Seasonal occurrence of southeast Pacific blue whale songs in southern Chile and the eastern tropical Pacific

Passive acoustic data were collected January 2012 to April 2013 at four sites in the Chiloense Ecoregion (CER) in southern Chile (≈43°S–44°S, 71°W–73°W) and 1996–2002 from one site in the eastern tropical Pacific (ETP) (8°S, 95°W). Automatic detectors were used to detect the two songs (SEP1 and SEP2) described for southeast Pacific (SEP) blue whales. There was a strong seasonal pattern of occurrence of SEP songs in the CER from December to August, peaking March to May. In the ETP, the occurrence of songs was an order of magnitude lower but songs were present year‐round, with a peak around June. These findings support austral summer/autumn seasonal residency in the CER and a seasonal movement of blue whales towards the ETP during June/July, returning in December. Interannual differences in the ETP were possibly linked to the 1997–1998 El Niño event. At both study sites, SEP2 was significantly more common than SEP1; both songs largely followed the same temporal trends. These findings contribute to our understanding of the seasonal movements of endangered SEP blue whales and can inform conservation strategies, particularly in the CER coastal feeding ground. We recommend future year‐round passive acoustic studies in the CER and the ETP (e.g., near the Galapagos Islands), ideally coupled with oceanographic data.     

Bacterial diversity in the oxygen minimum zone of the eastern tropical South Pacific

The structure and diversity of bacterial communities associated with the oxygen minimum zone (OMZ) of the eastern tropical South Pacific was studied through phylogenetic analysis. Clone libraries of 16S rRNA gene fragments were constructed using environmental DNA collected from the OMZ (60 m and 200 m), the sea surface (10 m), and the deep oxycline (450 m). At the class level, the majority of sequences affiliated to the gamma- (53.7%) and alpha-Proteobacteria (19.7%), and to the Bacteroidetes (11.2%). A vertical partitioning of the bacterial communities was observed, with main differences between the suboxic OMZ and the more oxygenated surface and deep oxycline waters. At the surface, the microbial community was predominantly characterized by SAR86, Loktanella and unclassified Flavobacteriaceae, whereas the deeper layer was dominated by Sulfitobacter and unclassified Alteromonadaceae. In the OMZ, major constituents affiliated to the marine SAR11 clade and to thiotrophic gamma-symbionts (25% of all sequences), a group not commonly found in pelagic waters. Sequences affiliating to the phylum Chloroflexi, to the AGG47 and SAR202 clades, to the delta-Proteobacteria, to the Acidobacteria, and to the 'anammox group' of the Planctomycetes were found exclusively in the OMZ. The bacterial richness in the OMZ was higher than in the oxic surface and deeper oxycline, as revealed by rarefaction analysis and the Chao1 richness estimator (surface: 45 +/- 8, deeper oxycline: 76 +/- 26; OMZ (60 m): 97 +/- 33, OMZ (200 m): 109 +/- 31). OMZ bacterial diversity indices (Fisher's: approximately 30 +/- 5, Shannon's: approximately 3.31, inverse Simpson's: approximately 20) were similar to those found in other pelagic marine environments. Thus, our results indicate a distinct and diverse bacterial community within the OMZ, with presumably novel and yet uncultivated bacterial lineages.     

Vertical relationships between chlorophyll, production and copepods in the eastern tropical Pacific

Data consisting of high resolution profiles of in situ chlorophyll,copepods and primary production have been measured with a towedBatfish and profiling pumping system at two sites named ‘BIOSTAT’(9°45'N, 93°45'W) and ‘DOME’ (7°19'N,83°25'W) sites during March 1981. Primary production profileswere generated from Batfish profiles using a chlorophyll/lightmodel and incubated pump samples, the latter with high verticalresolution of 3–5 m. The BIOSTAT site had a subsurfacechlorophyll maximum situated at {small tilde}50 m, and a productionmaximum at a depth of 40 m Copepods had a mean depth centroidcorresponding to the production maximum although their distributionwas more uniformly dispersed from 0 to 40 m. The latter observationindicated that copepods occurred at depths of high productionpotential and low biomass rather than high total productionand high biomass as found at 40 m depth. The DOME site had amixed surface layer of chlorophyll (0–20 m) while copepodswere located at the base of the chlorophyll layer and primaryproduction maximum located at the surface (0–10 m). Theareal daily production measured at the BIOSTAT and DOME siteswere 0.27 and 0.80 mg C m^–2day^–1 respectively.     

