Seawater Temperature Variations Research Articles

A revised marine fossil record of the Mediterranean before and after the Messinian salinity crisis

Abstract. The Messinian salinity crisis and its precursor events have been the greatest environmental perturbation of the Mediterranean Sea to date, offering an opportunity to study the response of marine ecosystems to extreme hydrological change and a large-scale biological invasion. The restriction of the marine connection between the Mediterranean and the Atlantic Ocean resulted in stratification of the water column and high-amplitude variations in seawater temperature and salinity already from the early Messinian. Here, we present a unified and revised marine fossil record of the Mediterranean (https://doi.org/10.5281/zenodo.13358435, Agiadi et al., 2024) that covers the Tortonian stage, the pre-evaporitic Messinian stage, and the Zanclean stage and encompasses 23 032 occurrences of calcareous nannoplankton, dinoflagellates, foraminifera, corals, ostracods, bryozoans, echinoids, mollusks, fishes, and marine mammals. This record adheres to the FAIR principles, is updated in terms of taxonomy, and follows the currently accepted stratigraphic framework. Based on this record, knowledge gaps are identified, which are due to spatiotemporal inconsistencies in sampling effort and the distribution of sedimentary facies, as well as the inherent differences in the preservation potential between the groups. Additionally, sampling bias in old records may have distorted the record in favor of larger, more impressive taxa within groups. This record is now ready to be used to answer both geological and biological questions about the Mediterranean Sea and beyond and is amendable when new fossil data are brought to light.

Seasonal exploitation of intertidal resources at El Mazo (N Iberia) reveals optimized human subsistence strategies during the Mesolithic in Atlantic Europe

Over the last few decades, research has significantly enhanced our understanding of the role played by shellfish in human subsistence during the Mesolithic period along the Atlantic coast of Europe. Instrumental to this advance has been the analysis of stable oxygen isotope measurements (δ18O) from mollusc shells, which offers valuable insights into the seasonality of shellfish exploitation. The δ18O values serve as reliable indicators of past seasonal seawater temperature variations experienced by the molluscs, enabling us to accurately determine the time of year when past humans collected them. Recent studies using this approach have successfully identified seasonal exploitation patterns of the topshell Phorcus lineatus (da Costa, 1778) in Atlantic Europe. However, uncertainties remain regarding the exploitation schedule of Patella depressa Pennant 1777, one of the most abundantly collected species in Mesolithic sites. Here we used shell δ18O values of P. depressa from the Mesolithic sites of El Mazo (Northern Iberia) to determine its seasonality of exploitation. Our study reveals that P. depressa was prevalently exploited during colder months. Modern specimens of the same limpet species were also collected during two annual cycles to assess potential seasonal changes in meat yield return. Results obtained has profound implications for better understanding how last coastal foragers managed available littoral resources throughout the year.

Simulated ocean circulation and its variability in the Northern Banda Sea from CROCO model

A simulation of 1/24º resolution 3-dimension regional ocean circulation of CROCO was successfully performed from 2015 to 2022 (8 years), covering the ENSO year in El Niño 2015 and La Niña 2022 in the northern Banda Sea (NBS). The model and data comparison of sea surface temperature/height reproduced the observed satellite datasets well, with correlation coefficients above 0.9. It is shown that the mean circulation in the NBS is fed by two inflows from western Buru and the Manipa Strait, resulting in a meandering eastward mean circulation with warmer water accumulated in the eastern NBS, associated with high current variance south of Buru and along the Manipa Strait. Seasonal variations in the oceanographic parameters were dominant in the study area. For example, during the southeast (northwest) monsoon period, the seawater temperature is minimum (maximum) and the salinity is maximum (minimum). Furthermore, the interannual timescale ENSO and IOD significantly modulated seawater temperature and salinity variation, particularly at the thermocline layer (110 m). Much cooler and saltier water is associated with El Niño 2015 and a positive IOD, in contrast to warmer and fresher water during La Niña 2022 and a negative IOD.

