Surface Tension and Oil: How Marine Pollution Kills Water Striders

Surface Tension

Australia is not immune to oil-related accidents. The Montara oil spill, which occurred in 2009, is considered one of the worst environmental disasters in the country.

Because marine life is a major source of livelihood in Australia, the country takes enormous steps to reduce oil pollution. For example, businesses that will have to deal with petroleum, such as truck fleets, will learn to contain it. Many use an oil and water separator to filter the oil even before the water goes into the disposal.

This is because oil can affect many things on the bodies of water, including surface tension.

What Is Surface Tension?

Surface tension is the property of the surface layer of a liquid that allows it to resist an external force. A simple example is when you put a pin or paperclip on the surface of the water, and it “stands up.” The molecules at the surface are pulled inwards by their mutual attraction, which results in a net inward force at the surface.

What Role Does This Play for Insects?

Common pond insects use surface tension as their principal means for locomotion over small bodies of water. These insects use the energy from beating their wings to lift themselves onto the surface where they can glide along using limiting friction between their bodies and feet and then sink into the fluid again when they beat down. They also use their wings for their forward motion.

Surface tension prevents any substantial sliding along the water’s surface and allows insects to stay upright even when moving quite fast. Without this capability, these animals would either fall over and be unable to return to the surface, or they would spend most of their time submerged in liquid. The bottom line is that surface tension allows insects to use less energy and obtain greater results.

Marine Life Benefits from Surface Tension

The insects that obtain the most benefit from this are commonly found near water:

Water Striders: they stand on top of the water and travel over it, obtaining their food and avoiding predators by taking advantage of surface tension.

Caddisflies: they emerge from an aquatic larval stage as sub-imagos (with functional wings) onto the moist rocks near the shoreline, where they crawl about until their wings dry and harden. They can fly very well once this happens.

Backswimmers: also known as reed bed bugs or marsh pond skaters, they spend most of their time on vegetation growing along the edges of wetlands but often forage in open shallow water.

Whirligigs: swim on their backs in shallow water with legs, moving rapidly to propel themselves over the surface, which allows them to escape predators.

Water Boatmen: they serve as prey for various animals living in or near wetlands, including fish, other aquatic insects, and spiders.

Aquatic Larvae of Various Families of True Flies: these spend much of their time cruising through pond vegetation at the surface. They feed on small invertebrates such as rotifers and cladocerans.

Reed Aphids: these live above the water on bulrushes and reeds drop into the water during hot, dry periods. They are highly predated upon by fish.

Water Scorpions: they are extremely predatory and feed on other insects, including water boatmen.

Pond Skaters: these sit with their legs sprawling out behind them to catch prey that floats or swims nearby using surface tension like a fishing rod. This is often considered the most efficient method of catching aquatic invertebrates because it does not require any energy for locomotion.

Aphids: these species live above the water line on submerged hydroid polyps, which need to move quickly through the surface film to avoid predators. The aphids also spend their time floating at the surface to feed on duckweed.

Dragonfly Nymphs:they spend their time cruising along the surface of the water using four nymphal gills that extract dissolved oxygen from it simultaneously with pharyngeal jaws that break up prey. This process requires a great deal of energy, and surface tension is important in allowing these creatures to get enough oxygen while staying on the surface where their top predators cannot attack them.

The Link between Oil Pollution and Surface Tension

Researchers have studied the effects of oil pollution on marine animals for years. But one of the less-discussed topics is how this significant problem can affect water insects and striders.

In an experiment, a minuscule amount of oil killed at least 50 percent of the water striders inside a tank in 48 hours. One explanation says that oil weakens surface tension. Animals that depend on surface tension might not be able to float or “walk on water.” Worse, if they do, they cannot sustain it and end up drowning underneath the oil slick.

Implementing preventive measures will ensure that the country can continue protecting its marine life for years until Australia doesn’t need to depend on petroleum.