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Indicators of environmental pressure in artificial and natural habitats: Analysis of fluctuating asymmetry in otoliths from Cynoglossus joyneri
Abstract
Since the 20th century, as research on the fluctuating asymmetry (FA) of otoliths in sedentary fish has deepened in a gradual way, many scholars have focused on exploring the ability of their otolith FA to indicate different environmental pressures. In this study, a typical benthic fish – Cynoglossus joyneri from three artificial habitats (artificial reef area (ARA), oyster reef area (ORA) and kelp cultivation area (NCA)) and a natural habitat (natural area (NA)) of Haizhou Bay (Lianyungang, Jiangsu Province, China) was selected as the research object, of which four otolith characters (length, width, perimeter, and area) were used to detect FA based on the squared coefficient of asymmetry variation (CV2a). The results showed that the CV2a of otolith in C. joyneri tended to decrease as their body length increased. In terms of indicating environmental pressure, the CV2a of otolith length in NA was significantly higher than those in the other area (P<0.05); the CV2a of otolith width in NA was significantly higher than those in ARA and ORA (P<0.05), and those in NCA were significantly higher than those in ORA (P<0.05); and the CV2a of otolith area in NA was significantly higher than those in ARA (P<0.05), and those in NCA were significantly higher than those in ORA (P<0.05). Generally, the otolith FA of C. joyneri in artificial habitats has lower CV2a than that in natural habitats, indicating that the environmental pressure in artificial habitats is lower than that in natural habitats. We believe that C. joyneri can serve as an indicator species for environmental pressure between different habitats, which could be considered as a groundbreaking milestone in the study of otolith FA in fish. The findings not only advance the ability to assess environmental pressure in sedentary fish, which provide new insights into evaluating environmental pressure in artificial and natural habitats.
Fluctuating asymmetry (FA) in fish otoliths is a measure of subtle, random differences between paired otoliths, indicating deviations from perfect symmetry due to environmental influences during development. It reflects variations in growth and development within aquatic environments subjected to significant environmental pressures. In our study, we examined 238 Larimichthys polyactis from Haizhou Bay (Jiangsu, China), calculating the Asymmetric Square Coefficient of Variation (CV2a) for four otolith characters: length, width, perimeter, and area of the left and right lateral sagittal otoliths. Our results showed that otolith width had the lowest CV2a (1.78), whereas otolith perimeter had the highest (4.52). Notably, the CV2a for otolith length and width in fish with a body length of less than 110 mm was significantly higher than in fish exceeding 150 mm (P<0.05). However, we observed no obvious pattern in the CV2a changes across different habitats for each otolith character, except that a significant difference in CV2a for otolith width was detected between the NA and the ORA (P<0.05). We hypothesize that ontogenetic variations in L. polyactis otolith FA are associated with the species' feeding habits and habitat preferences. The spatial sensitivity of otolith FA to environmental pressures remains an area requiring further investigation. Future research will expand our dataset to include otolith FA from additional Sciaenidae species, aiming to enhance the accuracy and reliability of environmental pressure assessments in coastal waters.
Fluctuating Asymmetry (FA) in fish otoliths is an indicator of arbitrarily tiny variations between bilateral otolith characters, and it serves as an effective indicator of growth and developmental differences due to environmental conditions. Due to their unique resident traits, the Coilia brachygnathus can provide a potential insight to the environmental pressure reflected by its otolith FA. In this study, 228 C. brachygnathus from Changhu Lake were examined, assessing the Asymmetric Square Coefficient of Variation (CV2a) across four characters: the length, width, perimeter, and area of the left and right lateral sagittal otoliths. Results showed that otolith length exhibited the lowest CV2a, while otolith perimeter displayed the highest. Although no clear pattern emerged in the change of CV2a with increasing body length for each otolith character, the CV2a of otolith width within the 160–180 mm body length group was significantly higher than that in the 120–140 and 220–240 mm groups. Generally, otolith CV2a within the middle and upper lake sections surpassed that in the open water sections of the lower reaches. Our findings indicated that ontogenetically, variations in C. brachygnathus otolith FA are linked to its feeding and habitat preferences, while the spatial responsiveness of otolith FA to environmental pressure warrants further exploration. Future studies will encompass the collection of otolith FA data from additional Coilia species, with particular emphasis on distinguishing migratory and sedentary Coilia, ultimately enhancing the reliability and precision of environmental pressure assessments in inland waters.
Otolith mass asymmetry can significantly affect the vestibular system functionalities; usually, the X values of mass asymmetry vary between −0.2 and + 0.2 (−0.2 < X < + 0.2). These values can change during a fish life and therefore they are not related to the fish total length. We collected a total of 404 fish specimens from the Gulf of Tunis, including three pelagic species: Sardina pilchardus (Walbaum, 1792) (74 otolith pairs), Trachurus mediterraneus (Steindachner, 1868) (66 otolith pairs), and Chelon auratus (Risso, 1810) (60 otolith pairs) and three benthic species: Gobius niger Linnaeus, 1758 (77 otolith pairs), Mullus barbatus Linnaeus, 1758 (60 otolith pairs), and Trachinus draco Linnaeus, 1758 (67 otolith pairs). The relation between the total length and the otolith mass asymmetry was first calculated and compared, and then was evaluated. The comparison of the otolith mass asymmetry between benthic and pelagic species showed a significant difference ( P < 0.05), where the absolute mean value of X does not exceed the critical value (0.2) for all the studied species. No relation has been found between the magnitude of the otolith mass asymmetry and the length in both benthic and pelagic specimens. Environmental factors have an indirect effect on somatic growth and otolith accretion. The significant difference found in this study can be due to the difference between the benthic and pelagic environments.
