Abstract
The Sargasso Sea, located in the North Atlantic subtropical gyre, is one of the most well-known ocean surface ecosystems on the planet. It supports numerous ecologically and economically important fish species, juvenile turtles, and endemic species. However, in addition to the floating algae Sargassum from which the sea derives its name, numerous floating neustonic animals also live at the surface, yet their basic natural history remains poorly known. Without the basic knowledge of these species, understanding ecosystem function, food webs, and pollution impacts is impossible. This is especially problematic because pollutants like plastic are now increasing at the surface at alarming rates. This study examines the diet, reproduction, and behavior of four neustonic animal species: Velella velella, Janthina janthina, Janthina pallida, and Glaucus atlanticus. All mollusk species showed unique predatory preferences and behaviors, indicating possible methods of niche partitioning among these species. For example, Glaucus atlanticus showed an equal preference for all prey but preyed primarily by crawling below to consume the underside of prey, while large J. janthina often preyed more on the margin of V. velella and P. physalis, in contrast, J. pallida only preyed on V. velella. Of the four species observed, two reproduced in the lab (G. atlanticus and V. velella), and the embryo cases of J. pallida were examined from both collected snails and discarded bubble rafts. High fecundity rates were observed in all species, which may be an adaptation to high loss rates. This study lays the groundwork for future research on neustonic animals in the Sargasso Sea.
Highlights
Organisms that live on the ocean’s surface—termed neuston—are adapted to survive in this razor-thin environment
G. atlanticus ate all parts of the small V. velella, on several larger polyp, the G. atlanticus first bit the margin, and if it was not repelled, ate the more protected zooids below the mantel (Fig. 2a, b)
During feeding on a V. velella, slight squeaks and scraping noises could be heard emanating from the G. atlanticus, the squeaks may have been from air escaping the gut and scraping noises from the radula grinding against the V. velella float
Summary
Organisms that live on the ocean’s surface—termed neuston (or sometimes pleuston)—are adapted to survive in this razor-thin environment. Concentrated neustonic life is the foundation of the Sargasso Sea: a floating ecosystem in the North Atlantic subtropical gyre. The Sargasso Sea is named after the floating neustonic Sargassum algae (Trott et al 2011; Pendleton et al 2014) and serves as a haven for biodiversity in the open ocean. The Sargasso Sea is a nursery ground for a variety of threatened and endangered organisms (Trott et al 2011)
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