Biophysical Features
The following are two published descriptions of spawning aggregation sites that range from complex to simple. These examples may prove useful in helping MPA managers compile descriptions of their FSAs. The complexity or simplicity of describing FSA sites is typically a function of where or how the information is to be presented, and whether, for example, site descriptions are needed in MPA design, or in management decision-making. Technical reports, scientific articles, or informative presentations have different requirements, and we leave it to readers to determine which are best suited for their purposes. Nonetheless, having records of the biophysical features of the reef surrounding the FSA may help other managers or researchers in the future and site descriptions may later be used for comparative purposes.
Sample 11
Gladden Spit is a reef promontory located along the Belize Barrier Reef at 16 35° N; 88 W. The promontory is located adjacent to the 1000 m isobath, which parallels the southern reef in a northeasterly to southwesterly direction. The reef bends at a 90° angle towards the northwest, separating from the shelf break and forming a promontory. A narrow channel cuts through the reef at Gladden Spit. The fore reef, north of the channel, slopes gently (<3 from the horizontal) from the reef crest for ca. 1 km to 25 m depth where the shelf angle increases gradually to a depth of 35 m and then drops vertically for at least 400 m to create a large fore reef area adjacent to a steep shelf. The shelf edge parallels the reef promontory and bends by 90° on the north edge of the channel and is dominated by low relief (1 m) hard corals and gorgonians. Beginning 400 m north of the promontory and extending northward, the fore reef exhibits poorly developed spur and groove morphology. Current measurements and numerical modeling of currents indicate that currents at Gladden Spit flow parallel to the reef at mean speeds of 3-15 cm s-1, driven by winds and the arrival of transient meso-scale eddies from the east. The currents at the spawning site flow predominantly towards the southwest but are highly variable.
Satellite and bathymetric profile of the spawning site at Gladden Spit. From Heyman et al. 2005.
Gladden Spit is located at the centre of the Gulf of Honduras and experiences a tropical climate. Watersheds of the Gulf impact the study area and receive annually 3000-4000 mm of highly seasonal rainfall. There is a distinct wet season from July to October, during which time freshwater discharge exceeds dry season discharge by a factor of five to nine. The resulting coastal water salinity is 8 during the rainy season, but remains generally high (36-37) at Gladden Spit during the entire year. Salinity at Gladden can occasionally be reduced to 32 ppt after periods of exceptionally high wet season rainfall or hurricane associated rains (August to October). Day length at Gladden varies from 11 h 7 min to 13 h 8 min from winter to summer solstice. Surface water temperatures vary seasonally from 27 to 31° C.
The spawning site is limited to a surface area of about one hectare.
Sample 22
The aggregation site is located on the seaward edge of the reef near the Kehpara Marine Sanctuary. The reef flat extends seaward 20–30m from the reef crest and is comprised of low (<1m) to high (2–3 m) relief corals with scattered sand and rubble patches. From the outer edge of the reef flat, the wall drops 30–40m at a 10–15° angle to the reef slope. Low-relief hard corals and occasional sea fans are associated with the wall, which is characterized by numerous crevices and cuts. The slope extends seaward from the wall at a 5–10° angle, consisting of low-relief corals and scattered sand patches.