse conditions for seagrasses (e.g. sediment anoxification) and indirectly favoring their substitution. The replacement of seagrassess by seaweeds usually triggers deep ecosystem transformations with the potential for generating alternative states and the loss of the valuable ecosystem functions and services that seagrass habitats provide. During the 1970s, the Mar Menor coastal lagoon (SE Spain) experienced a deep transformation due to human-induced changes in the hydrographic conditions of the ecosystem. The widening of a navigational channel reduced salinity levels of lagoon waters allowing the introduction and massive spread of the seaweed Caulerpa polifera. Subsequent studies in this coastal lagoon have assumed that the introduced seaweed had replaced Cymodocea nodosa populations living in deep bottoms (Lloret et al., 2005; Ruzafa el al., 2012). The modification of sediment properties (e.g. increase in silt and organic matter content) provoked by the high abundance of C. prolifera, in combination with reduced light levels, have been argued as the major causes of seagrass decline in deep bottoms of the Mar Menor lagoon. This hypothesis, however, has been derived from studies using inappropriate sampling techniques for estimating seagrass abundance (e.g. Van Veen drag) and with very low spatial coverage (i.e. a few sampling points). Moreover, there is no evidence to support the existence of competitive interaction between both benthic macrophytes so far.
In this study, the competitive interaction between C. nodosa and C. prolifera has been evaluated in the Mar Menor lagoon by (i) a high resolution and precision mapping of benthic communities and (ii) exploring relationships between seagrass abundance and macroalga abundance and abiotic factors (e.g. depth and sediment properties) using Bayesian linear regression models. Benthic cartography was obtained based on direct visual observations and recordings from trawled underwater videocamera. Abundance of both macrophytes was measured by divers at different spatial scales in 49 sampling points distributed throughout the lagoon. Macrophytes abundance was characterized at the landscape level (macrocover) and within meadow patches (mesocover and biomass). For C. nodosa, shoot density was also measured within patches. Granulometry and organic matter content were used to describe sediments properties.
Our results showed that the dominant benthic macrophytes in the Mar Menor were C. nodosa and C. prolifera. The seaweed occurred over most lagoon areas (90% of the surface), whereas the seagrass was present in 60% of the lagoon bottoms, forming mixed meadows with C. prolifera in deep bottoms (>3 m, 55% of the lagoon area) and relatively continuous monospecific meadows in shallow areas. These results contrasted with the absence of C. nodosa in deep bottoms of the lagoon described in previous studies (Lloret et al., 2005; Ruzafa el al., 2012).
Figure 1. Macrophyte species distribution in the Mar Menor lagoon.
Linear models did not recognized C. prolifera abundance as a relevant factor for most C. nodosa descriptors (macrocover, mesocover and biomass). However, the interaction between alga mesocover and depth or organic matter showed a positive effect on seagrass abundance at the meadow level. This finding evidenced that the greatest seagrass abundance in deep bottoms of the lagoon occurred simultaneously with a strong presence of C. prolifera, which supported the absence of a competitive interaction between both macrophytes.
Figure 2. Relationships between C. nodosa mesocover, depth and C. prolifera mesocover based on the 49 sampling points distributed throughout the Mar Menor lagoon
Our findings confirm that C. nodosa has not been replaced by the seaweed C. prolifera in deep areas of the lagoon, where both species live together developing high abundances. Curiously, this pattern of distribution suggested the existence of potential positive interaction between both species, although experimental manipulative works would be necessary to obtain a thorough understanding of this interaction.
Acknowledgements
This research has been funded by the Project “Conservación de arenales y lagunas costeras en el sureste de la península ibérica” financed by the “Fundación Biodiversidad“ and runned by the Spanish Institute of Oceanography and Asociación de Naturalistas del Sureste
References
Lloret, J., Marin, A., Marin-Guirao, L., & Velasco, J. 2005. Changes in macrophytes distribution in a hypersaline coastal lagoon associated with the development of intensively irrigated agriculture. Ocean & Coastal Management, 48(9-10), 828-842.
Pérez-Ruzafa, A., Marcos, C., Bernal, C. M., Quintino, V., Freitas, R., Rodrigues, A. M., ... & Pérez-Ruzafa, I. M. 2012. Cymodocea nodosa vs. Caulerpa prolifera: Causes and consequences of a long term history of interaction in macrophyte meadows in the Mar Menor coastal lagoon (Spain, southwestern Mediterranean). Estuarine, Coastal and Shelf Science, 110, 101-115.
Keywords:
Cymodocea nodosa,
Caulerpa prolifera,
Mar Menor lagoon,
Competitive interaction,
Benthic cartography,
Bayesian Models
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Ecology, Biodiversity and Vulnerable Ecosystems
Citation:
Belando
M,
Bernardeau-Esteller
J,
Paradinas
I,
Ramos-Segura
A,
Garcia-Muñoz
R,
Garcia-Moreno
P,
Marin-Guirao
L and
Ruiz
J
(2019). Assessment of long-term interaction between an opportunistic macroalga and a native seagrass in a Mediterranean coastal lagoon.
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00190
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Received:
26 May 2019;
Published Online:
27 Sep 2019.
*
Correspondence:
Dr. Jaime Bernardeau-Esteller, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Murcia, Spain, jbernardeau@gmail.com