Subtropical Waters Research Articles

Monthly progression rates of the coral-killing sponge Terpios hoshinota in Sesoko Island, Okinawa, Japan

Terpios hoshinota is a black, encrusting sponge that hosts numerous symbiotic cyanobacteria in its tissues. The sponge often overgrows live scleractinian corals, thereby causing widespread and accelerated coral loss. However, our understanding of how subtropical waters influence the seasonal change in the progression rate of the sponge is poor. To elucidate the progression dynamics over a year, we obtained monthly measurements of linear progression of T. hoshinota (mm month−1) on the branching coral Montipora digitata in the subtropical waters of Sesoko Island, Okinawa, Japan from 2019 to 2020. The progression rate of T. hoshinota varied monthly throughout the year. The progression rates were the highest in summer (July, August, and October) with a mean value of 66 mm month−1, except in September, when strong typhoons came close to Okinawa and the progression rate decreased temporarily. The progression rates were the lowest in February 2020, at 9 mm month−1. The mean annual linear progression rate was estimated to be 28 mm month−1. Therefore, the progression dynamics of T. hoshinota could be linked to their growth mechanisms in relation to the seasonal changes in subtropical waters.

Species Delimitation of Southeast Pacific Angel Sharks (Squatina spp.) Reveals Hidden Diversity through DNA Barcoding

Angel sharks are distributed worldwide in tropical to subtropical waters. Across the Eastern Pacific Ocean (EPO), two valid species are reported: The Pacific angelshark Squatina californica and the Chilean angelshark Squatina armata; however, there is still uncertainty about their geographic distribution, mainly along the northern Peru coast where the species have been reported to be sympatric. The aim of this study is to describe the genetic differences between the genus Squatina from the EPO, including samples from northern Peru, and using DNA barcoding and three species delimitation models: Poisson tree processes (PTP) model, Bayesian implementation of the PTP (bPTP) model and the general mixed Yule coalescent (GMYC) model. The three approaches summarized 19 nominal Squatina species in 23 consensus Molecular Taxonomic Units (MOTU). Only 16 of them were in accordance with taxonomic identifications. From the EPO, four Squatina MOTUs were identified, one from North America (S. californica USA/Mexico) and three sampled in northern Peru, S. californica Peru, S. armata and Squatina sp. (a potential new species). This study contributes to the management and conservation policies of angel sharks in Peru, suggesting the presence of an undescribed species inhabiting the northern Peruvian coast. The use of molecular approaches, such as DNA barcoding, has the potential to quickly flag undescribed species in poorly studied regions, including the Southeast Pacific, within groups of ecologically and economically important groups like angel sharks.

Microbial rhodopsins are increasingly favoured over chlorophyll in High Nutrient Low Chlorophyll waters.

Microbial rhodopsins are simple light-harvesting complexes that, unlike chlorophyll photosystems, have no iron requirements for their synthesis and phototrophic functions. Here, we report the environmental concentrations of rhodopsin along the Subtropical Frontal Zone off New Zealand, where Subtropical waters encounter the iron-limited Subantarctic High Nutrient Low Chlorophyll (HNLC) region. Rhodopsin concentrations were highest in HNLC waters where chlorophyll-a concentrations were lowest. Furthermore, while the ratio of rhodopsin to chlorophyll-a photosystems was on average 20 along the transect, this ratio increased to over 60 in HNLC waters. We further show that microbial rhodopsins are abundant in both picoplankton (0.2-3 μm) and in the larger (>3 μm) size fractions of the microbial community containing eukaryotic plankton and/or particle-attached prokaryotes. These findings suggest that rhodopsin phototrophy could be critical for microbial plankton to adapt to resource-limiting environments where photosynthesis and possibly cellular respiration are impaired.

