Amazon River water in the northeastern Caribbean Sea and its effect on larval reef fish assemblages during April 2009

Abstract

During April to June 2009, a large bolus of Amazon River water impacted the northeastern Caribbean Sea. Shipboard observations collected near Saba Bank, the U.S. and British Virgin Islands, and the Anegada Passage showed low surface salinity (35.76 ± 0.05 Practical Salinity Unit (PSU)), elevated surface temperature (26.77 ± 0.14°C), high chlorophyll‐a (1.26 ± 0.21 mg m−3) and high dissolved oxygen (4.90 ± 0.06 mL L−1) in a 20‐ to 30‐m thick surface layer in the riverine plume. The water was ~1°C warmer, 1 PSU fresher, 0.3 mL L−1 higher in oxygen and 1.2 mg m−3 higher in chlorophyll‐a than Atlantic Ocean waters to the north, with Caribbean surface waters showing intermediate values. Plankton net tows obtained in the upper 100 m of the water column revealed larval fish assemblages within the plume that were significantly different from those of the surrounding waters and from those encountered in the area in previous years. The plume waters contained higher concentrations of mesopelagic fish larvae from the families Myctophidae and Nomeidae, which as adults typically inhabit offshore, deep water habitats. Concentrations of larvae from inshore and reef‐associated families such as Scaridae, Serranidae, Labridae and Clupeidae were lower than those found outside the plume in similar shallow areas, particularly in near‐surface waters. An event like the one observed in 2009 had not been documented in at least the past 30 yr, and yet it was followed by another similarly extreme event in 2010. The ecological implications, including any long‐term consequences of such recent extreme events, are important and merit further study.

Upper ocean response to Hurricane Gonzalo (2014): Salinity effects revealed by targeted and sustained underwater glider observations

“…Salinity is, in general, an ocean parameter less accurately reproduced by the model used here, which is partially due to the scarcity of salinity observations assimilated into the model. This is an important issue, given that regions off Puerto Rico are sensitive to different freshwater sources, such as the Amazon and Orinoco rivers [Kelly et al, 2000;Corredor et al, 2003;Balaguru et al, 2012a;Johns et al, 2014]. The assimilation of precipitation and fresh water sources in the model as well as the improvement in vertical discretization may enable a better representation of salinity features, such as the shallow low-salinity layer observed above 20 m.…”

Pelagic Sargassum in the Tropical North Atlantic

“…Furthermore, the NBCR forms at about the same time which shunts drifters into the NECC. Drifters can reach the Lesser Antilles in summer either through a narrow coastal current (Guiana Current) or via rings which break off from the NBCR and drift northwestward to the Caribbean (Johns et al 2014). A ring break-off occurred in the first pelagic Sargassum incursion events of the Lesser Antilles in 2011 (Franks et al 2011), creating uncertainty in direction of incursion until model backtracking revealed its path.…”

Influence of oceanographic conditions on abundance and distribution of post‐larval and juvenile carangid fishes in the northern Gulf of Mexico

“…Most of the carangid species examined here spawn in neritic coastal waters, where most previous surveys have focused sampling effort in shallow water <100 m deep (Espinosa‐Fuentes & Flores‐Coto, ; Katsuragawa & Ekau, ; Leak, ; Shaw & Drullinger, ). In contrast, samples in this study were collected far offshore in depths ranging from 500 to 3,000 m. Thus, the gear types used here and areas sampled most likely captured late stage larvae to early/late juveniles that were either passively entrained in circulation patterns of the expansive river plume (Grimes & Finucane, ; Johns et al., ) or actively engaging in ontogenetic migrations from nearshore to offshore habitats (da Costa, Albieri, & Araújo, ) or aggregating in the hydrodynamic nutrient rich and productive frontal regions (Ditty et al., ; Raya & Sabates, ).…”

“…The commonalities and differences in species‐environment relationships were also exhibited in the RDA ordination plots, where S. setapinnis, C. crysos , and C. chrysurus were correlated positively with SST and SSHA, and negatively correlated with salinity whereas C. hippos was opposite of those three species. Other studies have demonstrated that river plume features can be characterized by low salinity and increased temperature (Johns et al., ). The higher abundance of S. setapinnis, C. crysos , and C. chrysurus post larvae at lower salinities and warmer SST suggests association with the river plume that could either result from passive entrainment of small buoyant larvae due to hydrodynamic convergence zones (Bakun, ; Govoni, Hoss, & Colby, ) or active seeking out of plume waters for feeding (Govoni & Chester, ).…”

“…Non-significant variables not plotted F I G U R E 9 Response plots for Chloroscombrus chrysos abundance in relation to sea surface temperature (SST), sea surface height anolomy (SSHA) and salinity determined from GAM models for fish collected using MOC and LMT. Nonsignificant variables not plotted either passively entrained in circulation patterns of the expansive river plume (Grimes & Finucane, 1991;Johns et al, 2014) or actively engaging in ontogenetic migrations from nearshore to offshore habitats (da Costa, Albieri, & Ara ujo, 2005) or aggregating in the hydrodynamic nutrient rich and productive frontal regions (Ditty et al, 2004;Raya & Sabates, 2015).…”