Benjamin C. Victor

Planktonic larval duration of one hundred species of Pacific and Atlantic damselfishes (Pomacentridae)

The plankton larval duration for 100 species of Pacific and Atlantic damselfishes was estimated from daily growth increments on the otolith of juvenile fish collected at various localities between July 1987 and September 1988. For newly-settled fishes, larval duration was determined by counting the entire number of increments present on the otolith, while for older juveniles estimates were made by counting the number of increments between the center of the otolith and a mark corresponding to settlement. We document the development of otolith formation during the period when eggs are incubated on the reef and show that daily increments are only accreted after larvae hatch and enter the planktonic phase. The planktonic larval duration for damselfish is shorter and less variable, both between and within species, compared to other groups of reef fishes such as wrasses and surgeonfishes. Larval duration ranged from 12 to 39 d. Average duration between species ranged from 13.1 to 35.2 d. The time spent in the plankton was not significantly correlated with geographic distribution when evaluated among species, however, genera with confined regional distribution have a shorter mean larval life than do widely distributed genera. Size at settlement was positively correlated with time spent in the plankton among species, but a significant correlation between these variables was only evident within one of ten species. The low variance in planktonic larval duration within species indicates that most damselfish are unable to delay metamorphosis following competency. This inability to postpone settlement limits the potential for dispersal, especially when dispersal time between suitable habitats is greater than about 30 d.

Duration of the planktonic larval stage of one hundred species of Pacific and Atlantic wrasses (family Labridae)

The planktonic larval durations of a preliminary sample of one hundred species of wrasses from both the Pacific and Atlantic Oceans were estimated with the use of the daily otolith-increment aging-technique. Larval durations were determined by counting the number of daily increments between the center of the otolith and the mark corresponding to settlement. The duration of the planktonic larval phase of wrasses appears to be extremely variable between species, ranging from 15 d in Diproctacanthus xanthurus to 121 d in a specimen of Thalassoma ballieui. Larval durations within species were also variable, especially in species with relatively long durations. Congeners tended to have similar larval durations and similar otolith-increment characteristics. Hawaiian and Eastern Pacific species had longer larval durations than their Caribbean or Western Pacific congeners. Similarly, Hawaiian populations had significantly longer larval durations than their Western Pacific conspecifics. The implications of these findings for biogeographical studies are discussed.

Daily otolith increments and recruitment in two coral-reef wrasses, Thalassoma bifasciatum and Halichoeres bivittatus

Increments on the otoliths of two common coral reef fishes, the bluehead wrasse Thalassoma bifasciatum and the slippery dick Halichoeres bivittatus, were demonstrated by mark-recapture experiments to be daily. Otoliths were marked in two ways; by depriving fish of light, food, and temperature cycles and also by supplemental feeding in the field. Both experiments were performed in late 1980 in the San Blas Islands of Panamá. A mark corresponding to settlement of the planktonic larva onto the reef was found on the otoliths of the bluehead wrasse. This settlement mark was used to calculate the dates of settlement of a collection of juveniles of this species taken from a patch reef in the San Blas Islands of Panamá in 1981. Settlement occurred in short and irregular bursts. The number of daily increments before the settlement mark indicates a planktonic larval life of 40 to 72 d.

El Niño mass coral mortality: a test of resource limitation in a coral reef damselfish population

SummaryThe mass mortality of reef corals in the eastern Pacific as a result of the 1982–1983 El Niño oceanographic anomaly permitted the first large scale test of resource limitation for a coral reef fish. Population densities of territorial herbivorous damselfish did not respond to the massive regional increase in space available for the cultivation of algal food following the El Niño event. The proportion of juveniles in the population was low and new recruits were uncommon, indicating that recruitment rates rather than resource supply probably control the abundance of this coral reef damselfish.

