Data from: Tropical rabbitfish and the deforestation of a warming temperate sea

A striking example of climate-mediated range shifts in marine systems is
the intrusion of tropical species into temperate areas worldwide, but we
know very little about the ecological consequences of these range
expansions. In the Mediterranean Sea, the range expansion of tropical
rabbitfishes that first entered the basin via the Suez Canal provides a
good example of how tropical herbivorous fish can impact the structure of
rocky bottoms in temperate seas. Two species of rabbitfishes have now
become a dominant component of total fish biomass in the southernmost part
of the eastern Mediterranean. Experimental evidence shows these species
can profoundly transform benthic communities, turning algal forests into
‘barrens’, but the specific mechanisms that facilitate this shift have not
been established. We surveyed ~1000 km of coastline in the eastern
Mediterranean and identified two clearly distinct areas, a warmer group of
regions with abundant tropical rabbitfish and a colder group of regions
where these consumers were absent/ extremely rare. In regions with
abundant rabbitfish, canopy algae were 65% less abundant, there was a 60%
reduction of overall benthic biomass (algae and invertebrates) and a 40%
decrease in total species richness. Video-recorded feeding experiments
showed that the extensive barrens characteristic of regions with abundant
rabbitfish were not due to greater rates of herbivory by these tropical
consumers, but rather by functional differences among the herbivores.
Temperate herbivorous fish displayed the greatest macroalgae consumption
rates overall, but they fed exclusively on established adult macroalgae.
In contrast, in regions with abundant rabbitfishes, these consumers fed
complementarily on both established macroalgae and on the epilithic algal
matrix, which typically contains macroalgal recruits. Synthesis:
Range-shifting tropical rabbitfish can severely reduce the biomass and
biodiversity of temperate reefs at a scale of hundreds of kilometres. A
shift from macroalgal dominance to barrens is mediated by the addition of
functionally diverse herbivores that characterise tropical reefs. This
work highlights the importance of assessing the functional traits of
range-shifting species to determine potential mechanisms of impact on
ecological communities.