Multidecadal-to-interannual modulations of Late Holocene climate variations reconstructed from oxygen isotope ratios of a 237-year-long lived fossil coral in Kikai Island, southwestern Japan

For this study, to elucidate the East Asian monsoon variations on seasonal, interannual, and decadal timescales during the Late Holocene, we generated a 237-year-long time series of bimonthly resolved oxygen isotope ratios (δ18O) from a 3.5–3.2 ka Porites coral in Kikai Island, southwestern Japan. The coral data clearly show seasonal-to-interdecadal variations reflecting seawater temperature and salinity variations for 237 years, which can be a robust benchmark with respect to subtropical Pacific climate variability during the Late Holocene. Along with modern and fossil coral records published earlier from Kikai Island and Okinawa Island, the time-weighted δ18O averages for overlapped 14C ages demonstrate that the annual and summer values had slightly increased by <0.2‰ for 6–3 ka and that the winter values had increased by ∼0.2‰ for 6–5 ka and decreased by ∼0.2‰ for 5–3 ka. The result indicates that the mean climate state around the island had been almost stable on a centennial-to-millennium timescale throughout the transition from the Middle to Late Holocene, but with several short-term cooling excursions of ∼1 °C at 4–3 ka. On interdecadal-to-interannual timescales, amplitudes of the fossil coral δ18O variations for winter and summer were similar or larger at 3.5–3.2 ka relative to today, revealing significant periodicities at 36–38 years, 20–21 years, 6–9 years, and 3–4 years by spectral analysis at 95% confidence intervals. Furthermore, winter and summer coral δ18O time series of the respective periodic components indicate that interannual variations of SST (and/or seawater δ18O) around the island have changed on interdecadal and decadal timescales, which have been modulated on a multidecadal timescale of approximately 60–90 years/cycle. These results imply that the relationships of the East Asian winter and summer monsoon to the El Niño/Southern Oscillation and Pacific Decadal Oscillation dominant in the North Pacific might have been modulated by or associated with the Atlantic Multidecadal Oscillation dominant in the North Atlantic during the Late Holocene.

Valve gaping behaviour in the European oyster (Ostrea edulis) in response to changes in light intensity when combined with variations in salinity and seawater temperature

Valve gaping behaviour in bivalve molluscs controls the flow of water across gills that provides both food, and oxygen for respiration. Closure of the valves also provides protection from predators and poor-quality water conditions. Research presented here used a flow through seawater system with controlled changes in salinity and temperature, combined with continuous measurement of valve gape using Hall effect sensors, to study how changes in these variables affect the valve movements of the European oyster (Ostrea edulis) held under controlled long day-length conditions. A clear relationship between periods of reduced light intensity and maximum valve gape was recognised in preliminary studies and provided a benchmark against which to compare how changes in environmental conditions linked to climate change may alter the behaviour of these coastal marine bivalves. Oysters collected from the southwest coast of Norway in August 2022 were held for 72 h at full seawater salinity of 33.6 and a temperature of 15.8 ± 0.5 °C prior to exposure to a reduction in salinity down to 18.2 over a 3 h period. Oysters showed an initial reduction in valve gape width as salinity reached 31.4, with valve gape decreasing further as salinity fell to 28.8. All valves were fully closed at salinity 20.5. Oysters remained in this condition throughout the subsequent 21 h exposure period with salinity at 18.2. Thereafter salinity was increased in 3 steps. In the first step, salinity reached 24.2 over 2 h, and was held there over the following 22 h. All oysters commenced re-opening valves between salinity 22.8 and 24.2. When salinity was further increased to 27.3 over the subsequent 24 h, oysters returned to approximately their pre-exposure valve gape widths. When salinity 33.8 was delivered to the tanks there were 2 d during which maximum valve gape was significantly reduced, after which valve gape width returned to a pre-exposure condition. The predicted pattern of valve opening during reduced light intensity periods was maintained when seawater temperature was raised from 15.8 °C up to 20.1 °C in approximately 1 °C steps every 24 h. However, reduction of temperature from 20.1 °C in similar sized increments altered the expected patterns of behaviour. The results indicate that increasing occurrences of fluxes in salinity and temperature due to climate change have the potential to disrupt normal valve gaping behaviour in European oysters, creating an additional challenge to those they already face from invasive species and disease.

