Taxonomy and biology of deep-sea polychaetes: temporal variability in polychaete assemblages of the abyssal NE Atlantic Ocean

摘要

Taxonomy and temporal variability of deep-sea polychaete assemblages was assessed over a 9-year period. Macrofauna 300 ?m fraction samples, taken with USNEL box core (0.25 m2), were studied from Porcupine Abyssal Plain, NE Atlantic Ocean from 8 cruises between August 1989 and September 1998. A taxonomic study at species level was carried out for the two most abundant families: Cirratulidae and Spionidae. 15 different morphotypes of Cirratulidae and 13 of Spionidae were recognized and described. For Cirratulidae eight morphotypes belonged to Chaetozone, there were six species of Aphelochaeta and one of Tharyx. For Spionidae three morphotypes belonged to Minuspio, two to Prionospio, one to Aquilaspio, two to Laonice, two to Spiophanes and two to indeterminate spionids. Aurospio dibranchiata also was recorded. The polychaete communities were characterized by high numbers of individuals (abundance) and high family richness. Highest abundance occurred in the upper 1 cm sediment layer (53.2% of total abundance). The most abundant families were the Cirratulidae, Spionidae, Opheliidae and Paraonidae. Surface deposit-feeders were the dominant trophic group (67.4% of total abundance). Significant temporal variability was evident with significant differences in polychaete abundance between sampling periods (cruises). There were stepwise increases in abundance in September 1996 and March 1997 coinciding with similar increases in abundance in large invertebrates (megafauna) in the same area (known as the ‘Amperima Event’ after a species of holothurian that increased in abundance by over three orders of magnitude). A similar trend was observed for abundance within different layers of the sediment, main families and trophic groups showing significant differences between cruises. A comparison made of samples taken 1) before the ‘Amperima Event’ (1989-1994) and 2) during the 'Amperima Event' (1996-1998) showed significant differences in the polychaete abundance in the upper 3 cm of the sediment. There were significant differences in some trophic groups (predators, deposit-feeders and burrowers) and the dominant families (Cirratulidae, Spionidae and Opheliidae). Changes in surface deposit feeders were particularly evident. The temporal variability is likely to be related to seasonal and interannual variability in organic matter input. Greater food supply in some years may allow the growth and development of deposit feeding polychaetes. However, not all elements of the polychaete community showed a response (e.g. the Paraonidae). At the species level, the most abundant cirratulid and spionid species not always appear to respond in the same way as the family. Only Aphelochaeta sp. 647D, Minuspio sp. 4 and Prionospio sp. 81 showed a clear response, with significant differences between cruises and between pre ‘Amperima Event’ and ‘Amperima Event’ periods. Chaetozone sp. 1, Chaetozone sp. 55A and Prionospio sp. 613 only showed significant differences between cruises, while Aphelochaeta sp. 13A and Aurospio dibranchiata did not show any significant change with time. In the Paraonidae, where no apparent response was detected, the species level response in the most abundant species was similar. Temporal changes in some polychaete species could be attributed to ‘Amperima Event’ conditions. However, for polychaete species that did not response in a clear way to the ‘Amperima Event’, their temporal variability observed appear to be related to interannual variations in organic matter input to the seabed throughout the deposition of phytodetritus. In general, seasonal and interannual fluxes in food supply appear to determine changes in polychaete assemblages at the Porcupine Abyssal Plain, affecting to a greater degree polychaete abundance, and to a lesser extent faunal composition.