Depth Of Habitation Research Articles

Changing water quality and thermocline depth along an aquaculture gradient in six tropical crater lakes

Understanding how lakes respond to changes in nutrient loading along a productivity gradient can help identify key drivers of aquatic change, thereby allowing appropriate mitigation strategies to be developed. Physical, chemical and biological water column measurements combined with long-term water monitoring data for six closely located crater lakes, in Southeast Asia, were compared to assess the response of lakes along a productivity gradient equating to a transect of increasing aquaculture intensity. Increasing chlorophyll a (phytoplankton biomass) in the upper waters appeared to modify the thermocline depth and light availability causing a shift from a deep chlorophyll maximum at low aquaculture intensity to the emergence of algal dead zones lower in the water column with high aquaculture intensity. High phosphorus loading and light limitation from enhanced algal biomass, associated with high aquaculture intensity, exacerbated nitrogen drawdown, leading to the prevalence of potentially nitrogen-fixing cyanobacteria. Seasonal overturn during the cooler season resulted in low dissolved oxygen concentrations in the epilimnion, potential harmful algal blooms, a reduction in the habitable depth for fish and ultimately increased mortality amongst farmed fish.

Inferring ecological strategies of Psenopsis spp. (Teleostei: Centrolophidae) inhabiting Indian waters from morphological features

ABSTRACT Morphology of the fish and otoliths are popularly used in the discrimination of species/stocks/populations and also to gather meaningful conclusions about their ecology. This approach is useful to enhance our understanding of the relationship between form and function in fishes when a direct assessment is impossible. Inter-species variation was analysed using geometric morphometric analysis for fish body shape, while morphometry and wavelet functions for sagittae morphology. A clear ecomorphological pattern in the body, as well as otolith shape, is evident among species as deeper inhabiting species possess a deeper body with oblong otoliths compared with shallower species that possess a more streamlined body with fusiform otoliths. We also observed that deeper species (P. obscura) possess bigger eyes for the optimum use of available light and bigger otoliths with higher otolith sensory area and otolith area ratio (S:O) for better sound reception capacities. Our hypothesis supports that the differences in fish morphological as well as sensorial traits (otoliths), which are closely related to their locomotion, foraging pattern and depth of habitation, lead to trophic segregation which in turn encourages their coexistence. This is the first work that discusses the relationship between body shape, otolith morphometry and morphology in deep-sea fishes and their ecomorphological interpretations. http://zoobank.org/lsid:zoobank.org:pub:663DD393-80B0-407D-907C-51E3F33ECCFB

Constraining rapid sea level change through radiometric dating of corals growing over a range in paleowater depths

Corals do not all grow near the sea surface. Different species favour different ranges in depth and can survive at different depths from 0 to 5 m to over 0–100 m. Fossil corals, as markers of sea level, are the preferred choice in radiometric dating. Timing and magnitude of sea-level variations are determined from the location and age of a set of in-situ coral samples, and mark the lower bound in sea level. In addition, they have to be assigned an uncertainty to define the upper bound in sea level. This is referred to as the paleowater depth (PWD) and creates a major ambiguity in estimating the appropriate span of habitable depth in sea level. This uncertainty also has an impact on constraining the timing and magnitude of rapid changes in sea level. However, there are approaches that may minimize PWD uncertainties. These include assessing sea level data for groups of coral, during relatively stable sea levels, rather than individually. If samples were recovered in multiple drill-cores, along a sea-bed transect, tighter PWD constraints may apply for samples, in each core, depending on the magnitude of the slope of the sea bed. This method is particularly useful in cases of rapid sea level change over shallow continental shelves when the shift in the shoreline, with sea level change, is large. In these circumstances, the presence of a shallow-water reef established up or down-slope is indicative of a rapid change in sea level.

