Effects of Changing Weather, Oceanographic Conditions, and Land Uses on Spatio-Temporal Variation of Sedimentation Dynamics along Near-Shore Coral Reefs

Abstract

Sedimentation is a critical threat to coral reefs worldwide. Major land use alteration at steep, highly erodible semi-arid islands accelerates the potential of soil erosion, runoff, and sedimentation stress to nearshore coral reefs during extreme rainfall events. The goal of this study was to assess spatio-temporal variation of sedimentation dynamics across nearshore coral reefs as a function of land use patterns, weather and oceanographic dynamics, to identify marine ecosystem conservation strategies. Sediment was collected at a distance gradient from shore at Bahia Tamarindo (BTA) and Punta Soldado (PSO) coral reefs at Culebra Island, Puerto Rico. Sediment texture and composition were analyzed by dry sieving and loss-on-ignition techniques, and were contrasted with environmental variables for the research period (February 2014 to April 2015. Rainfall and oceanographic data were analyzed to address their potential role on affecting sediment distribution with BEST BIO-ENV, RELATE correlation, and linear regression analysis. A significant difference in sedimentation rate was observed by time and distance from shore (PERMANOVA, p < 0.0100), mostly attributed to higher sediment exposure at reef zones closer to shore due to strong relationships with coastal runoff. Sedimentation rate positively correlated with strong rainfall events (Rho = 0.301, p = 0.0400) associated with storms and rainfall intensity exceeding 15 mm/h. At BTA, sediment deposited were mostly composed of sand, suggesting a potential influence of resuspension produced by waves and swells. In contrast, PSO sediments were mostly composed of silt-clay and terrigenous material, mainly attributed to a deforestation event that occurred at adjacent steep sub-watershed during the study period. Spatial and temporal variation of sedimentation pulses and terrigenous sediment input implies that coral reefs exposure to sediment stress is determined by local land use patterns, weather, and oceanographic dynamics. Comprehensive understanding of sediment dynamics and coastal ecosystem interconnectivity is fundamental to implement integrated and adaptive management strategies aimed to promote sustainable development at watershed and Otaño-Cruz et al.Sedimentation Dynamics Along Near-Shore Reefs island wide-scale to fully mitigate terrigenous sediment impact to marine ecosystems. Furthermore, decision-making processes and policy needs to address sedimentation stress in the context of future climate to reduce land-based threats and strengthen coral reef resilience.

Caribbean Near-Shore Coral Reef Benthic Community Response to Changes on Sedimentation Dynamics and Environmental Conditions

“…Abundance decline during fall and winter seasons was related to the occurrence of extreme and acute weather events caused by a tropical trough and tropical storms that impacted the northern Caribbean region from August to November 2014. These atmospheric events produced the combined effect of sediment-laden runoff from disturbed coastal watersheds and increased wave action on shallow reefs (Otaño-Cruz et al, 2017). Coral reef benthic community structure and its ecological response is not only associated with variation in land-derived sediment input and distribution dynamics but is also related to bathymetry, as well as changes in local weather and oceanographic conditions.…”

“…In PSO reef, coral recruit abundance declined on the reef zone farthest from shore (>60 m) and it had a significant relationship with increased the proportion of silt-clay sediment deposition after an extensive deforestation event that disturbed the adjacent coastal watershed. Increased sediment influx and distribution of fine sediments through PSO reef was documented after strong precipitation events that were followed by wind-induced waves and currents that transported fine, land-based sediments until they were deposited in calmer waters (Otaño-Cruz et al, 2017). The effects of cold front events, characteristic of the winter season across the northern Caribbean, can produce strong long-period swells and a significant increase in sedimentation rate by both sediment bedload transport and resuspension (Otaño-Cruz et al, 2017).…”

“…Sediment samples were collected on a monthly basis and processed at the laboratory. Sediment samples were oven-dried at 60 • C for 24 h and total dry weight was recorded to calculate sediment accumulation rate (Edmunds and Gray, 2014;Otaño-Cruz et al, 2017). Sediment texture (silt-clay <63 µm and sand >63 µm) were analyzed through dry sieving, while loss on ignition techniques were applied to determine the organic matter (3 h oven dry 550 • C), carbonate matter (3 h oven dry 950 • C) and terrigenous sediment composition (Otaño-Cruz et al, 2017).…”

“…Sediment samples were oven-dried at 60 • C for 24 h and total dry weight was recorded to calculate sediment accumulation rate (Edmunds and Gray, 2014;Otaño-Cruz et al, 2017). Sediment texture (silt-clay <63 µm and sand >63 µm) were analyzed through dry sieving, while loss on ignition techniques were applied to determine the organic matter (3 h oven dry 550 • C), carbonate matter (3 h oven dry 950 • C) and terrigenous sediment composition (Otaño-Cruz et al, 2017). Rainfall events were documented with HOBO RG3 (Onset Computers, Co.) rain gauges located in coastal watersheds near study sites, while sea surface temperature at both study sites were recorded with HOBO Watertemp Pro V2.…”

“…These land-based stressors are mostly related to increasing trends of land-use changes, coastal urban sprawl and tourism-based activities with direct effects on sedimentladen runoff and sediment distribution along coastal waters (Rogers, 1990;Larsen and Webb, 2009;Hernández-Delgado et al, 2012;Ramos-Scharrón et al, 2012, 2015Bégin et al, 2013). This is particularly true for small tropical semi-arid islands, where an alteration of sediment delivery and distribution dynamics along near-shore reef ecosystem has been documented as a result of watershed alteration combined with changes in local weather patterns (Otaño-Cruz et al, 2017). Increased terrigenous sediment influx to coastal waters increases coral reef vulnerability and susceptibility to experience phase-shift toward alternate states, often dominated by non-reef building taxa and macroalgal assemblages (Acevedo et al, 1989;Fabricius, 2005Fabricius, , 2011Bellwood and Fulton, 2008;Dudgeon et al, 2010;Hughes et al, 2010).…”