Flow modifications over a tropical coral reef system

Abstract

Hydraulic jumps, transitions from supercritical to subcritical flows, tend to maintain suspended particles in the water column and enhance biological productivity near the surface. Transitions occur from flow adjustments as the flow moves through a cross-section reduction, such as a reef crest. Hydraulic jumps can also inhibit the settlement of coral larvae and bivalve mollusks, but could favor connectivity among reefs by dispersing planktonic organisms to surrounding areas. The Veracruz Reef System (VRS) was chosen as a case study of hydraulic jumps produced over reef crests. This system is located in the southwestern part of the Gulf of Mexico (GoM) and features 50 coral reef structures. The area is influenced by vertical stratification that modifies its dynamics. Hydrographic and yearlong current data collections in the area during 2009 identified fronts and a cyclonic recirculation. On the other hand, the presence of a hydraulic jump weakened the cyclonic recirculation on the leeward side of the reefs. The vertical gradient of the horizontal velocity suggested the influence of vertical eddies at least 35% of the time throughout the entire year. Moreover, the current velocity profiles showed a bidirectional behavior in spring and summer conditions of stratified waters. These bidirectional flows contrasted the unidirectional structure caused by frictional dynamics during northerly winds.