Tolerance of Sponge Assemblages to Temperature Anomalies: Resilience and Proliferation of Sponges following the 1997–8 El-Niño Southern Oscillation

Abstract

Coral reefs across the world are under threat from a range of stressors, and while there has been considerable focus on the impacts of these stressors on corals, far less is known about their effect on other reef organisms. The 1997–8 El-Niño Southern Oscillation (ENSO) had notable and severe impacts on coral reefs worldwide, but not all reef organisms were negatively impacted by this large-scale event. Here we describe how the sponge fauna at Bahia, Brazil was influenced by the 1997–8 ENSO event. Sponge assemblages from three contrasting reef habitats (reef tops, walls and shallow banks) at four sites were assessed annually from 1995 to 2011. The within-habitat sponge diversity did not vary significantly across the study period; however, there was a significant increase in density in all habitats. Multivariate analyses revealed no significant difference in sponge assemblage composition (ANOSIM) between pre- and post-ENSO years for any of the habitats, suggesting that neither the 1997–8 nor any subsequent smaller ENSO events have had any measurable impact on the reef sponge assemblage. Importantly, this is in marked contrast to the results previously reported for a suite of other taxa (including corals, echinoderms, bryozoans, and ascidians), which all suffered mass mortalities as a result of the ENSO event. Our results suggest that of all reef taxa, sponges have the potential to be resilient to large-scale thermal stress events and we hypothesize that sponges might be less affected by projected increases in sea surface temperature compared to other major groups of reef organisms.

Global conservation status of sponges

“…Chondrilla nucula was mostly responsible for the increased abundance in response to more substrate becoming available through coral mortality. Increases in sponge abundance for an entire sponge assemblage following the same ENSO event were also reported in a 16‐year study (1995–2011) in Bahia, Brazil (Kelmo et al ), where the abundance of most subtidal benthic organisms declined dramatically and in some cases were extirpated. Although the abundance of many sponge species increased more than 10 times their initial densities by 2011, others showed decreased abundance.…”

Gene Expression Dynamics Accompanying the Sponge Thermal Stress Response

“…For example, the growth and survival of several Carribean sponges remained unaffected by exposure to thermal stress [11]. Furthermore, the sponge assemblage in Bahia, Brazil, did not change between pre- and post-El Niño Southern Oscillation (ENSO) years [12]. In contrast, some studies have described the negative effects of elevated temperature on different sponge species.…”

Changes in deep reef benthic community composition across a latitudinal and environmental gradient in temperate Eastern Australia

“…While the potential impacts of climate-driven ocean changes are well documented for kelp (Wernberg et al 2010, Johnson et al 2011) and coral species (Spillman et al 2013), there remains uncertainty about how future climate change is likely to influence the distribution of non-coral benthic sessile invertebrates (Przeslawski et al 2008, Kelmo et al 2013. Recent studies have shown inconsistent results, with some indicating that under warmer future climate conditions, deep sessile organisms, particularly sponges, may benefit (e.g.…”

“…Recent studies have shown inconsistent results, with some indicating that under warmer future climate conditions, deep sessile organisms, particularly sponges, may benefit (e.g. colonise and establish on newly available reef space due to declines in other habitat-forming species, such as corals; Norström et al 2009, González-Rivero et al 2011, Kelmo et al 2013, while others suggest negative impacts (e.g. mass mortalities due to extreme climatic events such as marine heat waves; Cerrano et al 2000, Perez et al 2000, Garrabou et al 2009, Cebrian et al 2011).…”