occasionally climb mangrove prop roots. Field predation tethering experiments found a 
differential risk of predation among microhabitats and strong tidal and seasonal 
differences in predation rates. In field experiments that tested tolerance to exposure in 
various microhabitats species exhibited different responses to temperature and 
relative humidity conditions in each microhabitat. The unique physiognomy and 
characteristics of mangroves provide a habitat that ameliorates environmental 
conditions and provides varied structural refuge from predation for crabs. The 
differential physiological suitability of refuges and risk of predation among 
microhabitats means that crabs must balance the constraints of physiological 
tolerances and the avoidance of predation in a system that has a seasonally variable 
risk of predation and environmental conditions. This study took place from 1982 
through 1984. 
1982 - 1984 
Wilson, K. A. (1985) Physical and biological interactions that influence habitat use of 
mangrove crabs. Ph. D. Dissertation, University of Pennsylvania, Philadelphia, PA. 167 pp. 
[NO COPY OF PAPER AVAILABLE. ABSTRACT FROM SCHMIDT (1991).] This study 
examines the relative importance of biological and physical factors in the microhabitat 
use and distribution of four species of crabs in mangrove forests in south Florida 
including Florida Bay. Three aspects were investigated: (1) Estimation of risk of 
predation among microhabitats in the mangrove; (2) Evaluations of competitive 
interactions for refuges; and (3) Definition of suitable physiological microhabitats and 
measurements of responses to exposure in microhabitats in the field. The four species 
of mangrove crabs, Aratus pisonii, Eurytium limosum, Sesarma curacaoense, and Uca 
thayeri broadly overlap in habitat use and share periodic shifts in microhabitat 
locations. Field experiments show a differential risk of predation among microhabitats 
by tide levels and show that a change in predation intensity and predator type results in 
strong tidal and seasonal components of refuges. Crabs must balance the constraints of 
physiological tolerances with the avoidance of predation. No single physiological factor 
can be labeled as the cause of distributional patterns. 
1982 - 1986 
Parsons, G. R. (1993) Geographic variation in reproduction between two populations of the 
bonnethead shark, Sphyrna tiburo. Environ. Biol. Fishes. 38(1-3):25-35. 
A study of two populations of the bonnethead shark, Sphyrna tiburo, was conducted in 
Florida Bay and Tampa Bay, Florida from September 1982 to December 1986. The 
maintenance of sharks in captivity at the Marine Science and Conservation Center in the 
Florida Keys, and the collection of sharks from widely separated geographical areas 
allowed the examination of latitudinal variation in reproduction. Several reproductive 
parameters were found to differ: (1) size at maturation, (2) age at maturation, (3) 
time of fertilization, (4) rate of embryonic development, (5) size at birth, (6) the 
energetic investment in producing offspring, (7) gestation period, and (8) the incidence 
of infertility. Average litter size and maximum age of females was not different 
between the two populations. These contrasting life history parameters are not easily 
explained. Food limitation and seasonal differences between the two areas are 
considered as factors controlling reproduction in these populations. It is noteworthy 
that the average size of adult females in Tampa Bay is significantly greater than that of 
Florida Keys sharks. This size difference may be important in explaining the observed 
differences in reproduction. 
1982 - 1986 
Parsons, G. R. (1993) Age determination and growth of the bonnethead shark Sphyrna 
tiburo: A comparison of two populations. Mar. Biol. (Berlin), 117 (1):23-31. 
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