Artificial reefs are now commonly used as a tool to restore degraded coral reefs and have a proven potential to enhance biodiversity. Despite this, there is currently a limited understanding of ecosystem functioning on artificial reefs, and how this compares to natural reefs. We used water sampling (bottom water sampling and pore water sampling), as well as surface sediment sampling and sediment traps, to examine the storage of total organic matter (as a measure of total organic carbon) and dynamics of dissolved inorganic nitrate, nitrite, phosphate and ammonium. These biogeochemical parameters were used as measures of ecosystem functioning, which were compared between an artificial reef and natural coral reef, as well as a degraded sand flat (as a control habitat), in Bali, Indonesia. We also linked the differences in these parameters to observable changes in the community structure of mobile, cryptobenthic and benthic organisms between habitat types. Our key findings showed: (1) there were no significant differences in inorganic nutrients between habitat types for bottom water samples, (2) pore water phosphate concentrations were significantly higher on the artificial reef than on both other habitats, (3) total organic matter content in sediments was significantly higher on the coral reef than both other habitat types, and (4) total organic matter in sediment traps in sampling periods May and September were higher on coral reefs than other habitats, but no differences were found in November. Overall, in terms of ecosystem functioning (specifically nutrient storage and dynamics), the artificial reef showed differences from the nearby degraded sand flat, and appeared to have some similarities with the coral reef. However, it was shown to not yet be fully functioning as the coral reef, which we hypothesise is due its relatively less complex benthic community and different fish community. We highlight the need for longer term studies on artificial reef functioning, to assess if these habitats can replace the ecological function of coral reefs at a local level.
The fluctuating asymmetry (FA) of fish otoliths can reflect the difference in the growth and development of fish in sea areas greatly affected by environmental pressure, thus enabling the assessment of different habitats. In this study, using 113 Collichthys lucidus samples collected from different functional areas (estuary area, aquaculture area, artificial reef area and natural area) in Haizhou Bay, the square coefficient of asymmetry variation (CV²a) of four characters (length, width, perimeter and area) of the left and right sagittal otoliths was calculated. The results showed that the CV²a value of otolith width was the lowest and that of otolith length was the highest. The CV²a value had no obvious regularity with increasing fish body length. In addition, the CV²a values of the four characteristics reached their lowest values in the artificial reef area, indicating that the construction of marine ranching dominated by artificial reefs may partly improve the aquatic environment in this functional area. We consider that the otolith FA of C. lucidus can be used as a characteristic of environmental stress between different areas/regions/habitats.
Otoliths, calcified structures in the inner ears, are used to estimate fish age, and their shape is an efficient fish stock identification tool. Otoliths are thus very important for the management and assessment of commercial stocks. However, most studies have used left or right otoliths, chosen arbitrarily without evaluation of the difference between these otoliths. In this study, the asteriscii otoliths from 263 common carp (Cyprinus carpio; Linnaeus, 1758) were sampled in three Iraqi rivers to test the potential asymmetry and the geographical effect on otolith growth from three measurements (length, width and weight), and on shape from two shape indices (ellipticity and form-factor). Among all asteriscii otolith features, there was significant fluctuating asymmetry between fish length and every otolith descriptor. At one fish length, the size and/or the shape of otoliths could be different between two individuals and/or between left and right asteriscii otoliths for the same individual. Moreover, the relationship between fish length and otolith shape/growth was significantly dependent on the studied geographical area and, more especially, the environmental effects as the water temperature and pH. Finally, the relationships between fish length and otolith shape indices showed that the otolith evolves into the elliptical shape during the life of the fish. To use the otolith shape, it is essential to take into account the developmental stage of individuals to integrate the ontogenetic effect. Our results highlight the importance of verifying potential otolith asymmetry, especially for the asteriscii otoliths (lagenar otoliths) before their use in fisheries research.
Global declines of foundation species have reduced ecological function at population, community, and ecosystem levels. Restoration of foundation species promises to counter such losses, despite unknown recovery timelines, undefined benchmarks, and uncertainty about whether restored ecosystems approximate natural ones. Here, we demonstrate through a 15‐year large‐scale experiment in coastal Virginia, USA, that restored oyster reefs can quickly recover multiple ecological functions and match natural reefs. Specifically, abundances of oysters and a key crab mesopredator on restored reefs equaled reference reefs in approximately 6 years, indicating that restoration can initiate rapid, sustained recovery of foundation species and associated consumers. As reefs matured and accrued biomass, they became more temporally stable, suggesting that restoration can increase resilience and may stabilize those ecosystem processes that scale with foundation species biomass. Together, these results demonstrate that restoration can catalyze rapid recovery of imperiled coastal foundation species, reclaim lost community interactions, and help reverse decades of degradation.
