STAUROMEDUSAE UK
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.
The Stauromedusae of Mounts Bay
Five species of stauromedusae have been found to occur on sheltered shores of Mounts Bay and one of the reasons for this will be because of the bays geology. The geology appears to provide just the right environmental conditions needed to support the populations that are seen here. Granite intrusions and outcrops occur across the bay at Marazion, St. Michael’s Mount, Little Hogus, Long Rock, Western Cesars, Albert Pier Reef, Battery Rocks, Chimney Rocks, Wherry Rocks and Larrigan Rocks. Great Hogus was the site of an ancient underwater volcano. Between the layers of hard granite are found much softer layers of Mylor slate and in some areas the slate has degraded and is bored by piddock communities.
The hardness and softness of the rock types, marine erosion has created runnels, gullies and interlinking pools on the shore that run from the middleshore to lowest tide level, and beyond, across the bay; the runnels have been found to provide incredibly good habitat for all species of stauromedusae and have allowed various species to be best studied and recorded. Finding stalked jellyfish is no longer by chance but often by prediction.
It has been found that stauromedusae are more likely to occur within these runnels and pools close to a constriction, and where pools narrow and drain into each other. The constriction provides the species with a greater flow of water in which to feed and food may be more concentrated at these points. It is also known that stauromedusae reproduce quite locally, therefore the sediments at the bases of these pools in the bay probably best support the conditions needed for reproduction also. Local reproduction is supported by NECR043, a Natural England Commissioned Report, ‘’Meeting the MPA Network, Principle of Viability, Feature specific recommendations for species and habitats of conservation importance’’. The rockpools in Mounts Bay also contain plenty of the most suitable algal species for all the species that have been found, namely Sargassum muticum, Japweed or Wireweed; Corallina officinalis, Coral weed; Chondrus crispus, Carragheen or Irish Moss; and various Ceramium species. There are also beds of Zostera marina, Eelgrass, intertidally and offshore. The most frequent species of stauromedusae found across Mounts Bay include Haliclystus octoradiatus, Calvadosia campanulata and Calvadosia cruxmelitensis. Craterolophus convolvulus is also found but isn't common here, and Haliclystus auricula has been historically recorded.
The stauromedusae listed here need algae from which to feed, the algae also appear to give them a level of protection from tidal flow and predation, fewer stauromedusae are found where pools or runnels become increasingly congested with algae, towards the summer Haliclystus octoradiatus records tend to tail off noticeably, and very few stauromedusae are found when Sargassum muticum, Japweed, congests local pools and starts fruiting. Stalked jellyfish are therefore best found from September to May, the optimum period from November - March.
I have not yet observed any predation but I would suggest that the main predators or threats would be from weed cleaners such as Palaemon sp., Prawns; crabs and rockpool fish such as Parablennius gattorugine, the Tompot blenny.
Chondrus crispus, Carragheen or Irish moss is specifically important for Calvadosia cruxmelitensis, and is found frequently on it. It must be noted that away from the runnels, that eelgrass is important for all the species mentioned, including Calvadosia cruxmelitensis. I have found stauromedusae amongst eelgrass in a similar manner to that of finding species within runnels and pools and stauromedusae seem to prefer areas of increased water flow and are more common on the outer edges of eelgrass beds, or where tides and currents have cut less dense areas within a bed, or where the bed may have become damaged. The greatest concentrations of stalk jellyfish can be found where saltwater run-offs, or small streams, filter water through a bed on a receding tide.
Drainage and water flow would seem to be a factor in where to find them at various sites, even on exposed shores like on the north coast of Cornwall at Trevaunance Cove, St. Agnes. Here large numbers of juvenile Haliclystus octoradiatus have been found in pools on Ceramium sp., on the southern side of large rocks that protect pools from the large surf that occurs on that coast, Calvadosia campanulata has also been frequently found at the same location.
So areas of increased water flow, such as around rock outcrops and boulders, (but ones that may give some protection from large waves), saltwater drainage from rockpool to rockpool as the tide recedes, and the right algal species, would appear to provide the most favorable conditions. Such places along our coastline are of course not uncommon.
Finding stauromedusae on the shore (in images)
Looking within larger pools
Pool constriction and drainage
Pools draining into one another
Sudden changes in water flow (water depth / obstruction)
This section has to be concluded by stating that the information provided in this section is a guide based on general observations made on studying a number of species of stauromedusae at various locations around Cornwall throughout the year. It has to be noted that certain species of stauromedusae can be seasonally abundant, and sometimes, that large congregations (blooms) may occur on the shore, at these times they may be seen not just in the places described, but all over the shore, including on algae out of water. Sometimes blooms may occur intertidally and include the middle and lowershore, sometimes they may be limited to the lowershore, low tide line, or may only occur sub-tidally.
It is usual for stauromedusae to occur quite sporadically on a shore because of local factors which may influence where they are found and their frequency, the guide here should help with this. On a wider scale, in Mounts Bay the winter storms of 2013/14 may have been responsible for concentrating stauromedusae into more sheltered areas of coastline, the more sheltered areas, which included areas of suitable habitat, may have assisted their settlement. Multiple factors may therefore influence their frequency and when and where they are found.
An increase in understanding of where and how to find stauromedusae may increase the level of recording; all this largely because there's never been such an opportunity to promote such an obscure and overlooked group. Because of the internet there is now increased promotion and greater access to information, and from websites such as this; through social media such as Facebook; image websites such as Google Images, Flickr etc.; and recording sites such as iRecord.
In increasing the profile of stauromedusae through greater promotion, they may become quite 'fashionable', they are certainly very photogenic; a greater level of understanding may help to increase the level of actively, promote searching, leading to an increase in recording. This is especially important in terms of promoting the more obscure species, such as Depastrum cyathiforme, where there are plenty of historic records but few or no recent ones, and where we need to determine the present distribution to know whether to conserve or even legally protect. Much is the same with Haliclystus auricula, since H. octoradiatus has been separated from this species in 1997, there have been very few UK records. Historically different characteristics were used to determine H. auricula, so we cannot be sure of it's historical distribution, or know where to suggest looking for it. We have to use recent European records as a guide, and these would suggest the species is best looked for in May / June, and on Laminarians or Eelgrass (Zostera marina).
On looking at records in the future one has to consider that a general increase in numbers of stauromedusae will but observed, but that this may be from an increase in the level of recording, because of promotion and greater level of understanding and awareness, and not necessarily because there is an increase and they are becoming more common. Although an increase in recording may find that certain species are more widespread than presently considered.
An increase in the level of recording may of course allow us to best determine the overall level of distribution around the UK, but in order to determine an overall decline or increase, records have to be looked at for specific sites over a number of years. With stauromedusae, what needs to be established is the conditions necessary for providing the stability of good 'natural' populations. Locations where records have been sourced that are closer to population centers, might have suffered anthropogenically (influenced by man), and factors such as pollution may have had an impact on population size in certain localities, possibly even artificially increasing them.
