Coral reef health in the Gulf of Honduras in relation to fluvial runoff, hurricanes, and fishing pressure.

The Gulf of Honduras includes extensive coral reefs in Belize and Guatemala, classified into four biogeographic zones, which are differentially affected by runoff, hurricanes, and fishing. Runoff mostly impacts the coastal and adjacent channel reefs. The Belize Barrier Reef (BBR) experiences less runoff impact due to the prevailing cyclonic ocean circulation. Hurricane waves powerfully impact the BBR, only occasionally the lee-side of Glover's Reef, and rarely the coastal and channel reefs. Fishing pressure is most intense on the coastal and channel reefs, comparatively modest on the BBR, and low at Glover's Reef. The effects of the three local stressors were evaluated using observations from 24 sites in the Gulf of Honduras. Data were analyzed using the Reef Health Index (RHI), with the highest RHI (4.3) for two Glover's Reef sites, medium RHI (2.6) for 10 sites on the barrier reef, and lowest RHI (2.1) for 8 coastal reef sites.

Response of Thalassia Testudinum Morphometry and Distribution to Environmental Drivers in a Pristine Tropical Lagoon.

This study was undertaken to determine the relationships between the biomass, morphometry, and density of short shoots (SS) of the tropical seagrass Thalassia testudinum and the physical-environmental forcing in the region. Seasonal sampling surveys were undertaken four times in Bahia de la Ascension, a shallow estuary in the western Mexican Caribbean, to measure plant morphology and environmental variables. The estuary has a fresh water-influenced inner bay, a large central basin and a marine zone featuring a barrier reef at the seaward margin. Leaf size was positively correlated with increasing salinity, but total biomass was not, being similar across most of the sites. Aboveground biomass exhibited seasonal differences in dry and rainy seasons along the bay, most markedly in the brackish inner bay where an abrupt decline in biomass coincided with the rainy season. The relationship between nutrients and biomass indicates that the aboveground/belowground biomass ratio increases as nutrient availability increases. Areal cover was inversely correlated with SS density during both dry and rainy seasons. Maximum SS recruitment coincided with the rainy season. Peaks in SS density were recorded in the freshwater-influenced inner bay during an ENSO cold phase in 2007 ("La Niña") which is associated with a wetter dry season and following a strong storm (Hurricane Dean). The onset of the rainy season influences both shoot density and T. testudinum biomass by controlling the freshwater input to the bay and thus, the system's salinity gradient and external nutrients supply from the coastal wetland.

Land-sea mercury transport through a modified watershed, SE Brazil.

River management has altered the land-sea transport of water, sediments, and chemical compounds with profound impacts on the structure of continental and costal ecosystems. Understanding riverine transport across modified watersheds allow for better assessment of the influence of river management on material fluxes to coastal waters. Here, we assess the quantitative and qualitative aspects of mercury (Hg) transport across a modified watershed by diversion of Paraíba do Sul River waters into Sepetiba Bay, Brazil. We measured concentrations and speciation of Hg in water samples collected at sites within the modified watershed. These data, together with water discharge and sediment load from numerical models and measurements were used to estimate mass balances. In the Sepetiba watershed, mercury is mainly associated with suspended sediments (90%) and therefore Hg flux displayed the characteristic trend of downstream reduction due to trapping efficiency of particulate load by successive reservoirs. The mass balance suggests that the major source of mercury to Sepetiba Bay is the erosion of soil-derived particles from the drainage basin rather than mercury diverted from Paraíba do Sul River watershed.