Rhodolith

The rhodolithic growth habit has been attained by a number of unrelated coralline red algae,[1] organisms that deposit calcium carbonate within their cell walls to form hard structures or nodules that resemble beds of coral.

[2][3] While corals are animals that are both autotrophic (photosynthesize via their symbionts) or heterotrophic (feeding on plankton), rhodoliths produce energy solely through photosynthesis (i.e. they can only grow and survive in the photic zone of the ocean).

[5][6] Rhodolith beds have been found throughout the world's oceans, including in the Arctic near Greenland, in waters off British Columbia, Canada, the Gulf of California, Mexico,[7] the Mediterranean [8] as off New Zealand[9] and eastern Australia.

[33][23] The widespread distribution of rhodoliths hints at the resilience of this algal group, which have persisted as chief components of benthic marine communities through considerable environment changes over geologic times.

This revealed a stable live rhodolith microbiome thriving under elevated pCO2 conditions, with positive physiological responses such as increased photosynthetic activity and no calcium carbonate biomass loss over time.

These findings reinforce the existence of a close host-microbe functional entity, where the metabolic crosstalk within the rhodolith as a holobiont could be exerting reciprocal influence over the associated microbiome.

[23] While the microbiome associated with live rhodoliths remained stable and resembled a healthy holobiont, the microbial community associated with the water column changed after exposure to elevated pCO2.

Characteristic mauve coloured rhodolith
Benthic communities found in rhodolith beds
Example of the seaweed and zoobenthic communities found in rhodolith beds on the Brazilian coast. This picture highlights the presence of gastropods, echinoderms and a turf algae assemblage. [ 5 ]
Vertical and latitudinal changes observed in the size and density of rhodoliths on the floor of the continental shelf off Espírito Santo in Brazil [ 5 ]
A view of rhodolith beds impacted by the warmer and more acidified oceans predicted by the IPPC. [ 22 ] [ 5 ]
Climate change and the rhodolith holobiont
Expected parabolic relationship between climate change stressors and rhodolith holobiont fitness. Under normal conditions healthy rhodoliths possess stable microbiomes , important to holobiont function. However, beyond the thresholds of algal physiological tolerance, disruption of positive host-microbiome interactions occurs, detrimentally affecting holobiont fitness. [ 23 ]