Climate change alterations to ecosystem dominance: how might sponge‐dominated reefs function?

Abstract

Anthropogenic stressors are impacting ecological systems across the world. Of particular concern are the recent rapid changes occurring in coral reef systems. With ongoing degradation from both local and global stressors, future reefs are likely to function differently from current coral-dominated ecosystems. Determining key attributes of future reef states is critical to reliably predict outcomes for ecosystem service provision. Here we explore the impacts of changing sponge dominance on coral reefs. Qualitative modelling of reef futures suggests that changing sponge dominance due to increased sponge abundance will have different outcomes for other trophic levels compared with increased sponge dominance as a result of declining coral abundance. By exploring uncertainty in the model outcomes we identify the need to (1) quantify changes in carbon flow through sponges, (2) determine the importance of food limitation for sponges, (3) assess the ubiquity of the recently described "sponge loop," (4) determine the competitive relationships between sponges and other benthic taxa, particularly algae, and (5) understand how changing dominance of other organisms alters trophic pathways and energy flows through ecosystems. Addressing these knowledge gaps will facilitate development of more complex models that assess functional attributes of sponge-dominated reef ecosystems.

A community perspective on the concept of marine holobionts: current status, challenges, and future directions

“…Moreover, understanding how the community and functional structure of resident microbes are resilient to perturbations remains critical to predict and promote the health of their host and the ecosystem. Yet, this notion is still missing in most mathematical or formal models, or additional information on biological interactions would be required to make the former more accurate (Bell et al 2018).…”

Thermal stress modifies the marine sponge virome

“…Throughout evolution, sponge holobionts have colonized most habitats including coral reefs, where they provide essential ecosystem services for the benthos and water column. However, these ecosystems are experiencing increasingly frequent and severe thermal stress events that are reducing coral populations and directly threatening the survival of reef‐associated taxa including sponges (van Hooidonk et al ., ; Hughes et al ., ; Bell et al ., ; Bell et al ., ). Given the established importance of symbionts to sponge health (Pita et al ., ), understanding the role of microbial and viral associates in the host stress response and/or environmental adaptation is critical.…”

Will coral reef sponges be winners in the Anthropocene?

“…As a result of these ecological changes, coral reefs have become the “poster child” for ecosystems experiencing profound ecological changes now, and predicted to worsen into the future in the Anthropocene, where high biodiversity coral reefs will probably exist in very few places (Hoegh‐Guldberg et al, ). Sponges, in particular, have been predicted to become “winners” under these climate change scenarios when phase shifts in community structure occur (Bell, Bennett, Rovellini, & Webster, ; Bell, Davy, Jones, Taylor, & Webster, ; Bell, Rovellini, et al, ). But there is not widespread support for a general increase in sponge populations on shallow reefs; site‐specific increases (McMurray, Finelli, & Pawlik, ) and decreases (Wulff, ) have been reported for sponge populations monitored over extended time periods.…”