Coral community decline at Bonaire, Southern Caribbean

We assessed the status of coral reef benthic communities at Bonaire, Netherlands Antilles, in December 2008 and January 2009 through ∼5 km of photo transects taken at depths of 5, 10, and 20 m at 14 locations around the island. Univariate and multivariate analyses detected significant variation in benthic communities among depths and locations, as well as between leeward and windward sides of the island. Mean percentage cover of scleractinian corals ranged between 0.2% and 43.6% at the study sites and tended to be lowest at 5-m depth. The survey recorded 40 scleractinian coral species from 19 genera, within 10 families. Faviidae were by far the most abundant scleractinian family at all depths (predominantly Montastraea spp.), followed by Agariciidae at 20 and 10 m, and by Astrocoeniidae at 5-m depth. Macroalgal cover exceeded scleractinian coral cover at nearly all sites, averaging 34.9% (all samples pooled), compared with a pooled mean coral cover of 15.4%. Windward reefs were characterized by prolific growth of the brown algae Sargassum spp., and leeward reefs by growth of turf algae, Dictyota spp., Trichogloeopsis pedicellata (Howe) I. A. Abbott & Doty, and Lobophora variegata (Lamouroux) Womersley ex Oliveira. Damage from recent hurricanes was evident from the presence of toppled and fragmented corals, the movement of sand, and exposure of cemented Acropora cervicornis (Lamarck, 1816) rubble on the shallow reef platform. The combination of algal dominance and low to moderate coral cover are symptomatic of partly degraded reef systems, particularly as they coincide with elevated nutrients and reduced herbivory

Context-free pairs of groups I: Context-free pairs and graphs

Let $G$ be a finitely generated group, $A$ a finite set of generators and $K$ a subgroup of $G$. We call the pair $(G,K)$ context-free if the set of all words over $A$ that reduce in $G$ to an element of $K$ is a context-free language. When $K$ is trivial, $G$ itself is called context-free; context-free groups have been classified more than 20 years ago in celebrated work of Muller and Schupp as the virtually free groups. Here, we derive some basic properties of such group pairs. Context-freeness is independent of the choice of the generating set. It is preserved under finite index modifications of $G$ and finite index enlargements of $K$. If $G$ is virtually free and $K$ is finitely generated then $(G,K)$ is context-free. A basic tool is the following: $(G,K)$ is context-free if and only if the Schreier graph of $(G,K)$ with respect to $A$ is a context-free graph

Groups, Graphs, Languages, Automata, Games and Second-order Monadic Logic

In this paper we survey some surprising connections between group theory, the theory of automata and formal languages, the theory of ends, infinite games of perfect information, and monadic second-order logic

Reflection of ionizing oblique shockwaves

The difficulties encountered in obtaining a solution for the regular reflection of an oblique ionizing shock wave at a wall are discussed. In general it was not possible to obtain the entire solution for the shock pattern from one dimensional flow considerations. However, in the flow region relatively far removed from the wall, a free stream region, a solution may be obtained which will give both the equilibrium and nonequilibrium fluid properties behind the incident and reflected shocks as well as the reflected wave angle. It is also shown that for the case where reaction thicknesses may be considered negligible this will be the complete solution. In order to obtain a solution for the flow across a shock wave, the conservation equations of mass, energy, and momentum are solved simultaneously with the equation of state and an expression for the ionization reaction rate. Due to the nature of the equations only a numerical solution was possible, therefore, the method is demonstrated for a particular set of initial conditions

Reduced salinity decreases the fertilization success and larval survival of two scleractinian coral species

Successful reproduction by scleractinian corals is essential for the maintenance of populations that form the foundation of coral reef ecosystems. Laboratory experiments were done to determine the effects of reduced salinity on the fertilization success and larval survival of two coral species, Platygyra daedalea and Acropora millepora, from the Great Barrier Reef, Australia. Fertilization rates of P. daedalea and A. millepora were significantly reduced at 25.8 psu and 33.1 psu, respectively, and completed blocked at 18.4 psu for A. millepora. The estimated larval survival times were similar from 36.8 to 25.8 psu (P. daedalea 291–312 h, A. millepora 207–264 h), whereas the 18.4 psu treatment resulted in estimates of 153 h and 24 h for P. daedalea and A. millepora, respectively. These results demonstrate that reduced salinity is detrimental to the reproductive success of these corals, and if salinity is lowered by natural or anthropogenic sources during spawning, this would lead to decreased reproductive success and recruitment on reefs

Site-specific female-biased sex ratio of humpback whales during a stopover early in the southern migration

Previous research on humpback whales (Megaptera novaeangliae (Borowski, 1781)), in both the Northern and Southern Hemispheres, has reported site-specific male-biased sex ratios in breeding grounds and along migratory corridors. However, one recent Southern Hemisphere study reported a female-biased sex ratio in a feeding area within a coastal migratory corridor, indicating that females may preferentially occupy some habitats. We investigated the classes and relative seasonal timing of humpback whales using Hervey Bay as a stopover early in the southern migration. Modeling and analyzes were undertaken using data from resighting histories of 361 individually identified whales between 1992 and 2009. The data consisted of 2,131 sightings categorized by either sex, age, reproductive or maturational status. A female-biased sex ratio of 2.94:1 indicates that Hervey Bay is a preferential stopover for females. The data revealed that the bay is important for mature females who co-occur with immature males and females during August. While during September and October mothers with calves accompanied by a few escorts dominate the Bay. Immature males and females socialize with mature females during August and September. The data support the hypothesis that habitat preferences and differential migration of females and males provides a plausible explanation for site-specific sex-bias in breeding grounds, migratory stopovers and along migratory corridors.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author