Influence of Ecklonia radiata patch characteristics on associated communities

Variability in the structure of habitat-forming species which modify local environmental conditions is likely to elicit complex effects on the associated communities and have important ramifications for the biodiversity and stability of the ecosystem. This thesis examines how kelp patch characteristics affect benthic species associated with kelpdominated rocky reefs. Using an experimental array of artificial reefs with transplanted Ecklonia radiata (Australia's most dominant canopy-forming kelp species), I investigated how kelp patch size and density impacted: 1) understory algae and sessile invertebrates, focussing on turf-forming and foliose algal species as well as kelp recruitment; 2) native oysters (Ostrea angasi), which form critically depleted shellfish reef ecosystems and are focal species for restoration projects across Australia; 3) secondary production assessed as the growth of mobile epifaunal invertebrates which provide a critical trophic link for coastal food webs; and, 4) fish communities along with the recruitment of cryptobenthic fishes. The work found that the absence of kelp and decreasing patch size led to the proliferation of algal turfs, which primarily appeared to flourish in response to greater light availability (due to reduced shading by the canopy). Cover of algal turfs was negatively correlated with the cover of foliose algal species and native oysters, which both increased in abundance with patch size. Oysters were the most dominant benthic macroinvertebrate but were most prevalent on reefs with intermediate densities of kelp. Conversely, secondary productivity of grazing epifauna declined with kelp patch size and was reduced on reefs with intermediate kelp densities, most likely due to a negative association with the most dominant species of foliose understory algae (Ulva. sp.). The density of fish recruits as assessed by a standardised artificial collector declined with patch size and showed a non-linear response to kelp density in that recruitment was reduced on reefs with low and medium densities of kelp compared to reefs without kelp or high densities of kelp. On the contrary, the abundance and species richness of fish communities were positively affected by increases in kelp patch size and high densities of kelp. Overall, these results highlight the importance of kelp patch characteristics in structuring communities spanning multiple trophic levels through modifications to abiotic and biotic ecosystem properties. The findings allude to potential consequences associated with different forms of kelp habitat decline; however, they also demonstrate that it is not only possible to establish E. radiata patches from transplants, but these patches will rapidly promote the (re-)establishment of the associated communities.