Habitat influences skeletal morphology and density in the snailfishes (family Liparidae)

We tested the hypothesis that deep-sea fishes have poorly mineralized bone relative to shallower-dwelling species using data from a single family that spans a large depth range. The family Liparidae (snailfishes, Cottiformes) has representatives across the entire habitable depth range for bony fishes (0 m–> 8000 m), making them an ideal model for studying depth-related trends in a confined phylogeny. We used micro-computed tomography (micro-CT) scanning to test three aspects of skeletal reduction in snailfishes (50 species) across a full range of habitat depths: 1) reduction of structural dimensions, 2) loss of skeletal elements, and 3) reduction in bone density. Using depth data from the literature, we found that with increasing depth, the length of the dentary, neurocranium, and suborbital bones decreases. The ventral suction disk decreases width with increasing maximum habitat depth and is lost entirely in some deeper-living taxa, though not all. Although visual declines in bone density in deeper-living taxa were evident across full skeletons, individual densities of the lower jaw, vertebra, suction disk, hypural plate, and otoliths did not significantly decline with any depth metric. However, pelagic and polar taxa tended to show lower density bones compared to other species in the family. We propose that skeletal reductions allow snailfishes to maintain neutral buoyancy at great depths in the water column, while supporting efficient feeding and locomotion strategies. These findings suggest that changes in skeletal structure are non-linear and are driven not only by hydrostatic pressure, but by other environmental factors and by evolutionary ancestry, calling the existing paradigm into question.

Using statolith shape analysis to identify five commercial Loliginidae squid species in Chinese waters

Identification of squids in the family Loliginidae is a time-consuming exercise because of the highly overlapping distributions of species and their overall similarity (fin shape and size, sucker ring dentition, and color). Identifying squid based on statolith morphology is considered more accurate than identifying species based on beaks or gladius morphology. We report and compare the statolith shape of five commercially Loliginidae squid (Uroteuthis (Photololigo) duvaucelii, U. edulis, U. chinensis, Loliolus beka, L. japonica) to determine how well these structures discriminate species. Based on statolith morphology, variation in the lateral and dorsal domes enables an 84.8% success rate at classifying species. Environmental factors correlate with statolith shape, and for vertically migrating squid, statolith relative size decreases with increased depth of habitation. Statolith morphology can be used to effectively and accurately identify species of Loliginidae squid occurring in Chinese waters, and may prove valuable for identifying and managing squid resources.

Depth Affects Seagrass Restoration Success and Resilience to Marine Heat Wave Disturbance

Accelerating losses of seagrass meadows motivate the restoration of these highly productive and beneficial ecosystems. Understanding how environmental parameters including depth and temperature affect restoration trajectories through time is key to conserving and restoring seagrass meadows. We used a long-term (12-year), landscape-scale experiment to test the effect of depth on eelgrass (Zostera marina) restoration success and resilience to a marine heat wave (MHW) disturbance. We found that depth was a critical determinant of seagrass restoration success, with no long-term success at sites deeper than 1.5 m below mean sea level (MSL) or shallower than − 0.8 m MSL. Seeds germinated below − 1.5 m MSL, but shoots did not persist, confirming earlier predictions from a hydrodynamic-vegetation model. Depth was also a significant predictor of seagrass resilience following MHW disturbance. Our results suggest that areas of restored seagrass that are resilient to temperature stress exist across an intermediate depth range, excluding the shallowest and deepest portions of the full habitable depth range for restored seagrass. Over the next decades, sea-level rise will likely affect both the habitable area and the resilient area, available for seagrass restoration. However, seagrass enhancement of sediment accretion may at least partially offset sea-level rise rates. As ocean temperatures warm and MHWs occur more frequently, the resilience of seagrass meadows to temperature stress will be of increasing concern. These results suggest that depth is a critical parameter that will help determine what areas are most resilient and therefore most suitable for conservation and restoration.

