Bryozoans, or Moss Animals, are colonial lophophorates, which is to say animals that feed using a lophophore, a horseshoe-shaped structure bearing ciliated tentacles around the mouth, that form encrusting or weed-like colonies. The individual 'animals' are
on average about 0.5 mm in length, and live inside a protective
covering from which they extend a crown of cilia-covered tentacles
called a lophophore. These are not true individuals though as they
develop as buds on the colony and share nutrients; for this reason they
are referred to as 'zooids'. Bryozoans are widespread globally, but are often overlooked because they
are small and the colonies resemble plants. Members of the Class Phylactolaemata are found only in freshwater environments. Unlike other Bryozoans they do not have separate reproductive zooids not capable of feeding, rather all of the zooids in a colony are capable of feeding and reproducing, being simultaneous hermaphrodites. The colonies can also reproduce asexually, by producing special zooids called statoblasts, which are entirely enclosed within chitinous, bivalved shells, which either remain adhered to the colony or sink to the bottom (or in some cases float, in which case they are known as floatoblasts), remaining dormant through periods of adverse conditions, before opening and growing into new colonies.
In a paper published in the journal ZooKeys on 12 March 2020, Rafael Carballeira of the Departamento de Ciencias da Terra and the Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, Cosme Romay of the Grupo de Investigación en Bioloxía Evolutiva and Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, and Atocha Ramos of the Grupo de investigación Química Analítica Aplicada and Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, report the first known occurence of Freshwater Bryozoans in Cuba.
The freshwater Bryozoan fauna of the insular Caribbean has been mainly studied in the Leeward Islands (Aruba, Bonaire, Klein Bonaire and Curaçao), with three known species from the study of colonies and floatoblasts (statoblast buoyant with the annulus composed of gas chambers): Plumatella agilis, Plumatella casmiana, and Plumatella longigemmis. In addition, Plumatella repens has been reported in Puerto Rico. Unidentified Plumatella colonies and floatoblasts were reported on the islands of Cuba and Trinidad in the 1940s.
Knowledge of the distribution of Freshwater Bryozoans in the Caribbean is scarce despite the great biogeographical interest of this area. It constitutes a complex island system located between two large continental biogeographic regions: Nearctic and Neotropical.
The La Niña Bonita Reservoir is located in the council of Bauta (Artemisa Province, Cuba). This water body is a freshwater wetland with an area of 12 000 m² and a maximum depth of 10 m. This reservoir dams the Jaimanitas River, with a basin of 9.2 km² dominated by limestone rocks, and is used mainly for irrigation and Fish farming.
Ciénaga de Zapata Swamp is located in the Zapata Peninsula (Matanzas Province, Cuba). This wetland is the largest (2600 km²) and best conserved marsh swamp in the insular Caribbean, as well as the one with the greatest biodiversity. It has been declared a national conservation area by the government of Cuba and has been internationally recognized as a Ramsar Site. The shallow marshes show an important accumulation of organic matter and the lithology is dominated by limestones and dolomites with seeping underground waters (cenotes). The waters are bicarbonated-calcic with a great spatial heterogeneity depending on the input of groundwater seeps or marine intrusions. Also, there is a great salinisation of groundwater as a consequence of the exploitation of freshwater aquifers.
(A) Location map. (1) La Niña Bonita Reservoir and (2) Ciénaga de Zapata Swamp (B) Aerial photograph of the La Niña Bonita Reservoir (ESRI World Imagery, ArcGIS 10.0) C Aerial photograph of the Ciénaga de Zapata Swamp (ESRI World Imagery, ArcGIS 10.0). Carballeira et al. (2020).
In shallow wetland areas, samples of 2 cm³ of surface sediment were collected in the La Niña Bonita Reservoir and in the Ciénaga de Zapata Swamp. 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% sodium hydroxide for 1 minute under agitation at room temperature, then subjected to an ultrasonic bath for 15 seconds, and finally washed in deionised water. Floatoblasts for scanning electron microscopy 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 Coruña’s Research Support Service.
The morphometry of the examined floatoblasts showed that they belong to the species Plumatella repens. The shape of the floatoblast is broadly oval, both valves are equally convex in lateral view, and the floatoblast annulus is smooth, without tubercles. Floatoblast measurements were 318.5–350.2 μm in total length and 217.3–252.6 μm in total width. The fenestra of floatoblasts is rounded oval in dorsal view and oval in ventral view, covered with rounded tubercles and a relatively intense reticulation.
Plumatella repens, floatoblast from La Niña Bonita Reservoir and the Ciénaga de Zapata Swamp (Cuba), scanning electron micrographs: (A) View of dorsal valve. (B) View of ventral valve. (C) Suture between valves is a single cord with a row of low tubercles on either side. (D) Section of the annulus showing the connection between gas chambers, with circular pores with filiform extensions along the border. Scale bars: 50 µm (A), (B); 10 µm (C); 5 µm (D). Carballeira et al. (2020).
The length of the dorsal fenestra is larger than half the total length of the floatoblast. The annulus is smooth, without tubercles, occasionally with moderate nodulation and some large tubercles on the periphery, around the fenestrae especially on the ventral side. The measurements of the dorsal fenestra are 130.9–176.4 μm in length and 105.5–163.7 μm in width, while the ventral fenestra measures 187.5–247.3 μm in length and 141.2–188.7 μm in width. The suture between the valves is a single cord with tubercles on both sides. A section of the annulus shows circular pores with filiform projections connecting the gas chambers.
These new records of Plumatella repens are the first certain record of a Freshwater Bryozoan species in Cuba; only Plumatella sp. was reported on the island previously, without specifying a locality. This extends the distribution range of the species in the Caribbean area, with a single record in Puerto Rico so far. The presence of Plumatella repens on the island of Cuba is consistent with the existence of records of the species in the insular Caribbean and the cosmopolitan distribution of this species.
The ecology of Plumatella repens in Cuba and Puerto Rico is associated with permanent freshwater ecosystems and coastal wetlands with highly mineralized waters caused by the predominant limestone lithology, and influenced by seawater mixing within an oligohaline range (0.5–5‰). The species also experiences a wide range of nutrient concentrations (nitrates, phosphates) and high levels of dissolved organic matter.
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