Effects of turbidity on the kelp Ecklonia radiata

Increasing turbidity poses a major yet often overlooked threat to coastal marine ecosystems. By reducing light available for key benthic primary producers, increasing turbidity has the capacity to restructure marine communities and adversely impact coastal primary production. An important step to mitigating the effects of turbidity on coastal marine ecosystems is a better understanding of how the physiological and ecological performance of foundational species, such as kelp, are affected by turbidity. This research combined field studies across a large-scale turbidity gradient in the Hauraki Gulf, north-eastern New Zealand, and mesocosm experiments, to determine the effects of turbidity, and light, on the physiological performance, productivity and persistence of a subtidal kelp, Ecklonia radiata. Results from field studies showed that light was a primary driver of the morphology, photoacclimation response, distribution, and productivity of E. radiata in the Hauraki Gulf. Photosynthetic acclimation to low light was indicated by higher photosynthetic efficiencies and photosynthetic pigment content occurring at low light sites and in low light seasons. Field and mesocosm experiments also indicated that increases in seawater nitrogen availability had positive effects on the development of tissues in E. radiata, which may act to alleviate some of the physiological stress associated with living in low light environments and facilitate the persistence of E. radiata in turbid environments. Though E. radiata showed a marked capacity to acclimate to low light spatially and temporally through adjustments of the photosynthesis-irradiance response and thallus morphology, the growth, productivity and distribution of E. radiata was greatly reduced at the lowest light sites of the inner Hauraki Gulf. In these areas, the subtidal fucoid Carpophyllum flexuosum became the dominant canopy forming macrophyte suggesting that in low light environments E. radiata is unable to maintain dominance over low-light tolerant species such as C. flexuosum. This was corroborated by mesocosm experiments that suggested C. flexuosum was more tolerant to persistent low-light conditions than E. radiata. Results presented in this thesis show that the productivity of kelp forests declines with increasing turbidity and a shift from kelp-dominated to fucoid-dominated communities, which will likely be facilitated by future increases in turbidity, may have implications for overall ecosystem functioning and primary production.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Marine Science

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2018

Author dc:creator

• Blain, Caitlin

Advisors dc:contributor.advisor

• Shears, N
• Rees, A

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/37593

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/37593