Research on the Operational Performance of Organic Rankine Cycle System for Waste Heat Recovery from Large Ship Main Engine

Based on the analysis of the waste heat distribution characteristics of a typical ship two-stroke low-speed main engine (model: MAN 8S65ME-C8.6HL, the specified maximum continuous rating SMCR: 21,840 kW) under different loads, two different types of organic Rankine cycle (ORC) systems, namely the basic system (BORC) and the preheated system(PORC), were constructed to recover the ship main engine’s exhaust gas waste heat and jacket cooling water waste heat. Using the thermodynamic simulation model of the system, the main performance indexes, including net output power of the two ORC systems were studied with the variation of seawater temperature and main engine load, and the annual ship fuel saving and annual carbon emission reduction generated by the two systems were compared and analyzed. It was found that the maximum net output power of the BORC system and PORC system were 445.3 kW and 491.3 kW, respectively, when the ship’s main engine load was 100%, and the outboard seawater temperature was 20 °C; the maximum thermal efficiency was 12.84% and 12.71%, respectively; under the annual operation, the fuel saving of BORC system and PORC system can be 456 tons and 510 tons, respectively, and the carbon emission reduction was 1416 tons and 1581 tons, respectively. The analysis found that the net output power of the PORC system is always greater than that of the BORC system. When the outboard seawater is lower, and the main engine load is more than 80%, the net output power difference between the PORC system and BORC system gradually expands, and the improvement of ORC system performance is more evident by adding a preheater. It can be concluded that when the ship was mainly operated in the sea area with low seawater temperature and the main engine was running under high load most of the time, selecting the PORC system to recover the waste heat of the main engine was more advantageous.

Spatial pH variability of coral reef flats of Kiritimati Island, Kiribati

Ocean acidification poses a threat to carbonate-dominated marine systems, such as tropical coral reefs, as it impacts the ability of organisms to calcify. For assessing the susceptibility of coral reef flats to open ocean acidification it is crucial to better understand the dynamics between the carbonate chemistry of open ocean waters flowing onto coral reef flats and the ecological and hydrodynamic processes that locally modify seawater conditions.In this study, variations in seawater pH and temperature were measured along cross-reef flat transects in high resolution (∼0.3 m) and complemented by surveys of the benthic community composition and reef flat bathymetry.Results represent a snapshot in time and suggest that reef flat hydrodynamic processes determine spatial pH modifications, with little influence of variations in benthic community composition. As mean reef flat pH largely equals ocean conditions, ocean acidification has had and will have an unhampered impact on narrow fringing reef flats.

Formation conditions of Ediacaran–Cambrian cherts in South China: Implications for marine redox conditions and paleoecology

The Ediacaran–Cambrian transition period was a critical time interval for the environmental fluctuations and organismal evolution in geological history, popularly known as the “Cambrian Explosion”. The diagenetic mechanism of the widely developed Liuchapo bedded cherts in South China remain unclear and controversial during this critical time interval. To address this, we examined silicon and oxygen isotopes, as well as major and trace elements in the Liuchapo cherts from three wells developed from slope to basin facies in South China. Results reveal that the bedded cherts from the three wells were affected by episodic hydrothermal activity, and the percentage of hydrothermal fluids is highest in the Xc1 well and lowest in the Xb1 well. The paleo-seawater temperature, calculated from chert oxygen isotope values, present a gradual increasing trend from shallow- to deep- areas in South China from 542 to 526 Ma. Redox proxies indicate that the water column of the Xa1 and Xc1 wells were dominated by suboxic condition, while those of the Xb1 well was mainly in oxic conditions. There should exist an oxygen minimum zone (OMZ) during the shelf and slope transition. A suitable temperature and oxic environment are conducive to biological reproduction, which is consistent with higher primary productivity and abundant acritarch fossils in the Xb1 well. Silicon isotope values range from −0.6 ‰ to 1.2 ‰ in the three wells. The diagenetic origin of the Xa1, Xb1, and Xc1 wells was the consequence of the mixture of hydrothermal fluid and seawater, biological activity, and direct hydrothermal precipitation, respectively. Due to the redox condition and seawater temperature variation, silica-secreting organisms should be relatively limited. The episodic hydrothermal fluid, biological activity, and replacement of precursor rock may jointly affect the formation of the Liuchapo bedded cherts during the Ediacaran–Cambrian transition.

A New Look at Physico-Chemical Causes of Changing Climate: Is the Seasonal Variation in Seawater Temperature a Significant Factor in Establishing the Partial Pressure of Carbon Dioxide in the Earth’s Atmosphere?

