Major loss in algal species over 150 years of data: is ocean heating driving species loss in a biodiversity hotspot and how can it inform effective restoration?

We are in the midst of a global biodiversity crisis, with global heating and extreme events reshaping entire communities. Key amongst our concerns is the loss of habitats which support biodiversity and enhance ecosystem function. In many coastal marine systems, seaweeds are not only the major primary producers but also form extensive habitats. Yet, data on the effects of ocean heating and marine heatwaves on these algal assemblages is restricted to a few well-studied regions. Here, we have assembled a database of algal species records from the temperate-tropical climatic transition zone along the southern coast of China spanning ~170 years. We found that up to 150 species of algae have potentially been lost from the waters of Hong Kong, possibly representing poleward range shifts of a large percentage (>60% of recorded species) of the algal community. We then used in situ physiological measurements and laboratory warming experiments to demonstrate that warming winter (not summer) water temperatures over the past 3 decades have shortened the winter growth season for forest-forming Sargassum spp. Therefore, to save these once extensive seaweed forests from local extirpation we have begun implementing pre-treatment of juveniles in an attempt to “heat harden” them to future proof restoration attempts. Higher survival of heat-treated juveniles after out-planting points to potential early success, but also provides information to improve outcomes in future up-scaling of seaweed forest restoration.

Presentation Preference: Standard Oral (12 Minutes)

Primary Presenter: Bayden Russell, University of Hong Kong (brussell@hku.hk)

Authors:

Alison Freeman, Swire Institute of Marine Science and Area of Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China  (u3011687@connect.hku.hk)

Rhian Evans, Swire Institute of Marine Science and Area of Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China  (rhiane@hku.hk)

S.A.M. Shariar Islam, Swire Institute of Marine Science and Area of Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China  (shariar.du12@gmail.com)

Juan Diego Gaitan-Espitia, Swire Institute of Marine Science and Area of Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China  (jdgaitan@hku.hk)

Bayden Russell, Swire Institute of Marine Science and Area of Ecology and Biodiversity, School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China  (brussell@hku.hk)