River Yealm Research Articles

UK meteotsunamis: a revision and update on events and their frequency

<scp>UK</scp> meteotsunamis: a revision and update on events and their frequency

An examination of the gardens at Langdon Court

The modest manor house of Langdon Court, near Plymouth in south Devon, has a complicated but decipherable architectural history . The history of its garden, however, is more mysterious. Sited in a sheltered combe above the River Yealm, Langdon was originally a modest Domesday manor. In 1564 it was granted by Elizabeth I, for services to the Navy, to Vincent Cahnady, a Devon lawyer; and Langdon remained a seat of the Calmadys, prosperous merchants and lawyers, until 1875. Vincent constructed a new manor house there in 1577 on traditional medieval lines with projecting gabled wings on either side of a central hall, using stone and timber from the nearby dissolved Plympton Priory. Minor sequential improvements followed with increased prosperity (the plaque over the porch on the east front is dated 1688 and the sundial plaques on the garden front are dated 1693); and the house was extensively reworked in 1707 by Vincent's great-grandson, Josias (d. 1714). Josias Calmady was a wealthy and influential man: MP for Okehampton from 1679 to 1680, High Sheriff of Devon from 1694 to 1695, and Deputy Lieutenant from 1701 to 1714; and both the house and garden flourished under his ownership. He created a new west front, infilling between the wings to create a more substantial, square mansion with a central open court yard; and significantly developed the formal gardens.

A comparison of vegetated and unvegetated soft-sediment macrobenthic communities in the River Yealm, south-western Britain

Macrofaunal community structure was examined in a shallow sublittoral sea grass bed (Zostera marina L.) and adjacent unvegetated sediment in the River Yealm, Devon, south-west Britain, on a single sampling occasion in August 1995. The presence of Zostera had a significant influence on macrobenthic community structure in the River Yealm. Samples from inside the sea grass bed were characterized by significantly higher numbers of individuals and species, as well as by greater species richness and high faunal dominance (i.e. low evenness) compared with the unvegetated samples. High faunal dominance within the sea grass bed was attributable to the large numbers of a few species (e.g. the polychaetes juvenile capitellids, Spio filicornis, Exogone hebes, Nereis pelagica and the tanaidacean Apseudes talpa), while increased species richness was a result of a large number of additional rare (1–2 individuals) species. The greatest number of individuals was found in samples with the highest sea grass biomass. Multivariate ordination revealed a distinct separation of macrofauna communities from vegetated and unvegetated sites. Significance testing with ANOSIM shows that there were significant differences in community structure between vegetated and unvegetated habitats.

Forty Years of Changes in Species Composition and Population Density of Barnacles on a Rocky Shore Near Plymouth

The abundance of the common intertidal barnacles, Chthamalus montagui, Chthamalus stellatus, Semibalanus balanoides and Elminius modestus has been monitored since 1951 at a site near Cellar Beach, River Yealm, south Devon. Counts are made at 12 levels on a transect between high tide and low tide. The two chthamalids are of warm-water distribution while S. balanoides is a boreo-arctic species; changes in the abundance of these species are linked to environmental temperature. Maximum fluctuations occur in the lowermost third of the intertidal zone. The proportion of Chthamalus adults is correlated with annual mean inshore sea temperature two years earlier, while the proportion of S. balanoides adults is negatively so correlated. This relationship accounts for over 40% of the variance. A smaller part of the variance (&lt;20%) is explained by intensity of larval settlement, also related to climate. The fourth barnacle, E. modestus, is an Australasian immigrant that arrived in England during World War II and reached south Devon in 1948. It increased during the 1950s on the transect but has since stabilized at a low level of abundance that shows large interannual variations not directly related to temperature. Between 1951 and 1975, coinciding with a secular decline in sea temperature, there was a long-term trend towards reduction of Chthamalus and increase in S. balanoides; this trend has reversed since. Removal of the long-term trend reveals a short-term fluctuation of approximately 10-y frequency that correlates with a cycle in sea temperature two years earlier. These cycles are close to the 10–11 y solar (sunspot) cycle between 1951 and 1975.