Seasonal oscillations in the partial pressure of carbon dioxide (pCO2) in the Earth’s atmosphere, stronger in northern latitudes, are assumed to show that terrestrial photosynthesis exceeds respiration in summer, reducing the pCO2 in air but increasing its value in winter when respiration exceeds photosynthesis. We disagree, proposing that variation in the temperature of the surface mixing zone of seawater also reversibly regulates the pCO2 in air as a non-equilibrium process between air and seawater. We predict by thermal modelling that carbonate (CO32−) concentration in the surface mixed layer seawater declines in winter by conversion to bicarbonate with CaCO3 (calcite or aragonite) becoming more soluble and, proportional to the fall of temperature, calcite decalcifying more strongly, allowing more CO2 emission to air. Paradoxically, the increasing CO2 concentration in seawater favoring photosynthesis peaking in mid-summer declines simultaneously in autumn and early winter, forced by boundary layer fugacity into phase transfer to the atmosphere, supporting peak atmospheric pCO2 by late winter. These physico-chemical processes reverse in late winter and spring as seawater warms favoring calcification, fugacity forcing CO2 from the atmosphere as bicarbonate declines and carbonate increases, augmenting suspended calcite particles by several percent. Our numerical computation predicts that the larger range of thermal fluctuations in the northern hemisphere could reversibly favor absorption from air of more than one mole of CO2 per square meter in summer with calcite formation potentially augmenting shallow limestone reefs, despite falling pH, if there is a trend for increasing seawater temperature. Another assumption we challenge is that upwelling and advection from deeper water is the sole cause of increases in dissolved inorganic carbon (DIC) and alkalinity in surface waters, even in the southern hemisphere. Instead, some calcite dissolution is favored as water temperature falls near the surface. Standard enthalpy analysis of key DIC reactions indicates why this oscillation is more obvious in the northern hemisphere with seasonal variations in water temperature (ca. 7.1 °C) being almost twice those in the southern hemisphere (ca. 4.7 °C) with a greater depth of the surface mixing zone of seawater in the southern oceans. Questions remain regarding the relative rates of biotic and abiotic inorganic precipitation and dissolution of CaCO3 in the mixing zone. In summary, rapid biogenic calcification is favored by summer photosynthesis, but slower abiotic calcification is also more likely in warmer water. We conclude that the relative significance of terrestrial biotic and seawater abiotic processes in seawater on the seasonal oscillation in the atmosphere can only be assessed by direct seasonal measurements in seawater.

Oxygen and carbon isotope variations in Chamelea gallina shells: Environmental influences and vital effects.

Stable isotopes in mollusc shells, together with variable growth rates and other geochemical properties, can register different environmental clues, including seawater temperature, salinity and primary productivity. However, the strict biological control over the construction of biominerals exerted by many calcifying organisms can constrain the use of these organisms for paleoenvironmental reconstructions. Biologically controlled calcification is responsible for the so called vital effects that cause a departure from isotopic equilibrium during shell formation, resulting in lower shell oxygen and carbon compared to the equilibrium value. We investigated shell oxygen and carbon isotopic composition of the bivalve Chamelea gallina in six sites along with a latitudinal gradient on the Adriatic Sea (NE Mediterranean Sea). Seawater δ18 O and δ13 CDIC varied from North to South, reflecting variations in seawater temperature, salinity, and chlorophyll concentration among sites. Shell δ18 O and δ13 C differed among sites and exhibited a wide range of values along with the ~400 km latitudinal gradient, away from isotopic equilibrium for both isotopes. These results hampered the utilization of this bivalve as a proxy for environmental reconstructions, in spite of C.gallina showing promise as a warm temperature proxy. Rigorous calibration studies with a precise insight of environment and shell growth are crucial prior to considering this bivalve as a reliable paleoclimatic archive.

Wind-driven retreat of cold water pool and abrupt sea temperature rise off the southwest coast of Korea in summer 2017

