Ocean climate drivers and phytoplankton life strategies interact in a complex dynamic to produce harmful algal blooms (HABs). This study aims to integrate historical biological data collected during “red tide” events along the Ecuadorian coast between 1997 and 2017 in relation to five ocean variables derived from satellite remote sensing data to explain the seasonal drivers of coastal processes associated with HABs dynamics. Seasonality of the occurrence of HABs was assessed in relation to oceanographic variables by applying multiple correspondence analysis (MCA) to the Ecuadorian central coast (Zone 1) and at the outer and inner Gulf of Guayaquil (Zone 2). Sixty-seven HABs events were registered between 1997 and 2017. From a total of 40 species of phytoplankton identified, 28 were identified as non-toxic and the remaining 12 are well known to produce toxins. Dinoflagellates were the taxonomic group most highly associated with potential HABs events along the entire Ecuadorian coast. HABs appear to be constrained by the Humboldt coastal upwelling, high precipitation, and associated coastal runoff, with higher biomass abundance in the Gulf of Guayaquil than in the central coast. Results from the MCA reveal that in the central Ecuadorian coast (oligotrophic system), toxic HABs occurred with low abundance of dinoflagellates, while in the Gulf of Guayaquil (eutrophic system), toxic HABs corresponded to a high abundance of dinoflagellates. In both cases, high values were found for sea surface temperature, precipitation, and irradiance—characteristic of wet seasons or El Niño years. Non-toxic HABs occurred with a high abundance of dinoflagellates, ciliates, and centric diatoms, corresponding to colder waters and low levels of precipitation and irradiance. These findings confirm that dinoflagellates display several strategies that enhance their productive capacity when ocean conditions are warmer, allowing them to produce toxins at high or at low concentrations. Considering that the Gulf of Guayaquil is essential to tourism, the shrimp industry, fisheries, and international shipping, these findings strongly suggest the need to establish an ecosystem health research program to monitor HABs and the development of a preventive policy for tourism and public health in Ecuador.
In this paper, we investigate the occurrence and spatial variability of marine heat waves (MHWs) off the southeast coast of Queensland, Australia. The focus is on identifying sea surface temperature (SST) variability in two key ecological hotspots located south of the Australian Great Barrier Reef. This coastal region is bordered in the east by the intensification zone of the East Australian Current (EAC). It includes Hervey Bay, which is part of a UNESCO declared marine biosphere and the Southeast Fraser Island Upwelling System. The analysis of remotely sensed SST for the period 1993 to 2016 identifies the largest number of MHW days for Hervey Bay with a mean length of 12 days. The maximum length of 64 days occurred during the austral summer 2005/2006. The years with the largest number of MHW days was found to occur following the El Niño events in 1998, 2010, and 2016. A cross-correlation and Empirical Orthogonal Function analysis identified a significant correlation with a time lag of 7 months between SST anomalies in the Niño 3.4 region and the southeast Queensland coast. 78% of variance in SST anomalies is explained by the first mode of variability. The strength of the relationship with El Niño was spatially variable and the weakest in Hervey Bay. Due to its sheltered location and shallowness, it is argued that local weather patterns and air-sea fluxes influence this area more than the other two regions, where remotely forced changes in oceanic heat advection may have a stronger impact on generating MHWs. Biodiverse coastal shelf ecosystems are already under tremendous pressure due to human activities. This is likely to be compounded by continued climatic change and an increasing number of MHWs. Thus, similar studies are encouraged for other regional shelfs and smaller scale coastal systems.
We revisit the challenges and prospects for ocean circulation models following Griffies et al. (2010). Over the past decade, ocean circulation models evolved through improved understanding, numerics, spatial discretization, grid configurations, parameterizations, data assimilation, environmental monitoring, and process-level observations and modeling. Important large scale applications over the last decade are simulations of the Southern Ocean, the Meridional Overturning Circulation and its variability, and regional sea level change. Submesoscale variability is now routinely resolved in process models and permitted in a few global models, and submesoscale effects are parameterized in most global models. The scales where nonhydrostatic effects become important are beginning to be resolved in regional and process models. Coupling to sea ice, ice shelves, and high-resolution atmospheric models has stimulated new ideas and driven improvements in numerics. Observations have provided insight into turbulence and mixing around the globe and its consequences are assessed through perturbed physics models. Relatedly, parameterizations of the mixing and overturning processes in boundary layers and the ocean interior have improved. New diagnostics being used for evaluating models alongside present and novel observations are briefly referenced. The overall goal is summarizing new developments in ocean modeling, including: how new and existing observations can be used, what modeling challenges remain, and how simulations can be used to support observations.