Growth, dispersal, and identification of planktonic labrid and pomacentrid reef-fish larvae in the eastern Pacific Ocean

Planktonic larvae of six genera of labrid and pomacentrid reef fishes were captured in march 1985 in the eastern Pacific Ocean several hundred kilometers from the nearest reefs. The larvae were identified to genus by fin-ray counts as well as by comparison of their larval otolith morphology with that of known species. The larval otolith morphologies of known species were derived from measurements of the larval otolith embedded within the otoliths of settled juveniles (as delineated by the daily otolith-increment marks corresponding to the late larval period). The body morphology and melanophore patterns of the eastern Pacific labird and pomacentrid larvae closely matched those of congeneric larvae described from other oceans. Growth rates of larvae less than about 70 d old were similar between taxa (from 0.13 to 0.19 mm d-1). After about 70 d in the plankton, labrid larvae grew much more slowly (0.06 mm d-1 in Xyrichtys sp.). Labrid larvae had long larval durations (up to 131 d in Xyrichtys sp.), while the larval lives of the pomacentrids appeared to be shorter and much less variable. Larvae of many different ages occurred within the same water mass, and young cohorts of larvae appeared continuously over the sampling period. Some larvae were as young as 21 d, indicating that reef-fish larvae are capable of rapid long-distance dispersal (at least 18 km d-1).

Regional differences in duration of the planktonic larval stage of reef fishes in the eastern Pacific Ocean

Regional variation in the duration of the planktonic larval phase of three species of reef fishes, Thalassoma lucasanum (Labridae), Stegastes flavilatus, and Microspathodon dorsalis (Pomacentridae) was investigated between 1982 and 1991 at several sites in the tropical eastern Pacific over a distance of 3500 km, encompassing virtually their entire range of distribution. Durations of the larval phase, determined from counts of daily otolith increments, were significantly different (1.3 to 1.6 x) between sites. Populations of all three species had a consistently shorter larval life at the most northern site, Cabo San Lucas (Mexico) compared to Panamá and the offshore islands of Galápagos and Cocos. Analyses of otolith increment width over the precompetent period revealed that this disparity in larval duration primarily reflected differences in larval growth rates: faster growing fish spent less time in the plankton. In T. lucasanum, some of the variation in larval duration between Panamá and offshore sites (Galápagos Islands and Cocos Island) may be accounted for by a higher frequency of individuals delaying metamorphosis at the offshore sites. These data indicate that conditions in the planktonic environment are not homogeneous throughout the tropical eastern Pacific and may have a profound effect on aspects of the larval ecology of reef fishes in this region.

VARIATION IN COMPONENTS OF REPRODUCTIVE SUCCESS IN AN UNDERSATURATED POPULATION OF CORAL-REEF DAMSELFISH: A FIELD PERSPECTIVE

The main issue we have attempted to address in this paper is whether resource-based variation in reproductive success (excluding competition for mates through sexual selection) among individuals in a population necessarily arises only when populations approach their carrying capacity. We describe conditions under which differential reproductive success can develop within and between local populations even when available resources do not limit overall population size. We contend that if resource quality varies spatially and predictably, as is probably the case for most natural systems, then significant variation in the reproductive success of individuals can arise through behavioral mechanisms (territoriality) or through physical isolation. Behavioral mechanisms could result in selection for attributes to enhance competitive ability; isolation should promote habitat selection and concomitant specializations. In support of our argument, a study of a territorial coral-reef damselfish, Stegastes acapulcoensis, in Panama shows that significant habitat-related differences in the components of reproductive success (body size and female gonad size) can occur in a population limited by recruitment. In areas cleared of damselfish, conspecific adults rapidly and almost completely replaced damselfish at shallow-water sites, where components of reproductive success are high. In contrast, at deep-water sites, where these parameters are lower, few or no replacement individuals of any age moved in after removals. We interpret these results as evidence for the existence of intraspecific competition in a population whose size is not limited by resources.

DNA Sequence data

UZH researchers have discovered a previously unknown way in which proteins interact with one another and cells organize themselves. [11] Dr Martin Sweatman from the University of Edinburghs School of Engineering has discovered a simple physical principle that might explain how life started on Earth. [10] Nearly 75 years ago, Nobel Prize-winning physicist Erwin Schrödinger wondered if the mysterious world of quantum mechanics played a role in biology. A recent finding by Northwestern Universitys Prem Kumar adds further evidence that the answer might be yes. [9] A UNSW Australia-led team of researchers has discovered how algae that survive in very low levels of light are able to switch on and off a weird quantum phenomenon that occurs during photosynthesis. [8]