Phylogenomic and morphological relationships among the botryllid ascidians (Subphylum Tunicata, Class Ascidiacea, Family Styelidae)

Ascidians (Phylum Chordata, Class Ascidiacea) are a large group of invertebrates which occupy a central role in the ecology of marine benthic communities. Many ascidian species have become successfully introduced around the world via anthropogenic vectors. The botryllid ascidians (Order Stolidobranchia, Family Styelidae) are a group of 53 colonial species, several of which are widespread throughout temperate or tropical and subtropical waters. However, the systematics and biology of this group of ascidians is not well-understood. To provide a systematic framework for this group, we have constructed a well-resolved phylogenomic tree using 200 novel loci and 55 specimens. A Principal Components Analysis of all species described in the literature using 31 taxonomic characteristics revealed that some species occupy a unique morphological space and can be easily identified using characteristics of adult colonies. For other species, additional information such as larval or life history characteristics may be required for taxonomic discrimination. Molecular barcodes are critical for guiding the delineation of morphologically similar species in this group.

A Visitor of Tropical Waters: First Record of a Clymene Dolphin (Stenella clymene) Off the Patagonian Coast of Argentina, With Comments on Diet and Metazoan Parasites

The poorly known Clymene dolphin (Stenella clymene) is a small oceanic cetacean distributed in tropical and subtropical waters of the Atlantic Ocean. In this study, we report, for the first time, a vagrant individual of Clymene dolphin in Argentina (Rada Tilly) that represents the current southern-most record for this cetacean species. We provide a molecular identification of the dolphin, based on partial sequences of the mitochondrial cytochrome b gene, generated from DNA extracted from its metazoan parasites. Three prey species, namely Argentine hake, Patagonian squid and lobster krill were identified from hard pieces collected in the stomach. Seven metazoan parasite taxa (three in adult stage, one immature stage and three in larval stage) were identified using morphological and molecular data, i.e., the digenean Pholeter gastrophilus (new host record), the cestodes Tetrabothrius (Tetrabothrius) forsteri, Clistobothrium grimaldii unidentified phyllobothriid plerocercoids, the nematodes Anisakis pegreffii (new host record), Halocercus delphini and the acanthocephalan Corynosoma australe (new host record). Our study provides the first molecular exploration of the metazoan parasite diversity in delphinids from the southwestern Atlantic, and contributes significantly to understand the poorly known parasite fauna of the Clymene dolphin.

A view of the Brazil-Malvinas confluence, March 2015

The encountering of the subtropical Brazil Current (BC) and the subantarctic Malvinas Current (MC) along the western margin of the Argentine Basin forms the Brazil-Malvinas Confluence (BMC), one of the most intense open-ocean fronts in the world ocean and a site for the formation of intermediate water masses. Here, we provide a comprehensive description of the BMC based on physical and biogeochemical data – hydrographic stations, profiling floats and subsurface drifters – gathered in March 2015. We use these data in order to characterize the impinging and outflowing currents and to describe the cross- and along-frontal thermohaline structure. In addition, we compare the in-situ measurements with both climatological data and the Mercator Ocean eddy-resolving reanalysis. The hydrographic sections illustrate the contrasting properties between the two western boundary currents: warm, salty, nutrient- and oxygen-poor oligotrophic subtropical waters carried southward by the BC and the cold, fresh, oxygen- and nutrient-rich subantarctic waters carried northward by the MC. The frontal system is also characterized by the presence of thermohaline intrusions, with the cross-frontal gradients and along-front velocities sharpening as the colliding currents shape the frontal system. We also observe brackish waters spreading on top of the frontal jet as a result of both the confluence dynamics and off-shelf advection favored by north-easterly winds. These low-salinity waters are positively correlated with surface ageostrophic speeds over the frontal jet. The cruise data illustrates the high regional and mesoscale variability as compared with climatological conditions, and further document the submesoscale subsurface complexity, which is not properly captured by available operational models.

Taxonomy of the sea stars (Echinodermata: Asteroidea) from Bahia State, including ontogenetic variation and an illustrated key to the Brazilian species.

