Mission Santo
Document Actions

Preliminary Report on the Biology of the anchialine Loren Cave

Preliminary Report on the Biology of the anchialine Loren Cave

By Geoff Boxshall, Damià Jaume, Franck Bréhier

A brief description

Loren Cave (S = 14°58,850’; E = 167°03,553’) is situated on the east coast of Cap Queiros and some 30 meters from the coastline. The entrance, 2m wide by 1 meter high, leads to a big chamber occupated by a pool of water. From there, a small gallery leads to sump 1. This one is 60 m long and –6 m depth and has a restriction (although enlarged). Behind, a 100 meters-long gallery leads to sump 2. In this gallery,the height bove the water is around 4 meters whereas the depth reaches 8 meters. The section is narrow above the water but wider below. The walls are very sharp, and there is very few accretions. Another “dry” gallery of some 150 meters ends up on one side on a restriction, and on a sump that connects with sump 2 on the other side. Sump 2 is 150 long and 10 meters depth and emerges on a 5 meters air-bell. Sump 3 begins just behind. It has been explored on 190 meters and at a maximum depth of –28 meters. Exploration at the ultimate point is over, but severals other passages still have to be explored. Altogether, more than 1 kilometer has been surveyed, more than 700 meters being underwater. The opportunity of news findings remains great.

Loren cave : an anchialine cave

Loren cave has all the characteristics of a true anchialine cave : it has a superficial freshwater layer which overlies a deeper marine water layer. Water has been sampled along the water column and salinity has been measured by means of a salt tester (Oaklon SaltTestr). A first halocline can be observed in the first meters of the water column, depending on the tide level. Another halocline occurs at a depth of –26 m, below which the salinity is that of sea water. Corresponding thermoclines are noticable as well. There is a marked tidal effect – with an amplitude of about a metre (estimate) - and there seems to be considerable exchange of water which may lessen the stability of the water column structure.

Biology of Loren cave

The entrance pool is shallow and dimly illuminated from the entrance. It contains copepods of the genus Halicyclops (Family Cyclopidae) and at least one species of harpacticoid copepod. Large shrimps of the genus Macrobrachium are visible in the water and a species of fish is also present.

Deeper into the cave we laid baited traps in the first cave lake, which were left in position at depths from about 5 to 7m, for between 2 and 4 days. In these traps we caught numerous decapod crustaceans : small crabs (provisionally identified as Orcovita sp. and Laubuanium trapezoideum by Peter Ng), and shrimps belonging to the families Palaemonidae (2 species) and Atyidae (3 species). A terrestrial crab (Discoplax longipes) was caught by hand in dry passages deep into the cave. In addition, more harpacticoid and cyclopoid copepods (Halicyclops) were taken in small numbers in the first cave lake by hand net and occasionally in the traps.

Beyond the first sump traps were placed and retrieved by the divers and these produced more shrimps and crabs. Several specimen of Macrobrachium cf microps were caught in the traps, most of them in the deeper and more saline waters. Hand-net samples were also taken by the divers and sampling was performed to a depth of 28 metres, into the deep saline water below the halocline. These deep samples caught two spectacular copepods – members of the typical anchialine faunal suite that is restricted to such habitats. A single adult male calanoid copepod (Family Epacteriscidae) was taken. This male is about 2mm in length and is almost certainly a new species, possibly of the genus Enantiosis (to be confirmed). A second, equally important discovery, is a single female misophrioid copepods. This tiny copepod, less than 1mm in length, belongs to the family Speleophriidae, and is probably a new species of the genus Speleophria. Like most cave crustaceans, Speleophria lacks eyes, but it has an extremely well developed chemosensory system which it uses to find food items in the oligotrophic cave waters. Both these discoveries are exciting and raise questions about how these blind, cave-adapted copepods are able colonise such widely distributed localities. Durring a last attempt in the deepest parts of the cave, several amphipods have been seen swimming in the water column, but unfortunately the divers failed in getting them.

A fish of the same species than those at the entrance, but partly depigmented, has been caught.

Close to the entrance of the cave is a small pool into which an active spring discharges water (S = 14°58,823’ ; E = 167°03,536’). At high tide the water flow is greatly reduced and the water is slightly brackish (3.2 ppt). This pool may well be connected to the Loren cave system. Samples taken by hand-net contained a small amphipod in large numbers, belonging to the family Sebidae. It is probably a new species of the genus Seborgia, and may be closely related to the new species of Seborgia currently being described by Damia and Geoff, from a cave in Lifou in the Loyalty Islands. In addition we found many tanaids in this pool, living within a thick blackish mat of algae/bacteria that coated the surface of the submerged stones. Tanaids are rarely found in non-marine waters so this is an unusual and interesting discovery.

Geoff Boxshall, Damià Jaume, Franck Bréhier