Distribution of holoplanktonic typhloscolecids (Annelida-Polychaeta) in the eastern tropical Pacific Ocean

The distribution and composition of the holoplanktonic speciesof the family Typhloscolecidae are reported from 579 samplesobtained over an extensive area in the eastern tropical PacificOcean. The EASTROPAC Oceanographic Program collected the samplesin twelve cruises during five periods made between January–September1967 and January–April 1968. The 2105 specimens identifiedbelonged to three genera and four species. Typhloscolex muelleriand Sagitella kowalewski were dominant together, accountingfor 57–59% of the relative abundance and 36–49%of the occurrence. Travisiopsis dubia is recorded for the firsttime from the eastern tropical Pacific, and Travisiopsis lanceolatais reported in almost the same locality as its first recordin the surveyed region.     

Spatial variability of mangrove fish assemblage composition in the tropical eastern Pacific Ocean

Mangroves in the tropical eastern Pacific (TEP) constitute a dominant coastal ecosystem that harbours diverse and economically important fish assemblages. We describe here regional scale patterns in the composition of this poorly documented mangrove ichthyofauna. A review of available studies (including own data) from five countries covering the entire region was performed. Species abundance distribution curves were constructed and compared among studies. Relative abundance data of fish species and families were analysed with classification and ordination techniques. Common species and families responsible for differences among localities were identified. Overall, 315 fish species associated to mangroves of the TEP were identified. Fifteen fish families accounted for 80 % or more of the relative abundance of all studies. Despite the use of different sampling techniques, common features arose for most of the mangrove fish assemblages. Clupeidae were numerically dominant throughout the region, while Gerreidae were particularly dominant in the northern mangroves. The catch mass contributions of families from studies where these data were available indicated a dominance of Ariidae, Centropomidae, Lutjanidae and Tetraodontidae. A relatively uniform composition at the family (and sometimes species) level supports recent claims to merge the Panamic with the Mexican province in the TEP according to the distribution of the shore fish fauna. Similarities found with other estuarine-mangrove ichthyofaunas in the Neotropics may be related to the connectedness of these regions in past geological times. Quantitative assessments of mangrove fish communities in four areas of the TEP would improve further zoogeographic analyses and facilitate the development of conservation strategies.     

Morphometric relationships for some species of elasmobranch from tropical eastern Pacific

This study proposes length relationship equations to determine total length of four species of sharks (Carcharhinus falciformis, Mustelus lunulatus, Sphyrna lewini and Carcharhinus limbatus) based on trunk lengths (TrL) and interdorsal lengths (IL) caught in Colombia and Central America Pacific Ocean. In Central American Pacific, data were recorded for C. falciformis, C. limbatus and S. lewini between 2006 and 2012. In the Colombian Pacific, data was recorded in 1994–1995 and from 2006 to 2012 for C. falciformis, S. lewini and M. lunulatus. In the Central American Pacific the IL – TL relationship was acceptable for C. falciformis (r² = .69) and C. limbatus which presented a good relationship (r² = .81) where most specimens were juveniles; the same trend was found for S. lewini (r² = .96). The TL‐TrL relationship estimated for species caught in the Colombian Pacific was significant for C. falciformis (r² = .98) and for M. lunulatus (r² = .84); however, for S. lewini this relationship was low (r² = .55). Results indicate this is a useful tool for fishery statistics and fishery management for elasmobranch species of the Eastern Tropical Pacific.     

