Osmotic and ionic regulation

Osmotic regulation in crustaceans

In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L−1. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases.

A review of the salt sensitivity of the Australian freshwater biota

Osmotic and ionic regulation in the Crustacea is mostly accomplished by the multifunctional gills, together with the excretory organs. In addition to their role in gas exchange, the gills constitute organs of active, transepithelial, ion transport, an activity of major importance that underlies many essential physiological functions like osmoregulation, calcium homeostasis, ammonium excretion and extracellular pH regulation. This review focuses on structure-function relationships in crustacean gills and excretory effectors, from the organ to molecular levels of organization. We address the diversity of structural architectures encountered in different crustacean gill types, and in constituent cell types, before examining the physiological mechanisms of Na(+), Cl(-), Ca(2+) and NH(4)(+) transport, and of acid-base equivalents, based on findings obtained over the last two decades employing advanced techniques. The antennal and maxillary glands constitute the principal crustacean excretory organs, which have received less attention in functional studies. We examine the diversity present in antennal and maxillary gland architecture, highlighting the structural similarities between both organ types, and we analyze the functions ascribed to each glandular segment. Emphasis is given to volume and osmoregulatory functions, capacity to produce dilute urine in freshwater crustaceans, and the effect of acclimation salinity on urine volume and composition. The microanatomy and diversity of function ascribed to gills and excretory organs are appraised from an evolutionary perspective, and suggestions made as to future avenues of investigation that may elucidate evolutionary and adaptive trends underpinning the invasion and exploitation of novel habitats.

A structure-function analysis of ion transport in crustacean gills and excretory organs.

Salinity Tolerance and Osmotic Behavior of Animals in Athalassic Saline and Marine Hypersaline Waters

1. Syncaris pacifica (Atyidae) is restricted to fresh water, like most members of the family. The striking osmotic adaptation in this shrimp is elaboration of urine markedly hypo-osmotic to blood. In fresh water, the following average body fluid concentrations were found: blood,Δi 0.73° C. (F. P. depression), chloride, 185 meq./L.; urine, Δi 0.18° C. This is the first report of dilute urine in any decapod other than crayfishes.2. Palaemon macrodactylus (Palaemonidae) is a strong regulator over the range 2-150% SW, and inhabits a wide range of salinities in the San Francisco Bay estuarine system. Blood and urine are isosmotic throughout the tested range of salinities. Hyper-regulation occurs below 60% SW, and hypo-regulation in higher salinities. Between 20% and 100% SW, Δi increases only from 1.19° to 1.65° C., as environmental salt concentration increases from Δ0 0.50° to 2.08° C.

John W. Born

Papers

Osmoregulatory capacities of two caridean shrimps, syncaris pacifica (atyidae) and palaemon macrodactylus (palaemonidae)