Neritic Larval Fish Distribution in the Oceanic Area of the Campeche Bay, Gulf of Mexico

Abstract

Composition and abundance of larval fishes in Campeche Bay were studied during two seasons, winter, 2013 (24 stations) and summer, 2014 (31 stations). Sampling was carried out with open-close nets, mouth 75 cm and 505 µm mesh. The data of salinity and temperature allowed distinguishing three oceanic sub-regions: North, East, and West. There were 236 taxa, belonging to 74 families, 168 species, 154 taxa occurred in winter and 171 in summer; the composition in both cruises was similar with around 70 % of oceanic and 30 % of neritic larvae. The larval density was almost three times larger in summer than winter. The Campeche Bay hydrodynamics fits well with the results; the West sub-region is located where a cyclonic gyre takes place, the North and East sub regions are located in the area of influence of warm currents over the Yucatan shelf. The hydrodynamics also allows understanding the differences in the proportion of neritic larvae among the three oceanic sub-regions, the West and East with the lower and higher number of neritic larvae, respectively. The large difference among regions is related to some neritic taxa occurring exclusively in some of them. Of the total taxa, 55 neritic occurred only once and it means that more than a half of neritic taxa were represented by one organism, 31 from 85 neritic taxa occurred in the layers of 600 to 1000 m depth. Of the neritic larvae, only Syacium papillosum and Apogon sp. appear among the 20 more abundant.

Citation

Flores-Coto C, Zavala-García F and Sanvicente-Añorve L. Neritic Larval Fish Distribution in the Oceanic Area of the Campeche Bay, Gulf of Mexico. Int J Fisheries Sci Res. 2018; 2(1): 1003.

Introduction

The composition, abundance, and distribution of ichthyoplankton in the oceanic waters of Campeche Bay, the southern Gulf of Mexico have not been studied. Most the studies have been carried out on the continental shelf, and few include some oceanic stations but no samples below 200 m. It could mention the papers of Olvera-Limas et al., [1] on some particular species, Flores-Coto and Ordónez-López [2] on the mesopelagic fishes, Flores-Coto and Sánchez-Ramírez [3] on carangids, and Flores et al., [4] with a summary of ichthyoplankton research in the area.

Such papers let us have an idea of the dominant taxa in a general way, for an instant, the dominance in the oceanic area of families of mesopelagic species mainly Myctophidae and Gonostomatidae and those of neritic habitat on the continental shelf, like Sciaenidae, Carangidae, Clupeidae, Engraulidae.

Larval fish distribution around the world depends on the biology of the species and the hydrodynamic regime [5-10]. On the first item, the plankton biomass which means food availability is significant. In the southern Gulf of Mexico, the zooplankton biomass and ichthyoplankton density have a direct relationship, and their distribution patterns are similar, with the lowest values in the oceanic area [11,12]; high biomass densities occurred in the coastal regions of the main rivers [13].

In the continental shelf off Tabasco y Campeche, the hydrodynamics are dominated by a current over the Yucatan shelf (which is a branch of the Yucatán current) and the continental water discharges; environment very different from the oceanic adjacent area in the Campeche Bay where the hydrodynamic is driven by a semi-permanent cyclonic gyre [14] and coastal currents generated by wind force, which change of direction depending on the climatic season [15].

But also the Yucatan shelf current (from now on called YSC) has a significant role because the composition and distribution of larval fish assemblages are determinate firstly by the reproductive habits of the adults, but finally, modulated by the hydrographic stressors that characterize each area.

Richards et al., [16] in their analysis of larvae at the borders of the Loop current in the center of the gulf, recorded among the 25 more abundant families a high proportion of neritic components; however, one would expect in the oceanic waters of Campeche Bay a lower density of larvae and a lower proportion of neritic larvae, as it has been previously reported by Flores-Coto et al., [17] and Espinosa-Fuentes et al., [18].

The present paper analyzes the neritic larval fish composition and distribution in the oceanic waters of Campeche Bay from the surface to 1000m depth, during winter and summer seasons of 2013 and 2014, assuming that the dominant hydrographic features are the controlling factors and to a lesser extent, the larvae biology.

Materials and Methods

The study area was located in the oceanic waters of Campeche Bay, the southern Gulf of Mexico between 18º and 21º 30´N and 93º and 96ºW. The zooplankton samples were obtained, from 24 stations made during the winter (ZOOMEP I, January 23-February 3, 2013) and 31 in the summer (ZOOMEP II, June 4-14, 2014). In the sampling, we used open-close nets 75 cm mouth and 505µm mesh, in five 200 m strata (0 to 1000m) resulting in 270 samples (Figure 1).