Cleaning interactions by gobies on a tropical eastern Pacific coral reef

The present study describes the cleaning interactions among species of cleaner gobies Tigrigobius spp. and Elacatinus puncticulatus (family Gobiidae) and the client fish species they clean in a coral reef of Gorgona Island, Colombia. In 419 cleaning events, we observed 27 species acting as clients of Tigrigobius spp., whereas only nine were clients of E. puncticulatus. Paranthias colonus and Cephalopholis panamensis were the species most commonly cleaned by Tigrigobius spp., while Ophioblennius steindachneri and Stegastes acalpulcoensis were the clients most commonly cleaned by E. puncticulatus. The abundance (but not the body size) of clients was an important variable predicting the cleaning frequency observed for clients of Tigrigobius spp., but this was not the case for clients of E. puncticulatus. Additionally, Tigrigobius spp. preferred cleaning planktivores, sessile invertebrate feeders and territorial herbivores (Ivlev's index >0·15), whereas E. puncticulatus did not exhibit any preference. We observed two major peaks of cleaning activity for Tigrigobius spp., one in the early morning and another one in the late afternoon. These results suggest that Tigrigobius spp. is a specialized cleaner goby, whereas E. puncticulatus is a facultative cleaner that cleans sporadically.     

Latest Oligocene through early middle Miocene diatom biostratigraphy of the eastern tropical Pacific

Study of DSDP Sites 71, 77, and 495 has allowed the development of a refined diatom biostratigraphy for the latest Oligocene through early middle Miocene of the eastern tropical Pacific which is well correlated to the low-latitude zonations for planktonic foraminifers, coccoliths, and radiolarians. Six zones and 7 subzones are proposed, and correlation with high-latitude diatoms zonations for the North Pacific, the Norwegian Sea, and the Southern Ocean is suggested by the discovery of selected diatoms in these tropical sediments which were previously thought to be restricted to high latitudes. Six new species and one new variety of diatoms which are stratigraphically useful are proposed: Actinocyclus hajosiae, n. sp., A. radionovae, n. sp., Coscinodiscus blysmos, n. sp., C. praenodulifer, n. sp., Craspedodiscus rydei, n. sp., Thalassiosira bukryi, n. sp., and Coscinodiscus lewisianus var. robustus n. var.     

A preliminary assessment of the invasiveness of the Indo-Pacific sponge Chalinula nematifera on coral communities from the tropical Eastern Pacific

This is the first report of a sponge that overgrows live corals in the tropical Eastern Pacific ocean. Chalinula nematifera, native from the Indo-Pacific region, is an invasive sponge recorded for the first time in 2003 on coral communities from the Isla Isabel National Park (Mexican Pacific Ocean). Later, in 2006, it was found also on coral reefs from the Cabo Pulmo National Park; 217 nautical miles far away. It has been suggested that C. nematifera was introduced as fouling on ship hulls that have arrived at Isla Isabel from the Indo-Pacific. In this paper we examined the habitat specificity and the distribution and abundance through time of C. nematifera. While there were no significant variations in abundance through time, this species showed a very high specificity for living on live corals of the genus Pocillopora (94% vs. 6% on rocks). One of the environmental parameters that may explain this specificity for ramified corals is the low light intensity inside the coral colony, which was 96% lower than outside it. Coral reefs are currently struggling with a multitude of impacts that have weakened their resilience and pushed them away from equilibrium. As a result, more attention on ecology of corals is necessary. Although the abundance of C. nematifera seems to be stable, long-term monitoring programs (including studies of growth rates and recruitment) are needed to determine if this species could represent a threat to the Mexican coral ecosystem in the future.     

Reproduction and morphology of Central American and Tres Marias spinner dolphins in the eastern tropical Pacific

Four geographic forms of spinner dolphin (Stenella longirostris) occur in the eastern tropical Pacific. Two of the forms are pelagic: the eastern and whitebelly, and two are coastal: the Central American and Tres Marias spinner dolphins. Of these, only the Tres Marias form lacks recognition appropriate for developing management and conservation plans. Vertical aerial photographs of 57 spinner dolphin schools taken between 1988 and 2006 were used to examine the range of coastal forms and to characterize their calving seasons. On the basis of adult body length, spinner dolphins photographed off Guerrero, Mexico, were identified as those of the Central American form, which is north of their known range, and those photographed farther north, approximately 112 km off Nayarit, Mexico, were identified as the Tres Marias form. Calving peaked from October through March, and there was evidence that calving seasons differed among geographic forms with coastal forms calving later than pelagic forms. We present the first life history parameter estimates for the coastal forms of spinner dolphins, provide additional support for recognition of the Tres Marias form, and the first evidence of the Central American form occurring north of the Gulf of Tehuantepec, Mexico.     

