The 1998 bleaching event and its aftermath on a coral reef in Belize

Widespread thermal anomalies in 1997-1998, due primarily to regional effects of the El Niño-Southern Oscillation and possibly augmented by global warming, caused severe coral bleaching worldwide. Corals in all habitats along the Belizean barrier reef bleached as a result of elevated sea temperatures in the summer and fall of 1998, and in fore-reef habitats of the outer barrier reef and offshore platforms they showed signs of recovery in 1999. In contrast, coral populations on reefs in the central shelf lagoon died off catastrophically. Based on an analysis of reef cores, this was the first bleaching-induced mass coral mortality in the central lagoon in at least the last 3,000 years. Satellite data for the Channel Cay reef complex, the most intensively studied of the lagoonal reefs, revealed a prolonged period of elevated sea-surface temperatures (SSTs) in the late summer and early fall of 1998. From 18 September to 1 October 1998, anomalies around this reef averaged +2.2°C, peaking at 4.0°C above the local HotSpot threshold. In situ temperature records from a nearby site corroborated the observation that the late summer and early fall of 1998 were extraordinarily warm compared to other years. The lettuce coral, Agaricia tenuifolia, which was the dominant occupant of space on reef slopes in the central lagoon, was nearly eradicated at Channel Cay between October 1998 and January 1999. Although the loss of Ag. tenuifolia opened extensive areas of carbonate substrate for colonization, coral cover remained extremely low and coral recruitment was depressed through March 2001. High densities of the sea urchin Echinometra viridis kept the cover of fleshy and filamentous macroalgae to low levels, but the cover of an encrusting sponge, Chondrilla cf. nucula, increased. Further increases in sponge cover will impede the recovery of Ag. tenuifolia and other coral species by decreasing the availability of substrate for recruitment and growth. If coral populations are depressed on a long-term basis, the vertical accretion of skeletal carbonates at Channel Cay will slow or cease over the coming decades, a time during which global-warming scenarios predict accelerated sea-level rise.     

Ist eine intrazelluläre Eisbildung bei Tieren tödlich? Versuche mit Polypen der Gattung Laomedea

Many authors are of the opinion that intracellular freezing causes death of cells. Observations on organisms tolerating intracellular freezing have been regarded not convincing or exceptional. In this investigation, experiments dealing with polyps of the cnidarians Laomedea flexuosa and L. loveni are described. A special experimental procedure made it possible to induce, selectively, extra- and intracellular freezing or extra-cellular freezing alone. Ice crystals could not be observed directly, but darkening of the test individuals is indicative of ice formation in the cell; this darkening (flashing or black-out) always follows ice formation in the surroundings. Intracellular ice formation is endured for a short period of time (Fig. 1). Small differences in freezing temperature exert great influence on survival rates (Fig. 2). These depend also on the duration of exposure to freezing conditions. Freezing resistance is lower after intracellular ice formation; the difference, however, appears to involve quantitative rather than qualitative aspects, although intracellular ice formation could possible destroy protoplasmic structures.     

Catastrophe and the life span of coral reefs

A strong earthquake in the western Caribbean in 2009 had a catastrophic impact on uncemented, unconsolidated coral reefs in the central sector of the shelf lagoon of the Belizean barrier reef. In a set of 21 reef sites that had been observed prior to the earthquake, the benthic assemblages of 10 were eradicated, and one was partially damaged, by avalanching of their slopes. Ecological dynamics that had played out over the previous 23 years, including the mass mortalities of two sequentially dominant coral species and a large increase in the cover of an encrusting sponge, were instantaneously rendered moot in the areas of catastrophic reef-slope failure. Because these prior dynamics also determined the benthic composition and resilience of adjacent sections of reef that remained intact, the history of disturbance prior to the earthquake will strongly influence decadal-scale recovery in the failed areas. Geological analysis of the reef framework yielded a minimum return time of 2000-4000 years for this type of high-amplitude event. Anthropogenic degradation of ecosystems must be viewed against the backdrop of long-period, natural catastrophes, such as the impact of strong earthquakes on uncemented, lagoonal reefs.     

Der einfluß von temperaturänderungen auf enzyme der fischmuskulatur. Versuche mit goldorfen Idus idus

Succinate respiration and various enzyme activities were measured in the white dorsal muscles of golden orfs (goldcoloured race of Idus idus L.) adapted to different temperatures. Some of the values obtained on enzyme activities measured on successive days revealed significant differences in fish adapted to the same temperature. These differences could not be attributed to variations between experimental groups, nor to disturbances caused by the removal of some fish (Figs. 2 and 3). In adaptation experiments, attention must be paid to diurnal fluctuations in enzyme activity; such fluctuations were especially apparent with isocitrate-dehydrogenase. Season can also influence the level of enzyme activity, possibly through changes in day-length. Succinate respiration of golden orfs adapted to 5°C is about 10% higher than in individuals adapted to 20°C (experimental temperature 25°C). Following reverse adaptation from 20° to 5°C (at the rate of 5C^o/h), the values approach, after fluctuations, those of 5°C individuals. After raising or lowering the adaptation temperature at the rate of 5 or 2 C^o/h), fluctuations in several enzymes appeared initially, as in the abrupt transfers reported by Lehmann (1970a); even if significant, these were, however, not always reproducible. Change in temperature causes a limited phase of increased functional lability.