MEPS 437:103-117 (2011)  -  DOI: https://doi.org/10.3354/meps09283

ABSTRACT: Because of their ephemeral nature and patchy distribution, hydrothermal vents on mid-ocean ridges are newly colonized by allochthonous larval sources after catastrophic eruptions, but their hydrothermal benthic invertebrate populations are maintained by local larval supply. In the present study, I examined spatial patterns of larval abundance and associated adult assemblages at hydrothermal vents on 3 seamounts each at the Mariana Arc and Kermadec-Tonga Arc. Because seamounts are topographically distinct features on the ocean floor, colonization processes may differ from those on mid-ocean ridges. On every seamount, the chemosynthetically based macro-epifaunal populations were patchy, spatially constrained and consisting of 1 to 3 numerically dominant taxa that differed among locations within a seamount and among seamounts. Larval abundance was generally greater at 2−7 m above the sea floor than 20−30 m higher, and in 5 of the 6 seamounts, it was lower than has been measured at the same elevations in previous studies on mid-ocean ridges. I examined changes in vertical distribution in experiments using 2 vent species of gastropod larvae hatched from egg capsules collected in situ. For Shinkailepas cf. kaikatensis, larvae were initially more abundant near the water surface, but were more abundant near the bottom 3 d after hatching, whereas for Shinkailepas n. sp., they remained near the bottom for the duration of the experiment. The observed larval distributions in the field and experiments suggest high larval retention, which can result in high local recruitment, but low colonization of new locations within or among seamounts. In combination with gregarious settlement and potentially limited habitat availability, low colonization is likely to give rise to the paucity of the adult chemosynthetic assemblages observed in the present study, and effect recruitment limitation beyond the local source population of vent species on highly disturbed seamounts that are volcanically active.

KEY WORDS: Marine benthic invertebrates · Larval abundance · Larval behaviour · Vertical distribution · Propagule source · Chemosynthetic communities · Volcanic seamounts