Bleaching of the giant barrel sponge Xestospongia muta in the Florida Keys

Abstract

The giant barrel sponge Xestospongia muta is now the dominant habitat-forming organism on many Caribbean coral reefs and has been observed to undergo cycles of bleaching similar to those seen for reef-building corals. We examined bleaching of X. muta at 15-m, 20-m, and 30-m depths over 2000-2005 on Conch Reef, Key Largo, Florida, to determine the spatial and temporal patterns of bleaching, whether bleaching affected sponge mortality, and whether there was a relationship between bleaching and seawater temperatures. Bleaching increased significantly with depth and was greater in autumn than spring, but the response was not uniform across the sponge population. Bleaching of X. muta did not result in sponge mortality, corroborating the conclusion that cyanobacterial symbionts of the sponge provide little or no benefit to the host. There was greater sponge bleaching with higher minimum daily seawater temperature anomalies within 30 d of surveys in the spring. For both the spring and autumn, there was greater bleaching with a higher number of positive 0.5uC daily anomalies within 14 d before surveys. Anomalously warm seawater temperatures fail to completely explain the variability of the observed bleaching response, however, and additional work would be required to conclusively determine whether a causal relationship between bleaching and temperature exists. As has been described for corals, bleaching of X. muta is likely a complex response that may be affected by multiple factors, including light availability and differences in bleaching susceptibility among Synechococcus symbionts.

Variation in sensitivity of large benthic Foraminifera to the combined effects of ocean warming and local impacts

“…Our results demonstrate that, similar to other holobiont organisms, such as reef building corals38, giant clams48, sponges49 and tropical sea anemones50, increases in nutrient and temperature can negatively impact LBF. Local adaptation of the photo-symbionts can shape thermal tolerance of reef corals51, and adaptive differentiation occurs in several other marine invertebrates in response to selection imposed by strong gradients of abiotic and biotic conditions52.…”

Trophic ecology of sponges from shallow to mesophotic depths (3 to 150 m): Comment on Pawlik et al. (2015)

“…They indicate that there were no significant differences in growth rates across depths and a lower abundance of sponges at 30 m, in contrast to predictions that these metrics should be greater with the increased POC at this depth. Their results may have less to do with an increase in food with increasing depth (Leichter et al 1998, Lesser 2006, and may instead be due to increased bleaching stress suffered by X. muta at depths of 30 m on Conch Reef (McMurray et al 2011), and reduced growth due to energetic trade-offs between growth and the repair of damage associated with environmental stress. Pawlik et al (2015, p. 276) note that manipulative experiments represent 'the most valid approach to testing food limitation of sponges', and they present an assessment of the only 2 studies to examine this issue to date (Trussell et al 2006, Pawlik et al 2013).…”

A review of evidence for food limitation of sponges on Caribbean reefs

“…Another recent set of studies was instigated, not to examine bottom-up influences, but to gather basic information about growth and demography of what is now the most important habitat-forming organism on most Caribbean reefs, the giant barrel sponge Xestospongia muta (McMurray et al , 2010(McMurray et al , 2011. Fortuitously, these studies, which involved tagging individual sponges on 12 permanent circular plots (16 m diameter) and monitoring them for more than a decade, were done within 3 plots at each of 3 depths (15, 20, 30 m) on Conch Reef, Florida, where the gradient of increasing particulate food with depth is particularly well described (Leichter et al 2005).…”