Sample collection and processing

In shallow wetland areas, samples of 2 cm³ of surface sediment were collected in the La Niña Bonita Reservoir (23°02'24.53"N, 82°29'37.09"W; 42 m a.s.l.) (Fig. ​(Fig.1b)1b) and in the Ciénaga de Zapata Swamp (22°25'44.55"N, 81°27'25.26"W; 5 m a.s.l.) (Fig. ​(Fig.1c).1c). Sediment samples were screened through a 50 μm mesh; the larger fractions were examined under a stereoscopic microscope, and floatoblasts were collected with a pipette. Floatoblasts were treated with 2% NaOH for 1 min under agitation at room temperature, then subjected to an ultrasonic bath for 15 seconds, and finally washed in deionized water. Floatoblasts for scanning electron microscopy (SEM) were mounted on aluminium stubs, sputtered with platinum/palladium (15 nm) for 1 min using a Cressington Sputter Coater 208HR SEM, and studied with a JEOL Field Emission SEM JSM 7200F operated at 15 kV in the University of A Coruña’s Research Support Service (Servizo de Apoio a Investigación, S.A.I.).