Microhabitat distribution of Smacigastes micheli (Copepoda: Harpacticoida: Tegastidae) from deep-sea hydrothermal vents at the Mid-Atlantic Ridge, 37° N (Lucky Strike), with a morphological description of its nauplius.

Abundant nauplii and copepodid stages attributed to Smacigastes micheli Ivanenko & Defaye (Crustacea: Copepoda: Harpacticoida: Tegastidae) were collected during the MoMARETO cruise (2006) on the Eiffel Tower edifice, the species type locality at the Lucky Strike vent field (37° N) of the Mid-Atlantic Ridge at a depth of 1698 m. Specimens were sampled within different faunal assemblages dominated by either Bathymodiolus azoricus mussels or Mirocaris fortunata shrimps and the physico-chemical conditions of their related microhabitats were characterized. A new preparation method for examination of copepod nauplii with confocal microscopy was developed and applied to the specimens. The description of the sixth naupliar stage of S. micheli revealed a number of distinctions from the only known last naupliar stage of the tegastid copepod Tegastes falcatus living associated with a shallow water bryozoan. Morphological features and ecological observations suggest that S. micheli copepods could be feeding on the thick microbial mats that cover different surfaces on the Eiffel Tower edifice. The nauplii, copepodids and adults of S. micheli were found in >80% of the microhabitats sampled. These microhabitats were characterized by temperatures varying from 4.8 to 7.5 °C representing low hydrothermal inputs. Canonical analysis shows that the relative abundances of nauplii and adults of S. micheli were higher at the lower end of the chemical conditions, whereas the abundance of the subadult stages appears to be linked with slightly higher hydrothermal inputs. Whether this distribution is influenced by distinct physiological tolerances or nutritional needs of the different developmental stages is unknown. Total dissolved sulfur was the variable best explaining the distribution of S. micheli on the Eiffel Tower edifice. [ABSTRACT FROM AUTHOR]