Nematode assemblages were studied from four sublittoral sites at 50–56 m depth in the Gulf of Maine, north-eastern coast of the USA, within the context of an open ocean aquaculture experimental site. All four sites, two potential impact and two control sites, had a similar muddy–sand bottom and low organic content. Seventy genera in 27 families were recorded from a total of 1072 individuals. All but one taxa could be related to known genera. Family Comesomatidae was the most dominant with close to a third (27·6%) of the total individuals. At the genus level Sabatieria and Setosabatieria were most dominant with a quarter of the total number of individuals. Composition of dominant families from the Gulf of Maine differed from all hitherto reported sublittoral or deep-sea communities from both sides of the Atlantic, and most similar with European estuaries.

Nematode diversity at the genus-level was reasonably high and was comparable with Mediterranean samples. Most diversity indices ordered the four sites similarly with Site 2 as the most diverse followed by Site 5 and then Site 6. By contrast the relative diversity of Site 4 depended on the index employed and its k-dominance curve crossed that of the others. Furthermore based on clustering the community at Site 4 was least similar to the others. Although these observations could be related to the fact that Site 4 is within the expected impact zone of the fish cage, the low number of fish introduced by the time of sampling and the lack of any difference in the maturity index among all the sites argue that these results can be considered before-impact data for further monitoring of the open ocean aquaculture experiment.

A new paradigm where morphological information is documented and communicated using digital multifocal images is introduced. Each video image is comparable with visualization of a specimen under a microscope where the movie can be played back and forth to mimic focusing through a specimen. Web-based and openly accessible digital multifocal images were used to document and effectively communicate the morphology of all the identified genera in this study. This approach for documenting and communicating survey results is proposed as a benchmark for future similar studies that would enhance standardization and quality control of meiofaunal taxonomy, ecology and biodiversity studies.