Thalassas: An International Journal of Marine Sciences最新文献

Dugong are one of the marine mammals known to occur in the Gulf of Kachchh (GoK), Gujarat, India. In the past, very few studies were focused on dugong in the GoK, when studies did occur, they only employed interview surveys and stranding record-based methods. This study was carried out with the purpose of obtaining information based on interview surveys of the local fishermen, land-based monitoring, boat surveys and intertidal area survey for habitat assessment. In the course of the study, a single live sighting of dugong was observed, the first in twenty years. In addition, characteristic feeding trails were detected at six different sites in the region. This study found, the distribution of dugong was identified to be between Okha and Bedi. Evaluation of habitat indicated five different species of seagrass of which, Halophila ovalis and Halodule uninervis were found to be most commonly occurring in the GoK, and has produced seagrass distribution maps through Remote Sensing. Seagrass area was estimated to be around 22.93 (23) km² in GoK. Maps of seagrass species and area indicate potential dugong habitat in the GoK.

A new species of soft coral, Lobophytum andamanensis sp. nov., is described and illustrated, along with a specimen of Lobophytum patulum Tixier-Durivault, 1956, which is reported herein as a new record for India. The type locality of Lobophytum patulum is Diego Suarez bay in Madagascar, and it was later from recorded from the Seychelles, Kenya, Mauritius, and the Indian Ocean coast of South African. Both these species are recorded from the North Andaman group of Islands of the Andaman and Nicobar Archipelago.

The study was carried out to assess the shorebird abundance and its diversity during September 2021 to September 2023 using direct observation and block count method, on the southeast coastline of India, with a study site located at Muttukadu backwaters (12.8006^oN latitude and 80.2363^o E longitude), Chengalpet district of Tamil Nadu. Our study documented 28 shorebird species from Muttukadu backwaters with four families that belongs to the order Charadriiformes. The mean abundance of shorebirds was higher in the post monsoon and followed by monsoon period due to the increased abundance of migratory species. The highest diversity of shorebirds was observed in the monsoon season. The data from rarefaction curve showed that post monsoon and monsoon had higher species richness than pre monsoon and summer. This survey of wintering shorebirds in the study area can be used for proposing the habitat management strategies.

In the Mexican Caribbean, the magnitude of the Sargassum events and the uncoordinated efforts have made it difficult to achieve successful management. This study contributes to understanding the dynamics of the Sargassum accumulations on a sandy beach in Puerto Morelos, Quintana Roo, through monitoring for 18 months (2018–2019). Temporal changes in the abundance of strandings and species composition (including holopelagic and benthic marine macrophytes) were recorded throughout the study period, with the highest biomass in May 2019 (12.6 ± 3.7 kg m^− 2 of dry weight). Nine taxa of Sargassum, three seagrasses, and six taxa of other benthic macroalgae were found at the study site, whose relative abundances changed throughout time. The species S. pteropleuron is reported here for the first time in the Mexican Caribbean; the implications related to its distribution range are discussed. Detailed taxonomic descriptions of holopelagic and benthic Sargassum taxa are included. In addition to massive accumulations of holopelagic Sargassum (53.2–99.4% of the total fresh biomass) for most of the study period (15 of the 18 months), seagrasses were an important component in the strandings, especially during the cold season (reaching up to 76–100% of the total fresh biomass). The ecological implications of changes in species composition and their abundance in the strandings are discussed for coastal ecosystems. This baseline information must be considered to develop sustainable management and promote the conservation of coastal ecosystems.

Graphical abstract

This paper aims to validate the micro increment deposition in the sagittal otoliths of young of the year (YOY) Lithognathus mormyrus in the shallow waters of Çanakkale, Turkey. Wild YOY specimens of L. mormyrus were captured and reared to validate the daily micro increment formation in sagittal otoliths. The formation of daily sagittal micro increments was validated using by alizarin Red S (ARS), at a concentration of 0 (control), 50 mg/lt, 100 mg/lt, 150 mg/lt, 200 mg/lt and 300 mg/lt. The natural photoperiod was applied, and no food was given throughout the marking period. The tanks kept strongly aerated to maintain the pH ~ 7. YOY fish were kept in different aquariums for 17 days post-dyeing and then re-dyeing as before and kept alive for a further 20 days. ARS marks were clearly observed in 71.7% of the YOY L. mormyrus sagittal otoliths under a fluorescent microscope. However, no mark could be observed in any of the samples of 50 mg/lt ARS treatment. Chi² tests revealed that the linear regressions of the number of micro increments between ARS marks against number of elapsed times was not statistically significant. This result showed that micro increment deposition on the sagitta were laid down daily under the experimental conditions and can be used to detect the daily age information for YOY L. mormyrus.

In this study, it was aimed to determine some basic population parameters (age, length, sex composition, length-weight relationship, age-length relationship, growth parameters, condition factor, GSI) of garfish (Belone euxini, Günther, 1866) in the southern Black Sea region coasts. A total of 917 fish were sampled in the study, and their average length and weight were determined as 37.31 ± 0.147 cm, 58.74 ± 0.876 g. The ages were between 1 and 7 and 40.89% of fish consisted of 3 years old. Sex ratio (F:M) is determined as 1:1.81. Length-weight relationship equations W = 0.0005*L^3.196, W = 0.0009*L^3.040, W = 0.0005*L^3.196 for females and males and all, respectively. Asymptotic length (L_∞) and the growth coefficient (k) were estimated at 78.20 cm and 0.119 year^− 1 for females, 69.82 cm and 0.120 year^− 1 for males and 92.06 cm and 0.082 year^− 1 for all indivuduals. Instantaneous total mortality, natural mortality and fishing mortality rates were calculated as Z = 1.02 year^–1, M = 0.16 year^–1, and F = 0.86 year^–1 for combined sexes. Exploitation rate was E = 0.84. The population of Belone euxini was affected by fishing during the study period, according to the estimated E values. According to the GSI values ​​calculated for Belone euxini, it was determined that reproduction started in July and continued until October.

