By Charlie Self
This collection of five papers and one short report provides an issue of Cave & Karst Science that is varied in both scientific content and geographical area.
Kents Cavern is an important archaeological site that was excavated in the late 19th and early to mid- 20th centuries to reveal stratified Middle and Upper Palaeolithic deposits. In this cave was found the oldest modern human fossil in Britain. A recent re-assessment of the cave established that the Northeast Gallery was a significant source of sediment during the Devensian(last glacial period, UK) and that a previously unrecorded entrance could be nearby. Outside the cave, removal of a wall of concrete blocks revealed this entrance and a 2.1 metre high section of bone-bearing sediments in a sequence similar to that previously excavated elsewhere in the cave. This is a very exciting discovery!
This is a sympathetic portrayal of a Scottish lawyer who later changed career and became a prominent figure in natural history circles in mid- 19th century Britain. His particular interests were in entomology (the study of insects) and botany. Reports of blind insects in American and European caves led him to make the first attempt to find similar species in a British cave, but in this he was unsuccessful. Murray was a firm believer in Biblical "special creation" and debated both publically and privately with Charles Darwin on the origin of species. At the time, Murray was the foremost authority on cave animals (a special interest of his and a subject that puzzled Darwin) but his religious beliefs led him to the wrong conclusions. If not for this, he could have made a lasting contribution to cave biology but instead left no significant legacy in this subject.
Auto-ecology is the ecology of a single species (i.e. the relations between that species and its environment). There are over 300 described species and sub-species of freshwater shrimps of the genus Niphargus. They are one of the most widespread and diverse of the groundwater inhabitants, living in streams and pools in caves, fractures in phreatic aquifers, interstices in granular aquifers and in the hyporheic zone (the zone of saturated sediments beneath and adjacent to surface streams). Four species of Niphargus are found in Britain, but only N. aquilex and N. glennii are found in Devon. This study was conducted in Joint Mitnor Cave, Devon.
Joint Mitnor Cave is in the Higher Kiln Quarry site of special scientific interest (SSSI) and has been set up as a scientific demonstration site, complete with electric lighting, access steps and a raised shelf area. Three aquaria were installed on this shelf (with the assistance of a Research Initiative grant from BCRA), two as holding tanks for the two shrimp species and one for running experiments. The third tank could be divided into chambers by panels with access holes cut in them, for simple avoidance/ attraction experiments. The aquarium sediments, water and both species of shrimp were collected from a nearby cave within the SSSI.
In the first experiment, a LED light source was fitted to one side of the aquarium with panels dividing the space into three chambers. Chamber 3 was thus illuminated, Chamber 2 had twilight conditions while Chamber 1 was in almost complete darkness. Shrimps were then introduced to the tank and their movement between the chambers monitored. The experiment was repeated for each species using an ultra-violet light source (which is more harmful than visible light for these pigment-free crustaceans). Finally, the aquarium was moved to the cave entrance and one chamber exposed to shaded daylight. For N. aquilex, there was a slight overall pattern of migration away from the light source (LED and daylight), with a stronger response to UV light. For N. glennii, the response was less pronounced (and there were counting problems because individuals of this much smaller species were often hidden). A more negative phototactic response might be achieved with stronger lighting.
The second experiment was a temperature tolerance test, whereby an aquarium water heater was placed in the third chamber to produce a thermal gradient across the aquarium. In a separate cooling test, shrimps were put into a small water-filled tray which was placed first in a refrigerator and then a freezer until the water temperature dropped to 1°C; the tray was then allowed to warm to ambient temperature in a dark cupboard. In the aquarium test, N. glennii evenly distributed themselves between the three chambers while N. aquilex preferred the warmer Chamber 3 where they used the heater itself as a refuge; this preference continued even when the temperature was raised to 26°C. In the cooling experiment, N. glennii became torpid at 4°C, N. aquilex at 2°C. All recovered upon warming except one juvenile who was possibly damaged when ice formed in the tray. For obligate groundwater inhabitants, these animals are able to tolerate a surprisingly wide temperature range, though how their metabolism would be affected in the long term is unknown.
In the third experiment, the aquarium was set up with three areas of different substrate (fine silt, pea gravel and coarse gravel) but without separate chambers. The aquarium was allowed to settle for 4 weeks before introduction of shrimps, who were then monitored daily for a week. N. aquilex preferred the coarse substrate in which it can hide, while the much smaller N. glennii used all substrates but preferred the fine silt in which it can quickly burrow.
As a final experiment, four individuals of each species were kept together in a restricted space (a small plastic cup with three stones for refuge). A small quantity of specialist crustacean food was added. Within two days, only the four N. aquilex were seen. After a month, the smallest of the N. aquilex individuals was dead and partially dismembered. Opportunistic predation and cannibalism is an adaptation to nutritionally poor environments, even in the presence of other food sources.
