Journal of Marine Systems最新文献

Tropical Cyclone Yaas inflicted substanntial damage on Bhitarkanika National Park (BNP), an eminent wildlife sanctuary housing a vast diversity of flora and fauna, during its occurrence in 2021. The park has experienced a heightened frequency of cyclonic activity in recent years. This study undertakes a comprehensive analysis of the impacts of Tropical Cyclone Yaas on the mangrove forest within BNP, utilizing a broad array of physical, biological, and ecological indices. The assessment method employed in the study encompasses various indicators, such as ecological (Normalized Difference Vegetation Index – NDVI, Enhanced Vegetation Index – EVI, Leaf Area Index – LAI, Normalized Difference Water Index – NDWI, and Normalized Difference Salinity Index – NDSI), biological (Chlorophyll content and Gross Primary Productivity – GPP), and physical (flood monitoring and precipitation) measures. Our findings elucidate the destructive consequences of Cyclone Yaas on the mangrove forest, inflicting significant ecosystem loss attributable to the extreme precipitation and high wind speeds. The biophysical, ecological, and biological indicators reveal profound effects on the local ecosystem, manifested through a decline in vegetation vigor and alterations in soil conditions, notably marked by an increase in salinity.

Pelagic ecosystems around tropical oceanic islands are considered oases of high plankton biomass in the middle of oligotrophic “blue deserts”. To understand the dynamics of such a pelagic ecosystem, we used CTD and ADCP data and zooplankton samples taken from the waters off the remote Fernando de Noronha Archipelago (FNA), Tropical Atlantic. We analyzed how the flow and island topography interactions influence the spatial variability of chlorophyll-a fluorescence and zooplankton abundance, biovolume, and normalized biovolume size spectra (NBSS). We used a 500-μm mesh bongo net to obtain plankton samples in July and August 2010 in areas upstream and downstream of FNA. Zooplankton samples were analyzed with a ZooScan device. Chlorophyll-a peaks and a rise in thermocline indicated a topographic uplift and turbulence downstream of the island, i.e., the “Island Mass Effect”. The NBSS presented a mean slope of −1.19 ± 0.28, and a mean intercept of 3.98 ± 0.87. There were no significant differences in NBSS slopes and intercepts between upstream and downstream areas. Nevertheless, zooplankton and decapod community structures were significantly different between areas: meroplanktonic communities showed higher abundances and biovolumes downstream (p < 0.05). Zoeae of stenopodid cleaner shrimps, anomuran and brachyuran crabs, and fish eggs were significantly more abundant downstream, indicating a “Larval Island Effect”. Distinct peaks in size spectra due to teleost eggs and decapod larvae, downstream of FNA, also indicated a Larval Island Effect. Upstream of the island, there was a higher abundance of gelatinous organisms, holoplanktonic decapods, and advanced stages of brachyuran crabs (“Upstream Island Effect”). Also, copepods, gelatinous organisms, large-sized “other crustaceans” (e.g., euphausiids, amphipods, stomatopod larvae, mysids, etc.), teleost eggs, and stenopodids caused abundance peaks in the size spectra upstream. Our study highlights the need for careful management and conservation of parental spawning stocks of fishes and macroinvertebrates surrounding tropical oceanic islands.

Decapod crustaceans include many species of socioeconomic importance and are key components of pelagic ecosystems, both as adults and as larval forms. Knowledge on seasonal and spatial synchronicity of planktonic larvae in coastal tropical ecosystems is fundamental to understand the dynamics of these complex ecosystems. The objective of the present study was to quantify the contributions of decapods to the zooplankton in adjacent tropical estuarine, coastal and shelf ecosystems, while considering their seasonal life cycles and probable dispersal strategies. We evaluated the contributions of decapod biomass and biovolume in three distinct ecosystems: Rio Formoso estuary, Tamandaré bay, and Pernambuco continental shelf off Tamandaré, northeastern Brazil. Zooplankton samples were taken bimonthly from June 2013 to May 2015, with a 300 μm mesh net, and analyzed using a ZooScan equipment. Decapods were the second most important organisms (after copepods), in abundance, biomass and biovolume, in all sampling areas. Total decapods contributed on average with 33.6%, 4.4% and 7.1% relative abundance and 30.9%, 30.9%, and 15.2% relative biovolume in estuary, bay, and shelf areas, respectively. Overall, the most relevant decapod taxa and stages found in the three sampling areas were brachyuran crab zoeae and megalopae, penaeid shrimp postlarvae (mostly Penaeus spp.), holoplanktonic luciferids (adults, protozoeae and mysis), anomuran zoeae (mostly Paguridae and Diogenidae hermit crabs), pistol shrimp zoeae (Alpheidae), and porcelain crab zoeae (Porcellanidae). Brachyuran zoeae contributed with up to 81.3% abundance and up to 69% biovolume, in the estuary. Penaeid postlarvae comprised up to 28.1% of total abundance and up to 94.7% of total biovolume, on the shelf. These postlarvae were transported shorewards from the offshore shelf. Decapod contributions were especially relevant during massive larval release events of crab zoeae and during shoreward migration of pre-settlement stages. Seasonal peaks were clearly asynchronous between taxa and areas. Possible functional relationships between copepods and key decapod groups are discussed, as well as the processes triggering and regulating the input of larvae. Our results show the importance of quantitative, semi-automatic approaches and the relevance of decapod larvae for pelagic food webs in tropical coastal areas.