Otolith morphological variability is used as a reliable indicator to discriminate fish that experience different environmental conditions during their lifetimes. The present study examined the effects of developmental temperature (DT) during the egg and yolk-sac larval period on the otolith shape and asymmetry of Gilthead seabream in the later metamorphosis (56–58 days post-hatching, dph) and the early juvenile stage (93–95 dph). The experimental populations were reared at different water temperatures (17, 20, or 23 °C DT) from epiboly onset to the end of the yolk-sac larval stage (5–7 days post-fertilization, dpf) and then at a common rearing temperature (20 °C), up to the end of the trials (93–95 dph). Otolith shape and bilateral asymmetry were analyzed at metamorphosis (20–21 mm standard length, SL) and the early juvenile stage (31–32 mm SL). The results of elliptic Fourier analysis showed that DT significantly affected the otolith shape at both stages examined. Furthermore, elevated DT significantly increased the asymmetry levels of seabream otoliths in the early juvenile stage. The results are discussed in terms of the thermally induced long-term changes of seabream otolith morphology and the potential effects of the raised otolith asymmetry on wild seabream juveniles.
The otolith, found in both inner ears of bony fish, has mainly been used to estimate fish age. Another application that has been developing significantly in recent years, however, is the use of otolith shape as a tool for stock identification. Often, studies have directly used the shape asymmetry between the right and left otoliths. We tested the magnitude of directional asymmetry between the sagittal otoliths (left vs. right) of 2991 individuals according to their catch locations, and we selected species to evaluate whether directional asymmetry may itself be a tool to evaluate stock boundaries. Elliptical Fourier descriptors were used to describe the otolith shape. We used a flatfish, the common sole (Solea solea, n = 2431), from the eastern English Channel and the southern North Sea as well as a roundfish, the bogue (Boops boops, n = 560), from the Mediterranean Sea. Both species showed significant levels of directional asymmetry between the testing locations. The bogue otoliths showed significant asymmetry for only 5 out of 11 locations, with substantial separation between two large areas: the Algerian coast and the western part of the Italian coast. The sole otoliths showed significant asymmetry in the shape analysis (3.84%–6.57%), suggesting a substantial separation between two large areas: the English and French parts of the English Channel and the southern North Sea. Consequently, directional bilateral asymmetry in otolith shape is a potential new method for stock identification.
Otolith structure is a useful tool in discrimination among fish populations as it is a permanent record of the influence of endogenous and exogenous factors. In the present study we examined otolith morphology and fluctuating asymmetry (FA) for differences between wild‐caught (by bottom trawl) and reared specimens of Gilthead seabream (Sparus aurata). Based on the frequency of regenerated scales (degree of scale regeneration, SRD) on each specimen, a threshold of 30% SRD was used to assign wild‐caught fish individuals as wild (≤30% SRD, LR group) or as possible aquaculture escapees (>30% SRD, HR group). Based on the analysis of elliptic Fourier descriptors, significant differences were found in otolith shape between reared (Rr) and the wild‐caught groups (LR, HR). Reared fish had otoliths with significantly larger perimeter (OP) than wild‐caught fish. Furthermore, FA was significantly higher in the Rr than the LR group for OP and all except one shape descriptors (harmonics 2–7). The HR group exhibited intermediate levels of FA between the low and high FA levels observed in the LR and Rr groups. Results are discussed in terms of the value of combining otolith and scale morphology for the identification of escapees in wild Gilthead seabream stocks.
Artificial reefs are used around the world for many purposes, including widespread deployment to increase fishery yields. These reefs are well‐studied from a direct fisheries‐based perspective, drawing largely on traditional theory and methodological approaches from population and community ecology.
Here we provide an alternative perspective using basic tenets of ecosystem ecology. We focus largely on primary production, as this ecosystem process necessarily constrains the secondary production of fish and invertebrates.
We use this ecosystem ecology viewpoint to examine the long‐standing attraction/production question—do artificial reefs support ‘new’ fish production or simply attract individuals from other habitats? Central to this discussion is identifying ecological thresholds and self‐reinforcing feedbacks. For example, biological or physical processes may facilitate reaching nutrient supply thresholds where fundamental ecological dynamics are shifted, such as enhanced seagrass allocation of resources to above‐ground plant structures following aggregation of fish around reefs.
Synthesis and applications. We propose that the scope for enhanced primary productivity (or other accelerated ecosystem processes) is an under‐utilized guideline that can be used to prioritize artificial reef deployment as part of broader coastal management programmes. Such an ecosystem ecology perspective may provide new insights into the ecological role of artificial reefs and guide the optimization of their deployment and management.