The intra-population variability of a freshwater crustacean Polyphemus pediculus (Cladocera, Onychopoda)

A discriminant canonical analysis was employed to study the morphometric structure of a shallow-water local population during the open-water period, and of an autumn deep-water local population extending from the depths of 1.2 m to 23.6 m. Statistically treated data on 11 quantitative and 12 meristic features of 505 mature individuals from the shallow-water population and 294 specimens from the deep-water population were analyzed in the study. P. pediculus belongs to an ecologically polymorphic species. The morphometric structure of local populations of the species and its peculiarities are governed by the environmental conditions of the habitat and have an adaptive value. The population structure is unstable, subject to spatial and temporal variations together with the biotopic and seasonal variations of the environment. A continuous sympatric speciation proceeding in the populations leads to the formation of a number of phenotypes adapted to the existence in specific sub-niches. The morphometric structure of the shallow-water population is formed by three short-term seasonal races having statistically significant differences, and following in succession in correspondence with the change of season. Their morphometric diversity and variability reduce from spring to autumn; the highest statistically significant differences are peculiar to the autumn race. Crustaceans of the summer months do not display statistically significant differences between each other. Morphometric differences between seasonal races do not exceed the limits of the species variability range, and are conditioned mainly by variations in the total length of Ant II and in the number of setae in the medial rows of thoracic limbs of the I-III pairs. The morphometric structure of the deep-water population is more complex and stable, and is formed by three permanent morphoforms, which differ statistically significantly from each other and exist at different depths: the main (1.2–4.7 m), the intermediate (9.3 m) and the deep water (23.6 m). The degree and the accuracy of differences between the morphoforms increase with the depth of habitation. Permanent biotopic races are present at different depths within the morphoforms. The races of the intermediate and the deep-water morphoforms differ statistically significantly from the races of the main morphoform. The races of the main morphoform do not have any statistically significant differences between them. The number of crustaceans permanently present within the biotopic races increases with the habitation depth, and the number of individuals performing vertical migrations reduces. The deep-water morphoform is the most isolated and stable. A considerable divergence of quantitative features is observed in the specimens of this morphoform, resulting in the formation of a new species P. deepwater. Morphometric differences of the biotopic races are conditioned mainly by variations in the total length of Ant II, the length of the caudal stem and setae, Ant I free segments, the head diameter, and the number and length of setae on the third segments of endopodites of thoracic limbs of the I-III pairs.

The content of organic carbon, nitrogen and phosphorus in deep-water biocenoses of coralline algae of the South China sea

The study on the influence of the depth of habitation on the content of organic carbon (Corg), organic and mineral forms of nitrogen (N) and phosphorus (P) in the biocenosis of coralline algae, was carried out in spring in the South China Sea at depths of 5 to 150 m. It was shown that with an increase in depth to 150 m, the content of Corg in the tissues decreased from 72 to 42 g/m2. The content of N also decreased with depth, but to a lesser extent — from 15 to 10 g/m2, while the content of P increased linearly from 0.75 to 4.29 g/m2. The atomic ratio C/N/P in the biocenosis at depths of 5–10 m does not vary significantly and is on the average 187:31:1, which is comparable to the mean values obtained for mass species of reef-building corals. Unlike organic carbon and nitrogen, the phosphorus content in the algal biocenosis increased with depth more than 5 times. Correspondingly, the C/N/P ratio becomes 24:5:1 at a depth of 150 m. Such depth-dependent increase in the proportion of phosphorus in the biocenosis, with a simultaneous decline in the contents of organic carbon and, to a lesser extent, nitrogen, can be explained by release of phosphorus during destruction of the organic matter in the biocoenosis of coralline algae with the formation of insoluble calcium phosphates.

Hyperthermal-driven mass extinctions: killing models during the Permian-Triassic mass extinction.

Many mass extinctions of life in the sea and on land have been attributed to geologically rapid heating, and in the case of the Permian–Triassic and others, driven by large igneous province volcanism. The Siberian Traps eruptions raised ambient temperatures to 35–40°C. A key question is how massive eruptions during these events, and others, could have killed life in the sea and on land; proposed killers are reviewed here. In the oceans, benthos and plankton were killed by anoxia–euxinia and lethal heating, respectively, and the habitable depth zone was massively reduced. On land, the combination of extreme heating and drought reduced the habitable land area, and acid rain stripped forests and soils. Physiological experiments show that some animals can adapt to temperature rises of a few degrees, and that some can survive short episodes of increases of 10°C. However, most plants and animals suffer major physiological damage at temperatures of 35–40°C. Studies of the effects of extreme physical conditions on modern organisms, as well as assumptions about rates of environmental change, give direct evidence of likely killing effects deriving from hyperthermals of the past.This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.

