formed in the past several thousand years and that have remained at or below sea 
level, generally have not undergone much consolidation. However, a notable exception 
is found on Yellow Bank, south of New Providence Island in the Bahamas, where 
specimens of consolidated and semi-consolidated grapestone sediment have yielded 
radiocarbon ages of carbonate carbon ranging from 874 to 1792 yrs. The specimens 
were collected where the water is about 10 ft deep, and presumably, any sediment 
accumulating at this depth has been continuously submerged beneath the sea for at least 
the past 4000 yrs. Consolidation appears to be due to cementation by aragonite. 
Determination of carbon isotope ratios reveals that sediment specimens rich in 
aragonite tend to have relatively high 13 C per mil deviation values, whereas specimens 
rich in low-Mg calcite have relatively low 13 C per mil values. The association of high 
13 C per mil values with high proportions of aragonite may reflect the presence of 
inorganically precipitated aragonite that is enriched in 13 C. 
1959 - 1960 
Croker, R. A. (1960) A contribution to the life history of the gray (mangrove) snapper, 
Lutjanus griseus (Linnaeus). M. S. Thesis. University of Miami., Coral Gables, FL. 93 pp. 
Gray snapper are found primarily in inshore tropical and subtropical marine and 
brackish waters on both sides of the Atlantic Ocean. Their center of abundance can be 
considered as Florida, the Gulf of Mexico, the West Indies, and the Bahamas and 
Bermuda Islands. The southern limit of L. griseus is in the waters of Brazil while 
stragglers are reported as far north as Cape Cod, MA. The southern tip of the Florida 
peninsula and extreme southwest coast, comprising Dade, Monroe, Collier, and Lee 
counties coincides with the area of largest gray snapper commercial landings. The 
habitat of this area has a constant feature of mangrove growth and estuarine bays and 
lagoons. Juvenile gray snapper have been collected in shallow grassy areas, or in close 
proximity to mangrove growth where salinities have varied widely. Sub-adult gray 
snapper are abundant in inshore, shallow water over muddy, hard, and rocky bottoms, 
especially in mangrove areas such as estuarine bays and lagoons. The precise habitat 
preferences of mature gray snapper are not known. L. griseus occurs further north in 
North America than any other species of the genus Lutjanus. The gray snapper reported 
in northern waters are usually very small fish carried northward by the Gulf stream. 
Abnormally low temperatures in southern waters will adversely affect gray snapper 
depending on the suddenness and amount of temperature drop, the minimum temperature 
attained, and the duration of the cold. Gray snapper in the Everglades National Park 
waters are subjected to a considerable range of temperatures. During the period June 
1957 to June 1959, temperatures ranged at least from 15°C to 36.3°C in Park waters. 
Juvenile and sub-adult L. griseus are eurohaline, being tolerant of seawater higher than 
35 °/oo. brackish water, and excursions into Florida freshwater springs. During the 
period June 1957 to June 1959, inshore waters of the Everglades National Park where 
gray snapper are abundant, ranged in salinity at least from 4.5 to 4.7 %o. Scales of 
gray snapper are readable, and have been critically examined for age and growth 
determinations. The annulus on gray snapper scales appears to be a region of different 
refractive properties than the remainder of the scale, and is a result of discontinuous 
and non uniform circuli. The validity of the annulus on gray snapper scales is shown by 
the agreement of calculated lengths from scale readings with empirical lengths of fish 
of the same growth year, and by the appearance of a mode for the sport fishery catch, 
and for scale readings. The annulus on gray snapper scales is laid down during the 
period December to February in south Florida. The sex ratio for 770 gray snapper was 
404 to 366 (52.5 to 47.5%) females predominating. Females outnumbered males 
slightly in the most abundant age groups present in the most abundant age groups 
present in the sport fishery catch (age groups II and III). Gray snapper sampled from 
the sport fishery in the Everglades National Park ranged from one to five years of age. 
The 2- and 3-yr-old fish made up approximately 62 and 28% respectively of the catch. 
151 
