SEAGRASS MEADOWS

Snorkelling or diving in seagrass or sandy areas may seem at first sight to be less rewarding, however there can be a lot to see in these areas too.

Seagrasses are not related to seaweeds, which are algae not plants; they are the only group of "higher" (flowering) plants that can live completely submerged throughout their life. Seagrass ecosystems are most active at night but during the day you are likely to see rays and a lot of echinoderms: starfish, sea urchins and sea cucumbers. Sea cucumbers look like giant slugs but they are actually closely related to starfish and urchins, and a cross section through them would show the five-sided pentagon shape that is a feature of the echinoderms. Sea cucumbers have a unique defence mechanism: when harassed by predators they can spill out all their intestines through their mouth. The predator can eat the intestines and the animal remains alive and can subsequently regrow its guts. (Please don't try to make the animal do this! It is a last resort defence mechanism and they often die of starvation before the digestive system has grown back.) Sea cucumbers also form a rather unique habitat for another animal: a species of fish which takes refuge from predators by living inside the anus…

MANGROVES

Another important ecosystem which is part of this coastal habitat "mosaic" is mangroves. Mangroves are trees of several species which have adapted to life with their root systems submerged in seawater, something which normally causes plants problems with salt regulation and oxygen supply to the roots. Mangroves either have roots systems raised out of the ground like stilts, or upwards growths from

the roots that poke out of the ground - both of these are adaptations to ensure that the roots get enough oxygen. Some species (e.g. the white mangrove Avicennia marina - the most common in Egypt) have salt glands to get rid of excess salt; if you turn the leaves over you will find them coated with salt crystals.

Mangroves tend to occur in patches down the coast in Egypt; you may notice them particularly where a wadi (floodwater valley) enters the sea from the mountains. Although wadis appear dry except during occasional rain storms, they usually support a year-round trickle of groundwater. This supply of freshwater makes life easier for the mangroves. Mangroves have been used throughout the Red Sea for thousands of years, since they are one of the few sources of timber in this arid region. Traditional fishing boats are often made partly of mangrove wood, and buildings in the ancient cities of Arabia have beams made of mangrove wood.

Mangroves are key components of the coastal ecosystem "mosaic" because of their importance as a nursery ground for baby fish and shrimp. Fish and shrimp larvae have many predators, and require lots of shelter to survive to have a chance of surviving to a size where they can migrate into the seagrass and patch reef area and eventually out on to the reef. Mangrove roots provide a refuge from predators for the larvae and small juveniles of many reef species.

OTHER SPECIES

Four species of turtle nest along Egypt's coast: green, loggerhead, hawksbill and leatherback; turtles, particularly greens and hawksbills, are frequently seen by divers foraging on reefs. Hawksbills eat sponges, jellyfish and other invertebrates, greens algae and seagrass. Leatherbacks eat jellyfish and are less commonly seen on reefs. The Red Sea is an important route for migratory birds, particularly during spring and autumn: you may see songbirds and swallows from Europe; stocks, cranes and other waders; and birds of prey.
(Jo Gascoigne)