Air Pressure Regulation in Air Bladders of Ascophyllum nodosum(Fucales, Phaeophyceae)

Abstract

Diurnal and age-related changes in air pressure were measured in air bladders of Ascophyllum nodosum from the Atlantic coast of Nova Scotia. Exterior and interior bladder volumes vary significantly with 4 and 6 y bladders being about 40% larger than 2 y bladders (p < 0.01). Freshly collected bladders yielded a mean pressure of 40.8 ± 6.5 cm H 2 O. Overnight (20 h) dark treatment at 15°C generated pressure reductions by 80% in 2 y bladders but only by about 30% in 4 and 6 y bladders. Furthermore, in 2 y bladders 8 out of 11 bladders were reduced to atmospheric pressure. Pressure losses were inversely related to pressure recovery after 2.5 h in natural daylight, but after 5 h in daylight there was no significant difference in pressure within the age groups. Even under 25% of full illumination, bladders inflated to full pressure after 5 h. The results show that differences in bladder age and bladder wall thickness have roles in diurnal patterns of bladder inflation and deflation. These results confirm that bladder inflation is based on photosynthetic O 2 production and not on partial pressures of O 2 in the surrounding medium as was suggested for Sargassum. Chemical analyses of fluid recovered after the interior of bladders were washed with saline showed no evidence for the occurrence of surfactant that might be responsible for maintaining the air-liquid interface.

Enigmatic Ediacaran megascopic bedding plane structures on the Sonia Sandstone, Jodhpur Group, Marwar Supergroup, India: seaweed or problematica?

“…A few nodes are globular in shape [Figs. nitrogen, oxygen and water vapour) provides a scope for maximum sunlight exposure, which varies during daytime, for photosynthesis to the seaweed (Brackenbury et al, 2006). Diameter of globular nodes ranges up to 2.5 cm.…”

Under pressure: biomechanical limitations of developing pneumatocysts in the bull kelp (Nereocystis luetkeana, Phaeophyceae)

“…; Dromgoole , Brackenbury et al. ), however pneumatocysts produced by kelps (i.e., N. luetkeana , Macrocystis pyrifera , Pelagophycus porra ) evolved independently from those of other macroalgae at least once (Thiel and Gutow , Lane et al. ) and are developmentally distinct (Yoon et al.…”

“…In particular, pneumatocysts must remain “air‐tight” (Rigg and Swain , Foreman ) to avoid leaks and, because compressible gases are susceptible to volumetric change with pressure, must potentially resist rupturing (as gases expand) or buckling (as gases compress; Dromgoole , Brackenbury et al. ) when thalli move through the water column.…”

“…Gasfilled structures are known from many seaweed species, especially within the brown algae (e.g., Ascophyllum spp., Fucus spp., Sargassum spp., Durvillaea spp. ; Dromgoole 1981b, Brackenbury et al 2006), however pneumatocysts produced by kelps (i.e., N. luetkeana, Macrocystis pyrifera, Pelagophycus porra) evolved independently from those of other macroalgae at least once (Thiel andGutow 2005, Lane et al 2006) and are developmentally distinct (Yoon et al 2001, Lane et al 2006, Charrier et al 2012. Pneumatocysts of Nereocystis are particularly interesting because, unlike gas-filled floats in most other species, they inflate at depth and ascend through the water column toward the surface while experiencing a decreasing gradient of hydrostatic pressure (Fig.…”

“…Previous studies have shown that brown algae can resist mechanical forces as they develop by adjusting structural and mechanical properties to prevent organs (i.e., holdfast, stipe, blade, pneumatocyst) from breaking under extreme physical stress, such as wave forces or changes in hydrostatic pressure due to tidal fluctuations (Dromgoole 1981a,b, Johnson and Koehl 1994, Utter and Denny 1996, Koehl 1999, Hale 2001, Harder et al 2006, Starko and Martone 2016. In particular, pneumatocysts must remain "air-tight" (Rigg andSwain 1941, Foreman 1976) to avoid leaks and, because compressible gases are susceptible to volumetric change with pressure, must potentially resist rupturing (as gases expand) or buckling (as gases compress; Dromgoole 1981b, Brackenbury et al 2006) when thalli move through the water column.…”