Port Honduras Marine Reserve

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Chapter 3. SITE DESCRIPTION

a - General features of the site

Terrestrial surface under sovereignty, excluding wetlands:

0 sq. km

Wetland surface:

0 ha

Marine surface:

405 sq. km

b - Physical features

Brief description of the main physical characteristics in the area:

See descriptions below.

Geology:

The geological processes influencing southern Belize can be understood by breaking the continental margin and shelf into three components: the coastal margin, the near-coast shelf and channels, and the offshore reef tract (Sullivan et al., 1995).  The continental margin of Belize forms one of the sides of a deep oceanic basin that makes up the northwest Caribbean region of the Tropical Western Atlantic. This basin is surrounded by the Cayman Ridge and Trough System to the east, the Nicaraguan Rise to the southeast, and by Cuba to the north.

The geology of coastal Belize is complex, and reveals a history of rock strata formed from terrestrial and marine sediments altered by tectonics. The basement structure of the continental margin of Belize is characterized by groups of aligned rift blocks that trend approximately parallel to the coast but that diverge north-eastward (Sullivan et al. 1995). Early in the Mesozoic (65-248 million years ago) the orogenic phase occurred, characterized by block faulting in northern Central America and accompanied by deposition of continental red beds. This faulting progressed into Guatemala, Belize and western Honduras and it is during this period that the development of the north-western Caribbean occurred, opening a rift between the Yucatan peninsula and Honduras, creating the Gulf of Honduras (Sullivan et al. 1995). During the late Cretaceous period, marine red beds, siltstone and shale, detrital limestone and some reef-like carbonate rocks were deposited over much of Guatemala, Belize and Yucatan (Sullivan et al. 1995).

In the Cenozoic era (65 million years ago to the present), deltaic detritus and carbonates accumulated in restricted marine embayments of eastern Guatemala and southern Belize. The streams of southern Belize drain the Maya Mountains, but they flow across a relatively flat and narrow coastal plain into swamps and small lagoons before entering the sea.  The coastal and tidal wetlands serve as an efficient sediment trap, thus, large quantities of terrigenous material probably do not reach the Port Honduras Marine Reserve. The sedimentation regime may have changed little since the early Cretaceous times when development of the platform began (Dillon & Vedder 1973).

Soil:

N/A

Topography:

N/A

Bathymetry:

The Marine Reserve lies in a coastal basin with estuarine characteristics, into which six watersheds flow. Although much of the Reserve waters exceed 5m in depth, two shallow banks run parallel to the shore, providing a base for many of the cayes, and which act as sediment traps, preventing much of the riverine sediment from reaching the coral reefs (Sullivan et. al., 1995). Close inshore the water are generally quite turbid, beyond the shallow banks the water has far greater clarity.

 

Hydrodynamics:

Most of the area of Port Honduras is deeper than 5 meters.  These deeper basins are somewhat protected from vertical mixing by shallow banks, and retain the inertia of the tropical surface water circulated in from the Gulf of Honduras.  It is this volume of oceanic water that maintains oceanic salinities and the marine nature of the embayment.

The waters of the Marine Reserve exhibit pronounced haloclines – layering of waters with different concentrations of salinity. This vertical layering of the water column is particularly pronounced in areas where the rivers enter the bay, with the less dense surface waters from the rivers lying on top of the denser seawater. Mixing of these layers is limited by the shallow banks, protecting the inshore waters from significant offshore wave-action, and salinity can vary from freshwater to over 30 ppt. Most of Port Honduras is extremely turbid, and in general, turbidity was highest close to shore decreasing over deeper areas of the bay and in mangrove enclosed lagoons.

Volcanic formations:

N/A

Sand dunes:

N/A

Underwater formations:

Although much of the Reserve waters exceed 5m in depth, two shallow banks run parallel to the shore, providing a base for many of the cayes, and which act as sediment traps, preventing much of the riverine sediment from reaching the coral reefs (Sullivan et. al., 1995).