Recovery in Antarctic benthos after iceberg disturbance: trends in benthic composition, abundance and growth forms

Abstract

The response of an Antarctic benthic community to iceberg disturbance was investi- gated using underwater photographs (1 m 2 each) on the SE Weddell Sea shelf. This study: (1) char- acterises composition, coverage, number of patches and area of sessile benthic fauna, (2) describes faunal heterogeneity using MDS ordination and identifies 'structural taxa' of each recovery stage, and (3) analyses changes of growth-form patterns during Antarctic recovery. We observed changes in the space occupation of benthic organisms along the recolonisation stages. Uncovered sediment characterised the early stages ranging from 98 to 91% of the coverage. The later stages showed high (70.5%) and intermediate (52.5%) values of benthic coverage, where demosponges, bryozoans and ascidians exhibited a high number of patches and taxa. Several 'structural species' were identified among the stages, and information is provided on their coverage, number of patches and area. Over- all, maximum areas of patches increased as recovery proceeded. Early stages were characterised by the presence of pioneer taxa, which only partly covered the bottom sediment but were locally abun- dant (e.g. the bryozoan Cellarinella spp. and the gorgonian Primnosis antarctica with a maximum coverage of 13 and 3%, and 51 and 30 patches m -2 , respectively). Soft bush-like bryozoans, sheet-like sabellid polychaetes, and tree-like sponges, gorgonians, bryozoans and ascidians were the first colonisers. Mound-like sponges and ascidians as well as tree-like organisms with a long lifespan and different reproductive strategies defined the late stages. We conclude by comparing the selected 'structural species' and relating their life-history traits to differences in distribution in the course of Antarctic recovery.