Data from: Contrasts in the marine ecosystem of two Macaronesian islands: a comparison between the remote Selvagens Reserve and Madeira Island

The islands of Madeira and Selvagens are less than 300 km apart but offer
a clear contrast between a densely populated and highly developed island
(Madeira), and a largely uninhabited and remote archipelago (Selvagens)
within Macaronesia in the eastern Atlantic. The Madeira Archipelago has
~260,000 inhabitants and receives over six million visitor days annually.
The Selvagens Islands Reserve is one of the oldest nature reserves in
Portugal and comprises two islands and several islets, including the
surrounding shelf to a depth of 200 m. Only reserve rangers and a small
unit of the maritime police inhabit these islands. The benthic community
around Selvagens was dominated by erect and turf algae, while the
community at Madeira was comprised of crustose coralline and turf algae,
sessile invertebrates, and sea urchin barrens. The sea urchin Diadema
africanum was 65% more abundant at Madeira than at Selvagens. Total fish
biomass was 3.2 times larger at Selvagens than at Madeira, and biomass of
top predators was more than 10 times larger at Selvagens. Several
commercially important species (e.g., groupers, jacks), which have been
overfished throughout the region, were more common and of larger size at
Selvagens than at Madeira. Important sea urchin predators (e.g.,
hogfishes, triggerfishes) were also in higher abundance at Selvagens
compared to Madeira. The effects of fishing and other anthropogenic
influences are evident around Madeira. This is in stark contrast to
Selvagens, which harbors healthy benthic communities with diverse algal
assemblages and high fish biomass, including an abundance of large
commercially important species. The clear differences between these two
island groups highlights the importance of expanding and strengthening the
protection around Selvagens, which harbors one of the last intact marine
ecosystems in the North Atlantic, and the need to increase management and
protection around Madeira.