Long-term change in epibenthic assemblages at the Prince Edward Islands: a comparison between 1988 and 2013

As proxies and indicators of environmental conditions, offshore benthic assemblages are pertinent to understanding global change. To investigate long-term change in epibenthic assemblages, we compared digitally reprocessed historical (1988) and repeat (2013) benthic survey photographs from nearshore (40–130 m) and inter-island locations (140–500 m) at the sub-Antarctic Prince Edward Islands. Given changing interactions between regional oceanography and terrestrially influenced productivity at the islands, temporal change in the benthos is likely, and is expected to be dependent on proximity to the islands (nearshore vs. inter-island). Multivariate PERMANOVA analyses identified a significant interaction effect on epibenthic assemblages ( Year × Location ), with significant dispersion effects defining temporal differences within the inter-island region but not in the nearshore area. Differences in epibenthic assemblages observed between 1988 and 2013 were found to be driven primarily by increased abundances of several common suspension feeding taxa, including a significant increase in the density of a key bioengineering species, the polychaete Lanice marionensis . These higher abundances are congruent with local trophic evidence of long-term, climate-related shifts towards greater allochthonous food supply to the benthos. Given this congruence, a unifying explanation for the observed temporal differences in epibenthic assemblages is that long-term alteration of the position of the sub-Antarctic Front has changed the local primary productivity regime and hence the flux of food to the benthos. This study provides the first direct support for the notion of long-term change in epibenthic assemblage composition at the islands.