First record of a by-the-wind-sailor (Velella velella Linnaeus, 1758) in the Galápagos Archipelago - Ecuador

Abstract We present the first official record of the by-the-wind-sailor (Velella velella) for Ecuador. Twelve individuals were found along different beaches of San Cristóbal and Santa Cruz Islands in Galápagos Archipelago, Ecuador. These sightings may be influenced by El Niño Southern Oscillation events.


Introduction
Velella velella (Linnaeus, 1758) is a holoplanktonic athecate hydroid (Hydrozoa: Anthoathecata) from the Porpitidae family that is well known as "by-the-wind-sailor" (World Register of Marine Species 2018; World Hydrozoa Database 2019) due to its easily recognisable sail, which helps individuals to disperse over the ocean surface via wind currents (Purcell et al. 2012). Velella velella floats on the ocean surface during the asexual colonial stage where it primarily feeds on copepods and small fishes. In addition, it harbours symbiotic zooxanthellae that provide extra nutrition to the host (Purcell et al. 2012). It is also known by their occasional mass strandings in beaches, where millions of individuals become a great source of organic material to the shoreline (Kemp 1986;Flux 2008).
Even though V. velella could potentially have a cosmopolitan distribution due to its sail (i.e. aid for dispersal), its common distribution is in the northern hemisphere in the Pacific and Atlantic Oceans, as well as in the Mediterranean Sea  Chiriboga et al. 2016). Here, we report two separate sightings of the "by-the-wind sailor" in the Galápagos Islands, being the first record for Ecuador.

Results and discussion
During 2017 and 2018, separate sightings of Velella velella were recorded in two islands of the Galápagos Archipelago, off the coast of Ecuador (approx. 960 km to the west of South America). On 28 August 2017, approximately eight individuals of V. velella were spotted on La Lobería beach (0°55'36.64''S; 89°36'41.88''W) at San Cristóbal Island. We photographed one individual that corresponded to a "right-by-the-wind-sailor" due to the direction of its sail (Fig. 1). Almost a year later, on 16 June 2018, several individuals of V. velella were observed washed ashore on Tortuga Bay ( 0°45'40.5''S; 90°20'05.5''W), a beach at Santa Cruz Island. Although no exact counts are available, at least four different individuals were photographed (Fig. 2). Most individuals from Santa Cruz were right-bythe-wind-sailors. However, this was difficult to assess in one individual whose sail was not developed (individual "two", Fig. 2

c). All individuals from both San Cristóbal and Santa
Cruz Islands were of small size, ranging from a few mm to no more than 2 cm.   Southwest orientated, Tortuga Bay is a dissipative beach with a gentle slope exposed to southern swells. These features make Tortuga Bay a trap for drifting organisms when winds hit from the south. In this respect, we also observed several specimens of Porpita porpita (Linnaeus, 1758) and Physalia physalis (Linnaeus, 1758) washed up along with V. velella (Fig. 3). These multispecies strandings seem to be common (e.g. Thiel and Gutow 2005;Flux 2008).
To the best of our knowledge, this is the first official record of V. vellella in Ecuador. We suggest that they are likely uncommon in the Galápagos Archipelago. Araya and Aliaga (2018) reported that El Niño Southern Oscillation (ENSO) events are strongly correlated with blooms of jellyfishes and related fauna in the south-eastern coast of South America. In 2017 and 2018, a mild ENSO was detected in the region (ENFEN 2017;ENFEN 2018;World Meteorological Organization 2018). The changes in the intensities of trade winds and, hence, in the weather, was not extreme but these anomalies could explain why V. velella arrived at the Galápagos (ENFEN 2017; Araya and Aliaga 2018).