Forced convection modulates gas exchange in cnidarians

Comparative Biochemistry and Physiology Part A: Physiology - COMP BIOCHEM PHYSIOL PHYSIOL, 1972

The mean rate of oxygen consumption of 2.8 g (dry weight) specimens of Cur&us muenus in air is 177 ~1 O,/hr. This rate represents approximateIy 76.5 per cent of the rate in water which was initialiy 231.3 ~1 O,/hr. Following reimmersion in sea water, the mean rate increased from its aerial level to 206.3 ~1 OJhr.

Biogeosciences, 2013

Ocean warming will reduce dissolved oxygen concentrations which can pose challenges to marine life. Oxygen limits are traditionally reported simply as a static concentration thresholds with no temperature, pressure or flow rate dependency. Here we treat the oceanic oxygen supply potential for heterotrophic consumption as a dynamic molecular exchange problem analogous to familiar gas exchange processes at the sea surface. A combination of the purely physico-chemical oceanic properties temperature, hydrostatic pressure, and oxygen concentration defines the ability of the ocean to supply oxygen to any given animal. This general oceanic oxygen supply potential is modulated by animal specific properties such as the diffusive boundary layer thickness to define and limit maximal oxygen supply rates. Here we combine all these properties into formal, mechanistic equations defining novel oceanic properties that subsume various relevant classical oceanographic parameters to better visualize, map, comprehend, and predict the impact of ocean deoxygenation on aerobic life. By explicitly including temperature and hydrostatic pressure into our quantities, various ocean regions ranging from the cold deep-sea to warm, coastal seas can be compared. We define purely physico-chemical quantities to describe the oceanic oxygen supply potential, but also quantities that contain organism-specific properties which in a most generalized way describe general concepts and dependencies. We apply these novel quantities to example oceanic profiles around the world and find that temperature and pressure dependencies of diffusion and partial pressure create zones of greatest physical constriction on oxygen supply typically at around 1000 m depth, which coincides with oxygen concentration minimum zones. In these zones, which comprise the bulk of the world ocean, ocean warming and deoxygenation have a clear negative effect for aerobic life. In some shallow and warm waters the enhanced diffusion and higher partial pressure due to higher temperatures might slightly overcompensate for oxygen concentration decreases due to decreases in solubility.

Marine Ecology Progress Series, 2001

Limnology and Oceanography, 2010

The oxygen dynamics and pumping behavior in Dysidea avara and Chondrosia reniformis (Porifera, Demospongiae) were investigated using oxygen microelectrodes and heated thermistor flow sensors. Both field and laboratory experiments showed the common occurrence of low oxygenation approaching anoxia in both species, lasting up to 1 h. Strong temporal and spatial heterogeneity of oxygen concentrations were observed with replicate oxygen profile series across the sponge surface, though tissue close to an osculum was generally better oxygenated than deeper in the sponge body. Because of observed lag times between a pumping event and the respective oxygenation response, the state of oxygenation of sponge tissue could only be partially attributed to its pumping activity. Ambient flow also influenced oxygenation patterns of sponges. Larger individuals possessing a functional aquiferous system regulated their pumping activity according to the ambient flow regime, whereas a small D. avara sponge, yet to possess its first osculum, was passively oxygenated by ambient flow and became anoxic approximately 30 min after ambient flow was stopped in its laboratory tank. These studies showed (1) sponge tissue metabolism switched frequently from aerobic to anaerobic, (2) temporally and spatially dynamic oxygen-depleted regions were commonly found within those sponges, both in captivity and in the field, and (3) tissue oxygenation was regulated both by active behavior (pumping) and passive environmental events (ambient water flow). We concluded that the metabolism of both sponge cells and sponge microbes will be influenced by the sponges' ability to control oxygen concentrations in different regions of its body at any particular time. In addition, when a sponge is actively pumping in a particular region of its body, higher oxygen concentrations will favor aerobic symbionts and aerobic metabolism, whereas when active pumping ceases, anaerobic symbionts and anaerobic tissue metabolism will be favored.

Limnology and Oceanography, 2010

The oxygen dynamics and pumping behavior in Dysidea avara and Chondrosia reniformis (Porifera, Demospongiae) were investigated using oxygen microelectrodes and heated thermistor flow sensors. Both field and laboratory experiments showed the common occurrence of low oxygenation approaching anoxia in both species, lasting up to 1 h. Strong temporal and spatial heterogeneity of oxygen concentrations were observed with replicate oxygen profile series across the sponge surface, though tissue close to an osculum was generally better oxygenated than deeper in the sponge body. Because of observed lag times between a pumping event and the respective oxygenation response, the state of oxygenation of sponge tissue could only be partially attributed to its pumping activity. Ambient flow also influenced oxygenation patterns of sponges. Larger individuals possessing a functional aquiferous system regulated their pumping activity according to the ambient flow regime, whereas a small D. avara sponge, yet to possess its first osculum, was passively oxygenated by ambient flow and became anoxic approximately 30 min after ambient flow was stopped in its laboratory tank. These studies showed (1) sponge tissue metabolism switched frequently from aerobic to anaerobic, (2) temporally and spatially dynamic oxygen-depleted regions were commonly found within those sponges, both in captivity and in the field, and (3) tissue oxygenation was regulated both by active behavior (pumping) and passive environmental events (ambient water flow). We concluded that the metabolism of both sponge cells and sponge microbes will be influenced by the sponges' ability to control oxygen concentrations in different regions of its body at any particular time. In addition, when a sponge is actively pumping in a particular region of its body, higher oxygen concentrations will favor aerobic symbionts and aerobic metabolism, whereas when active pumping ceases, anaerobic symbionts and anaerobic tissue metabolism will be favored.

