Issue
17
Page
4
Shipworms are a particularly difficult group of molluscs to retrieve and identify for two main reasons. One is the fact that they can occur in very large pieces of timber and be stranded in very remote parts of the coastline making their retrieval difficult and physically challenging. The other is that in many cases the species cannot be accurately identified by their shells alone as these can be very variable and similar, it is essential therefore to have the appropriate set of pallets for each shell, the pallets being the most positive source of identification. These notes are a summary of the methods that I have found most helpful in dealing with Shipworm timber.
Retrieval:- In cases where the stranding was not in close proximity to a car parking facility, I found a two-wheel trolley to be a valuable asset where the terrain was suitable. In some cases however, the timber had to be cut into manageable sections on site and then carried manually sometimes for long distances, in these cases, a bow saw was the best cutting medium and the lightest to carry.
The worst case I have encountered so far was a tree trunk 10 inches in diameter by 12 feet long stranded at the mouth of the river Cefni on Anglesey between the northwest tip of Newborough Forest and the Bodorgan Estate on the opposite side of the river. The nearest location where a car could be parked was two miles away. The first two sections were removed on site using a bow saw, a total of three feet was removed. One section was carried in a rucksack and the other by rope sling, neither of these methods proving satisfactory considering the weight and distance involved, the journey being straight across Malltraeth Bay and through dense salt marshes at low tide. Eventually, a back mounted carrying frame like those used by mountaineers in the 1970’s was constructed from an old shopping trolley. This enabled me to carry the timber the two miles in lengths of about 2 _ feet, one at a time with relative ease. It took a total of five trips to retrieve all of the timber.
Chain saws can be an easy way of cutting the timber sections on site, these can however be heavy to carry for long distances along with the timber sections as well. Although the back mounted carrying frame is the most effective method of retrieval, the liquid that often pours out of the holes when carrying the timber may not necessarily be clean sea water, but can be an obnoxious fluid from the decaying tissue inside the wood. It was found advisable to carry the samples wrapped in bin liners when transporting them.
Provenancing the shells and pallets:- When there was only one species of Shipworm in the timber, identification was relatively straight forward providing the pallets were present, this fact however did not become apparent until some time into the dissection process.
The greater problem was found to be with multi-species strandings especially when there were warm water species present, such samples may have travelled a very long journey of probably several thousand miles and had been infested by any number of other species during its journey. Again, this was not apparent until some time into the dissection process.
For accurate identification in multi-species timber, it is essential to be able to accurately link the shells with their pallets and also a sample of their calcium linings. Bearing in mind the probability that the shells could be some considerable distance from their pallets and that the timber may have been cut into several sections on site to facilitate removal, the shells could be in a different section from the pallets. It is therefore important to retrieve all of the timber samples and to dissect the whole of the timber in a calculated and scientific manner. If the full range of species in a stranding is not known, the wrong shells can easily be linked up with the wrong pallets.
Dissection of timber samples:- There are three main methods of dissecting timber each of which has varied merits but incurs a different degree of destruction.
1. Cross Sections - With these there is the inevitable risk of cutting through important shells or pallets, yet causes the minimum degree of destruction to the timber, the sections can be numbered and put back together again to form the original object. This however does not help if one wants to extract a section of calcium lining.
2. Length Wise Splitting – This was done with care making sure that the splitting tool only went far enough into the timber to start a split which could then be carefully levered apart as the splitting tool destroys everything in its path. The presence of knots in the wood made splitting difficult and sometimes impossible. Length wise splitting can reveal good examples of calcium linings and enable one to follow a hole for a greater distance, this was however more destructive of the original timber specimen as the two pieces could not be put back together again without damaging exposed calcium linings.
3. Gouging Out – This was used in relatively thin flat specimens that were not too heavily infested. A rectangular section was cut into the flat face of the timber 1 or 2cm deep using a circular cutter, followed by carefully chiselling out the timber in an attempt to follow each hole from its entry point to the bore head. This revealed some wonderful examples of growth rate of the animal in relation to distance travelled through the timber. It did however involve destroying some holes in order to achieve this. The finished sculpture was then sanded smooth and varnished, this provided a permanent example of complete boreholes. The timber that was removed was however completely destroyed.
