Temperature‐induced stress leads to bleaching in larger benthic foraminifera hosting endosymbiotic diatoms

Abstract

Physiological mechanisms of bleaching were studied on larger benthic foraminifera (LBF) hosting endosymbiotic diatoms. Amphistegina radiata, Heterostegina depressa, and Calcarina hispida were exposed to increasing temperatures in static temperature experiments (23uC to 33uC, 6 d). Photosynthetic activity (F v : F m , measured with a pulse-amplitude modulated fluorometer), chlorophyll a (a proxy for symbiont biomass), and motility (a proxy for overall fitness of the foraminifera) were reduced in specimens at 32uC to 33uC, and cytoplasm color changes associated with bleaching were observed. A 30-d flow-through experiment at three temperatures (26uC to 31uC) and three levels of inorganic nitrate concentration (0.5 to 1.4 mmol L 21 ) confirmed negative effects of temperature at 31uC for A. radiata (including growth) and H. depressa. Another Calcarina species, Calcarina mayorii, was not affected. This suggests that temperature effects are species-specific. However, elevated nutrient concentrations did not affect any of the parameters measured. Temperatures . 30uC stress the foram-diatom endosymbiosis in some LBF species, which may lead to subsequent bleaching of the host. Given that a 2-3uC increase led to rapid bleaching of most species, we propose that, similar to corals, these species are threatened by sea-surface temperature increase predicted for tropical reef waters in the near future.

Interactive climate change and runoff effects alter O<sub>2 fluxes and bacterial community composition of coastal biofilms from the Great Barrier Reef

“…Such inner nearshore conditions shift the benthic community composition, resulting in dominance by macroalgae that spatially compete with coral re cruits, and consequently may promote decline in coral cover (Szmant 2002, Fabricius 2005, Schaffelke et al 2005. Local chronic eutrophication continues to affect coral reefs and may have an additive interaction with global stressors, such as rising SSTs, therefore posing a threat to coral reefs of the GBR (Uthicke & Altenrath 2010, Schmidt et al 2011, Uthicke et al 2012b. Coastal water quality management of local disturbances may help preserve coral reefs from the projected effects of climate change (Wooldridge 2009, Schmidt et al 2011.…”

“…Local chronic eutrophication continues to affect coral reefs and may have an additive interaction with global stressors, such as rising SSTs, therefore posing a threat to coral reefs of the GBR (Uthicke & Altenrath 2010, Schmidt et al 2011, Uthicke et al 2012b. Coastal water quality management of local disturbances may help preserve coral reefs from the projected effects of climate change (Wooldridge 2009, Schmidt et al 2011.…”

Is the meiofauna a good indicator for climate change and anthropogenic impacts?

“…They showed that temperature significantly influenced both nematode species, while salinity had relatively minor effects on fecundity and development times, but strongly impacted juvenile viability at the end of the salinity range (0 and 40‰; Moens and Vincx 2000). Furthermore, larger benthic foraminifera (e.g., Amphistegina, Heterostegina), hosting endosymbiotic algae, suffer remarkable bleaching (symbiont or pigment loss) due to temperature-induced stress in culture experiments (e.g., Talge and Hallock 2003;Schmidt et al 2011). …”

Decreased light availability can amplify negative impacts of ocean acidification on calcifying coral reef organisms

“…Carbonate system parameters (mean with SD in parentheses) of experimental conditions. TA = total alkalinity, DIC = dissolved inorganic carbon, pCO 2 = carbon dioxide partial pressure, HCO 3 -= bicarbonate, CO 3 2− = carbonate, Ω ar = aragonite saturation state, SW = seawater described in Schmidt et al (2011) and Vogel & Uthicke (2012), apical segments of algae were placed in 15 ml Falcon tubes on ice and 4 ml of cold ethanol (95% EtOH) was added. After crushing the segments with a homogenizer, extracts were heat-shocked in a water bath (78°C for 5 min), and left in a fridge for 24 h extraction.…”