Dissertation Abstract
Population ecology of bleaching-stressed Amphistegina gibbosa in the Florida Keys (1991-1999): Influence of solar radiation on reef-dwelling foraminifera
Williams, Dana E 2002
, University of South Florida163 pp.
Bleaching (symbiont loss) was discovered in populations of Amphistegina gibbosa on Florida Keys (USA) reefs in late June 1991. By November, abundance had declined by 95%, and remained low through summer 1992. Juveniles comprised less than 10% of the population indicating widespread recruitment failure. Between 1992 and 1996, populations were monitored monthly at Conch Reef. Bleaching symptoms disproportionately affected larger size classes. Each year, bleaching increased in early spring, peaked in mid-summer, and then declined to winter minima. Between 1992 and 1996, summer bleaching declined from 82% to 43% of the population, juveniles increased steadily and population densities partly recovered.
From 1994 to 1999, populations at Conch and Tennessee reefs were monitored quarterly; Conch Reef populations were consistently more impacted. Annual variations in stress impact on populations indicated that 1994, 1996 and 1998 were particularly stressful years: more individuals displayed bleaching, individuals were larger and recruitment was reduced. During 1997 and 1999 fewer individuals displayed bleaching, and higher recruitment resulted in higher abundances than in stressed years. Bleaching was positively correlated with average diameter and negatively correlated with juvenile abundances, indicating suppressed asexual reproduction in stressed individuals.
Laboratory experiments examined exposure to biologically effective ultraviolet radiation (UVB: 290-320nm), and compared high and low photosynthetically active radiation (PAR) photon flux densities (PFD) using blue and white PAR sources. Growth rates were light saturated at 8micromol/m2s1, and were not influenced by UVB=0.0162W/m2, but were inhibited by UVB at 0.105W/m2. Bleaching was higher with blue PAR than white PAR, increased with PAR PFD, and exposure to UVB. These experiments indicate that bleaching in Amphistegina can be influenced by environmental factors that influence either the spectral quality or the intensity of solar radiation.
Ecoepidemiological criteria were used to compare trends in bleaching stress and environmental parameters. Solar radiation was a coherent first order determinant of bleaching, however, the shorter wavelengths of solar radiation are more coherent as determinants of bleaching. The summer 1991 onset of bleaching is consistent with increased UVB:PAR resulting from global ozone depletion following the explosive eruptions of Mt. Pinatubo in June 1991, though possible chemical photosensitization is also suspected.
From 1994 to 1999, populations at Conch and Tennessee reefs were monitored quarterly; Conch Reef populations were consistently more impacted. Annual variations in stress impact on populations indicated that 1994, 1996 and 1998 were particularly stressful years: more individuals displayed bleaching, individuals were larger and recruitment was reduced. During 1997 and 1999 fewer individuals displayed bleaching, and higher recruitment resulted in higher abundances than in stressed years. Bleaching was positively correlated with average diameter and negatively correlated with juvenile abundances, indicating suppressed asexual reproduction in stressed individuals.
Laboratory experiments examined exposure to biologically effective ultraviolet radiation (UVB: 290-320nm), and compared high and low photosynthetically active radiation (PAR) photon flux densities (PFD) using blue and white PAR sources. Growth rates were light saturated at 8micromol/m2s1, and were not influenced by UVB=0.0162W/m2, but were inhibited by UVB at 0.105W/m2. Bleaching was higher with blue PAR than white PAR, increased with PAR PFD, and exposure to UVB. These experiments indicate that bleaching in Amphistegina can be influenced by environmental factors that influence either the spectral quality or the intensity of solar radiation.
Ecoepidemiological criteria were used to compare trends in bleaching stress and environmental parameters. Solar radiation was a coherent first order determinant of bleaching, however, the shorter wavelengths of solar radiation are more coherent as determinants of bleaching. The summer 1991 onset of bleaching is consistent with increased UVB:PAR resulting from global ozone depletion following the explosive eruptions of Mt. Pinatubo in June 1991, though possible chemical photosensitization is also suspected.