Figure 1: Study area and stations located in Campeche Bay, Gulf of Mexico. a - Winter cruise, b - Summer cruise

Samples were initially preserved in 4% formalin neutralized with sodium borate and changed into 70% alcohol 48h later. Fish larvae were all extracted from each sample and identified to the lower taxonomic level as possible. Salinity and temperature data were obtained from a Conductivity, Temperature and Depth profiler (CTD).

For the recognition of larvae assemblages, the Bray-Curtis similarity index was applied [19].

Results

Oceanic regions

Temperature and salinity properties of the sampled water masses allowed the identification of three oceanic sub-regions, here designated as North (NOR), East (EOR), and West (WOR) (Figures 2a and 2b).

Figure 2: Oceanic sub-regions delimited by the average temperature of 0-200 m layer.

<20°C, West sub-region, >21°C North sub-region, between 20 and 21°C East sub-region.

During the winter cruise considering the average temperature of the first level (0 - 200 m) the NOR had values of > 21°C, the WOR of < 19.8°C and the EOR between 20 and 21°C (Figure 2a). Interestingly, during the summer cruise, the same sub-regions were also identified, in similar geographic areas. The NOR with temperatures of > 21°C, the WOR with < 20°C, and the EOR with values between previous sub-regions (Figure 2b). The differences among sub-regions in both cruises were lower but persisted to depth levels of 800 - 1000 m (Figures 3a and 3b).

Figure 3: Temperature profiles (0-1000 m) in three sub-regions of the Campeche Bay, Mexico, during winter and summer cruises.

Salinity differences among sub-regions were small, in the winter cruise. The average values were <36.35 in WOR, >36.4 in the NOR and 36.33 to 36.4 in the EOR. In the summer cruise the values were 34.42 to 36.25, in the NOR, 36.00 to 36.24 in the WOR and 36.17 to 36.26 in the EOR (Figures 4a and 4b).

Figure 4: Salinity profiles (0-1000 m) in three sub-regions of the Campeche Bay, Mexico, during winter and summer cruises.

Common and exclusive taxa in the oceanic sub-regions

A total of 5,612 larvae were collected, only 3,431 larvae were identified corresponding to 236 taxa, 76 families, 148 genera, 161 species. In winter 154 taxa were recorded and 171 in the summer. About 88 taxa were common, 66 only occurred in winter and 83 in summer (Tables 1, 2, 3 and 4).

Table 1: Common taxa among oceanic sub-regions in Campeche Bay, Gulf of Mexico, during winter cruise (January 25 to February 3, 2013).

Values = average density. NOR = North Oceanic sub-region, EOR = East Oceanic sub-region, WOR = West Oceanic sub-region.

Table 2: Exclusive taxa in each oceanic sub-region in Campeche Bay, Gulf of Mexico, during winter cruise (January 24 to February 3, 2013).

Table 3: Common taxa among oceanic sub-regions in Campeche Bay, Gulf of Mexico, during summer cruise (4-14 June 2014).

Values = average density. NOR = North Oceanic sub-region, EOR = East Oceanic sub-region, WOR = West Oceanic sub-region.

Table 4: Exclusive taxa in each oceanic sub-region in Campeche Bay, Gulf of Mexico during summer cruise (4-14 June 2014).

The taxa composition in both cruises was similar with around 70% of larvae from an oceanic stock and 30% of the neritic stock. The larval density in summer represents 66.8% of the total of both cruises, and the density of neritic larvae was 13.1% in winter and 26.5% in summer.

The more abundant and frequent species in both cruises were Diogenichthys atlanticus, Notolychnus valdiviae, Benthosema suborbitale, Bregmaceros cantori, B. atlanticus, Gonostoma atlanticum, Sternoptyx diaphana and the genera Diaphus, Cyclothone y Argyropelecus. Of the neritic larvae, only Syacium papillosum and Apogon sp. appear among the twenty-first more abundant.

The composition of the larval community was analyzed with Bray-Curtis dissimilarity index using the total taxa or only neritic larvae. However, the resulting stations groups did not correspond with the oceanic sub-region determined by temperature and salinity.

Considering, firstly that from the 236 total taxa, 151 and 85 were oceanic and neritic larvae, respectively and secondly, that there was no correspondence between the ocean sub-regions and stations groups, we analyzed the differences among oceanic sub-regions, considering common taxa in the three regions, as well as those occurring in two or only one (Tables 1,2,3 and 4).

The larger number of common taxa among three sub-regions was oceanic: 24 and 47 in winter and summer, respectively, with only three and five neritic larvae in each cruise. The number of common taxa among two sub-regions was lower. The low number of common taxa among the WOR with the other two, as well as its low number of neritic taxa, making it different. Therefore, the greatest similarity was among the NOR and EOR particularly in the summer (Table 5).

Table 5: Number of common and exclusive, neritic and oceanic taxa, occurring in each oceanic sub-region and season.