Over the years, researchers have continued to put forward solutions to lessen the threats faced by whales within their ecosystem. The correct detection of the different species of whale is important in the search for solutions that will lessen the threats. In order to accurately detect and classify whale species, a number of techniques have been proposed over the years, with varying degrees of success. This research seeks to improve the performance of the hidden Markov models (HMMs), which is one of the most consistent methods for the detection and classification of whale vocalisations. The performance of HMMs is affected by the quality of the feature vectors fed into them. Thus, this research proposes feature extraction (FE) techniques based on principal component analysis. The principal components (PC) computed from PCA and kernel PCA were uniquely transformed into feature vector structures suitable for the HMMs. The emerging models, PCA-HMMs and kPCA-HMMs, were experimented with on passive acoustic monitoring (PAM) datasets containing southern right whale and humpback whale vocalisations. The results from the experiments showed that the kPCA-HMMs outperformed PCA-HMMs. This is due to kPCA’s ability to find non-linear subspaces that may exist in whale vocalisations. Furthermore, the results of the developed PC-HMMs were compared with other existing FE techniques used with HMMs in the literature for the detection of whale vocalisations. The proposed PC-HMMs did not only outperform the existing FE-HMMs but also offered lower computational complexity than the existing HMMs for the detection of whale vocalisations.

The year 2014 is between one of the coldest La Niña events (2011−2012), and one of the most intense warming events between (2013–2016) in the California Current System (CCS). The information provided in this work documents part of the missing information about zooplankton and oceanographic features for the year 2014 along the southern portion of the CCS off the western Coast of Baja California Peninsula (WBCP). The statistical analysis of environmental variables during the summer of 2014 distinguished three regions off the WBCP (north, transitional, and south), in coincidence with changes in zooplankton groups composition. Thermal and saline oceanic fronts off the central region coincided with an increasing abundance of gelatinous zooplankton, where two cold core eddies were present. These mesoscale structures represent physical barriers that seem to determine the distribution limits of planktonic communities. Since no day/night statistical differences in zooplankton composition were found, zooplankton community changes seem more related to the latitudinal environmental changes and mesoscale semi-permanent structures in the middle peninsula.

Coastal circulation influences the distribution of European anchovy (Engraulis encrasicolus) at early life stages (ELS) in the Bay of Biscay (BoB). However, how this happens is not yet fully understood. In this work, further insight is provided by performing Lagrangian diagnostics based on observations of ELS anchovies' initial distributions and currents. Surface diagnostics were obtained by using high-frequency radar (HFR) currents and were applied to analyse multiyear variability and detect the coastal processes that affect the distribution. Since ELS anchovies are also located at subsurface levels, subsurface diagnostics were obtained by using currents reconstructed from HFR and ADCP observations with a reduced order optimal interpolation (ROOI) method. The analyses included transport computations as well as the analysis of flow properties by Lagrangian Coherent Structures and chlorophyll-a satellite images.

Results suggest that ELS anchovies are mostly retained over the shelf and slope, and that transport patterns highly vary across different periods. Mesoscale structures such as eddies, fronts and along-slope currents within the slope and the Capbreton canyon area, as well as strong and persistent winds, could significantly impact the distribution of ELS anchovies. In some periods, the resulting distribution might be due to a combination of these processes. Circulation can also play a key role in ELS anchovy aggregation within short time scales (20 days). This work showcases the potential of observation-based approaches and emphasizes the relevance of coastal observatories for integrated studies.