Macrobenthos and megabenthos responses to long-term, large-scale hypoxia on the Louisiana continental shelf

The macrobenthos and megabenthos responses to long-term, recurring hypoxia on the Louisiana continental shelf were compared at four locations with different historical (2000–2010) episodes of annual exposure to bottom-water hypoxia. Measurements of abundance, biomass, species diversity, and community composition of the two size classes of benthos suggested that the macrobenthic response is driven chiefly by tolerance to hypoxia, whereas the megabenthic response was affected by the ability to migrate and the availability/unavailability of macrobenthos prey at the sediment surface. The site exposed to the historically lowest average bottom-water dissolved oxygen (BWDO) concentration exhibited the lowest species diversity for macrobenthos and the highest species diversity for megabenthos, exemplifying the differential effects of hypoxia on different size classes. The high diversity and smaller average size of the megabenthos at the lowest DO site was due to high abundance of invertebrates and a preponderance of small, less vagile fishes that appeared to remain in the area after larger dominant sciaenids had presumably emigrated. The average size and the depth of habitation in the sediment of macrobenthos prey may have also influenced the abundance and biomass of megabenthos foragers.

Effects of Oil from the 2010 Macondo Well Blowout on Marsh Foraminifera of Mississippi and Louisiana, USA

Foraminifera responded to both heavy and light oiling of marshes relative to unoiled control sites by changes to both standing stock and depth of habitation (DOH) in sediment following the 2010 Macondo well blowout. Push cores were taken from the middle marsh at sites classified as unoiled, lightly oiled, and heavily oiled based on concentrations of total polycyclic aromatic hydrocarbons ([TPAH]). Cores were sliced and stained with rose Bengal to detect live specimens of foraminifera. Short-term, sediment-mixing depths were determined using the penetration depths of excess (234)Th, and sedimentary organic carbon and carbonate were measured to distinguish depositional environments. Marsh foraminifera reacted to the highest oil concentration (5,000-18,000 ng/g of TPAH) by reducing standing stock and shortening the DOH compared with the control sites. At a second, less heavily oiled site, foraminifera responded with a shallower DOH, but with a boom in standing stock. Deformed, dead foraminifera occurred in all heavily oiled cores-but not elsewhere. Live foraminifera responded with a population boom at lightly oiled sites with [TPAH] near 1,100 ng/g. Changes in standing stock and DOH with [TPAH] suggest disturbance to the marsh food web, apparently due to oil pollution, and support the use of foraminifera as sentinel species.

The jumbo squid, Dosidicus gigas (Ommastrephidae), living in oxygen minimum zones II: Blood–oxygen binding

Dosidicus gigas is a large, metabolically active squid that migrates across a strong oxygen and temperature gradient in the Eastern Pacific. Here we analyze the oxygen-binding properties of the squid's respiratory protein (hemocyanin, Hc) that facilitate such activity. A high Hc–oxygen affinity, strong temperature dependence, and pronounced pH sensitivity (P50=0.009T2.03, pH 7.4; Bohr coefficient=ΔlogP50/ΔpH=−1.55+0.034T) of oxygen binding facilitate night-time foraging in the upper water column, and support suppressed oxygen demand in hypoxic waters at greater depths. Expanding hypoxia may act to alter the species habitable depth range. This analysis supports the contention that ocean acidification could limit oxygen carrying capacity in squids at warmer temperature leading to reduced activity levels or altered distribution.

