No abstract

Simultaneous measurements of flow rates and major electrolyte composition of urine and rectal fluid were made on five southern flounders, Paralichthys lethostigma, averaging 1,19 kg body weight. Rectal fluid is a residue of seawater swallowed by the fish, isosmotic to the blood plasma (336 mosmoles/l), and composed principally of magnesium (average 180 mmoles/l), sulfate (average 105 mmoles/l), and chloride (average 126 mmoles/l). Only 15.5% of the magnesium and 11.3% of the sulfate swallowed was absorbed from the intestine; all absorbed was probably excreted entirely by the kidney. The rate of seawater ingestion calculated from the total (renal + rectal) excretion of magnesium and sulfate yielded estimates averaging 4.6 ml/h × kg body weight. Of this volume, 24% (average 1.1 ml/h × kg) was eliminated as rectal fluid, 4% (average 0,18 ml/h × kg) was excreted as urine and 72% (average 3.3 ml/h × kg) was lost osmotically across the body surface. Nearly 99% of the sodium, 98% of the potassium, and 93% of the chloride swallowed was removed by an extrarenal route, presumably the gills. Of the calcium swallowed, 32% remained in the rectal fluid residue, 8% was excreted in the urine, and the rest (60%) was removed by unknown extrarenal pathways.

Comparisons between historical and recent ecological datasets indicate that shallow reef habitats across the central Galapagos Archipelago underwent major transformation at the time of the severe 1982/1983 El Niñ o warming event. Heavily grazed reefs with crustose coralline algae ('urchin barrens') replaced former macroalgal and coral habitats, resulting in large local and regional declines in biodiversity. Following recent threat assessment workshops, a total of five mammals, six birds, five reptiles, six fishes, one echinoderm, seven corals, six brown algae and nine red algae reported from coastal environments in Galapagos are now recognized as globally threatened. The 2008 International Union for the Conservation of Nature (IUCN) Red List includes 43 of these species, while two additional species (Galapagos damsel Azurina eupalama and 24-rayed sunstar Heliaster solaris) not seen for 425 years also fulfil IUCN threatened species criteria. Two endemic species (Galapagos stringweed Bifurcaria galapagensis and the damselfish A. eupalama) are now regarded as probably extinct, while an additional six macroalgal species (Dictyota galapagensis, Spatoglossum schmittii, Desmarestia tropica, Phycodrina elegans, Gracilaria skottsbergii and Galaxaura barbata) and the seastar H. solaris are possibly extinct. The removal of large lobster and fish predators by artisanal fishing probably magnified impacts of the 1982/1983 El Niñ o through a cascade of indirect effects involving population expansion of grazing sea urchins. Marine protected areas with adequate enforcement are predicted to ameliorate but not eliminate ecosystem impacts caused by increasing thermal anomalies associated with El Niñ o and global climate change.

Energy demands for osmotic regulation and the possible osmoregulatory role of the thyroid gland were investigated in the euryhaline starry flounder, Platichthys stellatus. Using a melting-point technique, it was established that flounder could regulate body fluid concentration independently of widely divergent environmental salinities. Small flounder experienced more rapid disturbances of body fluid concentration than large flounder after abrupt salinity alterations.The standard metabolic rate of flounder adapted to fresh water was consistently and significantly less than that of marine flounder. In supernormal salinities standard metabolic rate was significantly greater than in normal sea water. These findings agree with the theory that energy demands for active electrolyte transport are greater in sea water than fresh water.Thyroid activity was studied in flounder adapted to fresh water and salt water. Percentage uptake of radioiodine by the thyroid was shown to be an insensitive and inaccurate criterion for evaluating thyroid activity in different salinities because removal rates of radioiodine from the body and blood differed between fresh water and marine flounder. Using thyroid clearance of radioiodine from the blood as a measure of activity, salt-water flounder were shown to have much greater thyroid clearance rates and, hence, more active thyroid glands than flounder adapted to fresh water. The greater activity of the thyroid of marine flounder correlates with greater oxygen demands in sea water and suggests a direct or adjunctive osmoregulatory role of the thyroid gland of fish.

Abstract:We provide the first inventory of members of orders Actiniaria (sea anemones sensu stricto) and Ceriantharia (tube anemones) from the Galápagos Islands. Based on observations and collections at 48 localities throughout the archipelago that span nearly a decade, we report on eight species of actiniarians (representing families Actiniidae, Actinostolidae, Aiptasiidae, Hormathiidae, and Isophelliidae) and two of cerianthids (in families Arachnactidae and Botrucnidiferidae). We include live photographs and diagnostic features of the animals, as well as a key and map of their occurrence in the Galápagos. Two actiniarians and one cerianthid are resolved only to genus level; of those identified to species, three of the actiniarians and one of the cerianthids have an eastern Pacific distribution, one actiniarian appears to be endemic to the Galápagos Islands, and two actiniarians are broadly distributed in the Indo-West Pacific.