哥斯达黎加外海夏季表层浮游动物种类组成及分布

根据2009年7—8月在东热带太平洋哥斯达黎加外海(4°30’—10°24’N、91°20’—100°00’W)进行茎柔鱼探捕调查期间采集的表层浮游动物资料,对其种类组成、生物量及其分布进行了分析。结果表明,调查海域,鉴定出腔肠动物8目10科17属23种;甲壳动物8目30科43属74种;毛颚动物1目1科1属4种;尾索动物3目3科5属5种;环节动物为1目3科5属6种;软体动物1目1科3属3种;其他浮游动物有头足类的幼体、鱼卵和仔稚鱼以及浮游幼虫。调查海域总生物量和丰度的平均值分别为(124.78±176.83)mg/m3和(848±1219)个/m3,生物量较大的类群主要是甲壳动物的桡足类和毛颚动物的箭虫类其中桡足类的丰度(727个/m3)为最高,其次为箭虫类(373个/m3);出现频率较高的为桡足类、箭虫类、长尾类、头足类和鱼类仔稚鱼。     

Coral growth with thermal stress and ocean acidification: lessons from the eastern tropical Pacific

The rapid growth of scleractinian corals is responsible for the persistence of coral reefs through time. Coral growth rates have declined over the past 30 years in the western Pacific, Indian, and North Atlantic Oceans. The spatial scale of this decline has led researchers to suggest that a global phenomenon like ocean acidification may be responsible. A multi-species inventory of coral growth from Pacific Panamá confirms that declines have occurred in some, but not all species. Linear extension declined significantly in the most important reef builder of the eastern tropical Pacific, Pocillopora damicornis, by nearly one-third from 1974 to 2006. The rate of decline in skeletal extension for P. damicornis from Pacific Panamá (0.9% year⁻¹) was nearly identical to massive Porites in the Indo-Pacific over the past 20–30 years (0.89–1.23% year⁻¹). The branching pocilloporid corals have shown an increased tolerance to recurrent thermal stress events in Panamá, but appear to be susceptible to acidification. In contrast, the massive pavonid corals have shown less tolerance to thermal stress, but may be less sensitive to acidification. These differing sensitivities will be a fundamental determinant of eastern tropical Pacific coral reef community structure with accelerating climate change that has implications for the future of reef communities worldwide.     

Nitrite oxidation in the upper water column and oxygen minimum zone of the eastern tropical North Pacific Ocean

Nitrogen (N) is an essential nutrient in the sea and its distribution is controlled by microorganisms. Within the N cycle, nitrite (NO₂⁻) has a central role because its intermediate redox state allows both oxidation and reduction, and so it may be used by several coupled and/or competing microbial processes. In the upper water column and oxygen minimum zone (OMZ) of the eastern tropical North Pacific Ocean (ETNP), we investigated aerobic NO₂⁻ oxidation, and its relationship to ammonia (NH₃) oxidation, using rate measurements, quantification of NO₂⁻-oxidizing bacteria via quantitative PCR (QPCR), and pyrosequencing. ¹⁵NO₂⁻ oxidation rates typically exhibited two subsurface maxima at six stations sampled: one located below the euphotic zone and beneath NH₃ oxidation rate maxima, and another within the OMZ. ¹⁵NO₂⁻ oxidation rates were highest where dissolved oxygen concentrations were <5 μM, where NO₂⁻ accumulated, and when nitrate (NO₃⁻) reductase genes were expressed; they are likely sustained by NO₃⁻ reduction at these depths. QPCR and pyrosequencing data were strongly correlated (r²=0.79), and indicated that Nitrospina bacteria numbered up to 9.25% of bacterial communities. Different Nitrospina groups were distributed across different depth ranges, suggesting significant ecological diversity within Nitrospina as a whole. Across the data set, ¹⁵NO₂⁻ oxidation rates were decoupled from ¹⁵NH₄⁺ oxidation rates, but correlated with Nitrospina (r²=0.246, P<0.05) and NO₂⁻ concentrations (r²=0.276, P<0.05). Our findings suggest that Nitrospina have a quantitatively important role in NO₂⁻ oxidation and N cycling in the ETNP, and provide new insight into their ecology and interactions with other N-cycling processes in this biogeochemically important region of the ocean.     

