Tropicalisation and kelp loss shift trophic composition and lead to more winners than losers in fish communities

Climate-mediated species redistributions are causing novel interactions and leading to profound regime shifts globally.  For species that expand their distribution in response to warming, survival depends not only on their physiological capacity, but also on the ability to coexist or be competitive within the established community. In temperate marine reefs from around the world, the range expansion of tropical species, known as ‘tropicalisation’, has been linked to the disappearance of temperate habitat-forming kelps and shifts to dominance by low-biomass turfing algae. The consequences of these range expansions and habitat changes on resident fish communities are, however, unclear. Here, we use data derived from baited remote underwater video (BRUV) surveys to analyse changes in diversity and abundance of marine fishes over a 17-year period in warming reefs that have experienced kelp loss (occurring c. 2009). Despite the loss of kelp, we found that species richness and overall abundan...