Massive strandings ofVelella velella(Hydrozoa: Anthoathecata: Porpitidae) in the Ligurian Sea (North-western Mediterranean Sea)

Abstract

Velella velella, the so-called by-the-wind sailor, is a common member of the open-ocean pleustonic fauna, worldwide distributed in tropical and temperate regions. Thanks to their sail protruding above the sea surface, floating polymorphic colonies of this hydrozoan are carried by winds, and tend to aggregate in large swarms, that often get stranded along the shores. Although these events are commonly observed in springtime along the Ligurian coasts (North-western Mediterranean Sea), no quantitative characterization was ever made. The aim of this study was to characterize the stranding events that occurred in spring 2016 along the Ligurian coast, by evaluating the influence of the local sea conditions and by quantifying the abundance of the stranded colonies in each event. Their size-frequency distribution and biomass were examined, and the associated mollusc fauna identified and counted. The magnitude of these episodes was so relevant that, along the Ligurian coasts, the V. velella strandings constitute one of the most important biological deposition of organic matter; nevertheless, the ecological role of these remarkable and stochastic accumulations of chitin along the coast is still unexplored.

Spatial and temporal genetic structure of Velella velella (Hydrozoa, Porpitidae) and its predator Janthina pallida (Gastropoda, Epitoniidae)

“…These results are consistent with its pleustonic life style (Pires et al 2018). Partitioning in different banks of specimens belonging to a single offshore population, resulting in multiple strandings, is weather-induced (Betti et al 2019) with the colonies transported from one location to another through wind and superficial currents. To our knowledge, few studies were performed on the phylogeography of Hydrozoa (Govindarajan et al 2005, Churchill 2012, Boissin et al 2018) and all of them analyze the pattern of population structure at a spatial scale greater than our in the Atlantic, Pacific and Indian oceans.…”

“…Large-scale offshore blooms of V. velella (Figure 1b) occur seasonally in the Western Mediterranean Sea, reaching a peak of abundance in spring; this mass occurrence, combined with specific environmental factors, often result in pulse strandings along the coasts from April to June (Boero et al 2016, Pires et al 2018, with average densities ranging from about 600 to 11400 colonies m -2 (Betti et al 2019).…”

Relative Abundance of Floating Plastic Debris and Neuston in the Eastern North Pacific Ocean

“…To overcome the present knowledge gaps, we call for marine scientists studying ocean plastic pollution to also collect information on the neuston present in their samples. We further advocate for more quantitative research on the importance of natural neuston loss rates such as beaching of neuston onto coastlines (Betti et al, 2019), as well as on the ecological impact of other anthropogenic activities such as, for example, fisheries and shipping on the neustonic ecosystem. This study highlights that scientific collaborations between academic research institutions, nonprofit organizations, and private institutions provide a unique platform to conduct extended research on the spatiotemporal distribution of neuston and floating plastic debris in remote and difficult to access oceanic gyres.…”

Densities of neuston often not elevated within plastic hotspots territory inside the North Pacific Garbage Patch

“…Lastly, we advocate for more quantitative research on reproduction rates of neuston. Some neuston taxa have been observed to beach onto coastlines in high numbers (Betti et al 2019), indicating possible high reproduction patterns. However, current knowledge remains scarce.…”