Structure, life history and hybridization of atlanticGigartina teedii(Rhodophyta) in culture

The life history in cultured isolates of the marine red alga Gigartina teedii (Roth) Lamour, from the subtidal of the River Yealm, south Devon, England and the intertidal of the Rade de Brest, Brittany, France is described. Plants start to reproduce after about the same time at 20°C, 16 : h 15°C, 16 : and 15°C, 8 : h, but the morphology of the plants at the time of reproduction varies according to the regime. Plants grown at 10°C, 16 : h do not reproduce, and this may account partially for the observed northern limit of this species in European waters (south-west Britain). In both isolates, several successive, complete life histories have been achieved without any deviation from a Polysiphonia-type life history. Gametangial plants are always dioecious, and tend to reproduce more rapidly when unattached. Gametangial plants of G. teedii from England, France and Brazil are interfertile and fertile tetrasporophytes develop from the resulting carpospores. Gigartina teedii isolates from Brazil show Mendelian in...

The first occurrence of Sargassum muticum (Yendo) Fensholt in the Plymouth area

On 11 August 1976 an observant yachtsman noted an unfamiliar alga between Misery Point and Warren Point at the mouth of the River Yealm. Suspecting that it might be ‘Japweed’ he collected a piece and took it to Mr B. W. P. Sparrow of the International Marine Coatings Laboratory who contacted the Marine Biological Association, where Dr Boalch confirmed that it was a part of a fertile plant of Sargassum muticum, the first to be recorded from the Plymouth area (see Fig. 1).

Shell form in Venerupis rhomboides

SUMMARYTwo forms of Venerupis rhomboides occur in Plymouth waters. A more slender form, corresponding to that described by Pennant, occurs in the Eddystone shell gravel, and a more robust form, corresponding to the Venus sarniensis of Turton, occurs at the mouth of the River Yealm. The two forms differ in ratios of shell height, width and lunule width relative to shell length. A population with intermediate ratios is found at 6-5 m in Plymouth Sound.Plots of height/length ratios of these and another intermediate sample on probability paper did not indicate that the intermediate populations were composed of mixtures of the two extreme forms, and it was provisionally concluded that these were all variants of a single species.If the height/length ratios of series of samples from different localities are plotted against depth of water on a logarithmic scale, an inverse relationship, approaching a straight line, is obtained. Regression lines for median ratios in the 3-4 and 4-5 cm length groups have been plotted separately, as there is some change in proportion with increasing length. These show a highly significant negative correlation between shell ratios and depth.From the regression lines it has been possible to obtain an estimate of the depth inhabited by even quite small samples of shells. Depth estimations have been made for eight samples, consisting mainly of dead shells. Six samples lay within the expected limits, and discrepancies in the other two samples are attributed to transport along the sea floor.The possible causes of the differences in shell ratios are discussed. Previous work suggests that shell ratios may be affected by different rates of growth. Soil grade, temperature, food supply, and light penetration are considered unlikely causes of the observed differences in shell ratios, and it is suggested that the pattern of growth may be affected by pressure.The Appendix contains a key to British species of Venerupis.

Occurrence of Pelagia in the River Yealm Estuary, South Devon

THE scyphomedusan Pelagia was observed in some numbers in the River Yealm estuary, South Devon, on December 20, 1951. This is of more than merely faunistic interest, though on that score alone it is worthy of note, since the genus is purely pelagic and, so far as I am aware, has never before been recorded in the English Channel nearer inshore than the neighbourhood of the Eddystone, and then only very sparsely1. The present record is due to the vigilance of Miss Agnes Russell, of the yacht Ardglass moored in the Yealm estuary, who saw a specimen of the medusa as she was rowing ashore from her yacht; though not a biologist, she was quick to recognize its unfamiliar pattern and that, in any event, a ‘jelly-fish’ in December was a matter for further inquiry.

On Manganese in Sea and Fresh Waters

A method of estimating the maximum quantity of manganese available to plants in sea and fresh waters is described.Samples of sea water collected off Plymouth in 1948 contained 0·7–1·0 mg. Mn/m.3in solution plus any particles soluble at pH 4·6. After storage and sedimentation of particulate matter, the quantity decreased to 0·0–0·25 mg./m.3Samples collected off the Isle of Man, an area with a rich summer population of flagellates, contained 2·0–2·6 mg./m.3The river Yealm, south Devon, on leaving Dartmoor contained 1 mg., and after passing through agricultural land 10 mg.\m.3Lakes and streams in the English Lake District contained 6–40 mg.\m.3The least fertile waters contained the least soluble manganese.