Cannibalism can be a significant factor limiting the survival of pike, Esox lucius, early life stages in both natural and aquaculture conditions. In the present research, type I cannibalism was studied in pike larvae (size range: 9–32.5 mm standard length, SL) in controlled conditions for 45 days post-hatching (dph). For this purpose, the occurrence of cannibalistic pairs, i.e. prey caught by a cannibal inside the cannibal’s mouth, was monitored for 15 min periods by two observers six times daily. Cannibalism was not observed in fish that still had yolk-sacs, but it did occur as soon as the yolk-sac was absorbed on 5 dph at a body size of 13 mm at 22 °C and 10 dph at a body size of 13.4 mm at 15 °C. The ratio of prey to predator size was on average 87%, but the smallest observed size difference was only 1.3%. The intensity of cannibalistic attacks depended on water temperature with more intense cannibalism at 22 °C than at 15 °C, and no cannibalism at 10 °C. Fluctuating asymmetry (FA) in all three sagittal otolith size parameters (area, width, and length) was higher in prey than in cannibals, the differences were not statistically significant.
Hypothesis: Fluctuating asymmetry (FA) – random deviations from perfect symmetry that are used as a measure of developmental stability – is an effective indicator of stress and fitness in threespine stickleback.
Organisms: The threespine stickleback (Gasterosteus aculeatus) and two other species, the brook stickleback (Culaea inconstans) and ninespine stickleback (Pungitius pungitius), were the focus of a review of the literature. In addition, four populations of G. aculeatus – one anadromous population from the Kamchatka River, two marine populations from the White Sea, and one freshwater population from the White Sea basin – were studied in the field.
Methods: A review of the literature relating fluctuating asymmetry to different variables, and a comparison of fluctuating asymmetry in four populations of stickleback, which differed in geographical distribution and life history, using lateral plates and four cranial bones (operculum, lachrymal, third suborbital, quadrate).
Results: An appraisal of the literature on fluctuating asymmetry suggests that decreasing interest in FA studies has likely resulted from conflicting research results. To some extent, this problem is likely caused by the morphological structures used in FA analysis, which are generally limited to the lateral plates and pelvic fins. These structures can evolve quickly in response to various environmental changes, thus their fluctuating asymmetry reflects not only individual fitness and stress, but also multiple uncontrolled factors that may directly affect those same structures. Using four cranial bones in our analysis showed lower fluctuating asymmetry in anadromous stickleback from the Kamchatka Peninsula compared with marine and freshwater stickleback from the White Sea and its basin. This may be caused by more favourable feeding conditions in the North Pacific than in the White Sea. The different environmental conditions at these locations did not appear to have a significant effect on fluctuating asymmetry, although the comparison of freshwater, anadromous, and marine populations showed that the fluctuating asymmetry of the structures we used is responsive to these differences. Our FA analysis of the selected bone structures reveals clear heterogeneity in stickleback with different life histories. We suggest that these structures can be considered reliable for studies of fluctuating asymmetry in stickleback fishes.
The deployment of artificial reefs to enhance the abundance of reef-associated species in the coastal waters of China occurs on a very large scale. However, the ability of these artificial structures to mimic natural habitats for fauna has not been evaluated. This study examined the benthic fish and macroinvertebrates assemblages (sampled using trap nets) of artificial reef complexes deployed in shallow, nearshore (9-11 m) and deeper, offshore waters (20-30 m) in the Lidao artificial reef zone (Yellow Sea, China) to determine whether they differed from assemblages on adjacent habitats: i.e. natural reefs in nearshore and bare substratum in offshore waters. It also investigated the extent of any temporal variation in these assemblages. A greater total number of taxa were identified in offshore than nearshore waters, but nearshore waters supported higher total mean numbers and biomass. No significant differences were detected in the characteristics of the benthic fish and macroinvertebrate fauna between artificial reefs and their corresponding natural habitats in both depths. Faunal composition in both depths showed strong patterns of temporal variation, mainly due to changes in the abundance of some transient fish species such as Conger myriaster and Pseudopleuronectes herzenstein, which matched seasonal patterns in water temperature and clarity. The similarity of community structure between nearshore artificial reefs and natural habitats implies that the artificial reefs are mimicking natural habitats, which facilitates functional connectivity. Thus, in the Lidao artificial reef zone, artificial reefs and natural habitats can be considered as integrated habitat management units. In the offshore waters, however, the lack of a difference in composition between habitats possibly reflects the observed sinking of the artificial reefs. This highlights the importance of detailed site assessments before the deployment of artificial reefs, particularly in silty sediments.
Fluctuating asymmetry in otolith dimensions reflect the stress from environmental conditions such as temperature stress, nutritional stress and pollution. Sagittal otolith characters such as length, width, area and perimeter of Sargocentron spiniferum (sabre squirrelfish) from Shalateen fishing area were investigated. S. spiniferum samples were divided into four-total length groups. All length groups were examined for asymmetry values in the four otolith characteristic, the level of asymmetry of otolith width was higher than of other otolith characters and the highest asymmetry values were found in the group II (240-309 mm). The lowest asymmetry values in area and perimeter otolith characters were found in the first length group (170-239 mm) and the third one (310-379 mm). The asymmetry in these otolith characters may be a result of the stress from environmental conditions in Shalateen, Red Sea coast of Egypt.
