An online guide to the Stalked jellyfish (Stauromedusae) found
around the coastal waters of the United Kingdom and Ireland.
Includes notes on their identification, and where and how to find them.

Site profile for Great Hogus reef, Marazion, Cornwall.
Great Hogus, OS Grid. Ref. SW 513 305, is a rock outcrop which was once the site of an ancient underwater volcano. The rock surrounding the reef is extremely hard, a volcanic agglomerate, consisting of sometimes large chunks of basaltic lava, rock which was fragmented during an ancient volcanic explosion.

Great Hogus reef falls within the National Trusts St. Michael's Mount boundary. The reef is very roughly the shape of an elongated horseshore, with the open end nearest the shore. The reef is largely protected on it's inside, as it is surrounded by higher, and harder rocks and boulders. There is a system of pools draining from the south to north, and these empty at the NW edge of the reef. For purpose of studying stauromedusae, the long mid-reef pool is referred to as Sump Pool and the area where it drains, as Sump drain. So named because much of the surrounding area is much higher. Softer Mylor slate can be found at the base of Sump Pool, and old Piddocks borings can be found where the bedrock is exposed. Piddocks involved include Common, Little and Oval / Great piddock; Pholas dactylus, Barnea parva and Zirfaea crispata.

There are a couple of smaller pools close to the eastern edge of Sump Pool, I refer to these as Middle Pools; and a pool of reasonable size, surrounded by boulders, much further to the east and nearer the waters edge, East Pool.

Sump Pool
Sump Pool is the name given to a long narrow pool that lies in the center of Great Hogus. The pool is often shallow and drains on the north western edge of the reef, the drain is referred to as Sump Drain. The pools itself is largely quite shallow, its norther end has good areas of Chondrus crispus for searching, its southern edges sometimes fringed with species such as Corallina officinalis and Ceramium, with Sargassum muticum occurring in the central parts of the pool.

Sump Drain
As described above, Sump Drain lies at the north western end of Great Hogus, and is where Sump Pool drains down the reef into the sea. There area drains through several small pools, the drain and pools being quite rich in Chondrus crispus. Species like Haliclystus octoradiatus are found here due to the flowing water and suitable weed species.

Middle Pools
Middles Pools is an area of small pools that lie just to the east of Sump Pool and are of slightly higher elevation. All contain suitable species of algae for stauromedusae, species like Chondrus crispus and Sargassum muticum.

East Pool
East Pool is a narrow pool that is surrounded by large boulders, some of the boulders are also found within the pool. There are quite a few suitable algal species within this pool, species include Chondrus crispus, Corallina officinalis, Sargassum muticum, Calliblepharis jubata, Gastroclonium ovatum, Cladostephus spongiosus and Ceramium species. The pool is sheltered from the south west by the majority of the reef and local currents may bring stauromedusae to the reef from other local sites, including St. Michael's Mount itself, and the Eelgrass beds and reef to the NE of St. Michael's Mount.

Geological Ref: British Geological Survey - Mounts Bay

Great Hogus records SW 513 305
Grid refs. for each pool will be included later, the pool systems have yet to be surveyed. N.B. There aren't that many pools at Great Hogus, which is why it is easy to refer to individual pools. Images taken to help record and identify specimens, please don't expect glamorous photography.

04.10.12. 1 specimen, Haliclystus octoradiatus.

Haliclystus octoradiatus 1
10mm dia. specimen on Chondrus crispus at recorded at SW512603045. Record by David Fenwick.

14.03.14. 8 specimens, 6 Haliclystus octoradiatus and 2 Calvadosia cruxmelitensis. Cloudy day with some sea mist, high pressure. 10.16am low water. 1.4m low. Ref. Cornish Coast tide times 2014. Record by David Fenwick.

Calvadosia cruxmelitensis 1
11mm dia. specimen on Chondrus crispus, southern end of Sump Pool.

Calvadosia cruxmelitensis 2
8mm dia. specimen on Calliblepharis jubata, southern end of East Pool.
Haliclystus octoradiatus 1
10mm dia. specimen on Chondrus crispus in flowing water at Sump Drain.

Haliclystus octoradiatus 2
10mm dia. specimen on Chondrus crispus in flowing water at Sump Drain.

Haliclystus octoradiatus 3
15mm dia. specimen on Sargassum muticum in small pool at Middle Pools.

Haliclystus octoradiatus 4
Juvenile 7mm dia.? specimen on Chondrus crispus, northern end of East Pool.

Haliclystus octoradiatus 5
15mm dia. specimen on Chondrus crispus, northern end of East Pool.

Haliclystus octoradiatus 6
15mm dia. specimen on Chondrus crispus, northern end of East Pool.

This part of the website is "UNDER CONSTRUCTION", details and text may be unchecked. Adding profiles and records for each site can be quite time consuming, especially during periods of recording.

Stauromedusae Site profile Great Hogus reef Marazion Cornwall National Trust uk