Wildlife of Scapa Flow
Nestled in the heart of the captivating Orkney Islands, Scapa Flow is home to a wide variety of wildlife both above and below the water. While marine life darts about the wrecks beneath the waves, seabirds soar through the skies above.
The underwater wildlife is one of the quiet marvels of Scapa Flow. On a seabed comprising mainly of silt and sand, the wrecks have become rich artificial reefs. Each wreck is now a thriving ecosystem – benthic (ocean bottom) animals such as starfish and urchins cover the wrecks and inject vibrancy and colour. The multitude of nooks and crannies provide the perfect hiding spot for crabs and lobsters, while the wrecks teem with fish.
As well as changing as the years go by, the wrecks of Scapa Flow also change with the seasons. During spring the water starts to warm and this triggers an algal bloom, which causes reduced visibility for a few days. As larger organisms feed on the algae the bloom dissipates. The wrecks are soon surrounded by the eerie yet enchanting comb jellies and moon jellies. Both are avid predators of algae. As the comb jellies pulsate through the water column they refract light from their miniature swimming hairs called cilia. This appears as a rainbow-like aura running in thin lines down the delicate forms of the comb jellies. Neither the moon jelly nor the comb jelly can sting a human.
There is often a second algae bloom in early autumn. During this time the visibility can drop below five metres. However, the bloom clears as winter begins and this end of season diving is often the best of the year. It can be a little chilly at times but the crisp visibility offers plenty of reward for those who take the plunge.
The smaller organisms such as the algae and the jellies are the foundation of ecosystems in Scapa Flow – they sit at the bottom of the food chain. They support the multitude of life inhabiting the wrecks, including the larger fish.
Pollock (Pollachius pollachius) and its close relative the saithe (Pollachius virens) are two fish species that shoal around the wrecks in large numbers. As summer progresses these fish increase in numbers and size. When divers are in the water these two species tend to seek the quieter areas of the wreck.
In a similar fashion, cod (Gadus morhua) and ling (Molva molva) will dart out of view as soon as they detect a diver. Shoals of shimmering silver bellies can often be found by shining a torch into the darker recesses of the wrecks, where the smaller fish tentatively seek shelter.
Not all of the fish species are quite so wary. Various species of wrasse patrol the wrecks, many approaching divers with bold daring – or perhaps just bold hope; many divers have fed the wrasse over the years and the possibility of a free meal is evidently enticing. It is also believed the wrasse are attracted to the sound of a camera strobe firing. They seem to gather round when the cameras are out, as if waiting for their photograph to be taken. The wrasse seem especially confident around the shallower wrecks, which are more frequently visited by divers.
Photographers are sometimes lucky enough to be faced with larger subjects. Grey seals (Halichoerus grypus) and harbour seals (Phoca vitulina, also known as common seals) are a common sight in Orkney waters. On an even larger scale, basking sharks (Cetorhinus maximus) are sometimes found cruising on the surface in the summer months. They are an awesome sight and undoubtedly one of the most incredible animals to inhabit British waters.