45
coelenterates; tunicates; the by-the-wind-sailor (Velella velella) and the Portuguese
man-of-war (Physalia physalis), which have submerged bodies and aerial flotation devices; and insect genus Halobates living on top of the surface film (Beebe
1926; Hempel and Weikert 1972; Holdway and Maddock 1983; Zaitsev 1997). In
upwelling and coastal areas however, the growth of neuston is promoted by the
proliferation of phytoplankton supported by nutrient-rich waters and concentration
of animals in the uppermost layer may exceed the lower layer by several orders of
magnitude (Hempel and Weikert 1972).
During hours of high irradiation, the total number of neuston organisms is
relatively small, the competition for food is rather low, and this fact might compensate somewhat for the paucity of total food supply. Therefore, the few grazers
and predators which are well adapted to the adverse abiotic conditions of the surface stratum could find sufficient food as long as they are not selective; and at the
same time, a refuge from predation during daytime. At night, however, the surface
biotope becomes frequented by potential predators (Hempel and Weikert 1972;
Holdway and Maddock 1983). The neuston connect the sea surface and water column as planktonic larvae develop and migrate downward, and adult animals visit
the surface to feed and reproduce. Neustonic animals of moderate size (0.2–30 mm)
may be consumed by predators from the aquatic (fish; squids; turtles) and the aerial
(birds) environments. Some neustonic organisms may also consume aerobionts falling on the sea surface, such as insects (Zaitsev 1997).
The sea-surface is particularly subject to anthropogenic contaminants (oil;
chemicals; metals) and also eutrophication, forming an additional hazard to the
neustonic organisms (Hempel and Weikert 1972; Zaitsev 1997). In some regions
moreover, large quantities of floating tar, plastic, and other debris provide a habitat
for certain kind of neustonic organisms such as isopods, hydroids, and egg masses
(Holdway and Maddock 1983).
5.4 The Ice-Water Interface
Microalgae (mainly benthic diatoms) that develop at the ice-water interface (Fig. 5.1) are responsible for an important part of the productivity of polar
seas, where chlorophyll concentrations in the water column are generally low.
Microalgal growth starts during the initial period of sea ice formation in autumn;
then growth at the ice bottom slows down gradually and stops completely when
very low winter light intensities are reached, though ice algae are markedly shade
adapted (Demers et al. 1986; Flores et al. 2012). The growth of ice algae during
spring and autumn extends the short phytoplankton growing season in the water
column. Unlike phytoplankton, ice algae usually grow under relatively stable
conditions of light, temperature and salinity. Low frequency fluctuations of the
growth of ice algae have been associated with nutrient pulses driven by tides and
atmospheric events; the biological dynamics of the ice-water interface is therefore
coupled to the hydrodynamics of the underlying waters. Physical processes that
5.3 The Sea Surface-Atmosphere Interface
coelenterates; tunicates; the by-the-wind-sailor (Velella velella) and the Portuguese
man-of-war (Physalia physalis), which have submerged bodies and aerial flotation devices; and insect genus Halobates living on top of the surface film (Beebe
1926; Hempel and Weikert 1972; Holdway and Maddock 1983; Zaitsev 1997). In
upwelling and coastal areas however, the growth of neuston is promoted by the
proliferation of phytoplankton supported by nutrient-rich waters and concentration
of animals in the uppermost layer may exceed the lower layer by several orders of
magnitude (Hempel and Weikert 1972).
During hours of high irradiation, the total number of neuston organisms is
relatively small, the competition for food is rather low, and this fact might compensate somewhat for the paucity of total food supply. Therefore, the few grazers
and predators which are well adapted to the adverse abiotic conditions of the surface stratum could find sufficient food as long as they are not selective; and at the
same time, a refuge from predation during daytime. At night, however, the surface
biotope becomes frequented by potential predators (Hempel and Weikert 1972;
Holdway and Maddock 1983). The neuston connect the sea surface and water column as planktonic larvae develop and migrate downward, and adult animals visit
the surface to feed and reproduce. Neustonic animals of moderate size (0.2–30 mm)
may be consumed by predators from the aquatic (fish; squids; turtles) and the aerial
(birds) environments. Some neustonic organisms may also consume aerobionts falling on the sea surface, such as insects (Zaitsev 1997).
The sea-surface is particularly subject to anthropogenic contaminants (oil;
chemicals; metals) and also eutrophication, forming an additional hazard to the
neustonic organisms (Hempel and Weikert 1972; Zaitsev 1997). In some regions
moreover, large quantities of floating tar, plastic, and other debris provide a habitat
for certain kind of neustonic organisms such as isopods, hydroids, and egg masses
(Holdway and Maddock 1983).
5.4 The Ice-Water Interface
Microalgae (mainly benthic diatoms) that develop at the ice-water interface (Fig. 5.1) are responsible for an important part of the productivity of polar
seas, where chlorophyll concentrations in the water column are generally low.
Microalgal growth starts during the initial period of sea ice formation in autumn;
then growth at the ice bottom slows down gradually and stops completely when
very low winter light intensities are reached, though ice algae are markedly shade
adapted (Demers et al. 1986; Flores et al. 2012). The growth of ice algae during
spring and autumn extends the short phytoplankton growing season in the water
column. Unlike phytoplankton, ice algae usually grow under relatively stable
conditions of light, temperature and salinity. Low frequency fluctuations of the
growth of ice algae have been associated with nutrient pulses driven by tides and
atmospheric events; the biological dynamics of the ice-water interface is therefore
coupled to the hydrodynamics of the underlying waters. Physical processes that
5.3 The Sea Surface-Atmosphere Interface