When timber samples had been cut into sections, the number of holes in each cross section was noted as this in some cases indicated a general direction of movement of the species in the timber. When this was the case, the dissection was started in the timber section that contained the most holes, as this was where the original entry holes were situated and therefore where the majority of pallets would most likely be found. When a set of pallets were found in a particular hole, especially if they were of a warm water species, the movement of the hole was traced through the timber by placing the timber upright and pouring water down the hole using a small funnel or syringe and noting where the water came out, it should have only one exit. The pallet was put into a numbered container and both ends of the hole numbered likewise, the continuation of the hole was traced into the next section of timber and the holes numbered likewise. This process was continued until the water did not pour out of the end of the timber, this indicated that the end of the hole was that section and that the shells were probably there also. Inserting pipe cleaners into the hole was another method of tracing holes for short distances though care was taken not to damage any shells.
When the first section had been dismantled, the next section was systematically dissected and an attempt made to follow each numbered hole in search of the shells. Also by using a small Dremmel or by careful chiselling it was possible to extract an example of the calcium lining at the same time. This process resulted in a positive link between the shell, its pallets and the type of calcium lining and provided a valuable tool to aid the identification of it and other species. Failure to do this in a multi-species timber sample can result in a mass of similar looking shells with a number of very different pallets and the almost impossible task of matching them together.
Live/Recently Dead Specimens:- Because Shipworms can seal themselves up inside their boreholes using the pallets, they can survive for considerable lengths of time in stranded timber. Usually by the time stranded timber is found, retrieved and dissected, the animals are at the very least recently dead. Where specimens were found in a sufficiently fresh state, they were preserved in surgical spirit.
In the rare case of live specimens being found stranded on the shore at Traeth Crugan near Pwllheli on the Lleyn Peninsula, a sample of timber was brought home and placed in a tank of sea water with air circulation, some of these animals were still alive after six months including what looked like some perfect juveniles. This provided a rare opportunity to photograph some of the pairs of siphons of Nototeredo norvegica.
Recording the results:- All of the shells and pallets of each species found were counted, measured and recorded listing quantities, maximum, minimum and averages sizes and a description of the calcium linings made. Also noted was the maximum, minimum and average hole sizes. This information is important because in the case of Shipworms, the size of shell is not only indicative of maturity of the specimen but also of space limitation inside the timber.
Analysis of the results:- Species will only grow to their maximum size if there is sufficient space available for them to do so. This was indicated in a comparison of Shipworm strandings on Anglesey and the Lleyn Peninsula. In the Church Bay log which contained four species of Shipworms, some of which were warm water species, there were about 40 specimens of Psiloteredo megotara, only about four had reached adult size, the rest were quite small and were found mainly at one end amongst a mass of tightly packed entry holes. This suggests that when this species entered the timber, it was already heavily infested with other species leaving little space for them grow, this may well mean that they were the last species to enter the timber.
This also compares with the Pwllheli log which although it only contained Psiloteredo megotara, the infestation was heavy and they were therefore restricted in space available by their own numbers. In this specimen 414 shells were found but only a small percentage reached adult sizes, the rest were relatively small for this species.
Comparing these results with the Cefni log, which again only contained Psiloteredo megotara, the infestation was light leaving an abundance of free space inside the timber. In this timber 497 shells were found, the majority of these specimens were large up to 11mm high suggesting that there was no growth restriction. This provided some of the largest and best samples of this species.
Meticulously recorded information particularly for multi-species warm water strandings can reveal a considerable amount of information about the timber, its inhabitants, the journey it has travelled and possibly the order in which the species entered the timber. As these strandings are not very common, they can provide a rare opportunity to learn more about these remarkable animals.
Storage of Shells and Pallets:- All of the shells and pallets from each particular sample have been kept for future reference including fragments. In order to prevent the delicate apophysis from breaking in the shells, they have been mounted on specimen boards of black cartridge paper 3 inches by 15 inches using Gum Arabic, so that they can fit under a microscope. The specimen boards are stored in trays and fixed by white tack for easy removal. The dissected timber is labelled and stored in plastic trunks. Detailed dissection reports have been compiled for each stranding listing the contents, calcium linings along with pictures, diagrams and conclusions, these now form a volume entitled “Shipworm and Other Wood Borer Strandings 2006/2007”. Volume 2 for 2008 has already been started.
