Microscopic assemblages in kelp forests and urchin barrens

Kelp forests and urchin barrens are considered alternate stable states characterised by opposing structural and biological scales. Structurally diminutive urchin barrens that support microscopic taxa are considered biologically depauperate relative to macroscopic, structurally complex kelp forests. However, the extent to which this perception stems from the scale of sampling is unclear. Here, we match the scale of sampling to the scale of habitat by examining microscopic assemblages within barrens. We find that the diversity of microscopic taxa in barrens rivals that of kelp forests but is composed of diminutive and less desirable taxa such as ephemeral algae. Recruitment of kelp and foliose brown algae was extremely low in both habitats highlighting the role of episodic recruitment as well as physical and biological processes in structuring differences in assemblages between habitats. We contend that barrens are not biologically depauperate and the ephemeral taxa they support play an extant and emerging role in temperate reef ecology.