Marine Ecology Progress Series, 2007

We provide evidence from field experiments that within-coral colony variation in lightlimited electron transport rates through Photosystem II is positively correlated with water flow over the coral surface. We made in situ paired measurements of water flow and photosynthetic electron transport rates (rETR) over the upstream and downstream faces of several coral colonies at Conch Reef, Key Largo, Florida, USA. Using pulse amplitude modulated (PAM) fluorometry, we estimated rETR at increasing levels of photosynthetically active radiation (PAR). The rETR versus PAR relationship was fitted to a negative exponential curve parameterized by the initial slope (α) and the asymptotic maximum (rETR max ). We showed that flow speeds measured at 3 mm above the upstream faces of multiple branching colonies of Porites porites and hemispherical colonies of Siderastrea siderea were more than double those over the downstream faces. In both P. porites and S. siderea, these higher upstream flow speeds were associated with α values that were 4 and 12% higher, respectively, than those over the downstream faces. In contrast, there were no differences in flow speed, or in α between the upstream and downstream faces of plate-like colonies of Montastrea annularis. Ancillary measurements of oxygen concentrations over intact coral colonies in the field demonstrated that oxygen concentrations within 2 mm of the coral surface were between 2 to 110% higher than ambient (measured >1 m from the coral). Moreover, paired measurements over a single colony of S. siderea showed steeper velocity gradients over the upstream face relative to the downstream face, accompanied by lower oxygen concentrations, a thinner diffusion boundary layer, and higher α. Our results support the hypothesis that within-colony variation in photosynthesis by corals is related to water flow, and suggests that oxygen flux from the coral may be important.

Comparative biochemistry and physiology. Part A, Molecular & integrative physiology, 2011

Anemones are frequently found in rocky intertidal coasts. As they have highly permeable body surfaces, exposure to the air or to salinity variations inside tidal pools can represent intense osmotic and ionic challenges. The intertidal Bunodosoma caissarum has been compared with the subtidal Anemonia sargassensis concerning their response to air exposure or salinity changes. B. caissarum maintains tissue hydration through mucus production and dome-shape formation when challenged with air exposure or extreme salinities (fresh water or hypersaline seawater, 45 psu) for 1-2 h. Upon exposure to mild osmotic shocks for 6 h (hyposmotic: 25 psu, or hyperosmotic: 37 psu), B. caissarum was able to maintain its coelenteron fluid (CF) osmolality stable, but only in 25 psu. A. sargassensis CF osmolality followed the external medium in both salinities. Isolated cells of the pedal disc of B. caissarum showed full capacity for calcium-dependent regulatory volume decrease (RVD) upon 20% hyposmotic shock, at least partially involving the release of KCl via K + -Cl − cotransport, and also of organic osmolytes. Aquaporins (HgCl 2 -inhibited) likely participate in this process. Cells of A. sargassensis showed partial RVD, after 20 min. Cells from both species were not capable of regulatory volume increase upon hyperosmotic shock (20%). Whole organism and cellular mechanisms allow B. caissarum to live in the challenging intertidal habitat, frequently facing air exposure and seawater dilution.

American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 1998

The oral epithelial layers of anthozoans have a polarized morphology: photosynthetic endosymbionts live within endodermal cells facing the coelenteric cavity and are separated from the external seawater by the ectodermal layer and the mesoglea. To study if this morphology plays a role in the supply of inorganic carbon for symbiont photosynthesis, we measured the change in pH and the rate of OH−(H+) fluxes induced by each cell layer on a tentacle of the sea anemone Anemonia viridis. Light-induced pH increase of the medium bathing the endodermal layers led to the generation of a transepithelial pH gradient of ∼0.8 pH units across the tentacle, whereas darkness induced acidification of this medium. The light-induced pH change was associated with an increase of total alkalinity. Only the endodermal layer was able to induce a net OH−secretion (H+absorption). The light-induced OH−secretion by the endodermal cell layer was dependent on the presence of[Formula: see text] in the compartment ...

Journal of Experimental Marine Biology and Ecology, 1998

n a recent report, Benazet-Tambutte et al. (1996a) showed that the major source of dissolved inorganic carbon for photosynthesis of the sea anemone Anemonia viridis was external seawater and a minor source was the internal medium of the tentacles. In order to determine the mechanism of DIC transfer from the external seawater to the endodermal cells, we explored the different mechanisms potentially involved in this transfer: transepithelial passive diffusion of DIC across the oral epithelial layers, renewal of coelenteric fluid by the mouth or transepithelial active transport. In addition, we also studied the role of expansion / contraction of the tentacle in the transepithelial transport of DIC. We investigated diffusion of DIC, using isolated perfused tentacles, by measuring transepithelial 14 H CO flux. We found that the unidirectional transport of DIC was light-sensitive: the 3 transepithelial flux was about threefold lower in light than in dark conditions. The flux was insensitive to the anion transport inhibitor, DIDS, and to the carbonic anhydrase inhibitor, Diamox. It was directly proportional to the concentration of bicarbonate in the surrounding seawater. These results suggest that this flux is simply driven by diffusion via a paracellular pathway. Use of inhibitors and inside-out tentacles showed that the transepithelial flux measured in the dark was depressed in the light due to symbiont photosynthesis which diverts about 15% of the DIC flux. Consequently, the passive diffusional flux of DIC can account for less than 1 / 6 of the dissolved inorganic carbon used for symbiont photosynthesis under saturating light conditions. Expansion / contraction state of the tentacles did not significantly modify the permeability 25 25 21

PNAS, 2010