Variations in seawater temperature have a critical influence on marine ecosystems and aquaculture industries in coastal regions. From July 25 to August 5, 2017, the sea surface temperature off the southwestern coast of Korea rose rapidly from 17.1 °C to 27.3 °C, which induced environmental stress in marine organisms such as farmed abalone. This study investigated the cause of this abrupt sea temperature rise. Westerly winds from July 1 to 25 were favorable for the upwelling of cold subsurface water along the bottom slope in this coastal region, helping maintain cool surface water temperatures. As the wind changed to easterly, the cold subsurface water moved away and warmer, fresher surface water moved into the coastal region, where the surface currents changed from a southeastward flow to a northeastward flow from July 25 to August 5. Thus, to maintain stable, cool seawater temperatures during summer, both cold water supply and upwelling wind conditions are essential. The analysis of water masses indicated that the cold water was formed by the mixing of the Tsushima Warm Current Water and Yellow Sea Bottom Water in the northern East China Sea. The cold water advected eastward and formed a cold water pool in the intermediate depths (30–80 m) of the northern Jeju Strait, providing cold water to the coastal region during the upwelling period. The westerly winds were disrupted by the approach of a typhoon, which discontinued the supply of bottom cold water. The physical processes identified in this study will help predict short-term increases in water temperature and can assist in the development of countermeasures for the aquaculture industry against the negative effects of abrupt environmental changes.

Vertical Motion Control of an Underwater Glider with a Command Filtered Adaptive Algorithm

Underwater gliders are widely used in oceanic observation, which are driven by a hydraulic buoyancy regulating system and a movable mass. Better motion performance can help us to accomplish observation tasks better. Therefore, a command filtered adaptive algorithm with a detailed system dynamic model is proposed for underwater gliders in this paper. The dynamic model considers seawater density variation, temperature variation and hull deformation according to dive depth. The hydraulic pump model and the movable mass dynamic are also taken into account. An adaptive nonlinear control strategy based on backstepping technique is developed to compensate the uncertainties and disturbances in the control system. To deal with the command saturation and calculation of derivatives in the backstepping process, command filtered method is employed. The stability of the whole system is proved through the Lyapunov theory. Comparative simulations are conducted to verify the effectiveness of the proposed controller. The results demonstrate that the proposed algorithm can improve the motion control performance for underwater gliders under uncertainties and disturbances.

Evaluation of hybrid ocean thermal energy conversion system plantwide performance

Abstract Ocean Thermal Energy Conversion (OTEC) is a renewable energy source in which energy is produced by converting the heat stored in the sea or the ocean thermal energy into valuable work, based on the temperature difference between the warm surface seawater and the cold deep seawater. One of the OTEC system requirements is to have a seawater temperature difference at a minimum of 20 °C within a depth of 1000 m below sea level. Recognizing the importance of optimum sea water temperature, several studies have been conducted to optimize the OTEC system. However, none of these studies was attempted under a hybrid ocean thermal energy conversion (H-OTEC) setup. A H-OTEC system is a combination of closed-cycle and open-cycle OTEC system. The objective of this study is to evaluate the performance of the H-OTEC process system based on the impact of seawater temperature variation by simulating H-OTEC process system. Aspen HYSYS was used as a chemical process simulation platform for conducting this study. After the model was completed, verification test was conducted before the simulated data was recorded. The data for the pump work input and the turbine work output were acquired to determine the net power output and system efficiency. The net power output, Carnot efficiency, and thermal efficiency were recorded approximately 1.39 kW, 5.7%, and 1.45%. The data for net power output and the efficiencies of the system was recorded for every 1 °C of increment in surface seawater temperature. The results showed that the net power output increased slightly by 0.5kW, with efficiency difference for both Carnot cycle and actual cycle, recorded to be less than 3% and 0.1% respectively.

Effect of seawater temperature rising to the performance of Northern Gorontalo small scale power plant

The change of seawater temperature is suspected to affect the power plant condenser’s overall performance. In this paper, we present a gate cycle model of the Northern Gorontalo steam power plant system to investigate the effect of the seawater temperature variation used as the condenser cooling medium on the performance of the steam power plant. The model shows that the power plant can still achieve the required power output even when a significant change in the temperature occurs. Based on the gate cycle model, higher seawater temperatures result in smaller values of the generated power and efficiency of the steam power plant and an increased condenser’s load. This finding is consistent with the reported increased production cost of electrical energy. We have found that an increase in seawater temperature of 2.5 °C results in a 0.33% decrease in system efficiency compared to the reference value.