Under global change, the ion concentration of aquatic ecosystems is changing worldwide. Many freshwater ecosystems are being salinized by anthropogenic salt inputs, whereas many naturally saline ones are being diluted by agricultural drainages. This occurs concomitantly with changes in other stressors, which can result in additive, antagonistic or synergistic effects on organisms. We reviewed experimental studies that manipulated salinity and other abiotic stressors, on inland and transitional aquatic habitats, to (i) synthesize their main effects on organisms’ performance, (ii) quantify the frequency of joint effect types across studies and (iii) determine
the overall individual and joint effects and their variation among
salinity–stressor pairs and organism groups using meta-analyses. Additive effects were slightly more frequent (54%) than non-additive ones (46%) across all the studies (n = 105 responses). However, antagonistic effects were dominant for the stressor pair salinity and toxicants (44%, n = 43), transitional habitats (48%, n = 31) and vertebrates (71%, n = 21). Meta-analyses showed detrimental additive joint effects of salinity and other stressors on organism performance and a greater individual impact of salinity than the other stressors. These results were consistent across stressor pairs and organism
types. These findings suggest that strategies to mitigate multiple stressor impacts on aquatic ecosystems should prioritize restoring natural salinity concentrations.
Otolith shape analysis is an efficient fish stock identification tool. However, most applications used left and right otoliths or only one of them arbitrarily chosen without testing for biases resulting from potential directional bilateral asymmetry (DA) in otolith shape, i.e., a unimodal population-level deviation form bilateral symmetry between right and left otolith shape. In this study, 560 bogues (Boops boops) were sampled from 11 geographical locations from the Canary Islands to the Aegean Sea and Elliptical Fourier descriptors were used to describe their otoliths’ shape. Firstly, a significant otolith DA was observed at the global scale with an average amplitude of 2.77%. However, at the scale of sampling locations, DA was not always significant and varied in amplitude and direction. Secondly, population structure was investigated using the shape of either right otoliths or left otoliths or both together. Analyses based on right otoliths or both otoliths together, suggested 3 stock units: a North-Western Mediterranean Sea stock, an Eastern Mediterranean Sea stock and a Central-Eastern Atlantic Ocean and South-Western Mediterranean Sea stock. In contrast, no coherent geographical pattern was found based on left otoliths. Our results highlight the importance of accounting for potential otolith DA in otolith-shape based stock identification.
The purpose of this study is to examine fluctuating asymmetry of eye diameter, maxilla length, operculum length, and the number of pectoral fin ray and pelvic fin ray between ploidy and sex in diploid and triploid marine medaka, Oryzias dancena. In all experimental groups, eye diameter and maxilla length showed no significant difference between left side and right side (p>0.05). Results of operculum length in triploid male group and pectoral fin ray's number in diploid male group showed similarity ones with results of operculum length in triploid female group and pectoral fin ray's number in diploid female group (p<0.05). However, the operculum length in diploid male group and pectoral fin ray's number in triploid male group showed consinderable difference with those of operculum length in diploid female group and pectoral fin in triploid female group. Findings of pelvic fin ray's number in all groups were similar to those of pectoral fin ray's number in all groups (p<0.01).
While otolith shape analysis can provide a valuable tool for discriminating between fish populations, factors which may influence otolith shape, such as the effect of size, directional asymmetry in growth, and local environmental conditions, are often unknown. Here, we analyzed differences in otolith shape across three size classes of age-0 common sole Solea solea L. from nursery grounds off the Belgian coast and in the Wadden Sea. Across size classes, form-factor decreased and roundness remained consistently high in both nursery grounds, while ellipticity increased in the Belgian nursery. Directional asymmetry between left and right otoliths measured by Fourier coefficients accounted for 0.96 and 7.2% of the variance when comparing otoliths overall, and for each size class, respectively. Within the Belgian nursery, results were consistent across sampling years and locations. In addition, otolith shape was marginally different between nursery grounds, but highly variable within nursery grounds. A small divergent group, which seems partly related to fish size, was noted at both spatial and temporal scales. Based on these results and before embarking on a study of population structure using otolith shape in age-0 common sole, we recommend testing for directional asymmetry and fish size effects across the entire region of interest.
When an ocean current encounters a vertical structure, such as an artificial reef (AR), it can create a plankton-rich upwelling that provides a reliable feeding spot for fish. The fish attracted into the AR zones depends largely on the size, structure, and layout of the ARs. Thus, this study was conducted to demonstrate the effect of different layouts on the flow field around cubic ARs, a common type of AR in China. Water tank tests and numerical simulations were used to study the flow field around the cubic ARs. Experiment of hydrogen bubble was conducted in a water tank to observe the effect of the reef spacing on the flow field around the reefs. Using computational fluid dynamics, a three-dimensional numerical model was established based on the Navier-Stokes equation. The standard k-ϵ model was adopted to simulate the flow field around the ARs. On comparing the streamlines of the flow field around the ARs, it was found that the numerical results were in good agreement with the hydrogen bubble results. Using the numerical model, the flow around the ARs with different transverse or longitudinal spacing was simulated. When the transverse spacing distance is equal to the width of the AR, the upwelling becomes stronger. When the distance increases to 7L, the interaction between the reefs can be ignored. When the longitudinal spacing distance is equal to 1L, the effect of the interaction of the reefs on the back eddy is quite significant. However, as the distance increases, the interaction between two reefs gradually weakens.
