Scientific Diving - Scientific Technique
Marine science projects supported by scientific diving at Rothera fall into two categories, those associated with the long-term monitoring of the environment and specific shorter term studies.
The long-term monitoring programme involves regular measurement of sea temperature, water chlorophyll contents, major nutrients (ammonia, nitrate, nitrite, silicate and phosphate), ice cover and thickness, material sedimenting to the seabed from the water column, and feeding activity and reproductive status in a range of benthic invertebrates. Diving forms a key element in three of these activities:
- Sedimentation of material is measured with a sediment trap approximately 100 m to the south west of Trolval Island. The trap consists of eight collection pots each of 10 cm diameter held in a durapipe frame at 20 m depth, suspended above a 40 m depth seabed. The pots are changed monthly and material caught is used to identify organic and chlorophyll deposition to the seabed as well as being used for analysis for biomarkers and direct identification via microscopic analysis. The diving is complex, with several divers removing and replacing pots and cleaning the rig.
- Feeding activity is monitored in a range of sessile filter feeders by direct observation of feeding structures. Typical organisms in the study are anemones, sea cucumbers, terrebellid worms, bryozoa, hydroids and soft corals. Divers return to the same individuals or colonies at monthly intervals and note the status of their feeding activity. Two main sites are used, and 15 species are observed. This work requires detailed knowledge of many species, and their taxonomy.
- Reproductive monitoring involves the collection of monthly samples for analysis of gonad status in the UK. The bivalve Laternula, the brittle star Ophionotus, the nemertean Parbolasia, the limpet Nacella, the starfish Odontaster and Terebellid polychaete worms are all part of this study, and involve diving in different areas. The bivalve Laternula has to be dug by hand from clay sediments at depths of 10-30 m.
Short term studies vary more in their requirements, and range from the collection of biological samples for laboratory studies in Rothera, or for return to UK for use in BAS or university science projects. Recent projects have included:
- Measurements of growth rates in snails and urchins have involved collection and return to the laboratory of specimens by divers. These specimens are then measured, weighed and tagged before returning them to their sites of collection. Some of the tags used are electronic PIT tags either glued to shells or injected into body cavities. Tagged specimens are collected again at later dates for seasonal assessments of growth.
In excess of this, amongst many other projects, we have work using heartbeat monitors attached to limpets in the sea, deployments of Fyke nets for catching fish, and attempts to lay out arrays of markers to measure the extent of physical disturbance by ice. Diving science projects at Rothera are varied and demanding and are at the cutting edge of polar marine biology.