The Isles of Scilly are one of 7 locations identified in Great Britain as proposed statutory marine nature reserves. In order to provide information to assist in management of these areas, monitoring programmes are being developed which are aimed at detecting change in populations and communities of high nature conservation importance. In the Isles of Scilly, the specific objectives were to 'establish a monitoring programme to investigate changes in species and communities of high nature conservation interest. This will include studies on Zostera beds present on the sand flats between the larger islands'. In addition, 2 sites were established for monitoring littoral underboulder communities and some further surveys of sublittoral sites were carried out. This report describes part of the work undertaken in the Isles of Scilly. Studies of the sea urchin Echinus esculentus and an aerial photographic survey will be described elsewhere. Two adjacent sites at one location north of Gap Point on the east side of St Mary's were selected for photographic monitoring of Mediterranean-Atlantic species of high scientific interest. They were marked with pitons and a reference line was tied between the pitons. Both distance and close-up photographs were taken along the line. The photography worked well in providing record photographs and can be repeated in future years. The extensive beds of Zostera marina present in the Isles of Scilly are of considerable conservation importance. The work described here was undertaken in beds at English Island and Old Grimsby Harbour and was aimed at measuring the density of plants and length of leaves, recording the species associated with the Zostera and comparing the 2 sites. The English Island site was found to be much richer in the variety and abundance of associated species than the Old Grimsby Harbour site although the plants there were more dense. Underboulder communities at several locations in the Isles of Scilly are considered to be especially rich examples of this type of habitat. Two sites were selected for study and monitoring: at English Island Point and on the east side of Samson. Here, boulders selected for study were lifted, the undersides photographed using a picture area of 0.033 m/2, and the species present were noted. The location of the boulders was recorded on polaroid photographs. Dives were undertaken at 4 additional locations to provide further data and photographs for the descriptions of habitats and communities in the Isles of Scilly. Records were made from Peninnus Head, Giant's Castle and Deep Point (St Mary's) and from north of St Agnes. A summary of the main recommendations made were: Photographic monitoring - Re-photograph the site established in 1984 at about the same time of year in 1985 and make a detailed comparison. Zostera bed - Re-survey the English Island and Old Grimsby Harbour sites including descriptive and quantitative work at about the same time of year for the next 2 years to assess the stability of the different community types. - Undertake vertical aerial photography employing a specialist company to provide large format colour transparency photographs to a set scale for mapping. Underboulder communities - Re-survey and photograph the same boulders at about the same time of year in 1985 and make a detailed comparison. Concern was also expressed that sea-borne dumping at Gap Point had occurred very near to some of the richest populations of sponges in the Isles of Scilly and that protection was appropriate.