Fluctuating asymmetry was calculated for the otolith length and width of the adult fishes Chlorurus sordidus and Hipposcarus harid. The results showed that the level of asymmetry of the otolith length was the higher than that of the otolith width in both species. For C. sordidus, the lowest level of asymmetry in the otolith length was at the fish total length ranging between 150-260 mm, and the highest at the fish total length 160-260 mm. For the otolith width, the highest level of asymmetry is at the fish length ranging between 24-26 mm and it has zero value in the other length groups. For H. harid, the lowest level of asymmetry in the otolith length was at the fish length ranging between 160-170 mm, and the highest at the fish length 240-260 mm. For the otolith width, the highest level of asymmetry is at the fish length ranging between 240-260 mm and it has zero value in the other length groups. The possible cause of the asymmetry in these species has been discussed in relation to the general presence of pollutants in the area. An increasing asymmetry with the fish length (age) was noticed.
According to the survey data of water quality from 2010 of fifteen monitoring sites which in the area of artificial reefs, one mass index of water quality evaluation method, comprehensive quality index method of Water quality and eutrophication level index method were used to analyze the water quality status in Haizhou Bay. The results shows that, each site BOD5, COD, DIN accord with standard of sea water quality class 1. DIP mostly belong to 2 class standard; In addition to four monitoring sites’ water integrated quality in the slight pollution status for grade 3, the rest of the eleven regions of the sea water is relatively clean for grade 2; This sea water’s N/P maintain the balance basically, In addition to a site appears eutrophication phenomenon, most are in low and medium nutrient level.
The interaction of ice melting glaciers and oceanic stormy weather produce a large variability in the water column structure of the coastal sea from south Pacific Patagonia. This area is largely utilised as spawning and nursery ground for the mesopelagic fish Maurolicus parvipinnis (Sternoptichyidae) during the austral spring. Using microstructure analysis of sagitta otoliths and fluctuating asymmetry of M. parvipinnis larvae from 4.0 to 11.4 mm standard length (SL), we studied the spatial distribution, the variation of larval condition and recent growth during October-November 2009 between 50º06’S and 52º45’S. Hydrographic conditions varied between 1.4-9.5ºC, 14.6-33.5 units of salinity, 11.5-26.5 units of sigma-t and the stability ranged from 3.6 to 594 cycles h-1. Larval abundance ranged between 3.1 and 293.7 ind. 10 m-2, with highest abundances associated to channels connecting fjords and adjacent ocean. Larvae grew at a rate of 0.174 mm d-1, and those individuals collected in areas with intermediate water column stability (216-270 cycles•h-1) showed greater body condition, measured as recent otolith growth index (ROGI). However, these larvae had similar departure from ideal symmetry (FA1 residual model) than larvae collected in more stratified or well-mixed areas. Overall, larvae showed size-dependent asymmetry, being sagitta otoliths of smaller larvae (<7 mm BL) more asymmetrical than those of large larvae (P<0.05). This suggests that M. parvipinnis larvae may be experiencing differently the impacts of water column variability as well as other ecological interactions at different larval stages. Thus, water column structure at hatching would be important for the survival of this fish inhabiting Patagonian fjords of southern Chile.
Fluctuating asymmetry was calculated for the otolith width and length of adult teleost Rastrelliger kanagurta. The results showed that the level of asymmetry of the otolith length was the highest among the two asymmetry values obtained for the otolith of R. kanagurta. The results also showed that the level of asymmetry in the two characters studied at its highest and lowest values in fish ranging in length between 311-320 and mm and 261-270 mm, respectively. The value of asymmetry was zero in the fish length ranging from 221-260 mm for both characters. The possible cause of the asymmetry in this species has been discussed in relation to different pollutants and their presence in the area. A trend of increase in the asymmetry values with the fish length was noticed for the otolith length and width.
