Data from: Bolstered physical defences under nutrient-enriched conditions may facilitate a secondary foundational algal species in the South Pacific

1. Humans have a long history of changing species’ ranges and habitat
distributions, making studies of the ecological processes that may
facilitate these changes of key importance, particularly in cases where a
primary foundation species is replaced by another, less desirable species.
2. We investigated the impact of nutrients and herbivory on Turbinaria
ornata, a secondary foundational macroalga that depends on and likely
competes with coral, the primary foundational community. T. ornata is also
rapidly expanding in range and habitat across the South Pacific. We
conducted: 1) a mesocosm experiment assessing relative nutrient
limitation, 2) a field experiment comparing importance of nutrients (+/-)
and herbivory (+/-) to biomass accumulation, and 3) an herbivory assay and
toughness test comparing enriched and ambient thalli to assess changes to
anti-herbivory defences. 3. We found no evidence of growth being nutrient
limited in T. ornata; rather than stimulating growth, nutrient addition
deterred herbivores. However, when physical toughness was removed,
enriched algae were preferred, with consumption rates 25-fold those of
unenriched algae. Additionally, enriched thalli were tougher than ambient
thalli, suggesting physical defences were bolstered by nutrient
enrichment. 4. Synthesis. We found a unique interaction where nutrients
inhibit herbivory and facilitate Turbinaria ornata biomass accumulation.
While concern is often placed on degradation of foundation species via
anthropogenic change, instead here we show that anthropogenic change can
facilitate secondary foundation species. This facilitation may allow a
secondary foundation species to better compete with primary foundation
species.