Factors limiting distribution and activity patterns of the soldier crab Dotilla myctiroides in Phuket, South Thailand

This study was carried out between January and March 1995 on the intertidal sand flats of Tang Khen Bay, Phuket, South Thailand, where the soldier crab Dotilla myctiroides (H. Milne-Edwards) occurs in densities of up to 120 m⁻². In this bay, long, ribbon-like sand waves (wavelength 40 m, height 0.4 m) are interspersed with shallow pools, running approximately parallel to the shore. During daylight low-tides, exposure of the sand waves is followed 15 to 20 min later by the emergence of the crabs which have been buried under the sediment surface during high tide. Their subsequent burrowing and feeding activity results in the production of large numbers of sand pellets on the sediment surface. Most crabs retreat down their burrows, and some also plug the burrow entrance, prior to being covered by the incoming tide. The crab burrows have a distinct distribution on the sand waves. Burrows are most dense at the top of each sand wave, and a band of unburrowed sediment adjoins the adjacent tidal pools. Crabs are most abundant between mean high-water neap-tide level and mean low-water neap-tide level, where the median particle size of the surface sediment is ∼2 . Measurements of water-table depth below the sand waves and the exposure time of the sediment indicated that, where sediment size is suitable, the main factor controlling crab distribution is the duration of daytime exposure. This observation is in contrast to those of many previous studies, which have suggested that water-table height and sediment drainage are the main factors controlling the distribution of D. myctiroides. Received: 14 January 1998 / Accepted: 6 May 1999     

Early life history of tropical Anguilla leptocephali in the western Pacific Ocean

In order to examine the early life-history characteristics of tropical eels, otolith microstructure and microchemistry were examined in leptocephali of Anguilla bicolor pacifica (27.6-54.1 mm TL, n=20) and A. marmorata (22.0-47.3 mm TL, n=8) collected during a cruise in the western Pacific. A. bicolor pacifica occurred between 10°N and 15°N in the west and between 5°S and 10°N farther to the east. A. marmorata also occurred in two different latitudinal ranges in the Northern (15-16°N) and Southern Hemispheres (3-15°S) of the western Pacific. The increment widths in the otoliths of these leptocephali increased between the hatch check (0 days) and about an age of 30 days in both species, and then gradually decreased toward the otolith edge. Otolith Sr:Ca ratios showed a gradual increase from the otolith center to the edge. The ages of A. bicolor pacifica and A. marmorata leptocephali ranged from 40 to 128 days and from 38 to 99 days, respectively. Growth rates of A. bicolor pacifica and A. marmorata leptocephali ranged from 0.33 to 0.71 mm day^-1 and from 0.45 to 0.63 mm day^-1, respectively. These leptocephali had estimated growth rates that were spread out throughout most of the reported range of growth rates of the leptocephali of the temperate species, the Japanese eel and the Atlantic eels. Differences in the spatial distribution in relation to current systems, and the age and size compositions of the leptocephali of A. bicolor pacifica and A. marmorata suggested different spawning locations for these two species.     

Key Features and Context‐Dependence of Fishery‐Induced Trophic Cascades

Abstract: Trophic cascades triggered by fishing have profound implications for marine ecosystems and the socioeconomic systems that depend on them. With the number of reported cases quickly growing, key features and commonalities have emerged. Fishery‐induced trophic cascades often display differential response times and nonlinear trajectories among trophic levels and can be accompanied by shifts in alternative states. Furthermore, their magnitude appears to be context dependent, varying as a function of species diversity, regional oceanography, local physical disturbance, habitat complexity, and the nature of the fishery itself. To conserve and manage exploited marine ecosystems, there is a pressing need for an improved understanding of the conditions that promote or inhibit the cascading consequences of fishing. Future research should investigate how the trophic effects of fishing interact with other human disturbances, identify strongly interacting species and ecosystem features that confer resilience to exploitation, determine ranges of predator depletion that elicit trophic cascades, pinpoint antecedents that signal ecosystem state shifts, and quantify variation in trophic rates across oceanographic conditions. This information will advance predictive models designed to forecast the trophic effects of fishing and will allow managers to better anticipate and avoid fishery‐induced trophic cascades.     

Biogeography of soil nematodes

Biogeography is the study of distributions of organisms, plus an attempt to explain the distributions. Two approaches to explanation of biogeographic patterns may be termed ecological biogeography and historical biogeography. Most nematologists have taken the ecological approach, with a goal of determining why a particular species is restricted to certain areas, and not present in nearby areas. Historical biogeography is based on the premise that present-day patterns of taxa result largely from the history of the taxa and of the areas of the earth in which they have lived. Nematologists generally adhere to the classic view of dispersal in which a center of origin is postulated and long-range dispersal over barriers is invoked. The dispersal mechanism is often assumed to be man himself. Challenges to this approach exist in the form of methods which infer the biogeographic history from phylogeny. Vicariance biogeographers postulate fragmentation of widespread ancestral biotas, resulting from geological, climatic or other disjunctions, and further allopatric speciation among descendant biotas. Distributions amenable to general explanation can be distinguished from those which require unique dispersal events. Biogeography of soil nematodes is hampered by present limitations in systematics, including our inability to determine species limits with certainty.