34 research outputs found
Connectivity and systemic resilience of the Great Barrier Reef
Australiaâs iconic Great Barrier Reef (GBR) continues to suffer from repeated impacts of cyclones, coral bleaching, and outbreaks of the coral-eating crown-of-thorns starfish (COTS), losing much of its coral cover in the process. This raises the question of the ecosystemâs systemic resilience and its ability to rebound after large-scale population loss. Here, we reveal that around 100 reefs of the GBR, or around 3%, have the ideal properties to facilitate recovery of disturbed areas, thereby imparting a level of systemic resilience and aiding its continued recovery. These reefs (1) are highly connected by ocean currents to the wider reef network, (2) have a relatively low risk of exposure to disturbances so that they are likely to provide replenishment when other reefs are depleted, and (3) have an ability to promote recovery of desirable species but are unlikely to either experience or spread COTS outbreaks. The great replenishment potential of these ârobust source reefsâ, which may supply 47% of the ecosystem in a single dispersal event, emerges from the interaction between oceanographic conditions and geographic location, a process that is likely to be repeated in other reef systems. Such natural resilience of reef systems will become increasingly important as the frequency of disturbances accelerates under climate change
Caribbean-Wide, Long-Term Study of Seagrass Beds Reveals Local Variations, Shifts in Community Structure and Occasional Collapse
The CARICOMP monitoring network gathered standardized data from 52 seagrass sampling stations at 22 sites (mostly Thalassia testudinum-dominated beds in reef systems) across the Wider Caribbean twice a year over the period 1993 to 2007 (and in some cases up to 2012). Wide variations in community total biomass (285 to >2000 g dry mâ2) and annual foliar productivity of the dominant seagrass T. testudinum (2000 g dry mâ2) were found among sites. Solar-cycle related intra-annual variations in T. testudinum leaf productivity were detected at latitudes > 16°N. Hurricanes had little to no long-term effects on these well-developed seagrass communities, except for 1 station, where the vegetation was lost by burial below âŒ1 m sand. At two sites (5 stations), the seagrass beds collapsed due to excessive grazing by turtles or sea-urchins (the latter in combination with human impact and storms). The low-cost methods of this regional-scale monitoring program were sufficient to detect long-term shifts in the communities, and fifteen (43%) out of 35 long-term monitoring stations (at 17 sites) showed trends in seagrass communities consistent with expected changes under environmental deterioration.UCR::VicerrectorĂa de InvestigaciĂłn::Unidades de InvestigaciĂłn::Ciencias BĂĄsicas::Centro de InvestigaciĂłn en Ciencias del Mar y LimnologĂa (CIMAR
Fracture Stresses Induced by Rock Splitters
To complement field experimentation in the use of mechanical rock splitters for rapid excavation, an analysis of the stress distribution around a hole was made by means of the Airy stress function for two assumed pressure distributions. These were chosen to simulate the probable pressure distribution caused by a rock splitter, i.e. by two feathers separated by a hydraulically activated wedge. An induced stress factor of 1.0 was obtained for an even function p sin2 ?, and of 1.65 for a Fourier series function. Results show that the design of feathers is a critical factor in determining the magnitude dnd distribution of stresses
Seasonal and spatial heterogeneity of recent sea surface temperature trends in the Caribbean Sea and southeast Gulf of Mexico
Recent changes in ocean temperature have impacted marine ecosystem function globally. Nevertheless, the responses have depended upon the rate of change of temperature and the season when the changes occur, which are spatially variable. A rigorous statistical analysis of sea surface temperature observations over 25 years was used to examine spatial variability in overall and seasonal temperature trends within the wider Caribbean. The basin has experienced high spatial variability in rates of change of temperature. Most of the warming has been due to increases in summer rather than winter temperatures. However, warming was faster in winter in the Loop Current area and the south-eastern Caribbean, where the annual temperature ranges have contracted. Waters off Florida, Cuba and the Bahamas had a tendency towards cooling in winter, increasing the amplitude of annual temperature ranges. These detailed patterns can be used to elucidate ecological responses to climatic change in the region
Five drums at Carchemish: An Unrecognized Iron Age Burial along the Herald's Wall?
The present paper deals with the so-called âHeraldâs Wallâ at Iron Age Carchemish. It is argued that a stone installation at its middle may be the covering of a hitherto unrecognised grave. If this should be the case, it would confer on the wall and the whole ceremonial centre of the ancient City an unsuspected layer of meaning and be an important factor for the understanding of the cult of ancestors in Iron-Age Syro-Anatolia. First, an analysis of the Heraldâs Wall and of the circumstances of its excavation is given (§1). There follows a discussion of the re-use of sculptured slabs and of its consequences for a correct interpretation of the installation in question (§2). Then, a cist grave at the related site of Zincirli is set forth as a comparison (§3). Finally, the evidence for intramural burials and the ancestor cult in Carchemish is called upon (§4)