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PHYSICAL AND OCEANOGRAPHIC CHARACTERISTICS
OF GRAY'S REEF
The reef emerges irregularly from the sand as a series of roughly
northeast-southwest aligned rock outcrops of low to moderate
relief resembling large platforms. The tops of the platforms
are often covered with a thin veneer of sand and their southeast
margins often form ledges (shelf-like overhangs) to 6 feet (2
m) in height that may be broken, forming crevices and rubble
(Figure 2). There is some evidence that natural transport of
sediments periodically shifts the level of sand around the ledges,
increasing or decreasing apparent height.
Figure 2. Composite illustration of a typical outcrop at Gray's
Reef showing flat reef top, crevices, undercut reef, rocky rubble,
and sandy off-reef slope.
The sea conditions at Gray's Reef are generally moderate from the late spring through the fall (winds O to 15 knots; seas calm to four feet). During late summer, fall and winter seas can be rough (seven to nine feet) as a result of strong northeasterly winds and storms.
The oceanographic conditions at Gray's Reef have considerable influence upon the kinds of fishes that occur there. The regimes of water temperature, salinity (saltiness), turbidity (water clarity), and ocean currents all influence the dynamics of fish populations. Gray's Reef is closer to shore than to the edge of the continental shelf (see Figure 1) whose margin is 75 nmi offshore. According to Atkinson et al. (1983), the oceanographic properties of the Gray's Reef area are a mixed result of wind, Gulf Stream current, tidal flux and density forcing (salinity-temperature) influences at the margin of the inner- and midshelf. Figure 3 shows a seasonal profile of temperature and salinity for the Gray's Reef area. The lowest salinities occur during periods of peak river runoff (or shortly thereafter) with the remaining months reflecting Gulf Stream rather than inner shelf values (Atkinson et al. 1983).
Figure 3. Mean monthly sea temperature and salinity in the vicinity of Gray's Reef. (from Atkinson, pers. comm.)