Describing ontogenetic morphological change is an important part of integrative taxonomy; still, most taxonomic studies are based only on adult characters. Here, we provide illustrations and a morphological description of the sea stars from Bahia, including ontogenetic and intraspecific variation, and identify taxonomic issues. A total of 293 specimens from different localities along the Bahia State coastline and comparative material from other localities were examined. Eighteen species (11 genera, eight families) of Asteroidea were identified; Astropectinidae was the most representative family. All species identified also occur in subtropical Brazilian waters and most species are from shallow water habitats with soft bottoms. Most observed ontogenetic variation was quantitative in nature, such as the increase in the number of spines in the furrow and of spinelets in the paxillae with specimen growth. Genera that require further taxonomic studies are Astropecten and Othilia, whose specimens are commonly misidentified in local studies. One third of the species from Bahia are currently classified as "Vulnerable" in the Brazilian Red List, but baseline data on the population biology of these species are scarce. An illustrated identification key to the 65 Brazilian sea star species is also provided. This taxonomic study will facilitate the identification of specimens occurring along the Brazilian coast and help scientists and policy makers to establish the conservation status of the Brazilian species.

Interannual variability in the subduction of the South Atlantic subtropical underwater

The South Atlantic subtropical underwater (STUW) is a high-salinity water mass formed by subduction within the subtropical gyre. It is a major component of the subtropical cell and affects stratification in the downstream direction due to its high salinity characteristics. Understanding the interannual variability in STUW subduction is essential for quantifying the impact of subtropical variability on the tropical Atlantic. Using the output from the ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), this study investigates the interannual variability in STUW subduction from 1992 to 2016. We find that heat fluxes, wind stress, and wind stress curl cause interannual variability in the subduction rate. Heat fluxes over the subduction area modulate the sea surface buoyancy and regulate the mixed layer depth (MLD) during its deepening and shoaling phases. Additionally, the wind stress curl and zonal wind stress can modulate the size of the subduction area by regulating the probability of particles entrained into the mixed layer within 1 year of tracing. This analysis evaluates the influence of subtropical wind patterns on the South Atlantic subsurface high-salinity water mass, highlighting the impact of heat and wind on the interannual changes in the oceanic component of the hydrological cycle.

Real-time automated identification of algal bloom species for fisheries management in subtropical coastal waters

Harmful Algal Blooms (HAB) pose significant challenges to fisheries management and food and water security. The onset of a HAB is notoriously difficult to predict. Traditional methods of algal species identification under a microscope are also laborious and time consuming. A real-time system for identification and concentration measurement of algal bloom species has been developed at a marine fish culture zone (FCZ) in the subtropical coastal waters of Hong Kong. The system is based on analysis of high frequency algal cell images obtained from an underwater Imaging FlowCytobot (IFCB) deployed on the fish farm. An explainable supervised machine learning technique has been successfuly developed. The algal species classifier is trained by presenting a wide range of extracted image features to a random forest algorithm. An optimized set of 25 features is identified by a recursive feature elimination technique. The random forest (RF) classifier can identify 15 target HAB classes with an overall out-of-bag accuracy of 94.2%, with individual F1 score ranging from 0.8 to 1.0. The classifier performs equally well as a Convolution Neural Network (CNN) developed using transfer learning techniques. Based on the classifier, an automated real-time species identification and cell counting protocol has been developed, with a response time of 10 min after data collection. This work represents the first successful attempt of continuous algal species monitoring by IFCB and artificial intelligence (AI) – based detection of HAB in subtropical coastal waters.

New observations on the large hemidiscoid diatom Palmerina ostenfeldii and its symbiotic ciliate Vaginicola collariforma sp. nov. from subtropical Australian waters

The large hemi-discoid diatom Palmerina ostenfeldii was common in subtropical Moreton Bay, Australia, following a flood in January 2011. All diatom cells exhibited diagnostic subapical folds settled by loricate peritrich ciliates, but which readily abandoned stressed diatom cells. We characterized both diatoms and ciliates by morphological and molecular analyses, including careful video observations on non-preserved cells immediately after collection. The fold in the diatom cell wall comprises a narrow shelf upon which the ciliates attach (on average seven per fold, and similar for the two folds of a single diatom cell) but without penetrating the diatom wall itself. Folds were fully developed in newly formed internal valves, indicating that the ciliates play no role in their morphogenesis. SSU rRNA sequences of P. ostenfeldii from Moreton Bay (with ciliates) differed by 25 bp (1.5%) from those of P. hardmaniana from Texas (without ciliates), but surprisingly rbcL chloroplast sequences for both diatom species were indistinguishable. The ciliate species epiphytic on P. ostenfeldii, previously referred to as the cold-water tintinnid Amphorella borealis could not be assigned to any known species. We formally describe it here as Vaginicola collariforma sp. nov. within the crown clade of peritrichs which also includes the closely related genus Cothurnia (but distinguished as having an external stalk). Beating of the peritrich oral cilia was observed to drive rotational movement of the large discoid diatoms as in a ferris wheel. The observed diatom-ciliate symbiosis may represent a unique evolutionary adaptation in which the ciliate is host-specific and attaches in a specific locality on the host cell.

