Why is the sea salty?

When water comes into contact with the Earth’s crust either on land or on the seabed some of the minerals in the rocks dissolve and are carried by the water into the sea. When the water evaporates the salt minerals are left behind leaving salty water. In times past, several places in the harbour were set up to get salt from the sea for people to use. Chichester Harbour is a tidal estuary. Every day millions of tons of seawater flood in to Chichester Harbour from the Solent through the narrow entrance between East Head and Hayling Island.

It takes seven hours to fill the creeks and gullies of the Harbour. Then the tide turns and for five hours the water pours out again leaving only a trickle of water in many of the creeks and exposing vast areas of mud, sandbanks and saltmarsh for the hungry birds to dine on. This relentless process continues day after day.

The sea is a particularly important habitat for fish and shellfish and other invertebrates. These are a food resource for many birds including Osprey and Roseate Tern, which visit on migration.

At high tide when the Harbour is full, the great expanse of water teems with life. Many species of fish can be found such as bass, flounder, mackerel, mullet, and tope. Swimming alongside the fish you may be lucky to catch a glimpse of the harbour seals.

Some of the animals found underwater are:

Mackerel - swim in large shoals near the surface of the water and feed on small fish and crustaceans. Their eggs float on the surface of the water. They have a mottled blue and silver body.

Mullet - torpedo shaped with a thick top lip. They can grow up to 75 cm long and have a dark back and silvery sides. They are found in shallow water and feed on the mud and algae.

Cuttlefish - the cunning cuttlefish, a close relative of the octopus, is a master of disguise and can change its colour and pattern to match the environment. They can grow up to 40 cm long and feed on crabs and other crustaceans. They use jet propulsion for a quick getaway. Cuttlefish eggs look like black grapes and are sometimes found attached to moorings. Cuttlefish ink used to be used by artists and was known as sepia.

Sea Bass - a favourite of local fishermen. Many of the bass are born in the harbour. Chichester Harbour is a designated Bass nursery area. They start off as tiny balls that float on the surface of the water feeding on nutrients. As they grow they feed on small fish and worms and on each other! They can grow to 100 cm long. They have a long body with a darkish back and silvery sides. Only the lucky ones survive to swim out to sea where they might spend several years getting fat then later they return to the harbour.

Seals - hunt fish that come into the harbour. They can spend long periods under water searching for food but need to come to the surface for air. They feed on fish and other crustaceans. Females can live for up to thirty-five years and males about twenty-five years. They mate under water and the female gives birth to a single pup. The pup can swim within a few hours of being born. Learn more about the Solent Seal Project.

Eels - a snake like fish with no scales. They hatch from thin leaf shaped eggs. The larvae drift about on the surface of the sea feeding on plankton for 1-2 years before developing into young eels, known as elvers.

Snakelocks anemone - this animal looks like a plant because it attaches itself to rocks and stones. It waves its tentacles in the water to catch its food.

Feather worms - these worms catch their food with fan-like tentacles.

Spider Crabs - these have 8 long legs making them look a bit like a spider and two claws. They are sometime called Decorator Crabs because they cover their legs and shell with seaweed.

Barnacles - attach themselves to the rocks, the bottom of boats, and other structures in the water. They feed by putting out feathery legs, which catch bits of food that are floating in the water.

Seaweeds - Sea lettuce has bright green thin sheets .It attaches itself to rocks and stones by a pad known as a holdfast. Bladderwrack is a “popping” seaweed that has small swellings along its fronds, which help to keep the seaweed afloat.

On the water:

There are more than ten thousand sailing or motor boats in the Harbour.

Many people enjoy fishing in the Harbour and some boats use nets which they drag along the bottom of the seabed.

All the channels in the Harbour have to be marked to prevent people from ending up on the mud as the tide goes out.


  • People paint the underneath of their boats with antifouling to prevent barnacles from sticking to the boat. This goes into the water and can cause pollution.
  • Fuel from boat engines can also be a cause of pollution.
  • Farmers use fertilisers on their fields. Sometimes this drains into the sea and can encourage the growth of green algae such as Gutweed (Enteromorpha intestinalis), which can smother the beaches.
  • There is a danger that too many people will want to fish in the Harbour.
  • People throw rubbish overboard and this ends up in the Harbour and on the shore.
  • Dredging to maintain the deep-water channels and dragnet fishing can destroy the seabed.
  • Looking after the moorings can also disturb the seabed, and there are a lot of moorings in the Harbour!