As part of National Marine Week, we will be posting a series of articles focusing on different aspects of Scotland's incredible seas. In today's article, we give you the run down on some very important species and habitats that you may not have heard of before.

Scotland’s seas are rich with marine life, there’s no two ways about it. From basking sharks and humpback whales all the way down to blue mussels and hermit crabs, the species that live in our seas make Scotland a truly spectacular destination for any marine fanatic.

Scotland boasts a vast network of Marine Protected Areas (MPAs), Special Areas of Conservation, Special Protection Areas, and Sites of Special Scientific Interest that cover over 20% of its seas and protect many important habitats and species. As part of the process of designating Scotland’s MPA network, Scottish Natural Heritage created a list of no less than 81 habitats and species, known as Priority Marine Features, that it considers to be of conservation importance. Included within the list are large charismatic species, such as minke whales, bottlenose dolphins and killer whales, commercially important species like cod, European spiny lobsters and Atlantic herring, and also many lesser known but equally important species and habitats, such as burrowed mud and sandeels.

Here we have selected a few habitats and species from the list that may not be headline grabbers but certainly play an interesting and important role in supporting marine ecosystems and keeping Scotland’s seas healthy. 

Burrowed mud

Sure, the thought of burrowed mud might not fill the heart with excitement, but this simple looking and relatively featureless habitat is full of organisms that play a valuable role in supporting Scotland’s marine ecosystem and commercial fisheries. Found only in waters below 50m and in Scotland’s inner sea lochs where water movement is slow, burrowed mud habitats are home to a multitude of species, ranging from the seafood-lovers’ favourite, langoustine, to giant seapens, mud shrimps, angular crabs, rare sea squirts and various species of worms and bivalves.

Burrowed mud is a delicate habitat that is particularly vulnerable to changes in water flow (e.g. changes created by the construction of bridges or barrages), pollution, nitrification and damaging fishing practices. Many resident species are unfortunately disturbed, moved or killed as a result of bottom-trawl fishing for langoustine.  

Maerl beds – Phymatolithon calcareum and Lithothamnion glaciale

Maerl is the collective term used for various species of coralline red algae that form branched, nodular skeletons that do not attach to the seafloor. In the right conditions – on coarse sediments in clear, slow moving water – extensive maerl beds can form, growing at depths down to around 30m. The hard, skeleton structures of living (purple in colour) and dead (white) maerl build up over time, forming a gravel-like habitat that provides an important home for many marine species such as small fish, crustaceans (e.g. crabs and shrimps) and bivalves (e.g. scallops), and also important refuges for juvenile animals.

Maerl is a very slow growing species and beds can take hundreds, if not thousands of years to form. Their slow growth rate makes maerl highly susceptible to environmental changes and physical disturbance, most notably from pollution and bottom-trawling fishing practices. It is unlikely that any maerl beds that are lost through damage or removed will ever return and therefore, maerl is considered a non-renewable resource.

In Scotland, maerl is most commonly found on the west coast (along the coastline and within loch narrows), where some of the most extensive beds in Europe exist. Maerl used to be extracted for commercial reasons, primarily as a source of lime used in agriculture and water filtering, but today it is considered most valuable as a living resource, providing valuable habitats for many species, including many commercially important species. 

Ocean quahog – Artica islandica

The ocean quahog, known by various other names including the black clam, the black quahog and the Icelandic cyprine, is a species of edible clam native to the North Atlantic Ocean. Its shell, which grows up to 13cm in length, is heavy and rounded and has concentric lines visible on the surface. Their typical habitat is on sand or muddy sediments between 5 and 480m deep, making dredging the only commercially-viable way to collect the species. The highest reported age of an ocean quahog is an astonishing 507 years old. Nicknamed ‘Ming the clam’ due to its life beginning during the Ming dynasty, this individual was found off the coast of Iceland in 2006.

Risso’s dolphin – Grampus griseus

Of all the marine mammals that live in and visit Scotland’s waters, the Risso’s dolphin is probably the least known. Scotland’s seas represent the northern limit of the Risso’s dolphin’s range and when here, it inhabits deep waters where it feeds on squid, octopus and cuttlefish. Although rarely seen, the UK is home to roughly 86% of Europe’s Risso’s dolphins, of which Scottish waters are of particular importance.

Risso’s dolphins are long lived (over 30 years) and mature late, which makes populations particularly vulnerable to pressure. A particular threat to Risso’s dolphins are plastic bags, which resemble their prey species. The dolphins mistakenly eat the plastic bags, which can block their digestive systems and cause starvation and eventually death. Additional pressures include being caught as bycatch by fishermen, noise pollution from offshore drilling and pile-driving, vessel traffic, and bioaccumulation of marine pollutants such as PCBs and heavy metals. 

Sandeels – Ammodytes marinus and A. tobianus

Sandeels are small, eel-like fish that live in sandy habitats in the North Sea and often swim around in large shoals feeding on zooplankton. Although they may seem fairly insignificant, sandeels are considered a ‘corner-stone’ species in the North Sea, providing a valuable and abundant food source for many species of fish and seabirds, most notably wild salmon, common skates, kittiwakes and puffins. Sandeels are so important that changes in their abundance can directly influence the breeding and survival rates of many of Scotland’s seabird populations.

The health of sandeel populations in the North Sea is under a variety of pressures. Sandeels are commercially fished (for use as bait or livestock and aquaculture feed), at risk from bottom-trawl fishing practices that disturb their habitat and prey species, and finally by rising water temperatures caused by climate change. Sandeels feed primarily on zooplankton, whose distribution and abundance is influenced by water temperature. The North Sea is expected to get warmer, which will lead to changes in zooplankton abundance and distribution and result in a decline in sandeels and ultimately reductions in sandeel predator populations. 

Common skate – Dipturus intermedia and D. flossada (previously thought to be a single species D. batis)

Despite its name, the common skate is currently identified as ‘critically endangered’ on the IUCN Red List of Threatened Species. Historically, the common skate was found across much of the northeast Atlantic and throughout the Mediterranean, but due to intense fishing pressure the common skate can now only be found in northwest Scotland (although there are some occasional sightings outside this region).  The common skate is Europe’s largest skate, growing up to 285cm in length and capable of living for up to 100 years. The common skate is particularly vulnerable to overfishing because it doesn’t reach sexual maturity until around 11 years old and females only breed every other year. These factors have hindered the ability of the remaining skate population to recover to a healthy size and expand into areas it once populated.

It is now illegal for commercial fishermen to land common skate and they must be released. However, they are still a popular target amongst recreational anglers, but a catch and release practice must be followed.   

Orange Roughy – Hoplostethus atlanticus

The orange roughy is a widely-distributed deep-sea fish found in cold waters between 180 and 1,800 m deep. It is the largest species belonging to the ‘slimehead’ family, so-called because of the network of mucus-filled canals on their heads that form part of the sensory system. Like other slimeheads, the orange roughy is slow growing, late to mature and long-lived; the oldest known individual fish being an incredible 149 years old. Because of these characteristics, orange roughy are very susceptible to overfishing, yet are still a commercially-targeted species. The name ‘orange roughy’ (which is a slight misnomer because when alive they are actually vivid red, only fading to orange when they die) was in fact introduced in the 1970s by a US National Marine Fisheries Service programme in order to make it more marketable as its previous name of ‘slimehead’ was understandably less appealing to the consumer!