Oyster Rearing on the River Yealm

In a recent issue of this Journal Dr Hughes (1940) published records of a successful attempt to rear oysters in tanks on the River Yealm during the summer of 1939. In this paper he referred to plans for the following year, and it therefore seems desirable to record a few notes on the 1940 season.Since Dr Hughes left Plymouth I have kept in touch with Mr J. Kingcome, the owner of the fishery, and from time to time have visited his tanks and proffered technical advice. In this I have had the willing co-operation of Mr H. A. Cole of Conway whenever his opinion has been sought. Mr King come has most readily adopted suggestions we have made, and it is to his careful attention and unremitting work that the successful results here recorded are due.Further History of the 1939 SpatDr Hughes mentioned that in August 1939 some of the larger spat were detached from the tiles and placed in cages in the estuary of the river. At the time of writing (mid-October 1940) these range from 4.5 to 8 cm. in diameter. The remainder of the spat spent the winter on the tiles in tank C (Hughes, 1940, Fig. 1), being given almost daily changes of water from the estuary. They were detached from April to July 1940 and placed like the others in wire-meshed cages just above low-water mark spring tides. These oysters have by no means reached the size of those which have been out since August 1939, the size range being 2–4 cm. in diameter.

The breeding of oysters in tanks

The following paper is a record of certain work which was carried out at the River Yealm during 1939. No claim is made for original work, but it may serve some useful purpose as a record.Oysters from die River Yealm have been used in most of the experimental work carried out on the breeding of oysters at Conway. But, for some unknown reason, there has never been any relevant growth of native oysters in the Yealm. The beds are stocked every year with three-year-old Brittany oysters. These oysters thrive well in the Yealm and are of considerable commercial value.Certain old tanks at the Fisheries have been altered and repaired for the purpose of cleansing prior to their despatch to die London market. These tanks are in use for this purpose approximately from the end of August until die beginning of May. Therefore they are unused for approximately four mondis during die breeding season.

The Fungus on Zostera marina

THE fungus Ophiobolus halimus, which has recently been described as parasitic on Zostera marina L., has this summer been discovered on this plant in the British Isles. It has been found in several localities in Devon (Plymouth, Cawsand, River Yealm, Salcombe), the north coast of Guernsey and Lough Ine, Ireland. Dr. E. J. Butler has compared the British material with authentic specimens of O. halimus, Diehl et Mounce, recently described on Z. marina on the Atlantic coast of North America1, and finds it to be identical with the Canadian material.

Marine Biology at Plymouth

THE latest number of the Journal of the Marine Biological Association (N.S., vol. 14, No. 2, August 1926, 10s. net) is full of good things. Dr. Orton resumes the interrupted publication of his studies on the rate of growth of marine organisms with a paper on the cockle. The investigations were carried out mainly in an experimental box laid down in the estuary of the river Yealm, in which the growing cockles were exposed to practically natural conditions, and the results have been checked by observations on near-by cockle beds. Apart from the definite determination of growth-rate—a matter of some economic importance, though it may be expected that the growth-rate will vary in different localities—the main interest of the paper lies in the study of the growth rings on the shell. It appears that, in the main, the deeply marked rings do indicate the winter checks in growth, and may be used—with caution—to determine the age of the cockle. Dr. Orton has, however, made the interesting observation that the mere removal of the cockles from the box for an hour or so for the purpose of examination suffices to cause the appearance of a “disturbance ring” on the shell. Specially well - defined rings are induced by the technique adopted of marking the shells for identification purposes with a file. Such disturbance rings can also be induced in the mussel. Further, in mild winters the winter-ring may become extended and spread out into several rings, so that accurate determination of the age by means of winter-rings is a matter of some difficulty, especially in the larger individuals. The paper would have been improved by the addition of a summary.

On the Significance of “Rings” on the Shells of Cardium and other Molluscs

IN NATURE of February 3, p. 146, I referred to experiments on determining the rate of growth of a fixed population of marked cockles (Cardium edule). In this experiment the box which was fixed in the bed of the River Yealm and contained the cockles was visited monthly, and sometimes at intervals of only a fortnight, for the purpose of measuring the increment in growth since the previous visit. This method of work resulted in an interesting observation on the formation of rings on the shells of the growing cockles. It was found that in the young cockles, i.e. up to about 16 mms. in length, dark rings were formed monthly or fortnightly in a majority of cases, on the shells at the size they were when last measured, but that no similar formation of rings could be detected in the larger and generally older shells. On the other hand, both small and large cockles showed distinct rings after the winter period.