Spatial and Temporal Variations in Pyrodinium bahamense Cyst Concentrations in the Sediments of Bioluminescent Mangrove Lagoon, St. Croix, USVI

Abstract

Mangrove Lagoon, located on the island of St. Croix, US Virgin Islands (USVI), is one of few actively bioluminescent lagoons in a location experiencing significant anthropogenic impacts. The bioluminescence is due to an abundance of the dinoflagellate Pyrodinium bahamense in the water column. We recovered surface sediments and sediment cores from Mangrove Lagoon to analyze the spatial distribution and temporal variability of P. bahamense cysts in this system. Surface sediment P. bahamense cyst concentrations ranged from 0 to 466 cysts g −1 dry sediment, with higher abundances associated with elevated surface water nutrient concentrations and a mixed terrestrial-marine organic matter source regime. In combination with available bioassay data, we hypothesize that phytoplankton utilize nutrients rapidly and subsequent decay of organic matter makes nutrients available for dinoflagellates at the sediment-water interface in the eastern and northern quadrants of the lagoon. However, the nutrients are rapidly exhausted during counterclockwise lagoon circulation resulting in the decline of primary productivity and dinoflagellate abundance in the western quadrants. Downcore profiles suggest that P. bahamense blooms have been occurring for decades, declining in recent years. No cysts were present in sediments predating dredging activities of the 1960s that created Mangrove Lagoon. Recent reductions in cyst abundance may be the result of limited primary productivity caused by restricted water exchange with Salt River Bay due to shallowing of a sill at the mouth of the lagoon. This research highlights the need for more comprehensive geochemical and fossil analyses to better understand long-term ecological variability and inform conservation efforts of these unique habitats.

Seasonal abundance of Pyrodinium bahamense (order Peridiniales, family Gonyaulacaceae) in Mosquito Bay, Vieques, Puerto Rico

“…The abundance of P. bahamense in the samples varied from 0 to 244 organisms/mL. This range of abundance is similar to those found by other studies in Mosquito Bay [7][8][9]. P. bahamense counts of up to 273 organisms/mL were reported in Oyster Bay, Jamaica [3].…”

“…Tide levels were recorded from the National Oceanic and Atmospheric Administration equipment offsite and are therefore not spatial component to these values, but water temperature was recorded at each site and was similar among all sites even though they have different depths and proximity to the channel. This supports the view that differences in water chemistry impact P. bahamense population levels (and those of other phytoplankton) on the spatial scale of tens of meters [9]. Tables 4 and 5 can be used to see the dynamics of the bay more clearly.…”

Spatial sedimentary distribution, seasonality and the characteristics of organic matter on Fernando de Noronha insular shelf

“…A different aspect of this study was the positive correlation between the total nitrogen content in the gravel fraction (rs=0.864), which differed from the results observed in the Sueste Bay (Barcellos et al, 2016a), and those of Reidhaar et al (2016) for the saline mangrove swamp on the Saint Croix bay (US Virgin Islands), where nitrogen levels are higher in the finer fractions.…”

“…While the inorganic phosphorus (IP) fractions represent a minor part of the total phosphorus, varying from 0.06 to 0.18μmol/L. The total phosphorus values measured in this study are below the average observed by Reidhaar et al (2016) for the saline mangrove swamp of Saint Croix bay (average of 1.92μmol/g). This is also below the content observed by Ennis et al (2016) (2.0μmol/g) for the anthropic low-impact zone of St. Thomas island's coral region (US Virgin Islands).…”

“…Specially focusing on the sedimentary organic matter behavior that is very particular in this type of marine environment. Oceanic island shelves are very dynamic in hydrodynamic point of view and are subject to a limited organic matter (OM) terrigenous inputs, leading to a biogenic sediment character, dominated in general by OM of marine origin in tropical areas (Montalvo et al, 2010;Yamamuro and Kamiya, 2014;Reidhaar et al, 2016;Ennis et al, 2016).…”