Estabilidade osmótica dos fluídos celômicos de um pepino do mar (Holothuria grisea) e de uma estrela-do-mar (Asterina stellifera) (Echinodermata) expostos ao ar durante a maré baixa: um estudo de campo

Animais de entre-marés podem ser expostos ao ar durante a maré baixa, por pelo menos 1-2 horas. Os animais expostos ao ar são susceptíveis a perda de sal e/ou entrada de água durante chuva intensa, ou perda de água pela ação de dessecação do sol. A osmolalidade de amostras de fluido celômico obtidas do pepino-do-mar Holothuria grisea e da estrela-do-mar Asterina stellifera expostas ao ar, ou de animais controles imersos na água do mar adjacente foi determinada. As amostras foram obtidas imediatamente após a exposição ao ar, e novamente após uma hora de exposição ao ar, durante a maré baixa no campo, em tempo nublado, chuvoso, ou ensolarado, na Praia rochosa do Quilombo, Penha, Sul do Brasil. Uma hora de exposição a qualquer das condições climáticas indicadas não alterou a osmolalidade dos fluidos celômicos. Houve pequena redução nas osmolalidades dos fluidos celômicos durante a exposição ao ar com precipitação de chuva. Sugere-se que estes equinodermas possam imediatamente detectar sua exposição ao ar, e possam então reduzir a permeabilidade osmótica de sua parede do corpo, para evitar perda de água para o ar ou entrada de água/saída de sal durante a chuva. ABSTRACT Intertidal animals can be exposed to the air during low tide, for at least 1-2 hours. Animals exposed to the air are subject to salt loss (or water gain) from heavy rains or volume loss from the desiccating action of the sun. Coelomic fluid samples obtained from the sea-cucumber Holothuria grisea and the starfish Asterina stellifera exposed to the air or from control animals submerged in surrounding sea water have been assayed for osmolality. Samples were obtained right after air exposure and again after 1 hour of exposure to the air during low tide in the field, either under cloudy, rainy or sunny weather conditions, in the rocky beach of Quilombo, Penha, Southern Brazil. One hour of exposure to any of the conditions did not change coelomic fluid osmolalities. There was a slight reduction in coelomic fluid osmolalities upon air exposure during rainfall. It is suggested that these echinoderms can somehow immediately detect air exposure and reduce their body wall permeability to avoid water loss or water influx/salt loss during rainfall. RÉSUMÉ Animaux dentre-marées peuvent êtres exposés a lair libre pendant le reflux de la marée, pour environ une ou deux heures seulement. Ces animaux, quand exposés a lair libre, sont susceptibles de perdre du sel et dabsorber de leau pendant une période de pluie intense. Par contre, ils peuvent perdre de leau si soumis a laction de dessèchement due a une éxposition au soleil. On a réussi a determiner losmolalité déchantillons du fluide celomique obtenus du Pépin-de-mer Holothuria grisea et de lÉtoile-de-mer Asterina stellifera exposés a lair libre, e danimaux-controles immergés dans leau de mer voisin. Les échantillons ont été obtenus tout de suite après lexposition à lair et, une seconde fois, après une heure dexposition à lair libre, pendant la durée de la marée basse, soit sous la pluie, soit au soleil ou soit sous un ciel ombrageux, à la plage rocailleuse de Quilombo, Penha, au sud du Brésil. Une heure déxposition à nimporte quelles conditions climatiques indiquées, nont pas pu altérer losmolalité des fluides celomiques, ce que sugère la conclusion que ces échinodermes peuvent détecter immédiatement sa exposition à lair libre et peuvent tout de suite réduire la permeabilité osmotique de la membrane que recouvre son corps pour éviter perdre deau et, de la même façon, reduire labsortion de leau pendant la pluie. On a observé une petite réduction de fluides celomiques pendant lexposition a lair, avec ocurrence de pluie

Osmolality and ions of the perivisceral coelomic fluid of the intertidal sea urchin Echinometra lucunter (Echinodermata: Echinoidea) upon salinity and ionic challenges

The intertidal sea-urchin Echinometra lucunter (Linnaeus, 1758) has been submitted to diluted sea water (SW) of salinity 25, or concentrated sea water of salinity 45. In addition, ionic challenges have been offered, supplementing 25 SW with Mg2+, Ca2+ or K+, until the concentration of each of these ions would reach the level of full-strength 35 SW (control). Perivisceral coelomic fluid has been sampled after six hours in these treatments for measurements of osmolality and concentrations of Na+, Cl-, Mg2+, Ca2+, and K+. Urchins have been further observed until five days. SW concentration (45) lead urchins to death after two days of exposure, while urchins tolerated five days in 25 SW without any sign of distress. Urchins displayed osmoconformation and ion-conformation for NaCl, and occasional small gradients with respect to the water for Mg2+ (~6% in full-strength SW), and K+ (8.5% in 25 SW), after six hours. These results are consistent with data compiled from the literature, for echinoderms, which frequently show positive gradients (often higher than 25%) for the most relevant ions, between the coelomic fluid and external SW. Supplemented cations have shown mutual interference, mostly affecting their own coelomic fluid concentrations. Under the protocol used here, urchins of the species E. lucunter held gradients for Mg2+, Ca2+, and K+, but not for Na+ or Cl- or osmolality. They were also able to tolerate at least a 30% reduction in sea water salinity for five days, showing reasonable euryhalinity. However, when compared to other echinoderms, E. lucunter is not especially capable of maintaining large ionic gradients with respect to external SW

Distinct patterns of water and osmolyte control between intertidal (Bunodosoma caissarum) and subtidal (Anemonia sargassensis) sea anemones

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 (HgCl2-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