PENDAMPINGAN TEKNIK KONSERVASI PENYU LEKANG (Lepidochelys olivacea) DI PESISIR PANTAI LAMPUUK ACEH BESAR

The Olive Ridley Sea Turtle (Lepidochelys olivacea), is a species of sea turtle that lives in tropical and subtropical waters with shallow waters. The olive ridley sea turtle is found laying eggs in the Indian Ocean, the Pacific Ocean, and on the beaches of large islands. The main problem is the population of the olive ridley sea turtle were experiencing the reduction significantly. The aim of this program is to undertake the accompaniment of conservation technique of The olive ridley sea turtle to coastal community Lampuuk Aceh Besar. The stages of empowerment community including monitoring, the relocation, evacuation process, quarantine, and hatching release. We done enthusiasms to follow the empowering community program. We also hope with the conservation program to keep the population of The olive ridley sea turtle at coastal area from the disturbance of preadator and poaching.

Deep-Water Warming in the Gulf of Mexico from 2003 to 2019

AbstractA key consequence in climate change is the warming of deep waters, away from the faster warming rates of near-surface subtropical and tropical waters. Since surface and near-surface oceanic temperatures have been measured far more frequently in time and space than deep waters (>2000 m), deep measurements become quite valuable. Semi-enclosed basins, such as the Gulf of Mexico, are of particular interest as the waters below sills that connect with the neighboring oceans have residence times much longer than upper layers. Within the western Gulf of Mexico, near-bottom measurements at ~3500-m depths at four sites show a stable linear warming trend of ~16 ± 2 m°C decade−1 for the period 2007–18, and CTD data from eight oceanographic cruises occurring from 2003 to 2019 show a trend of ~18 ± ~2 m°C decade−1 from the bottom to ~2000 m below the surface. The bottom geothermal heat flux is a contributing factor to be considered in the warming and renewal of such waters, but it has not changed over millennia and is therefore unlikely to be the cause of the observed trend. The densest waters that spill into the Gulf of Mexico, over the Yucatan Channel sill, must mix substantially during their descent and in the near-bottom interior, losing their extreme values. A simple box model connects the observed warming, well within the Gulf interior, with that expected in the densest waters that spill from the North Atlantic into the Cayman Basin through Windward Passage and suggests that the source waters at the entrance to the Caribbean have been warming for at least 100 years.

The Formation of Subtropical Phytoplankton Blooms Is Dictated by Water Column Stability During Winter and Spring in the Oligotrophic Northwestern North Pacific

AbstractSubtropical phytoplankton blooms were observed in winter and late spring (rather than in early spring, as is typical) via shipboard observations in an area south of the Kuroshio Extension in the northwestern North Pacific subtropical gyre. Satellite‐based observations revealed that these submesoscale blooms occurred in warmer water masses in winter and in cooler water masses in late spring. The fact that winter blooms occurred in warmer areas suggests that they depend on water column stratification caused by solar heating. In contrast, the fact that the late‐spring blooms occurred in cooler areas suggests a breakdown of stratification due to a recurrence of convective mixing. Mesoscale blooms occurred at intermediate water temperatures in early spring, suggesting a repeating sequence of stratification and mixing during this period. Wintertime deep convective mixing in the northwestern North Pacific subtropical gyre creates Subtropical Mode Water. The behavior of the wintertime mixed‐layer depth, which determines the thickness of Subtropical Mode Water, also dictates the characteristics of subtropical blooms such as their magnitude and the timing of onset and demise. Based on in situ observations and a model analysis, we conclude that deeper winter mixing, which increases nutrient concentrations, will intensify early‐spring blooms and facilitate the formation of episodic blooms in winter and late spring. On the other hand, shallower winter mixing should increase stratification and thus facilitate the formation of smaller blooms, even in winter.