While sponges are well‐known to be suspension feeders, consumption of dissolved organic carbon (DOC) has recently been highlighted as a mechanism whereby sponges may avoid food limitation. Further, the sponge‐loop hypothesis proposes that sponges consume DOC and then release shed cellular detritus back to the reef benthos. We examined the carbon flux mediated by the giant barrel sponge, Xestospongia testudinaria, on reefs in the Red Sea across an inshore–offshore gradient that had previously been proposed to affect sponge nutrition in other parts of the tropics. Seawater samples were collected from the incurrent and excurrent flow of 35 sponges. Concentrations of total organic carbon and its components, DOC, live particulate organic carbon (LPOC), and detritus, were all significantly higher in incurrent seawater on inshore than offshore reefs. The diet of X. testudinaria was comprised primarily of DOC and detritus, with mean values across all reef sites of 61.5% DOC, 34.6% detritus, and 3.9% LPOC. Across the inshore–offshore gradient, there was evidence (1) of a threshold concentration of DOC (≈ 79 μmol C Lseawater−1) below which sponges ceased to be net consumers of DOC, and (2) that sponges on offshore reefs were food limited, with a mean carbon deficit relative to sponges on inshore reef sites. Sponges on offshore reef sites exhibited higher pumping rates, perhaps indicating optimal foraging for POC. As previously demonstrated for Xestospongia muta, and contrary to the sponge‐loop hypothesis, there was no evidence that X. testudinaria returned DOC to the benthos in the form of detritus.
Trait-based approaches to investigate (short- and long-term) phytoplankton dynamics and community assembly have become increasingly popular in freshwater and marine science. Although the nature of the pelagic habitat and the main phytoplankton taxa and ecology are relatively similar in both marine and freshwater systems, the lines of research have evolved, at least in part, separately. We compare and contrast the approaches adopted in marine and freshwater ecosystems with respect to phytoplankton functional traits. We note differences in study goals relating to functional trait use that assess community assembly and those that relate to ecosystem processes and biogeochemical cycling that affect the type of characteristics assigned as traits to phytoplankton taxa. Specific phytoplankton traits relevant for ecological function are examined in relation to herbivory, amplitude of environmental change and spatial and temporal scales of study. Major differences are identified, including the shorter time scale for regular environmental change in freshwater ecosystems compared to that in the open oceans as well as the type of sampling done by researchers based on site-accessibility. Overall, we encourage researchers to better motivate why they apply trait-based analyses to their studies and to make use of process-driven approaches, which are more common in marine studies. We further propose fully comparative trait studies conducted along the habitat gradient spanning freshwater to brackish to marine systems, or along geographic gradients. Such studies will benefit from the combined strength of both fields.
Dynamic energy budget (DEB) theory offers a comprehensive framework for understanding the overall physiological performance (growth, development, respiration, reproduction, etc.) of an organism over the course of its life cycle. We present here a simplified DEB model for the swimming crab Liocarcinus depurator. To the best of our knowledge, this is the first to be presented for this species. Most applications of the standard DEB model assume continuous growth in all size metrics (length, wet mass, carbon content) of the modelled species. However, in crustaceans growth, measured as an increase of carapace length/width, occurs periodically via moult. To account for this, we have extended the model to track the continuous increase in carbon mass as well as the episodic increase in physical size. Model predictions were consistent with the patterns in the observed data, predicting both the moult increment and the intermoult period of an individual. In addition to presenting the model itself, we also make recommendations for further development, and evaluate the potential applications of such a model, both at the individual level (e.g. aquaculture) and as a potential tool for population level dynamics (e.g. fisheries stock assessment).
Microbial plankton respiration is the key determinant in the balance between the storage of organic carbon in the oceans or its conversion to carbon dioxide with accompanying consumption of dissolved oxygen. Over the past 50 years, dissolved oxygen concentrations have decreased in many parts of the world’s oceans, and this trend of ocean deoxygenation is predicted to continue. Yet despite its pivotal role in ocean deoxygenation, microbial respiration remains one of the least constrained microbial metabolic processes. Improved understanding of the magnitude and variability of respiration, including attribution to component plankton groups, and quantification of the respiratory quotient, would enable better predictions, and projections of the intensity and extent of ocean deoxygenation and of the integrative impact of ocean deoxygenation, ocean acidification, warming, and changes in nutrient concentration and stoichiometry on marine carbon storage. This study will synthesize current knowledge of respiration in relation to deoxygenation, including the drivers of its variability, identify key unknowns in our ability to project future scenarios and suggest an approach to move the field forward.