Abundance and phylogenetic identity of archaeoplankton in the permanent oxygen minimum zone of the eastern tropical South Pacific

We assessed the abundance and molecular phylogeny of archaeoplankton in the oxygen minimum zone (OMZ) of the eastern tropical South Pacific, using specific-probe hybridization and phylogenetic analysis of the SSU-rRNA gene. Euryarchaea from Marine Group-II (MG-II) were most abundant in the surface oxic layer, representing 4.0±2.0% of the total picoplankton, while crenarchaea from Group I.1a (G-I.1a) peaked at the oxyclines, with a relative abundance of 8.1±4.3% (upper oxycline). In most of the stations, the abundance of both the groups decreased at the core of the OMZ, where a secondary maximum in cell density is commonly observed. The majority of the phylotypes affiliated with one of three groups: MG-II, euryarchaeal Marine Group-III (MG-III) and G-I.1a (75.9%, 12.8% and 10.3%, respectively). While MG-II phylotypes were found throughout the water column and G-I.1a ones were predominantly found within the oxyclines, MG-III phylotypes came almost exclusively from the OMZ core. Higher archaeal richness was found within the OMZ, with some of the exclusive lineages grouping with sequences from the deep ocean and hydrothermal vents. Moreover, G-I.1a sequences from the OMZ grouped into a different subcluster from the aerobic ammonium-oxidizer Nitrosopumilus maritimus. Thus, the community structure of archaeoplankton in OMZs is rich and distinct, with G-I.1a members particularly prominent at the oxyclines.     

Dispersal barriers in tropical oceans and speciation in Atlantic and eastern Pacific sea urchins of the genus Echinometra

Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and genetic structure of the Indo-West Pacific (IWP) species. We sequenced 630 bp of the cytochrome oxidase I (COI) mitochondrial gene to provide comparable information on the eastern Pacific and Atlantic species, using divergence between those separated by closure of the Isthmus of Panama 3.1 million years ago (Ma) to estimate dates for cladogenic events. Most recently (1.27-1. 62 Ma), the Atlantic species E. lucunter and E. viridis diverged from each other, at a time in the Pleistocene that sea levels fell and Caribbean coral speciation and extinction rates were high. An earlier split, assumed to have been coincident with the completion of the Isthmus of Panama, separated the eastern Pacific E. vanbrunti from the Atlantic common ancestor. Transisthmian COI divergence similar to that in the sea urchin genus Eucidaris supports this assumption. The most ancient split in Echinometra occurred between the IWP and the neotropical clades, due to cessation of larval exchange around South Africa or across the Eastern Pacific Barrier. Gene flow within species is generally high; however, there are restrictions to genetic exchange between E. lucunter populations from the Caribbean and those from the rest of the Atlantic. Correlation between cladogenic and vicariant events supports E. Mayr's contention that marine species, despite their high dispersal potential, form by means of geographical separation. That sympatric, nonhybridizing E. lucunter and E. viridis were split so recently suggests, however, that perfection of reproductive barriers between marine species with large populations can occur in less than 1.6 million years (Myr).     

Redescription of Ammodytoides gilli, the tropical eastern Pacific sand lance (Perciformes: Ammodytidae)

Ammodytoides gilli (Bean, 1895) is the correct name for the tropical eastern Pacific sand lance. Its range is extended from Cabo San Lucas, Baja California south to Panama, Ecuador, and the Galapagos Islands. Ammodytes lucasanus Beebe and Tee-Van, 1938 is a junior synonym. Types of both nominal species were re-examined. The species is redescribed based on 50 specimens (42.3-115 mm SL) from 12 lots and is compared with other known species of Ammodytoides. Changes in ontogeny from the smallest known specimen (42.3 mm SL, illustrated) are detailed including reduction in the posterior dorsal fin lobe and development of branched dorsal and anal fin rays.