Evidence of residential area of whale sharks in Saleh Bay, West Nusa Tenggara

Saleh Bay is one of the locations where whale sharks (Rhincodon typus) occurrence observed in Indonesia and can be found all year round. Whale sharks broadly distributed throughout tropical and sub-tropical waters of the world’s oceans. Immature male is less than 7 m long, while female is less than 10 m, mostly tend to coastal habitat related. Result of research by Conservation International presented at International Whale Shark Conference in Australia in 2019, Whale Sharks in Saleh Bay had home movement patterns. This study aims to prove that Saleh Bay is the residential area of the whale shark. This study was conducted from November 2019 to January 2020. The Photo-ID data obtained were compared with CI’s Saleh Bay Whale Shark ID Catalog data which last update on April 2020. Surface temperature was measured directly in the range of 29-320C, data for chlorophyll-a were taken from marine.copernicus.eu and bathymetry from cmap.ihms.us then interpolated using QGIS 3.10 software. From this study period, 24 Photo-IDs were obtained from 39 whale sharks, which identified as 23 males, 1 female, and 6 were new individuals from June 2019 to April 2020. The size of the whale sharks recorded in this study ranged from 2,5 to 7 m with 4,86 m in average, and considered as juveniles.

EDNA metabarcoding of small plankton samples to detect fish larvae and their preys from Atlantic and Pacific waters

Zooplankton community inventories are the basis of fisheries management for containing fish larvae and their preys; however, the visual identification of early-stage larvae (the “missing biomass”) is difficult and laborious. Here, eDNA metabarcoding was employed to detect zooplankton species of interest for fisheries from open and coastal waters. High-Throughput sequencing (HTS) from environmental samples using small water volumes has been proposed to detect species of interest whose DNA is the most abundant. We analyzed 6-L water samples taken from subtropical and tropical waters using Cytochrome oxidase I (COI) gene as metabarcode. In the open ocean, several commercial fish larvae and invertebrate species important in fish diet were found from metabarcodes and confirmed from individual barcoding. Comparing Atlantic, Mediterranean, Red Sea, and Pacific samples we found a lower taxonomic depth of OTU assignments in samples from tropical waters than in those from temperate ones, suggesting large gaps in reference databases for those areas; thus a higher effort of zooplankton barcoding in tropical oceans is highly recommended. This and similar simplified sampling protocols could be applied in early detection of species important for fisheries.

Biodiversitas ikan Amfidromus Gobiidae di Perairan Indonesia

Gobiidae fish are distributed widely in tropical and subtropical waters, and inhabit almost all benthic habitats ranging from freshwater, intertidal to offshore, with varied substrates such as muddy bottom, rocky, and coral beds. The diets of Gobiidae varies greatly, from microalgae to small fish. The life cycle follows the amphidromus migration pattern, the mature Gobiidae spawn in fresh water and the hatched larvae drift to brackish waters or to the sea, and will return to fresh water in a few weeks or months later. Species of Gobiidae varies greatly in Indonesian waters. The species composition of Gobiid fish schooling varies greatly by location and by seasonal appearance in estuary waters.

Metabolic plasticity of Salmonella enterica as adaptation strategy in river water

ABSTRACT The survival of Salmonella in subtropical river water depends on genetic and metabolic reorganization for the expression of alternative metabolic pathways in response to starvation, which allows Salmonella to use environmental carbon sources (C-sources). However, knowledge regarding the metabolic plasticity of Salmonella serotypes for C-source utilization when exposed to these conditions remains unclear. The aim of this study was to evaluate the metabolic response and level of environmental C-source consumption by environmental Salmonella (Oranienburg and Saintpaul) and clinical Salmonella (Typhi) serotypes by comparing laboratory growth against exposure to river water conditions. Metabolic characterization was performed using a Biolog® EcoPlateTM containing 31 C-sources. The results obtained under laboratory growth conditions showed that environmental serotypes used 74.1% of the C-sources, whereas the clinical serotype used 45.1%. In contrast, in river water, all strains used up to 96.7% of the C-sources. Salmonella exposure to river water increases its capacity to use environmental C-sources.

