Gigha South Pier
This is a scenic, shallow dive between Gigha South Pier and Gigalum Island. Maximum depth is only about 5m, and most of the dive was in the range 1 to 3m depth. There is a range of seaweeds and associated animals, and the clear, shallow water allows swimmers to enjoy much of the marine wildlife. The site is exposed, and moderate currents are possible at some states of the tide.
The coast line is composed of white sand with dark rocky outcrops, and occasional veins of quartz, plus a pier. Rocks have wide range of seaweeds, but these are not dense, and form a very pleasant backdrop to the dive. Seaweeds are also attached to the supports of the pier and the outer supports of the pier end. Inner supports (where light is reduced) have sponges, dead-men’s fingers, barnacles (no ID) and plumose anemones attached.
Attached seaweeds include:
- Sea oak, Halidrys siliquosa is perhaps the most common of the species present from the shore to a depth of 2m
- Furbellows, Saccorhiza polyschides occurs on suitable substrates, though individuals are not large
- Sugar kelp Saccharina latissima is found in slightly deeper water (1m), fronds are quite long but narrow, not the great expanses frequently seen in sheltered waters.
- Oyster thief, Colpomenia peregrina is quite common, growing on rocks or other algae.
- Sea lettuce Ulva lactuca (leaf form) is present.
- Velvet weed, Codium fragile is present, and quite abundant, and also seen in the strand line on Eilean Garbh and North end.
- Sea whip Chorda filum is present, but there are no dense beds of this
- Bushy strands of wireweed (Sargassum muticum) reaching several meters in length, stretching across the sand from their attachment point, are common in slightly deeper water (with smaller individuals in the shallows).
- The delicate brown seaweed Dictyota dichotoma is present as an understory plant.
- There is an understory of red algae - which are common as a whole, though I am able to name only one or two - including:
- Carragheen, Chondrus crispus, individuals often green/brown with red tips rather than strong red in colour throughout.
- Toothed weed Odontella dentata is probably common, but only a couple of photos are good enough to give a solid ID.
- Encrusting red algae are present on any available bare rock, and I found one solitary fragment of maerl (despite keeping an eye out for more).
- I have a single photo of what appears to be a species of Scinaia – a fleshy red alga about 6cm tall
Above: Seagrass fronds, some showing over-growth of algae, others with a coat of colonial seasquirt. Barley snails appear to be grazing off the surface algae (there is also a stalked jellyfish:-)
On open sand seagrass beds (Zostera marina) have established, though none are very large – typically up to 10m in any dimension. Many fronds are covered in either filamentous algal growth or extensive colonial seasquirts (possibly Diplosoma listerianum – with large raised exhalant siphons, but tiny bubble like bodies). Tiny banded snails (probably Barleeia unifasciata) are also common on seagrass blades – these may be helping the seagrass by cleaning algae and hydrozoa off the blade surface, rather than eating the grass itself.
Snakelocks anemones (Anemonia viridis) are very common, and found attached to seaweeds, seagrass and bare rock. There are a variety of sizes, some with purple tips, others less-so or no purple colouration. These animals have symbioic algae, on which they rely for much of their sustenance, so are restricted to shallow, well-lit waters. They are sufficiently prominent (with several individuals per square meter in good locations) as to be the signature species at this location.
Kelp fronds form a substrate for a number of hydrozoa, including Obelia geniculata. Bryozoans such as membranipora are also present on the kelp. I saw a single example of the stalked jellyfish (Haliclystus auricula) attached to a seagrass frond – a high point of the dive, as this was the first time I had seen this species.
Worm casts were uncommon on the sandy bottom, other than in the shallow bay to the west of the pier. There were occasional peacock worms (Sabella pavonina).
Amongst the echinoderms there were a small number of common urchins, and an almost solitary common starfish.
There are a number of crustacea present, including the cosmopolitan velvet swimming crab (Necora puber), sometimes called the devil crab because of its bright red eyes), the shore crab (Carcinus maenas) and the harbour crab (Liocarcinus depurator). The small spider crab Macropodia tenuirostris is very common on seaweeds, seagrass, and wandering the open sand in slightly deeper water (3m+), when they commonly had intricate camouflage of algae, making them look like a drifting piece of seaweed.
Of the burrowing molluscs, I saw one king scallop shell (Pecten maximus), but this was close to the pier, and may be a fishing casualty from elsewhere. I also saw a single large common otter shell (Lutraria lutraria) between 10 and 15cm long.
Fish included large numbers of two spot gobys (Gobiusculus flavescens) in the seagrass beds, and fifteen spined sticklebacks (Spinachia spinachia) in the weed in shallow water. A lot of sand gobys (Pomatoschistus minutus) were present on open sand patches, but they were unusually wary (they will often approach the camera lights, but not in this instance!). A dead dogfish (Scyliorhinus caniculus) about 2 feet long, had been washed up on the beach, so also probably present in the locality.
Surveys by Barry Kaye, 26th (swam) and 28th (dived) September 2017.