This is a large paper with detailed discussions of the experiments and their practical problems. These discussions also cover many experiments and observations made elsewhere involving other Niphargus species.
PostojnskaJama has been attracting foreign visitors since the 15th century and has been a venue for "show cave" tourism for almost 200 years. A unique feature of the tourist route is a railway, first installed in 1872 and made twin-track in 1964, which delivers visitors deep into the cave system. Visitor numbers peaked at over 900,000 in 1985, though the number has now reduced to around half a million per year. Postojnska Jama is an important archaeological site, with Pleistocene bones and Neanderthal artefacts. It also has a rich biodiversity, with more obligate cave species (terrestrial and aquatic) recorded here than in any other cave in the world. Its best-known animal is a blind cave salamander of the genus Proteus. The cave also supports a diverse zoology in the fine fractures above the cave (i.e. in the epikarst), which were collected from dripping water sources. 23 species of copepod (small crustaceans) were identified, six of them endemic to this cave.
A systematic study of the cave micro-climate has recently been conducted to determine the human impact of so many visitors. Since the opening of the present tourist entrance in 1866, the cave has been well-ventilated and external temperature dynamics penetrate deep into the system. Hourly temperature measurements taken at several locations show small diurnal and seasonal fluctuations, but the overall seasonal trends are delayed somewhat in comparison to the external climate. During the summer months, when tourist numbers are highest, there is an anthropomorphic heating effect but it is small compared with the warming by natural ventilation. Anthropomorphic heating by visitors in winter is more significant, notably around the busy Christmas/ New Year period. The tourist trains cause additional ventilation along their route and are a source of dust particles (including heavy metals) in the cave atmosphere. However, the most rapid micro-climate changes occur naturally in winter when a strong north wind known as "bora" is blowing. Cold air enters the cave, displacing warm air upwards into higher parts of the system. It has been observed that some side passages away from the principal air currents maintain an almost constant air temperature, so ventilation rather than visitor numbers seems to be the dominant factor driving changes in the cave micro-climate. Tourism at current numbers does seem to be sustainable, but dust raised by the popular cave trains is a cause for concern.
This paper gives a reconnaissance-level overview of the karst geomorphology along the Nam (River) Ou, a major tributary to the Mekong River system. This is urgently needed because of the current and planned construction of hydro-electric dams, agreed by the Laotian government at the insistence of foreign donors of aid. The electricity would be used by developing economies in neighbouring countries. The findings of any pre-development environmental assessments have not been released, so one purpose of this paper is to delineate the extent and the character of the karst and its natural and cultural heritage value.
The principle karst along the Nam Ou has formed in a belt of Carboniferous-Permian limestones in the lower part of the river, between the town of Muang Khua and the confluence with the Mekong. The river flows generally southwards in a broad alluvium-floored valley, except where it cuts through limestone hills. In these places, the river makes abrupt changes of direction before resuming its southerly course. These drainage corridors, which are probably due to major faults, are also present in tributary streams to the Nam Ou. The main limestone ridges show structural lineation along the strike.
Typically, the limestone hills are steep-sided with well-developed karren dissolution sculpture. Springs, stream sinks and small closed depressions are widespread, with one large closed depression described as a polje. Some caves are known to local people, but there has been negligible systematic recording of them. Active stream passages tend to be within 10 metres of the present river level, though relict passages are known up to 150 m higher. The use and modification of caves during the revolutionary war has made them part of the historical heritage of Laos. The limestone mountains are conspicuous, but areas of more subdued relief are also underlain by limestone and could have karstic drainage.
Any economic development assessment should take into account the environmental value of the Nam Ou basin as well as the social needs of the people who live there. Observant readers may notice a discrepancy in the spelling of place names between the text and the map. Such differences sometimes occur when transposing names from a different alphabet, or they may reflect local pronunciation; in this case, the text was changed on the advice of a referee but the map was left as drawn by the author.
The Red Hills Road Cave contains a sediment fill containing a great diversity of Late Pleistocene terrestrial invertebrate and vertebrate fossils. The study of the invertebrate fauna is now complete and has been published, but progress with the vertebrate remains has been slow. This paper is an interim report on the bird fossils. Because of their disarticulated and often fragmentary condition, only three species could be identified at the generic level. These were: flightless ibis (now extinct), Jamaican tody and an undetermined species of crow. Also present were a hummingbird, two species of cuckoo, a sandpiper and at least two and possibly seven additional species of passerines (perching birds). Further fragments that could not be identified suggest that the fossil avian biodiversity could be even higher.