Asymmetry was calculated for the otolith length, width, and thickness of two pelagic fi sh species, Sardinella sin-densis (Clupeidae) and Sillago sihama (Sillaginidae). The results showed that the level of asymmetry of the otolith width was the highest among the two asymmetry values obtained for the otolith of S. sindensis. For S. sihama, otolith thickness showed the highest value among the three otolith measurements. The asymmetry value was zero for the otolith thickness in S. sindensis. The lowest and highest values of asymmetry for the three otolith measurements are recorded in the following fi sh size classes of S. sindensis: for otolith length, 9.0-9.9 mm and 14.0-14.9 mm respec-tively; for otolith width, 9.0-9.9 mm, 14.0-14.9 mm respectively. In S. sihama, for otolith length, 19.0-20.9 mm. and 21.0-22.9 mm. respectively, for otolith width, 15.0-16.9 mm and 25.0-26.9 mm respectively; for otolith thickness, 17.0-18.9 mm and 19.0-20.9 mm respectively. The possible cause of asymmetry in these two species has been dis-cussed in relation to different pollutants and their presence in the area. The trend of an increase in the asymmetry value with the fi sh length was noticed in the width of the otolith of the two species studied. ASIMMETRIA FLUTTUANTE IN LUNGHEZZA, LARGHEZZA E SPESSORE DI OTOLITE IN DUE SPECIE DI PESCI PELAGICI DEL GOLFO PERSICO, VICINO A BANDAR ABBAS SINTESI L'asimmetria è stata calcolata per lunghezza, larghezza e spessore degli otoliti di due specie di pesci pelagici, Sardi-nella sindensis (Clupeidae) e Sillago sihama (Sillaginidae). I risultati hanno evidenziato che per l'otolite di S. sindensis, l'asimmetria era presente per due parametri, e il livello di asimmetria è risultato massimo per la larghezza dell'otolite. Per S. sihama, il valore più alto di assimetria si è registrato per lo spessore dell'otolite. Per S. sindensis invece, il valore dell'asimmetria per lo spessore degli otoliti era pari a zero. Sempre per S. sindensis, i valori minimo e massimo di asim-metria si sono registrati nelle seguenti classi di grandezza: per la lunghezza degli otoliti pari a 9,0-9,9 mm e 14,0-14,9 mm rispettivamente, e per la larghezza degli otoliti pari a 9,0-9,9 mm e 14,0-14,9 mm rispettivamente. Per S. sihama, i valori minimo e massimo di asimmetria si sono registrati per la lunghezza degli otoliti pari a 19,0-20,9 mm e 21,0-22,9 mm rispettivamente, per la larghezza degli otoliti pari a 15,0-16,9 mm e 25,0-26,9 mm rispettivamente, nonché per lo spessore degli otoliti pari a 17,0-18,9 mm e 19,0-20,9 mm rispettivamente. La possibile causa di asimmetria in queste due specie è stata messa in relazione a diverse sostanze inquinanti e alla loro presenza nella zona. Per entrambe le spe-cie, gli autori hanno registrato una tendenza all'aumento del valore di asimmetria in relazione alla lunghezza del pesce.
Published on-line: 17 December 2013 Asimetría de la masa de los otolitos del mugílido Liza klunzingeri (Day, 1888), capturados en el Golfo Pérsico junto a Bandar Abbas Se calculó la asimetría de masa, x, como la diferencia entre la masa de otolidos pareados a izquierda y derecha, dividida por la masa media. Se estudió la asimetría del otolito sacular de Liza klunzingeri. Como en otras especies de peces simétricos, el valor absoluto de x no dependió de la longitud del pez ni del ratio de cre-cimiento del otolito. El valor medio de x estuvo entre -0,2 y +0,2. Abstract The otolith mass asymmetry, x, was calculated as the difference between the mass of the right and left paired otoliths divided by av-erage otolith mass. Saccular otolith mass asymmetry was studied in the mugilid fish Liza klunzingeri. As in the case of other symmet-rical fish species, the absolute value of x in L. klunzingeri does not depend on fish length and otolith growth rate. The mean value of x was between -0.2 and +0.2.
Fluctuating asymmetry (FA) is assumed to reflect the developmental instability caused by environmental or genetic stress. Fish otoliths represent a very good tool for investigating the consequence of different effects on FA. Otolith FA analysis, coupled with genetic analysis, has been undertaken on two common West African estuarine species, Ethmalosa fimbriata (EFI) and Sarotherodon melanotheron (SME), in two neighbouring estuaries, in order to highlight the impact of salinity on developmental stability. The Gambia estuary has a normal functioning and the Saloum estuary is inverse (saltier waters in the upper river), reaching extremely high salinities (>100 psu) and constituting severe environmental stress. Five sub-populations of EFI and six of SME were studied along a salinity gradient. The differences between right and left otoliths were estimated with image processing by measuring five dimensions (area, perimeter, diameter, rostrum and posterior radii). Analyses of genetic differentiation at three EPIC and one anonymous nuclear gene loci for EFI and six polymorphic enzymatic loci for SME were carried out to measure the level of heterozygosity. Absolute FA in all otolith traits examined was unaffected by gender but increased significantly with fish size. Size-corrected absolute FA did not show any significant difference among sites differing largely in salinity, although a higher asymmetry in otolith area was recorded in the saltiest site. These findings suggest that otolith asymmetry is a poor indicator of osmotic stress. The individual heterozygosity level did not seem to have an effect on otolith FA for either species, even though a slight correlation appeared with otolith area or perimeter. Otolith FA cannot be considered to be a useful indicator for estimating changes linked with environmental or genetic stress in these estuaries.
