From micro to macro: the benefits and pitfalls of environmental generalism on coral reefs in the Anthropocene

As warming ocean temperatures culminate in large-scale mortality events across tropical, temperate, and deep-water reefs, a shift in environmental norms across marine ecosystems is causing species to expand into otherwise marginal environments. This widespread ecosystem restructuring raises the questions of which coral species in which locations will persevere under changing environmental conditions and what ecosystem structures and species interactions are likely to be the most stable in the coming decades of environmental disturbance. Environmental generalism refers to species whose physiological ranges allow them to occupy multiple environmental regimes. As environmental conditions change with increased intensity of extreme conditions, generalist coral species are likely to contribute to the structure of new coral reef ecosystems. This thesis assesses the advantages and pitfalls of environmental generalism in scleractinian corals exposed to warming temperatures through the lens of physiological ecology. By assessing corals exposed to thermal stress in either the field (e.g. a naturally occurring bleaching event) or in a laboratory setting (e.g. experimental manipulation) and measuring changes in symbiont densities, photosystem health, and bacterial communities, this thesis focuses on: 1). Defining the role of a generalist coral across environments 2). Physiological response to warming or environmental change in each of these environments To address these questions, this PhD thesis focused on first defining characteristics of generalist coral species on coral reefs along Australia’s east coast (Ch. 2), and then quantifying the role of the bacterial microbiome associated with Pocilloporid corals in the meta-organism bleaching response. Overall, despite ex situ thermal stress exposure and in situ reef-wide and colony-specific bleaching on two distinct coral reefs, the bacterial community composition of Pocillopora damicornis remained stable. Distinct host traits, such as light environment, seawater temperature, tissue thickness, and morphology, were found to contribute to variation in the bacterial taxa of Pocillopora samples, with dominant taxa driven by differences in host-specific traits between a specialist species and the generalist P. damicornis (Ch. 3). When thermal stress exposure caused a subsequent decline in symbiont densities and photophysiology, the P. damicornis bacterial community remained unchanged regardless of length of exposure to experimental thermal stress (Ch. 4). Hypothesizing that a conserved trait of the Pocilloporid bleached coral microbiome is stability (e.g. no increase in pathogenic taxa or evidence of dysbiosis) despite stress, we found continued patterns of stability in the bacterial microbiome of P. damicornis during in situ bleaching events in two distinct locations, Lord Howe Island and Heron Island (Ch. 5). The results from Chapters 3-5 therefore suggest that the microbiome of Pocilloporids is uniquely structured in a way that will contribute to their success as generalists on future reefs, and that Pocilloporid corals possess a unique set of life history traits that have the potential to aid their success on reefs undergoing large-scale change.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2023

Author dc:creator

• Bergman, Jessica

• coral reef
• microbial ecology
• climate change
• pocilloporid
• anzsrc-for: 310305 Marine and estuarine ecology (incl. marine ichthyology)
• anzsrc-for: 310703 Microbial ecology
• anzsrc-for: 31 BIOLOGICAL SCIENCES

Statement dc:rights

• open access
• CC BY 4.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

en

Identifier

https://doi.org/10.26190/unsworks/24718

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/101011