Genetic variation of longtail tuna Thunnus tonggol landed in four fish markets in Indonesia based on mitochondrial DNA

Abstract. Astarini IA, Ningsih EY, Simanungkalit D, Ardiana SA, Al Malik MD, Yusmalinda NLA, Sembiring A, Pertiwi NPD, Cahyani NKD, Collins A. 2021. Genetic variation of longtail tuna Thunnus tonggol landed in four fish markets in Indonesia based on mitochondrial DNA. Biodiversitas 22: 1644-1651. Longtail tuna (Thunnus tonggol, Family: Scombridae) is an economically valuable neritic species found in tropical and subtropical waters in the Indo-Pacific region. High catch numbers, which have been decreasing, could negatively impact this tuna’s population level. Little research has been conducted on the longtail tuna population in Indonesia. This study aims to determine the genetic diversity and potential population structure of longtail tuna landed in four fish markets in Indonesia (representing three sampling locations because two markets are relatively close to each other) based on sequences of a region of mitochondrial control region (d-loop). A total of 101 samples, out of 110, were identified and confirmed as T. tonggol species by amplifying and sequencing a fragment of d-loop (amplicons ranging from 482 - 523 bp). Neighbor-joining analysis resulted in a topology with all samples grouped into one clade with an average genetic distance of 0.020. Meanwhile, haplotype diversity (Hd) and nucleotide diversity (?) values of the longtail tuna samples were 0.9939 and 0.0192, respectively. The fixation index (Fst) value was -0.00507, with p> 0.05, which indicates that there is no significant population structure among the longtail tuna collected from four fish markets representing three sampling locations. The results of this analysis can be used as basic data in planning sustainable fisheries management efforts.

Distribution and Flora of Seaweed Beds in the Coastal Waters of China

Seaweed plays an important role in energy production in marine, coastal, and island ecosystems. The protection of seaweed beds is a key point for coastal ecosystem health, but the community characteristics, dominant species, and distribution of seaweed beds in the coastal waters of China are still unknown. Dividing seaweed beds based on their ecological function is also required for coastal ecosystem conservation, marine development, and utilization. We conducted ecological surveys on various types of ecosystems at approximately 50 sites dedicated to the conservation of seaweed bed biodiversity in China from 2018 to 2019. These seaweed beds were classified into different flora by water temperature and the attributes of the dominant species. The study showed that Sargassum dominated the coast of China. The coverage of the genus Undaria and the genus Laminaria in the coastal waters of Liaoning and Shandong was high and gradually decreased from Zhejiang to the south. The mean biomass of the seaweed beds along the coast of China was 7.29 kg/m2, and the mean coverage was 41.25%. The height and fresh weight of the dominant species gradually decreased with the decreasing latitude. The seaweed beds were distributed from the shallow water zone to the profundal zone along the coast from north to south, and the bathymetry of seaweed beds in Hainan was below 6 m. Based on the water temperature, the attributes of the seaweed beds, the temperature attributes of the dominant species, and the seaweed’s distribution, the seaweed beds in China can be specifically divided into temperate warm water types, subtropical warm water types, and tropical warm water types. This study is relevant to the development of regulations and directives to ensure biodiversity conservation and environmental sustainability.

Hyperiid amphipods distribution between the central coast and oceanic islands off Chile, southeastern Pacific

The composition, distribution, and abundance of hyperiid amphipods collected in the oceanographic cruise between the central coast and oceanic islands of Chile in the southeastern Pacific were analyzed. Thirty-four genera and 54 species were identified, grouped into two infraorders and 16 families. The presence of Hemityphis tenuimanus Claus 1879, and Laxohyperia vespuliformis Vinogradov & Volkov 1982, expands its geographical distribution as new records for the southeastern Pacific. According to the founded species, spatial distribution, and the bodies of water present in the study area, Chile’s central region would be a transition zone for species originating from the Magellan Province (Subantarctic water) and the Peru-Chile Province (Subtropical water).