Vertical Distribution and Migration Patterns of Nautilus pompilius

Vertical depth migrations into shallower waters at night by the chambered cephalopod Nautilus were first hypothesized early in the early 20th Century. Subsequent studies have supported the hypothesis that Nautilus spend daytime hours at depth and only ascend to around 200 m at night. Here we challenge this idea of a universal Nautilus behavior. Ultrasonic telemetry techniques were employed to track eleven specimens of Nautilus pompilius for variable times ranging from one to 78 days at Osprey Reef, Coral Sea, Australia. To supplement these observations, six remotely operated vehicle (ROV) dives were conducted at the same location to provide 29 hours of observations from 100 to 800 meter depths which sighted an additional 48 individuals, including five juveniles, all deeper than 489 m. The resulting data suggest virtually continuous, nightly movement between depths of 130 to 700 m, with daytime behavior split between either virtual stasis in the relatively shallow 160–225 m depths or active foraging in depths between 489 to 700 m. The findings also extend the known habitable depth range of Nautilus to 700 m, demonstrate juvenile distribution within the same habitat as adults and document daytime feeding behavior. These data support a hypothesis that, contrary to previously observed diurnal patterns of shallower at night than day, more complex vertical movement patterns may exist in at least this, and perhaps all other Nautilus populations. These are most likely dictated by optimal feeding substrate, avoidance of daytime visual predators, requirements for resting periods at 200 m to regain neutral buoyancy, upper temperature limits of around 25°C and implosion depths of 800 m. The slope, terrain and biological community of the various geographically separated Nautilus populations may provide different permutations and combinations of the above factors resulting in preferred vertical movement strategies most suited for each population.

Synergistic effects of climate-related variables suggest future physiological impairment in a top oceanic predator

By the end of this century, anthropogenic carbon dioxide (CO(2)) emissions are expected to decrease the surface ocean pH by as much as 0.3 unit. At the same time, the ocean is expected to warm with an associated expansion of the oxygen minimum layer (OML). Thus, there is a growing demand to understand the response of the marine biota to these global changes. We show that ocean acidification will substantially depress metabolic rates (31%) and activity levels (45%) in the jumbo squid, Dosidicus gigas, a top predator in the Eastern Pacific. This effect is exacerbated by high temperature. Reduced aerobic and locomotory scope in warm, high-CO(2) surface waters will presumably impair predator-prey interactions with cascading consequences for growth, reproduction, and survival. Moreover, as the OML shoals, squids will have to retreat to these shallower, less hospitable, waters at night to feed and repay any oxygen debt that accumulates during their diel vertical migration into the OML. Thus, we demonstrate that, in the absence of adaptation or horizontal migration, the synergism between ocean acidification, global warming, and expanding hypoxia will compress the habitable depth range of the species. These interactions may ultimately define the long-term fate of this commercially and ecologically important predator.

Temporal and spatial occurrence of UV-absorbing mycosporine-like amino acids in tissues of the antarctic sea urchin Sterechinusneumayeri during springtime ozone-depletion

From September to November 1991, UV-absorbing mycosporine-like amino acids (MAAs) were monitored in a natural population of the sea urchin Sterechinusneumayeri from a coastal area of Anvers Island (Antarctic Peninsula). MAA concentrations were determined for specific tissues (gonad, digestive tract and body wall) from adults collected at four depths (intertidal, 8, 15 and 24 m). Four MAAs were identified: mycosporine-glycine, shinorine, porphyra-334 and paly-thine. Concentrations of MAAs among replicate individuals varied considerably. Ovaries had high concentrations of MAAs (84 to 1389 μg g−1 dry wt), while testes had non-detectable levels. The relative abundance of specific MAAs in ovaries appeared to be related to the spawning cycle. Digestive-tract samples had MAA concentrations as high as 3000 μg g−1 dry wt, but the mean MAA content in intertidal individuals decreased by 70% over 3 mo during spring. The body walls of sea urchins had very low amounts of MAAs (≤ 0.08 μg g−1 dry wt). There were significant depth differences in the␣total MAA content of the ovary ( p <0.001), ( p <0.015), digestive tract ( p <0.001), and body wall with organisms from the intertidal and 8 m depth having the highest concentrations of MAAs. Biological dosimetry indicated that UV-B (280 to 320 nm) wavelengths penetrated 3 to 7 m below the sea ice during the study period. The total MAA content in ovaries decreased with depth on all sample dates; however, the MAA content of the digestive tract and body wall did not exhibit a consistent pattern of change with depth. The MAA content of tissues did not change significantly with the temporal gradient of light exposure that was established by both ozone depletion and increasing photoperiod, except in the digestive tract sampled from intertidal specimens. Adult urchins are probably well-protected from UV exposure by the water column and a calcareous test; however, the results of this study suggest that, even under ice cover, depth of habitation is a determinant of MAA content in S. neumayeri. Large daily and seasonal fluctuations in the light regime, which are characteristic of Antarctic coastal environments, apparently do not provide reliable cues to elicit a detectable, temporal, biochemical response.

