The rocky shore
Rocky shores are particularly rich in sea life and the Flow is bordered by many species-rich rocky shores. On almost all low lying areas of the coast around the harbour, there will be areas of rocky shore, whether it be sculpted sandstone boulders or rugged layers of flagstone.
Taking time out to watch a stretch of rocky coast is often rewarded by seeing a host of wildlife. It doesn't take long before spotting wading birds, gulls and ducks, pottering around the pools looking for food. Common or grey seals may be hauled out on skerries and for the very lucky, there may even be a glimpse of an otter searching for crabs or fish. All of these animals are a clue to the hive of activity beneath the surface.
A seemingly endless variety of seaweeds, fish and marine invertebrates inhabit the pools. Scapa Bay, The Bay of Houton and the Sands of Wright are good places to explore life in the pools around the Flow.
Seaweeds are often observed in soggy, brown heaps along the shore when the tide is out. However, on closer inspection, a huge variety of colours and species can be discovered and when shown underwater, the beauty of algae can really be appreciated.
Some organisms are sedentary, such as filter feeding anemones and sea urchins. Beadlet anemones are abundant on many rocky shorelines - they are a small anemone often red, orange or brown in colour. In slightly deeper water you may also spot the colourful dahlia anemone.
Starfish and brittlestars are frequently encountered. As their name suggests, common starfish are more frequently seen, but a pinky purple coloured character called a bloody henry may also be spotted. However, the most spectacular in terms of size is the spiny starfish. This species can grow up to 70cm long, but is more often seen at around 20cm in size along the shore.
Rockpools also provide the chance to see the inhabitants of the many empty shells that can be collected on the beaches, including limpets, dog whelks, flat periwinkles and mussels. The picture below shows a living cowrie or 'Groatie Buckie' as it is called in Orkney. Notice how the mantle wraps around the outside of the shell. The mantle covers the internal organs of molluscs and in some species also secretes the shell.
As well as molluscs with shells, it is also possible to occasionally encounter those apparently without them. In fact, sea hares and most sea slugs have a small internal shell. Species that can be found in the intertidal zone include sea lemons (Archidoris pseudoargus) and sea hares.
Many crustaceans inhabit the rocky shoreline. Maybe the most abundant and obvious are barnacles - often assumed to be a type of mollusc. Another, present by the thousand, are sandhoppers, inhabiting the upper shore under rocks.
A familiar member of the rocky shore community are crabs. A number of species can be found under rocks and in amongst seaweed. Most abundant are shore crabs but edible crabs, velvet swimming crabs and spider crabs can also be seen.
Hermit crabs are plentiful in rockpools and they can often be seen scuttling around in the discarded mollusc shells that they inhabit to protect their soft bodies. As the crabs grow in size they need to find larger shells to live in. Species of squat lobster (shown below) can also be found under rocks and hiding in crevices. These interesting creatures are not true lobsters, in fact they are more closely related to hermit crabs - which are themselves not true crabs!
Many fish inhabit rocky areas of the intertidal zone. Butterfish, named because of their slippery skin, and long-spined sea scorpions are commonly found. Other species include, shannies, eelpout, five-bearded rockling and fifteen spined sticklebacks.