Western Tropical Atlantic Ocean Research Articles

Composition and ecology of deep-water coral associations

Between 1966 and 1978 SCUBA investigations were carried out in French Polynesia, the Red Sea, and the Caribbean, at depths down to 70 m. Although there are fewer coral species in the Caribbean, the abundance of Scleractinia in deep-water associations below 20 m almost equals that in the Indian and Pacific Oceans. The assemblages of corals living there are described and defined as deep-water coral associations. They are characterized by large, flattened growth forms. Only 6 to 7 % of the species occur exclusively below 20 m. More than 90 % of the corals recorded in deep waters also live in shallow regions. Depth-related illumination is not responsible for depth differentiations of coral associations, but very likely, a complex of mechanical factors, such as hydrodynamic conditions, substrate conditions, sedimentation etc. However, light intensity determines the general distribution of hermatypic Scleractinia in their bathymetric range as well as the platelike shape of coral colonies characteristic for deep water associations. Depending on mechanical factors,Leptoseris, Montipora, Porites andPachyseris dominate as characteristic genera in the Central Pacific Ocean,Podabacia, Leptoseris, Pachyseris andCoscinarea in the Red Sea,Agaricia andLeptoseris in the tropical western Atlantic Ocean.

Observations of near‐surface currents and temperature in the central and western tropical Atlantic Ocean

Eleven satellite‐tracked drifting buoys were deployed in the central South Atlantic Ocean during two austral summer and two austral winter cruises. Between 7°S and 11°S and 23°W and 31°W during austral winter, net buoy drift was to the west. Surface geostrophic flow was to the east between 7°S and 9°S. It is proposed that strong southeast trade winds can induce directly driven surface flows to the west that are more intense than the eastward geostrophic flows associated with the South Equatorial Countercurrent (SECC). A sustained period of eastward drift within the SECC was observed during austral summer, when the trades are weaker. The trajectories indicate surface waters north of 8°S have a mean northward meridional component and those south of 8°S a southward component. The buoys which drifted north became entrained into the North Brazilian Coastal Current (NBCC) and those that drifted south into the Brazil Current. One buoy left the NBCC at about 5°N to drift northeastward in the North Equatorial Countercurrent (NECC). This trajectory and historical ship drift reports suggest that the NECC may extend only to 35°W to 40°W during boreal winter. Temperature data obtained as the buoys drifted westward and northward suggest that increases in upper layer heat content can be attributed to heat fluxes through the sea surface.

Variability of the tropical oceans

The western tropical Atlantic Ocean is a very energetic and highly variable region. It is one of the main contributors to the inter-hemispheric mass and heat transports. This study aim is to give a new picture of the space and time variability of this region using statistical tools applied to five different satellite measurements (Sea Surface Temperature, Sea Surface Salinity, ocean topography, wind stress vectors). We first processed each data set by using a Self-Organizing Maps (SOM), which is an efficient clustering methodology based on non-linear artificial neural networks to compress the information embedded in the data. The SOM was then combined with a Hierarchical Ascendant Classification (HAC) to cluster the different phenomena in a small number of classes whose physical characteristics are easy to identify. Three classes were identified which allowed us to analyse the dynamics of the North Brazil Current, and the North Equatorial Countercurrent, respectively, and their links with the Inter-Tropical Convergence Zone and the Amazon and Orinoco river runoffs. The SOM + HAC analysis gave a coherent picture of the concomitant seasonal variability of the variables. Furthermore, we were able to point out the correlations existing between salinity features recently discovered and wind, temperature, and dynamic topography structures. Applying our method to the interannual signals, we showed a year to year variability which deserves further analysis.

The community structure of a tropical marine lagoon

The structure of the benthic community in a nearshore tropical marine lagoon, in the upper Florida Keys, was examined in early spring and mid-summer in 1973 and 1974. Eight environmental parameters (water depth, tidal range, current flow, water temperature, salinity, pH, sediment depth and particle size) were monitored. The biota was compared along an intertidal-subtidal environmental gradient. The amount of vegetation present and the stability of the sediment modified the abundance and diversity of the benthic macrofauna. The results of this study are compared with those from other areas in the tropical Western Atlantic Ocean. The uniqueness of the lagunar environment made it possible to examine the changes in species abundance and diversity as a detritus-based food web graded into a phytoplankton based-food web.

Joint volume reverberation and biological measurements in the tropical Western Atlantic

Volume reverberation and biological data were gathered during January in the western tropical Atlantic Ocean. Day and night scattering strengths in 1/3‐octave bands from 1.0 to 20.0 kHz are presented which are compared to other data collected in the same area by a different agency. Identification of fishes captured, their lengths and computed swimbladder volumes, as well as resonance frequencies are given.

Primary productivity of the tropical western Atlantic Ocean near Barbados

Forty-four measurements of net primary productivity by 14C fixation were made at a station near Barbados, West Indies, over a period of 22 months; in addition 12 measurements were made at 7 deep-water stations in the tropical Western Atlantic Ocean. Average daily production was 0.288 g C/m2 and estimated annual net production 105 g C/m2. There was no evidence of seasonal variations in the rate of primary production nor of significant differences between production at the principal station and the additional deep-water stations. The data are, therefore, considered to be representative of the rate of primary production in this part of the tropical Western Atlantic Ocean and not significantly affected by proximity to land.

A Revision of the Filefish Genera Amanses and Cantherhines

share one or more of these characters with Amanses and Cantherhines. Eleven species of Cantherhines are recognized: longipinnis (endemic to Lord Howe Island); the Indo-Pacific dumerili (carolae and howensis are synonyms); macrocerus from the tropical western Atlantic Ocean (a large species long confused with pullus); multilineatus from Japan; fronticinctus from East Africa and the Indo-Malayan region; verecundus from Hawaii; tiki, a new species described from one specimen from Easter Island (unique in its produced snout and short first dorsal spine); melanoides from Queensland, Australia; sandwichiensis, a second Hawaiian endemic; the Indo-Western Pacific pardalis (a common species with 11 synonyms); and pullus, abundant on tropical Atlantic reefs. The last three species are closely related; all have 2 prominent white spots on the body, 1 at the posterior base of the soft dorsal fin and a small one at the posterior base of the anal fin. THE present study began with an attempt to determine whether the Atlantic monacanthid fish Cantherhines pullus (Ranzani) can be distinguished from the Indo-Western Pacific C. pardalis (Riippell) and to recover from synonymy the second Atlantic species of the genus, C. macrocerus (Hollard). The study was extended to a review of the genus which is here regarded as distinct from the monotypic Amanses. Eleven species of Cantherhines are reported, 1 of which from Easter Island is described as new.