-- Layton et al. Chemical microenvironments within macroalgal assemblages: implications for the inhibition of kelp recruitment by turf algae. Limnology & Oceanography. DOI:10.1002/lno.11138 -- Kelp forests around the world are under increasing pressure from anthropogenic stressors. A widespread consequence is that in many places, complex and highly productive kelp habitats have been replaced by structurally simple and less productive turf algae habitats. Turf algae habitats resist re-establishment of kelp via recruitment inhibition; however little is known about the specific mechanisms involved. One potential factor is the chemical environment within the turf algae and into which kelp propagules settle and develop. Using laboratory trials, we illustrate that the chemical microenvironment (O2 concentration and pH) 0.0–50 mm above the benthos within four multispecies macroalgal assemblages (including a turf-sediment assemblage and an Ecklonia radiata kelp-dominated assemblage) are characterised by elevated O2 and pH relative to the surrounding seawater. Notably however, O2 and pH were significantly higher within turf-sediment assemblages than in kelp-dominated assemblages, and at levels that have previously been demonstrated to impair the photosynthetic or physiological capacity of kelp propagules. Field observations of the experimental assemblages confirmed that recruitment of kelp was significantly lower into treatments with dense turf algae than in the kelp-dominated assemblages. We demonstrate differences between the chemical microenvironments of kelp and turf algae assemblages that correlate with differences in kelp recruitment, highlighting how degradation of kelp habitats might result in the persistence of turf algae habitats and the localised absence of kelp.

The phenotypic plasticity of habitat-forming seaweeds was investigated with a transplant experiment in which juvenile Ecklonia radiata and Phyllospora comosa were transplanted from NSW (warm conditions) to Tasmania (cool conditions) and monitored for four months. We used multiple performance indicators (growth, photosynthetic characteristics, pigment content, chemical composition, stable isotopes, nucleic acids) to assess the ecophysiology of seaweeds before and following transplantation between February 2012 and June 2012.

Seasonal patterns in the in situ ecophysiology of the common habitat-forming seaweeds Ecklonia radiata, Phyllospora comosa, and Macrocystis pyrifera were investigated at different latitudes and depths in southeastern Australia. We used multiple performance indicators (photosynthetic characteristics, pigment content, chemical composition, stable isotopes, nucleic acids) to assess the ecophysiology of seaweeds near the northern and southern margins of their range, along a depth gradient (E. radiata only), over a two year period (September 2010 – August 2012).