Crustose coralline algae can contribute more than corals to coral reef carbonate production

Abstract

Understanding the drivers of net coral reef calcium carbonate production is increasingly important as ocean warming, acidification, and other anthropogenic stressors threaten the maintenance of coral reef structures and the services these ecosystems provide. Despite intense research effort on coral reef calcium carbonate production, the inclusion of a key reef forming/accreting calcifying group, the crustose coralline algae, remains challenging both from a theoretical and practical standpoint. While corals are typically the primary reef builders of contemporary reefs, crustose coralline algae can contribute equally. Here, we combine several sets of data with numerical and theoretical modelling to demonstrate that crustose coralline algae carbonate production can match or even exceed the contribution of corals to reef carbonate production. Despite their importance, crustose coralline algae are often inaccurately recorded in benthic surveys or even entirely missing from coral reef carbonate budgets. We outline several recommendations to improve the inclusion of crustose coralline algae into such carbonate budgets under the ongoing climate crisis.

From local seafloor imagery to global patterns in benthic habitat states: contribution of citizen science to habitat classification across latitudes

“…6). For example, the clusters crustose coralline algae, crustose coralline algae and turf and turf provide an interesting template to describe the habitat transitions described in Cornwall et al (2023), which suggests that a shift from crustose coralline algae to turf domination reduces reef carbonate production. Similarly, the clusters branching coral, turf and sand and turf can be used to describe and quantify in a standardised manner the transitions between corals and turf dominated habitats that are occurring more frequently due to anthropogenic pressures (Jouffray et al 2015).…”

Corals at the Edge of Environmental Limits: A New Conceptual Framework to Re-Define Marginal and Extreme Coral Communities

“…In addition, positive net vertical accretion is closely linked to many ecosystem services that coral reefs provide, including habitat structure provision and coastline protection from storms and erosion (e.g., Beck et al, 2018). It should be noted, however, that calcium carbonate production can also stem from non-coral taxa such as calcareous algae and bryozoans (Cornwall et al, 2023), while habitat structure may be provided by sponges, for example. Furthermore, non-framework reefs or non-accreting coral communities, especially at high latitude, have often been considered "classic" marginal systems (e.g., Macintyre, 2003).…”

“…Importantly, these ecosystems may not necessarily be dominated by corals (e.g., corals growing on sponge reefs or in mangrove systems, Fig. S1f) and non-coral taxa such as coralline algae may be the main reef builders (Cornwall et al, 2023). We nevertheless refer to these ecosystems as coral communities due to our focus on scleractinian corals in this review.…”

Quantifying pigment content in crustose coralline algae using hyperspectral imaging: A case study with Tethysphytum antarcticum (Ross Sea, Antarctica)

“…Crustose coralline algae (CCA) are a highly diverse group of calcifying red macroalgae (Rhodophyta) within the sub‐class Corallinophycidae (le Gall & Saunders, 2007). Throughout the world's oceans, CCA create complex habitats that support biodiversity (Hofmann et al., 2020; Nelson, 2009) and play a role in large‐scale marine biogeochemical cycling (reviewed in Cornwall et al., 2023; van der Heijden & Kamenos, 2015). As a group, CCA are characterized for their adaptation to low‐light regimes, growing at 0.1% of surface photosynthetic active radiation (PAR) and surviving under 0.0005% (Steneck, 1986).…”