Abstract

Present work examines a long-term trend (2003–2020) of the chlorophyll-a concentration and impact of various controlling factors on it in the Arabian Sea using robust non-parametric Man Kendall analysis, two-way ANOVA statistical test, and two-stage least square regression technique. Climatological means and interannual variations of chlorophyll-a (Chl_a) concentration and other controlling factors viz. Sea surface temperature (SST), Aerosol optical depth (AOD) and sea surface wind (SSW) have been analysed. From the seasonal variation of Chl_a and AOD it is observe that the highest Chl_a (1.4 mg/m³) is observed during July, August, September and October, and the highest AOD (0.8) is observed during June, July, August and September over the Arabian Sea. There was a two-month delay in the peak concentration of Chl_a/AOD, SSW; however, one month delay is observed in the peak concentration of Chl_a/SST in the Arabian Sea. A long-term trend of Chl_a concentration and SSW shows a decreasing trend, whereas SST and AOD show an increasing trend in the Arabian Sea. From ANOVA and two-stage least square regression it is observed that SST plays a significant role in influencing the decreasing trend of Chl_a in comparison to the other two controlling factors (AOD and SSW). A rise of 1% in SST results into a decrease of 0.138 percentage point in Chl_a concentration that is statistically significant at 1% significance level. The present work helps to understand the impact of various controlling factors on the ocean's primary productivity and the effect of climate change on the marine ecosystem.

Deep-sea offshore northwestern Cuba is the less studied zone of the Gulf of Mexico (GoM). Our study aimed to set an environmental baseline and investigate a potential west-east gradient of sediment properties and nematode diversity along the northwestern Cuba. Sediments were collected by multicorer at nine sites in the insular slope between 974 and 1682 m depth. Sediment texture and composition showed a west-east gradient caused likely by narrowing of shelf width and increasing of downslope transport of terrigenous material. We found clear signatures of heavy metal pollution likely derived from Havana City but also from open-sky mining (Castellanos mining complex) and port dredging operations (Mariel). Nematode assemblages were dominated by the deep-sea genera: Acantholaimus, Metadasynemella, Desmodorella, Cervonema, Daptonema, Halalaimus, and Pselionema. α-diversity was about 20–50 genera and γ-diversity of about 100 genera. The β-diversity was substantial likely because small-scale patchiness of resources and heavy metals stress that increased assemblage variability. Individual weight decreased with depth indicating food-supply limitation in the deep sea; also, heavy metals were negatively correlated with weight suggesting deleterious effects on the growing. Our findings indicate that heavy metal pollution has reached deep-sea sediments and corroborate the long-range effects of anthropogenic activities on deep sea. Taxonomic diversity and biological traits (life strategy and trophic composition) constituted a powerful bioindicator of benthic health and benchmark for future potential disturbances in the region. Northwestern Cuba slope is still an understudied portion of the GoM and more research is needed to fully understand its biodiversity and biogeochemical patterns.

Abstract

Aceh province is renowned for its potential marine resources, including fish, with snapper being one of the most economically important coral fish. In Indonesia, this fish serves as the main target for coral fishing, particularly in Aceh, causing a decline in its wild population. This decline requires a sustainable development management plan by acquiring information on population dynamics and natural growth patterns. Therefore, this research aimed to analyze population dynamics related to aspects of fishing rate and population status as well as the natural growth patterns to evaluate ecological condition. The analysis focused on the two predominant snapper species in Aceh waters, namely Lutjanus bengalensis and L. lutjanus, consisting of 376 and 342 samples collected from January to September 2023. Growth pattern analysis showed that the coefficient b value that determined the growth pattern ranged from 0.63 ± 0.0–2.59 ± 2.25 for L. bengalensis with an average of 1.9 ± 0.64, indicating a negative growth pattern, while L. lutjanus had 0.50 ± 0.0–3.27 ± 0.0 with an average of 1.72 ± 1.11, also displaying a negative growth pattern with asymptotic length 287.7 mm and 242.55 mm. Population dynamics analysis showed a higher fishing mortality (F) rate for L. bengalensis and L. lutjanus at 1.98 year^− 1 and 1.41 year ^− 1, respectively which were higher than the natural mortality (M) rate with 0.86 year ^− 1 and 0.59 year^− 1. Current exploitation higher than maximum exploitation (E_curr > E_max ; E > 0.5) of both species L. bengalensis and L. lutjanus respectively with 0.82 year^− 1 > 0.81 year^− 1 and 0.80 year^− 1 > 0.79 year^− 1. In conclusion, the two snapper species had a negative allometric growth patterns, and population dynamic analysis indicating that their population experienced overfishing.

Abstract

A species of gastropod Vexillum interruptum has been documented for the first time in Chota Balu, South Andaman, situated within the Andaman Islands along the Southeast of mainland India. Specimens were discovered in association with surface vegetation of the seaweed Halimeda opuntia (Linnaeus) Lamouroux, 1816, collected during low tide from the intertidal region. This species is characterized by uniquely intersected short brown parallel lines in the lower part of the ribs, setting it apart from other Vexillum species. The paper provides a brief description, illustration, and outlines the geographical distribution of this species worldwide. The findings highlight the significance of the Andaman Islands in hosting unique marine species and emphasize the need for continued research and conservation efforts in this ecologically rich region.