First insights into population parameters and spatial distribution of the two morphotypes of Mactra stultorum (brownish and whitish) (Linnaeus, 1758) (Mollusca: Bivalvia) along the southwestern Spanish coast

ABSTRACT The aim of this study was to address an analysis of spatial distribution, reproduction, population parameters and secondary production of the natural beds of the well-defined morphotypes of the clam Mactra stultorum (brownish and whitish variants) along the SW Spanish coast. The main findings showed that the presence and the frequencies of both morphotypes increased near the estuaries of rivers, particularly the Guadalquivir River. However, subtle differences in habitat preferences have been revealed and the brownish variant showed a wider and deeper distribution. High similarity in the gonadal development was recorded for both variants. It started in January, continued into late winter and early spring and ended with a spawning period from April to August. An energy storage-utilization cycle, coupled to the reproductive and resting periods and driven by seawater temperature variations and food availability, was also observed. The abovementioned period of gamete emissions resulted in a recruitment pattern with a one-time settlement period per year. Von Bertalanffy growth functions provided an asymptotic length of 46.7 mm (whitish) and 50 mm (brownish) and growth constants of 0.55 (whitish) and 0.50 year−1 (brownish). The mean annual biomass () ranged between 0.062 (whitish) and 0.076 g AFDW m−2 year−1 (brownish) (AFDW: ash-free dry mass). Individual somatic production showed the highest value at 32 and 34 mm shell length, and annual production (P) ranged between 0.075 and 0.113 g AFDW m−2 year−1, resulting in renewal rate (P/) values between 1.21 and 1.37 for the whitish and brownish variants, respectively. These results provide basic knowledge about the reproduction and population dynamics of this species along the Atlantic coast, particularly in the sandflats near the estuary of the Guadalquivir River. They could also shed additional light upon taxonomic differentiation and clarify the ecological role of both variants when compared with two bivalve sympatric species of the intertidal and subtidal areas.

The role of environmental conditions in regulating long-term dynamics of an invasive seaweed

The mechanisms underpinning long-term dynamics and viability of invader populations in the receiving environment remain largely unknown. We tested the hypothesis that temporal variations in the abundance of a well-established invasive seaweed, Caulerpa cylindracea, in the NW Mediterranean, could be regulated by inter-annual fluctuations in environmental conditions. Abundance data of C. cylindracea, sampled repeatedly between 2005 and 2020 at the peak of its growing season (late summer/early fall), were related to interannual variations in seasonal seawater temperature, wind speed and rainfall recorded during different growth phases of the alga, in both subtidal and intertidal habitats. In both habitats, higher peak of C. cylindracea cover was associated with lower seawater temperature in spring and summer, when the seaweed exits the winter resting phase and starts a period of active growth. In addition, the peak abundance of subtidal C. cylindracea was positively associated with higher autumn wind speed intensity and spring daily total precipitation. Our study reveals the importance of seasonal and interannual variation of abiotic factors in shaping temporal patterns of abundance of C. cylindracea, in both subtidal and intertidal habitats. Identifying the factors underpinning invasive population temporal dynamics and viability is essential to predict the time and conditions under which an invader can thrive, and thus guide management strategies aimed to containing invasions under current and future climates.

Is bigger always better? Designing economically feasible ocean thermal energy conversion systems using spatiotemporal resource data

Ocean Thermal Energy Conversion (OTEC) produces electricity using the temperature difference between warm surface and cold deep-sea water. OTEC systems in literature only limitedly consider seasonal seawater temperature variations and thus might not be adequately sized for off-design conditions. This potentially leads to techno-economically sub-optimal design choices. This paper sheds light on which design approach yields the most economically feasible OTEC system considering off-design conditions with 19 years of seawater temperature data in 3-h time steps. We find that systems sized for worst-case thermal resources yield the highest and steadiest electricity production. If seawater temperature variations are moderate, these systems also perform best economically in terms of Levelized Cost of Electricity (LCOE). We demonstrate our model for a 136 MWgross plant in Ende, Indonesia, with an LCOE of 15.12 US¢(2021)/kWh against a local electricity tariff of 15.77 US¢(2021)/kWh. The model is validated for different cost assumptions, system sizes, and temperature profiles to be useful globally. We give recommendations to curb costs and to move large-scale OTEC closer to today’s state of the art, e.g. by using multiple smaller seawater pipes instead of few large pipes. The model is useful to prove OTEC’s global economic feasibility and to promote the technology’s commercialisation.

Growth Resilience of Subarctic Rhodoliths (Lithothamnion glaciale, Rhodophyta) to Chronic Low Sea Temperature and irradiance.

