Three Islands

The picture above was taken from South Ronaldsay, looking across Scapa Flow to the low Island of Flotta & the distant hill's of Hoy in the background.

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We are going to take a close look at the seashore around Orkney from the North sea on the east coast to the Atlantic on the western coast and what it has to offer the photographer and naturalist, from seashells to seaweed, We will check out rocky shores  as they are bit more productive .

Fucus serratus serrated wrack

First off we have a seaweed, Fucus serratus,  it is a robust alga, olive-brown in colour  It grows from a discoid holdfast up to 180 centimetres (6 ft) long. The fronds are flat, about 2 cm (0.8 in) wide,

 

Holdfast, A holdfast is a root-like structure that anchors aquatic organisms, such as seaweed, other sessile algae, and sponges, to the substrate.

Flat periwinkle : Littorina obtusata, These are empty shells washed up on the tideline.

Found amongst the seaweeds on which it feeds, the Flat periwinkle lives on the lower parts of the shore. It is most commonly associated with Bladder Wrack seaweed and can be mistaken for the air bladders that make the seaweed float. They come in lots of different colours, including orange, bright yellow, banded brown and olive green making them hard to spot amongst their seaweed home.

Velvet horn (Codium tomentosum)

A small green alga (up to 30 cm long) with a dichotomously branched, cylindrical frond. The frond is solid and spongy with a felt-like touch and has many colourless hairs which can be seen when the plant is immersed in water. The holdfast is disc-like and formed from many fine threads.

Codium tomentosum occurs mainly in the south west of the UK and is becoming quite rare.

Maerl found washed on the shore at the Hope.

Maerl beds stud the ocean floor like underwater brambles. They’re pastel pink and, despite their knobbly appearance, made up of red seaweed. This algae has a limestone skeleton which gives it a complex three-dimensional structure that is quite unlike the slimy seaweeds you may be more familiar with. In fact, the closest thing to a Maerl bed you’ve probably heard of is a coral reef. Like tropical reefs, the seaweeds in maerl beds interlock as they grow, creating nooks and crannies that serve as the perfect home for a huge range of sea life. Maerl beds are one of the world’s most biodiverse habitats, but unlike coral reefs, few people have heard of them and even fewer study them.

Maerl grows at a glacial pace – just 0.2 mm per year in Scotland. This makes it difficult for these habitats to respond to rapid changes in water temperature or ocean currents. But these are just the kind of environmental changes that are expected around Scotland over the coming century.

 

Ascophyllum nodosum knotted wrack or egg wrack.

Ascophyllum nodosum is a large, common cold water seaweed or brown alga being the only species in the genus Ascophyllum. It is a seaweed that only grows in the northern Atlantic Ocean, also known as rockweed or Norwegian kelp, knotted kelp, knotted wrack or egg wrack. It is common on the north-western coast of Europe (from Svalbard to Portugal) including east Greenland[1] and the north-eastern coast of North America, its range further south of these latitudes being limited by warmer ocean waters.[2]

21 May 2021, St Margaret's Hope Bay.

A sunny day but with a cold easterly breeze, after a two-hour wander around the area and with only a few images to show for it, decided to head back home, walking past the slipway on the pier road, I decided to walk along the shore, I headed for the strandline to see what the last tide had left behind, ours is a sheltered shallow bay and as we are inside Scappa flow we don't get large ragging sea's and the associated flotsam & jetsam, there was plenty of seaweed , mostly Bladder Wrack & Serrated Wrack, there were also a few small clumps of Kelp, something we don't see very often, as these are deep water weeds brought in after big storms on the Atlantic coasts, I turned over the first clump and to my surprise, there was a small twelve legged common Sunstar  (Crossaster Papposus), I've seen pictures before but not a live one, I moved it to a rockpool closer to the sea as there were no more high tides for a while, feeling quite pleased with myself I continued towards home, just one more patch of seaweed to check, on turning over another piece of Kelp only half the size of the last one, low and behold there was another starfish this time a blue-green Brittle Star with legs around four inches long, well that made my day.

Common Sunstar (Crossaster Papposus)  27 ‎May ‎2021, St Margaret's Hope Bay.

Common brittlestar (Ophiothrix fragilis)

The five arms are long (about five times the disk diameter) and spiny. The upper disk surface has a 5-rayed pattern of spines. This species is very varied in colour, commonly brown or grey but ranging through purple, red, orange, yellow, and white. Colouration may be plain or banded (particularly on the arms). The arms are fragile and often broken as in this specimen. The arms on this one were about 4inches long.

Sea mat (Membranipora membranacea)

Sea mat (Membranipora membranacea) Enlargement.

These are small marine organisms that build colonies on kelp, or as Damien, my son said " An ecosystems within an ecosystem"