Showing papers by "Hector M. Guzman published in 2000"

Reef coral reproduction in the eastern Pacific: Costa Rica, Panamá and Galápagos Islands (Ecuador). IV. Agariciidae, recruitment and recovery of Pavona varians and Pavona sp.a

Abstract: The reproductive ecology of two eastern Pacific zooxanthellate coral species was examined as part of a continuing series of studies relating bleaching/mortality events caused by the El Nino–Southern Oscillation disturbance, and is described for study sites in Costa Rica, Panama, and the Galapagos Islands (Ecuador). This study deals with the sibling agariciid species Pavona varians and Pavona sp.a over a 13 yr period (1985 to 1997). Both Pavona species are broadcast-spawners with some gonochoric, but mostly sequential hermaphroditic colonies. Minimum colony sizes (and ages) at first reproduction were 5 cm (5 yr) and 3 cm (2 to 3 yr), respectively, in P. varians and Pavona sp.a. In the Panama and Galapagos populations, gonochoric colonies spawn eggs or sperm at least monthly. Six fecundity attributes were not significantly different in the two species, but the eggs of P. varians are white to beige and positively buoyant, and those of Pavona sp.a are dark green and neutrally to negatively buoyant. Eggs of both species lack zooxanthellae. Both species are reproductively active year-round, with maximum activity in the dry season in the nonupwelling Gulf of Chiriqui, and in the wet season in the upwelling Gulf of Panama. Spawning is predominantly during full moon, and possibly also at new moon at most study sites. Spawning in P. varians and Pavona sp.a is 12 h out of phase, with the former species spawning ∼1 h before sunrise and the latter about 1 h after sunset. The fecundity of Pavona spp. at Cano and the Galapagos Islands was much greater (19 900 to 27 900 eggs cm−2 yr−1) than at all Panama sites (14 800 to 19 800 eggs cm−2 yr−1). Intraspecific crosses in both species resulted in swimming planula larvae after 25 to 36 h. Recruitment of P. varians was highest in Panama, moderate in Costa Rica, and nil in the Galapagos Islands, matching, respectively, the contributions of P. varians to the pre-1982/1983 El Nino coral-population abundances in these areas. Recruitment success of P. varians at Uva Island was significantly related to maximum monthly positive sea surface-temperature (SST) anomalies that occurred in the year preceding recruitment over the period 1982 to 1996; recruitment failed when SST anomalies exceeded 1.6 to 1.9 C° during the severe ENSO events of 1982/1983 and 1997/1998.

Control of transient disruptions in cell membranes by acoustic cavitation at 500 kHz

Abstract: Ultrasound‐mediated drug targeting and delivery is a nonchemical, nonviral, and noninvasive alternative for the transport of drugs and genes into cells Delivery of molecules is performed by using ultrasound to disrupt cell membranes by a mechanism believed to involve cavitation To develop efficient drug and gene delivery methods based on ultrasound‐mediated disruption of cell membranes, it is critical to understand the dependence of molecular uptake and cell viability on the acoustic parameters that govern the complex cavitation activity This study examined these effects in cell suspensions using two model cell lines (aortic smooth muscle and DU145 prostate cancer cells) and two model compounds (calcein and bovine serum albumin) at 500‐kHz ultrasound in the presence of Optison contrast agent The acoustic parameters varied in this study were: pressure, pulse length, and total exposure time Cell membrane disruption increased with both pressure and exposure time, but was not influenced by pulse length over the range examined A window of useful operating conditions was determined for delivering large numbers of molecules into viable cells Correlations between membrane disruption and the acoustic spectra of cavitation were observed to support the proposed cavitation mechanism [Work supported by Whitaker Foundation, NIH, and NSF]