Title : Does the expansion of limoniastrum monopetalum facilitate the maintenance of the parasitic species cistanche phelipaea in Mediterranean Estuaries
Limoniastrum monopetalum is a wild shrub (Plumbaginaceae), growing naturally in coastal salt marshes and new sandy deposits in estuaries of the Mediterranean coast. This species shows a high colonizing capacity in the sandy deposits growing in the form of successive hooks. Additionally, it exhibits a high potential for competition with other scrub species in the succession of estuarine habitats due to its special form of growth, developing a center of up to 2 meters in height and a surrounding surface motivated by decumbent stems of 40 cm in height, generating individuals up to 50 square meters of total area. Cistanche phelypaea (Orobancheae) is a holoparasitic species that inhabits the sandy deposits of Mediterranean estuaries. The set of host species of Cistanche phelipaea is reduced, the most important being Limoniastrum monopetalum, Arthrocnemum macrostachyum, Atriplex halimus and Halimione portulacoides. These species are part of the succession in the ecotones between dunes and marshes of the Mediterranean estuaries. Through the use of the stable isotope δ13C we have determined the reality of Limoniastrum monopetalum as a host species for Cistanche phelypaea. Using aerial photographs (1952-2022) we have revealed the colonization capacity of Limoniastrum monopetalum of the sandy deposits in the Marismas del Odiel Natural Area and Biosphere Reserve (Huelva, SW Spain), going from 162 to 594 individuals between 1952 and 2022. Its expansive capacity in the colonizing process of sandy deposits is very high, as well as its potential as a competitor species in estuarine ecotones. The surface of the individuals of Limoniastrum monopetalum ranges from 0.05 to 56.6 square meters. The ecotones between dunes and marshes constitute the habitat where the greatest number of stems of Cistanche phelipaea appears. From the point of view of the analysis of a system of biogeography of islands, the ecotone acts as a continent supplying a rain of propagules on the system of islands formed by individuals of Limoniastrum monopetalum colonizing through propagules supplied by the habitat of ecotone identified as continent. Limoniastrum monopetalum individuals as islands are found at a distance of the ecotone ranging from 8 to 83 meters. The number of stems of Cistanche phelipaea that appear in individuals of Limoniastrum monopetalum decreases with distance from the ecotone (r2 = 0.60; p‹0.005) showing a distance effect in the proposed island biogeography model. The relationship between the number of Cistanche phelipaea stems and the size of the stand shows less correlation although also statistically significant (r2 = 0.46; p‹0.005) since there are individuals (islands) of Limoniastrum monopetalum with different sizes at varied distances from the ecotone (continent as propagule source). Despite the dependence on the host species, the permanence of Cistanche phelipaea is ensured by the expansion of Limoniastrum monopetalum. Predicted climate change scenarios also favor Limoniastrum monopetalum due to its photosynthetic capacity at temperatures above 30°C.