Skipjack tuna (Katsuwonus pelamis) (SKJ) is one of the most commercially important marine fish species distributed throughout the world's tropical and subtropical oceans. The Indian Ocean is a main fishing ground for SKJ, whose exploitation rate is just below the maximum sustainable yield. Therefore, SKJ stocks may potentially be significantly affected by climate change. In this study, climatic oscillation indices related to the Indian Ocean, including the Indian Ocean Dipole (IOD), the mean water temperature anomaly in the Eastern Indian Ocean (EIO) and Western Indian Ocean (WIO), the Madden-Julian Oscillation Index at 80°E (MJO80) and the Arctic Oscillation Index (AOI), were associated with SKJ catch per unit effort (CPUE). This study aimed to understand the effect of these five climatic oscillations on SKJ, with the goal of optimizing the utilization of skipjack tuna in the Indian Ocean. We combined gradient forest analysis (GFA) and generalized additive models (GAMs) to evaluate the importance of each climatic index with a 0–5 year lag on the impact of SKJ CPUE and to establish an optimal prediction model. The GFA results show that MJO80 is the most important climatic index influencing SKJ CPUE, followed by MJO80_1, AOI_2, IOD_4, WIO_2, etc. The best GAM model includes MJO80, AOI_2, and WIO_2, which could be related to the recruitment and larval survival of SKJ by influencing water temperature. Meanwhile, there is a significant negative correlation between SST and SKJ CPUE in the tropical regions of the western and central Indian Ocean. Our results suggest that climate oscillations have a 0–2 year lag effect on the SKJ fishery in the Indian Ocean, which can be used to predict resource changes in SKJ over the next 2 years.

Long-term trend and interannual variability of heat content down to 300 m in the Arabian Sea during the period 2000–2017 are analyzed to understand the physical forcings that lead to the significant warming of the Arabian sea. The warming trend during spring and summer are primarily due to heat accumulated below the mixed layer (ML) while the heat accumulated in the ML contributes to the warming during the fall and winter. The study reveals that the combined effect of El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) drives the interannual variability of heat content below the ML and the corresponding thermocline variability during spring. During summer, advection of heat plays a key role. Air-sea fluxes mainly drive the variability of heat content in the ML. However, ENSO and IOD also add to the variability during fall and winter. This study indicates that the warming over the upper 300 m in the Arabian Sea is influenced by the number of positive IOD and El Niño years during the study period, while the air-sea fluxes are responsible for the warming of the surface ML. This analysis sheds new light on the Arabian Sea seasonal heat content trends, and underscores the need for evaluation of their implications for the regional climate variability, trend and extremes. The findings have implications for process understanding needed to better predict impacts on marine heatwaves, cyclones and the regional climate.

Based on satellite and in situ data and larval fish distributions obtained from two cruises during April 2012 (cold period) and September 2016 (warm period), larval fish habitats were analyzed in relation to the water masses that converge at the entrance of the Gulf of California. The distribution of environmental variables and the ocean upper layer water masses showed a clear-cut seasonal contrast. During April 2012, the Gulf of California Water extended southward to ∼21^oN, while in September 2016, the Transitional Water expanded northward to ∼23^oN to dominate the entrance of the Gulf of California as the Gulf of California Water retreated to the interior gulf. In addition, mesoscale eddies were frequently observed in both periods, mostly cyclonic in April 2012, and anticyclonic in September 2016. Multivariate analyses defined two larval fish habitats in each period: North and South of a boundary between 22 and 22.5^oN. The larval structure of the North larval fish habitat varied in both composition and abundance between periods, although the dominant species in both periods were Vinciguerria lucetia above the thermocline and Diogenichthys laternatus in the layer beneath the thermocline. These species had a higher abundance in April 2012 than in September 2016. The South larval fish habitats also had differences in their larval structures in the two periods, but Bregmaceros bathymaster was the dominant species, with the highest abundance in April 2012. The definition of the larval fish habitats and their changes in structure were associated with the seasonal contrast of the water masses, but the limits of the larval fish habitats were modulated by the mesoscale structures. The spawning of most species is seasonally controlled, but the dominant ones showed signs of resilience to environmental changes. This study displayed the influence of two different environmental scales on the fish larvae community, which might be a pattern in other regions of water mass convergence.