Data from: Mapping habitats in a marine reserve showed how a 30-year trophic cascade altered ecosystem structure

Time-series studies have reported trophic cascades in land, freshwater and
marine environments in many geographic areas. However, the spatial extent
of habitats, a key metric of ecosystem structure, has not been mapped in
these studies. Marine reserves can provide experimental, before-after and
inside-outside (control-impacted), situations for assessing the impact of
fishing on ecosystems. We mapped seabed habitats and their associated
communities (biotopes) in New Zealand’s oldest marine reserve for
comparison with pre-reserve maps created about 30 years previously. Areas
grazed bare by sea urchins were entirely replaced in the centre of the
reserve by kelp, or alga turf, an intermediate biotope between heavily
grazed encrusting algae and lightly grazed kelp. Urchins declined
following increased abundance and body size of spiny (rock) lobsters and
fish (especially snapper) in the reserve but maintained bare rock outside.
While this gradient in habitat change matched the gradient of predator
abundance, it also matched the extent of reef habitat area. Thus the
trophic cascade may be influenced by the effect of habitat on the
abundance and behavioural interactions of urchins and their predators.
Further ecosystem changes may arise should the abundance of
mega-predators, such as seals, cetaceans and large sharks, increase in the
region; if parasites become pathogenic; and/or when invasive species reach
the reserve. No-take Marine Reserves provide real-world experiments that
show the importance of species in food webs, and the consequences of
fishing for ecosystems. Because these changes in ecosystem structure may
continue, and will vary with environment, climate and species
distributions, reserves need to be permanent and replicated
geographically. Habitat maps should be produced for all reserves to enable
ecological changes in the ecosystem to be spatially quantified.