Rhodolith beds are pervasive marine biological systems in the subarctic North Atlantic. Limited knowledge about effects of temperature and irradiance on rhodolith growth limits the ability to anticipate the response of rhodolith beds to this ocean's chronic low, yet changing sea temperature and irradiance regimes. We carried out a 149-d laboratory experiment with Newfoundland Lithothamnion glaciale rhodoliths to test the predictions that growth (i) is inhibited at temperatures of ~0.5°C and (ii) resumes as temperature increases above 0.5°C, albeit at a higher rate under high than low irradiances. Rhodoliths were grown in experimental tanks at near-zero (~0.7°C) seawater temperatures during the first 85 d and at temperatures increasing naturally to ~6°C for the remaining 64 d. Rhodoliths in those tanks were exposed to either low (0.02 mol photons·m-2 ·d-1 ) or high (0.78 mol photons·m-2 ·d-1 ) irradiances during the entire experiment. Rhodoliths grew at a linear rate of ~281 μm·year-1 (0.77 μm·d-1 ) throughout the experiment under both irradiance treatments despite daily seawater temperature variation of up to 3°C. Near-zero temperatures of ~0.5 to 1.0°C did not inhibit rhodolith growth. Model selection showed that PAR-day (a cumulative irradiance index) was a better predictor of growth variation than Degree-day (a cumulative thermal index). Our findings extend to ~0.5°C the lower limit of the known temperature range (~1 to at least 16°C) over which growth in L. glaciale rhodoliths remains unaffected, while suggesting that the growth-irradiance relationship in low-light environments at temperatures below 6°C is less irradiance-driven than recently proposed.

Using Mediterranean Mussel Bio-Indicators to Assess the Initial Health State of Ecosystems Receiving Desalination Plant Effluents in Agadir Bay (Morocco)

Elazzaoui, A.; Kalla, Y.; Lefrere, L.; Bouhaimi, A., and Moukrim, A., 2022. Using Mediterranean mussel bio-indicators to assess the initial health state of ecosystems receiving desalination plant effluents in Agadir Bay (Morocco). Journal of Coastal Research, 38(1), 154–167. Coconut Creek (Florida), ISSN 0749-0208. Mussels are often used as a biological bio-indicator for the quality assessment of marine ecosystems. Adopting this approach, the present work aims to study the initial health status of two ecosystems in Agadir Bay, Morocco expected to receive seawater desalination plant effluents. This study was conducted between February 2015 and March 2017 in two stations, Tifnit-Douira and Cap Ghir. In addition to the gametic development, variations of sex ratio and gonadal index were also determined. The reproductive cycle of Mytilus galloprovincialis is spread throughout the year. Under natural conditions, three collective spawning periods were observed. The main one was during the spring and the two other periods were optional and were in winter and summer. Variations of seawater temperature can make some changes in mussel spawning, with one principal period lasting during spring and summer and the optional one during winter. In both studied stations, sexual rest was manifested by a small percentage of the population particularly during summer, and could not reach the whole population at the same time. This finding is consistent with the gonadal index that never reached the value of 1. A unique hermaphroditism case was revealed in Tifnit-Douira mussels, and it remained statistically insignificant. The sex ratio was perfectly balanced in both stations and was in favour of males. The gonad histology did not show any cellular abnormalities in the germinal tissue. These results are of great importance since they characterize the current state of the studied stations area before the installation of the desalination plant. This state must be maintained after installation in order to preserve the typical halieutic resources of these ecosystems. The present findings confirm the good environmental health status and the aquaculture potential of Agadir Bay, especially in the north ecosystems (Cap Ghir) due to upwelling-nutritional intake and optimum seawater temperature.

Global biogeography of living brachiopods: Bioregionalization patterns and possible controls.

The global distribution patterns of 14918 geo-referenced occurrences from 394 living brachiopod species were mapped in 5° grid cells, which enabled the visualization and delineation of distinct bioregions and biodiversity hotspots. Further investigation using cluster and network analyses allowed us to propose the first systematically and quantitatively recognized global bioregionalization framework for living brachiopods, consisting of five bioregions and thirteen bioprovinces. No single environmental or ecological variable is accountable for the newly proposed global bioregionalization patterns of living brachiopods. Instead, the combined effects of large-scale ocean gyres, climatic zonation as well as some geohistorical factors (e.g., formation of land bridges and geological recent closure of ancient seaways) are considered as the main drivers at the global scale. At the regional scale, however, the faunal composition, diversity and biogeographical differentiation appear to be mainly controlled by seawater temperature variation, regional ocean currents and coastal upwelling systems.