Until the 1990s, beaked whales were one of the least understood groups of large mammals. Information on northern bottlenose whales (Hyperoodon ampullatus) and Baird’s beaked whales (Berardius bairdii) was available from data collected during whaling, however, little information existed on the smaller species other than occasional data gleaned from beach-cast animals. Recent research advances have been plentiful. Increasing global survey effort, together with morphometric and genetic analyses have shown at least 22 species in this group. Longitudinal field studies of at least four species (H. ampullatus, B. bairdii, Ziphius cavirostris, Mesoplodon densirostris) have become established over the last three decades. Several long-term studies support photo-identification catalogs providing insights into life history, social structure and population size. Tag-based efforts looking at diving, movements and acoustics have provided detail on individual behavior as well as population structure and ranges. Passive acoustic monitoring has allowed long-term and seasonal monitoring of populations. Genetic studies have uncovered cryptic species and revealed contrasting patterns of genetic diversity and connectivity amongst the few species examined. Conservation concern for these species was sparked by mass strandings coincident with military mid-frequency sonar use. Fat and gas emboli have been symptomatic indicators of mortalities related to sonar exposure, suggesting that their vulnerability stems from the physiological exertion of extreme diving for medium-sized whales. Behavioral response experiments have now shown that beaked whales appear to cease foraging and delay their return to foraging and/or leave the area in association with exposure to mid-frequency signals at low acoustic levels. Future priorities for these species will be to (1) continue field-studies to better understand smaller-scale habitat use, vital rates and social structure; (2) develop better detection methods for larger-scale survey work; (3) improve methodology for monitoring energetics, individual body condition and health; (4) develop tools to better understand physiology; (5) use recent genetic advances with improved sample databanks to re-examine global and local beaked whale relationships; (6) further quantify anthropogenic impacts (both sonar and other noise) and their population consequences (7) apply acquired data for realistic mitigation of sonar and other anthropogenic impacts for beaked whale conservation.
Plastics in the ocean are of great concern nowadays, and are often referred to as the apocalyptic twin of climate change in terms of public fear and the problems they pose to the aquatic and terrestrial environment. The number of studies focusing on the ecological effects and toxicity of plastics has substantially increased in the last few years. Considering the current trends in the anthropogenic activities, the amount of plastics entering the world oceans is increasing exponentially, but the oceans have a low assimilative capacity for plastics and the near-surface layer of it is a finite space. If loading of the oceans with plastics continues at the current rate, the thin sea surface microlayer can have a substantial amount of plastics comparable to the distribution of phytoplankton, at least in the major oceanic gyres and coastal waters in the future. Also, processes like biofouling can cluster microplastics in dense fields in the near-surface layer. Plastics can contribute to the warming or cooling of the water column by scattering and attenuating incoming solar radiation, leading to a potential change in the optical and other physico-chemical properties of the water column. We propose a new notion that changes in solar radiation in the water column due to the plastics have the potential to affect the physical processes in the ocean surface and near-surface layers, and can induce climate feedback cycles. The future can be very different, if plastics evolve as one of the key players affecting the ocean physical processes and hence this is the time to tackle this puzzle with appropriate strategies or let the genie out of the bottle.
The Persian/Arabian Gulf (hereafter, ‘the Gulf’) is an environmentally extreme sea that is being increasingly affected by climate change and anthropogenic stressors, and concern is growing about the future of marine biodiversity in the region. However, identification of species and habitats most in need of conservation is challenging as comprehensive information on species-specific threats and population statuses is lacking. Through application of the International Union for Conservation of Nature (IUCN)Red List methodology – the global accepted standard for classifying extinction risk at the species level – we evaluated the regional conservation status of 471 species of marine bony fishes in the Gulf. The best estimate of the proportion of regionally threatened marine bony fishes, based on all species for which sufficient data were available for assessment, is 8.2%; this is at least twice the proportion of other regions where such assessments have been undertaken. Primary threats include those related to fisheries and& harvesting and those related to coastal development and loss of habitat, impacting 47% and 32% of marine bony fishes, respectively. Such threats are particularly acute in nearshore areas where spatial analyses indicated high species richness. The future of Gulf ecosystems, and the survival of the marine bony fishes, will depend on concerted, collaborative efforts among all Gulf States to develop efficient and effective local and regional marine conservation practices and policies, particularly for species assessed as regionally threatened.