Effects of oxygen, temperature and light gradients on the vertical distribution of rainbow trout,Oncorhynchus mykiss, in two North Island, New Zealand, lakes differing in trophic status

Abstract Vertical distributions of adult rainbow trout (> 25 cm fork length, FL) were determined with a SIMRAD ES470 split‐beam echosounder in two 80–90 m deep lakes differing in water quality. Between November 1993 and February 1994, most trout (> 80%) were between 10 and 40 m, within or close to the thermocline. However, a small group of fish occupied colder waters, deeper than 50 m. In February, surface water temperatures > 21.0°C and hypolimnetic oxygen levels < 2.5 g m−3 compressed the habitable depth range for trout in Lake Rotoiti to 12–35 m compared with 12–80 m in Lake Rotoma. Deeper‐dwelling trout inhabiting waters over 50 m in Lake Rotoiti would have been forced into shallower waters at this time. However, the vertical distribution of the remaining trout in Lake Rotoiti was not compressed. In March 1994, adult trout were still present in waters 10–40 m deep in both lakes, but many of the smaller fish had moved into shallower waters (< 10 m deep), probably because of declining water temperatures...

Pleistocene molluscan paleoecology and community structure of the Puerto Libertad region, Sonora, Mexico

An intertidal Pleistocene sandflat community is analyzed in terms of community structure, survivorship, inferred biomass distributions, predation patterns, and trophic structure. The distributions of the first-level consumers was controlled by substrate grain size. The distributions of the predators mirrored the concentrations of their prey. Because of differing burrowing abilities, the Libertad infauna produced a community stratification. This property concentrated large segments of biomass at different levels within the substrate. This mechanism buffered biospace-related competition. When similar interspecific depth habitation zones overlapped, one or the other taxon was density limited. Survivorship curves constructed from size-frequency data and the function D = S 1n ( T+1) demonstrated that Lucina approximata experienced constant mortality; Chione califonniensis had a well-developed bimodality of age distributions and Tagelus californianus had increasing population mortality. These contrasting mortality patterns were related to depth of habitation and substrate stability. The internal volumes displaced by a growth series of selected taxa were used to estimate biomass distributions. In terms of biomass, the dominant community members had largest volumes in juveniles — a characteristic of a stable population. Other accessory taxa had large volumes in adults — a property of stationary populations. Theodoxus lutteofasciatus had constant mortality, Cerithium stercusmuscarum, Nassarius tiarula and Natica chemnitzii had curves similar to Chione. Predation patterns demonstrated that two trophic subwebs existed among the predators. Muricanthus nigritus, Hexaplex erythrostomus and Melongea patula preyed on Ostrea palmula, Megapitaria squalida and Cerithium. Natica consumed the juveniles of Chione, Lucina, Nassarius and Theodoxus. The annelid predators Conus regularis, Acteocina inculta and Bulla gouldiana composed a third subweb, not attacked by any molluscan carnivore. The highest predation rate occurred in Nassarius, the lowest among the deep infauna. Differing food preferences by predators served as a stabilizing mechanism maintaining community homeostasis by providing alternative food reserves. It was shown that bore-hole loci changed through ontogeny in selected taxa. Likewise, borehole patterns differed slightly on right and left valves of the same prey species. In general predation rates declined rapidly with advancing age. Highly localized borehole sites were found in Theodoxus, Natica and Nassarius — the prey of Natica. Cerithum, the prey of Muricanthus, had less localized borehole loci. This suggests the latter's predator was less “sensitive” to prey- “induced” responses for selective manipulation. The Libertad community declined when the substrate closed to recruitment by the accumulation of the shells from previous generations.