Bioerosion and sediment ingestion by the Caribbean parrotfish Scarus vetula and Sparisoma viride:Implications of fish size, feeding mode and habitat use

Erosion rates and sources of sediment ingested were quantified for the 2 most abundant parrotfish species on a leeward fringing reef of Bonaire, Netherlands Antilles: Scarus vetula and Sparisoma viride. Direct estimates of erosion by different size classes were obtained from daily feeding rates and grazing scar frequency, scar volume and substrate density. Foraging preference and distribution of fish on the reef were used to examine patterns of bioerosion at 2 spatial scales: reef zones and individual substrates used for grazing. Sediment mass ingested by fish provided an independent check on erosion rates, and was partitioned according to source. S. vetula, employing a scraping feeding mode, removed less material from grazed substrates than similar sized S. viride, which forages by excavating the substrate. Erosion rates increased strongly with fish size in both species. The (indigestible) carbonate derived from epilithic algae accounted for all sediment ingested by juvenile fish. In adult fish, the proportion of freshly eroded carbonate substrate ingested increased with fish size. The distribution of adults of these large scarids over different reef zones determines the rate of bioerosion on a large spatial scale. The highest bioerosional rates occur on the shallow reef (ca 7 kg m(-2) yr(-1)), and they decrease with depth. Parrotfish foraging preferences, and the effects of food type and skeletal density of substrates on the size of the grazing scars, cause large differences in bioerosional rates on a small spatial scale. The highest rates of bioerosion occur on substrates infested with boring algae and of low skeletal density, while high-density substrates and substrates covered with crustose corallines undergo lower rates. Living coral is rarely eaten by scarids, and largely escapes erosion by grazing

Estimating oxygen uptake rate from ventilation frequency in the reef fish Sparisoma viride

Spontaneous fluctuations in oxygen consumption (R) and ventilation frequency (VF) of stoplight parrotfish Sparisoma viride were measured simultaneously in small now-through respirometers to establish the relationship between these variables. Respiration of 11 fish of varying size (14 to 1052 g) and life phase (juveniles, initial and terminal phase adults) was measured at naturally fluctuating temperatures. A large proportion of the variance in respiration could be explained by the equation: R = 0.00035 x VF1.369 x W-1.118 (r(2) = 93.1%, n = 380, p <0.001), with R in mg O-2 h(-1), VF in beats min(-1) and fish weight (W) in g. Oxygen concentration in the respiration chambers could drop below natural levels. Comparison of the R-VF relationships at different concentrations showed that correction for [O-2] hardly affected the predictions. No important differences were found between the 3 life phases, and inter-individual differences were no larger than the variation between replicate measurements. We conclude that the equation above appears quite robust and can therefore be used to predict the metabolic rate of undisturbed fish in their natural environment

A simple field method for stereo-photographic length measurement of free-swimming fish:Merits and constraints

A simple field method to correct for bias in stereo-photographic underwater measurements is presented and its usefulness to improve the accuracy of length estimates of free-swimming fish is tested. The calibration is based on the inclusion of stereo exposures of a slate of known dimensions at the beginning and end of each measuring session. and it allows correction for non-parallel optical axes, spherical aberration of the lenses, and for other sources of bias that may vary between sessions. A precision of +/-3% for replicate length measurements of a 30 cm slate is obtained at distances between 0.7 and 2.0 m. This compares well with reported values that are obtained with more sophisticated (laboratory) methods. However, application of this calibration does not significantly improve the accuracy of stereo measurements of the length of free-swimming fish (+/-2.5 cm or 7-11% of actual fish length), The limitations are caused by difficulties in recognizing identical extreme points at the body of fish that are photographed under field conditions. By averaging three or more replicate measurements the accuracy is improved to +/-1 cm (2.7-4.5%). We conclude that effort should be aimed at increasing sample size, rather than at improving equipment and correction procedures, when measuring free-swimming fish in their natural habitat

Contribution of viscous shear to friction in cold rolling of low-carbon steel

This work shows that for temperatures, pressures and shear rates that are common in cold rolling of low-carbon steel, viscous shear stress significantly contributes to the total friction force. Experiments were carried out to validate the theory on lubricant film formation and elasto-hydrodynamic lubrication, both with laboratory scale tribometers and a semi-industrial pilot mill facility. These experiments showed that at high shear rates, that are common in cold rolling, the lubricant does not behave as a Newtonian fluid anymore; moreover the viscosity at high pressure cannot accurately be described by a simple exponential law. With the correct relations implemented in a rolling model, both rolling force and forward slip are predicted with good accuracy for hydrodynamically lubricated cold rolling experiments.</p

The social and mating system of the herbivorous reef fish Sparisoma viride:One-male versus multi-male groups

We present a detailed description of the social and mating system of the protogynous reef herbivore Sparisoma viride at the fringing reef of Bonaire (Netherlands Antilles). Initial phase (IP) fish and terminal phase (TP) males occur either in one- or in multi-male groups, which are compared quantitatively with respect to the use of space, size composition, social interactions and sexual activity. One-male groups consist of one TP male plus 1-14 IP females, whereas in multi-male groups up to 14 TP males and about twice as many LP fish share a common home range. The two social units further show marked differences in vertical distribution (one-male groups are restricted to depths between 3 and 22 m, multi-male groups mainly residing <3 m), size composition (a larger proportion of small adults live in multi-male groups), size and stability of the range (larger in one-male groups) and sexual activity (daily spawning of one-male group members inside their normal home range; no activity in multi-male groups on the shallow reef). Sexual activity occurred daily, throughout the year, with no evidence for tidal tracking or major seasonal or lunar patterns. The one-male groups constitute less than 20% of the adult stock but control up to 77% of the inhabited reef. As a result they have access to higher-yield food patches and to suitable spawning sites inside their home range. Although members of both units appear to defend their common home range against intruding conspecifics, the degree of territoriality is clearly higher in one-male groups. We discuss the relative importance of food, shelter, mates and mating sites as defended resources and some life history implications. The complex social and mating system of S. viride shows much resemblance to that of another Caribbean scarid, Scarus iserti. This complexity seems to reflect the capacity of individuals to flexibly adapt their feeding, mating and life history styles to an unpredictable environment. We propose that S. viride is a good study animal to test adaptive explanations for its territorial organization and complex life history patterns