From shallow waters to the deep sea, the open ocean to rivers and lakes, numerous terrestrial and marine species depend on the surface ecosystem and the organisms found there.

[7][8][9] Most prominently, the surface is home to a unique community of free-living organisms, termed neuston (from the Greek word υεω, which means both to swim and to float).

[1] One of the most well-known surface ecoregions is the Sargasso Sea, an ecologically distinct region packed with thick, neustonic brown seaweed in the North Atlantic.

Multiple ecologically and commercially important species depend on the Sargasso Sea, but neustonic life exists in every ocean basin and may serve a similar, if unrecognised, role in regions across the planet.

[1] But there is another reason to study neuston: The ocean's surface is on the front line of human impacts, from climate change to pollution, oil spills to plastic.

[1] "Just before it was dark, as they passed a great island of Sargasso weed that heaved and swung in the light sea as though the ocean were making love with something under a yellow blanket, his small line was taken by a dolphin."

[1] Neustonic animals and plants live hanging from the surface of the ocean as if suspended from the roof of a massive cave, and are incapable of controlling their direction of movement.

Other species include the nudibranch Glaucus (blue sea dragon), which also feeds on floating hydrozoans [18] and swallows air to stay afloat.

These algae create habitat for a variety of Sargassum-associated species, particularly at the western edge of the North Atlantic Subtropical Gyre, known as the Sargasso Sea.

[34] Halobates lay eggs on a variety of objects, including floating feathers, wood, plastic etc.,[35] and unusually on pelagic molluscs like Atlanta turriculata.

[1] The sea surface microlayer (SML) at the air-sea interface is a distinct, under-studied habitat compared to the subsurface and copepods, important components of ocean food webs, have developed key adaptations to exploit this niche.

[46][40] Among zooplankton taxa living within the SML, neustonic copepods (phylum Arthropoda, class Crustacea) of the family Pontellidae have been frequently recorded in tropical regions of all oceans.

[47][48][49] The SML is regarded as a challenging or even extreme habitat because organisms are exposed to variable temperatures and high intensities of solar and ultraviolet (UV) radiation.

[50] Copepods are the most abundant metazoans on Earth [51] and show impressive short-term adaptation to environmental stressors, e.g. downregulation of the cellular heat stress response.

[52] Given their major role in marine food webs and ecosystem functioning,[53] knowledge of the tolerance limits of copepods to abiotic factors is essential if robust projections of the effects of global change on the world's oceans are to be possible.

For individuals arriving in the summer months in Helgoland (Germany; North Sea) the fundamental thermal niche is 16 °C, with the coldest tolerable temperature likely around 13 °C.

Well-known and ecologically important benthic fish associate with the surface when young, including species of: lefteye flounder, blenny, goby, seahorses, seadragons and pipefish.

Recent studies now indicate that the SML covers the ocean to a significant extent, and evidence shows that it is an aggregate-enriched biofilm environment with distinct microbial communities.

[71] In recent years, his hypothesis has been confirmed, and scientific evidence indicates that the SML is an aggregate-enriched biofilm environment with distinct microbial communities.

[76][69] Historically, the SML has been summarized as being a microhabitat composed of several layers distinguished by their ecological, chemical and physical properties with an operational total thickness of between 1 and 1000 μm.

In 2005 Hunter defined the SML as a "microscopic portion of the surface ocean which is in contact with the atmosphere and which may have physical, chemical or biological properties that are measurably different from those of adjacent sub-surface waters".

In 2005, Zaitsev described the SML and associated near-surface layer (down to 5 cm) as an incubator or nursery for eggs and larvae for a wide range of aquatic organisms.

[79] In 2017, Wurl er al. proposed Hunter's definition be validated with a redeveloped SML paradigm that includes its global presence, biofilm-like properties and role as a nursery.

[69] According to Wurl et al.m the SML can never be devoid of organics due to the abundance of surface-active substances (e.g., surfactants) in the upper ocean [73] and the phenomenon of surface tension at air-liquid interfaces.

Buoyant eggs hatch into planktonic larvae that develop and disperse in the ocean for weeks to months before transitioning into juveniles and eventually finding suitable adult habitat.

[96] Understanding the biophysical interactions that govern larval fish survival and transport is essential for predicting and managing marine ecosystems, as well as the fisheries they support.

More than 100 species of fishes develop and grow in surface slick nurseries before transitioning to adults (solid white lines radiating outward) in Coral Reefs (7–12), Epipelagic (13–15), and Deep-water (16–17) ocean habitats.

As adults these taxa (icons outlined in white) play important ecological functions and provide fisheries resources to local human populations.

[109] Ocean processes that drive convergent flow such as fronts, internal waves, and eddies, can structure plankton, enhance overlap of predators and prey, and influence larval dispersal.

[136][137][138][139][140][141] Depending on their size, airborne cyanobacteria and microalgae can be inhaled by humans and settle in different parts of the respiratory system, leading to the formation or intensification of numerous diseases and ailments, e.g., allergies, dermatitis, and rhinitis.