An unusual encounter with the Highland Dancer

Recently whilst diving at one of our local sites we came across an animal we had never seen before. It turned out to be a member of the sea slug family, though significantly larger than most common sea slugs, called the Highland Dancer Pleurobranchus membranaceus see photo below. These beautiful, yet odd looking creatures are found from the Western Mediterranean to the Atlantic coast of Ireland and France as well as the British Isles. An individual is usually about 70mm in length. They swim upside-down using an undulating foot to propel them through the water.

Sea slugs are part of the phylum mollusca, which encompasses animals such as bivalves and squid. The Highland dancer has a hidden in internal shell, different from say a mussel that has an exterior shell. When we saw the Highland Dancers there was an individual every metre or so laying a beautiful ribbon of eggs. The Highland Dancer is well camouflaged, probably the reason we had never noticed the species before. Yet the ribbon of eggs are bright white and each ribbon contains more than one million eggs. It was quite a magical experience watching them lay their ribbon of eggs.

The problem of Ocean acidification

Termed the ‘other carbon dioxide problem’ ocean acidification is becoming an increasing threat to the world’s oceans. Ocean acidification is the result of increased carbon dioxide released into the atmosphere from human activity such as burning fossil fuels, cement manufacturing and deforestation. The ocean is a carbon sink with 25-30% of anthropogenic carbon dioxide emissions being absorbed by the ocean, equivalent to ca. 1,000,000 tons of carbon dioxide absorbed hourly. This absorption of carbon dioxide on such a large scale is causing the oceans to become more acidic.

This is bad news for many marine organisms, especially marine calcifiers such as shell fish and corals. The more acidic water means that it is harder and more costly for many species to grow and develop. If the ocean continues to increase in acidity, reefs across the planet could be in dissolution states, which basically means coral structures will be breaking down in the increased acidity. As coral reefs are home to the widest biodiversity on the planet, if this were to happen it could be detrimental for many species.

Moreover, the effect of increasing acidity of the ocean could also impact countries economically worldwide. In the Northwest Pacific the effect of the acidity has already cost the oyster industry US$110 million, which puts 3,200 jobs at risk. With a growing population across the plant, achieving food security in the face of ocean acidification could be crucially important.

So what can you do to reduce the effect of ocean acidification on marine organisms?

  • Reduce your fossil fuel consumption- switch your energy provider to one which uses renewable energy sources. Drive less, use more public transport, car share or walk.
  • Be a conscientious consumer- don’t buy product that contain palm oil for example, as most palm oil plantations contribute to deforestation of the rain forest which is a massive carbon store.
  • Promote healthy marine environments- healthy ecosystem are more resilient to stresses such as ocean acidification. You can do this by simple things like doing a litter pick when you go down to your local beach.
  • Whilst diving reduce your impact on the marine environment with good trim and avoid touching marine organisms.
Seal Scuba Diving and Snorkelling

Seal Scuba Diving and Snorkelling

Scuba diving or snorkelling with seals is an amazing and memorable wildlife encounter and one of the most thrilling underwater experiences imaginable. Plunge into the cool waters of the North Atlantic Ocean and snorkel or scuba dive with the Grey Seal colony found around the infamous Blasket Islands. Interact with these playful and inquisitive wild animals in their natural habitat and on their terms. This day trip is one of the best activities you can undertake during your stay in Dingle! Not only will you snorkel/dive with the seals, but you will also experience the breath-taking views of The Blasket Islands from sea and view the stunning marine and coastal life found in and around our waters!

Check availability on our scuba diving or snorkelling seal trips

Contact us on +353(0)879111643 or email at info@divedingle.com.

 

Eastern Atlantic Grey Seal facts:

Seal Scuba Diving and Snorkelling
Grey seals have been known to dive to depths of up to 300 metres and stay underwater for up to 20 minutes!

Adult male statistics and info:

  • Measure between 1.95-2.5m in length
  • Weigh between 170-310kg
  • Males reach sexual maturity at 4-6 years of age, however may not attain territorial status until 8-10 years of age.
  • Live up to 25 years of age on average, with 29 years being the maximum recorded age.
  • Males tend to have dark brown-grey coats, sometimes nearly black with a few lighter patches.
  • Male adults have a distinctive long “Roman” nose with wide nostrils.

Seal Scuba Diving and SnorkellingAdult female statistics and info:

  • Measure between 1.65-2.1m in length
  • Weigh between 103-180kg
  • Females reach sexual maturity at 3-5 years of age
  • Live up to 35 years of age on average, with 46 years being the maximum recorded age.
  • Females are usually light grey-tan coloured, lighter on the front with dark spots and patches.

 

 

Seagrass

Most people have the misconception that Seagrass is like the grass we get in our back gardens, that it can be abused, dug up and cut. However, Seagrass is a lot more sensitive to environmental change. In the last few decades there has been a large decline in seagrass beds worldwide, approximately 50% of Seagrass Beds have been lost, this is not just bad news for the species the seagrass beds support as nursery grounds, but moreover it could be detrimental for mitigating the effects for climate change.

Dingle Peninsula Marine LifeSo why should anyone care about some grass in the sea?

If you like eating seafood, whether its Crab, Lobster, Fish or Shellfish and want to keep eating it, you need to do your bit to help protect the Seagrass. The beds provide microclimates for juvenile species, as there are lots of places to hide from predators. Seagrasses as primary producers are food for large numbers of herbivore species, such as Urchins and are also feeding grounds for many migratory species. Secondly, if you live close to the coast Seagrass beds reduce coastal erosion, filter water and trap sediment. It oxygenates the surrounding area for many other species. Seagrass sequest carbon dioxide in the surrounding water and are massive carbon dioxide sinks. So just like chopping down the rain if Seagrass beds are destroyed, not only will there be no further sequestration of carbon dioxide, if the routes of the Seagrass are ripped up it will all release carbon dioxide back into the surrounding water. This will add to the greenhouse gases already in the atmosphere and add to climate change.

Why are Seagrass Beds in decline and what threats do these habitats face?

Sewage, aquaculture and farming all add excess nutrients into the ocean, which leads to algae blooms, in turn restricting sunlight for the Seagrass and reducing oxygen. Coastal development in many areas has physically uprooted and destroyed Seagrass. Dredging for navigation reduces the light levels in the water and can suffocate the seagrass. Anchor damage is another increasing threat with a growing world population flocking to the coasts and increasing recreational boat use.

So what can you do to help?

Never anchor on a Seagrass Bed, find a sand patch. Support conservation bodies and organisations trying to change legislation to reduce water pollution. When driving a boat in shallow water over a Seagrass Bed tilt the engine up and turn it off as to avoid damaging the area. If you live near the coast don’t apply too much fertiliser/nutrient pellets to your garden to reduce the amount of nutrients running into the ocean.

Around the Dingle peninsula we have Seagrass Beds; one of my favourite dive sites just inside of the Dingle harbour mouth is a Seagrass Bed, which supports Thornback Rays, Cuttlefish and many other species!

By Hannah Green
Marine Biologist and Divemaster in training.