The search for pattern in the geographic occurrence of salt lake flora and fauna often reveals strong associations of specific taxa with certain types of water chemistry. Solute composition, along with salinity and habitat stability, may provide a templet shaping the distribution of many organisms inhabiting saline lakes. A review of studies demonstrating habitat associations, specific solute tolerance, and ionic and osmotic adaptations provide evidence of fidelity to particular conditions of environmental chemistry across a wide taxonomic spectrum. Under low salinity conditions, some species show osmoregulatory adaptability to varied solute composition but the capacity for such flexibility is reduced with increased salinity and only certain taxa are found in hypersaline waters dominated by a particular solute. Anionic ratios of chloride, bicarbonate–carbonate, and sulfate appear to be especially important determinants of distribution. Specific solute tolerance presents an alternative explanation to disrupted hydrographic connections in describing how biogeographic distributions may be restricted to certain aquatic habitats in arid regions. Physiological adaptations to chemistry, exemplified in the brine fly genus Ephydra, may be an integral part of the evolution, ecology and diversification of saline water organisms.
The current study aims to calculate and assess the asymmetry of the two goatfish species, Yellowstripe goatfish Mulloidichthys flavolineatus (Lacepède 1801) and Red Sea goatfish, Parupeneus forsskali (Fourmanoir & Guézé 1976) collected from Hurghada fishing harbour, Egypt. The asymmetry valuation for M. flavolineatus and P. forsskali is imperative to demonstrate the impact of asymmetry on the larvae settlement in this vital fishing ground. Asymmetry was calculated for the saccular otolith (Sagittae) biometry, namely length, width, and mass. The results showed that the otolith height had a lower asymmetry value than the otolith length for the two goatfish species inspected. No relationship between the asymmetry value of otolith length and width and total fish length was observed. Both goatfish species' calculated otolith mass asymmetry was higher than that of many teleost fish species.
We analyzed the feeding ecology of Cynoglossus joyneri by carbon and nitrogen stable isotope analysis based on the samples collected from the bottom trawl surveys during spring and autumn of 2018 in Haizhou Bay, China. The results showed that the δ13C and δ15N values of C. joyneri ranged from -20.75‰ to -15.91‰ and from 5.98‰ to 12.02‰, respectively. The mean values of the δ13C and δ15N were (-17.79±1.00)‰ and (9.37±1.33)‰, respectively. There was a significantly negative correlation between the δ13C values and standard length and a positive correlation between the δ15N values and standard length. The mean trophic level of C. joyneri was (3.43±0.97). There was a significantly positive correlation between the trophic level and standard length. The dominant prey groups of C. joyneri were fish, crabs, shrimps, mollusca, polychaeta, plankton and particle organic matter (POM). The trophic contribution of shrimps was the highest among these prey groups. The trophic contribution of fish, crabs and shrimps was higher in autumn than those in spring. This study would help to understand the role of C. joyneri in the material cycling and energy flow in Haizhou Bay ecosystem, and provide scientific basis for the protection and rational utilization of this species.
Macroalgae are being consumed by a growing number of people as functional food. Therefore, they are intensively cultivated to meet the rising demand. Mariculture is a potential source of microplastics (MPs). However, as a potential source of microplastics, little is known regarding the MPs pollution in macroalgae of open sea macriculture. Here we investigated the MPs characteristics in macroalgae in three sections of Haizhou Bay, an important mariculture area in China, during Pyropia culture (Pyropia yezoensis) and non-culture periods (Ulva prolifera, Sargassum horneri, Cladophora sp., Undaria pinnatifida, Ulva pertusa). It was found that P. yezoensis during the culture period had higher MPs abundance (0.17 ± 0.08 particles g-1fresh weight) than other macroalgae (0.12 ± 0.09 particles g-1 fresh weight) during the non-culture period, particularly for the nearshore sections. There were more fiber MPs in P. yezoensis (90.43%) in culture period compared to macroalgae (84.46%) in non-culture period. Highly similar spectrum of plastics in culture gears and macroalgae was verified. Pyropia culture gears released about 1, 037 tons plastics into the environment annually and the MPs abundances in seawater during the culture and non-culture periods were 1.04 ± 0.32 and 1.86 ± 0.49 particles L-1, respectively. The gap of MPs abundance between the two periods can be attributed to the tremendous trapping by massive biomass of P. yezoensis during the culture period and the continuous plastic release during the non-culture period. This study indicates that culture gears of macroalgae could be an important MPs source and the MPs can be transferred to human by edible macroalgae, and meanwhile macroalgae may be ideal biomonitors for MPs pollution in seawater due to their unbiased trapping and immovability.
The possible effects of disruptions in the geomagnetic field caused by different man-made constructions have been increasing considerably in recent years. These include, among others, the development of wind farms located in the sea and increased numbers of underwater cables. The objective of this study was to determine whether a magnetic field (MF) of 10 mT or a 50 Hz electromagnetic field (EMF) of 1 mT affected the developmental instability of the inner ear organ, which is responsible in fish for hearing and balance, in rainbow trout (Oncorhynchus mykiss) reared in a laboratory for 37 days (13 days in egg stage and 24 days in larval stage). This was done by analyzing the fluctuating asymmetry (FA) of otolith size. The MF and EMF values applied in this study are those recorded in the vicinities of underwater alternating current (AC) and direct current (DC) cables, respectively. The influence of MF on otolith FA was found to be statistically significant, with the highest significance occurring in the group of youngest larvae of 5 dph (compared to larvae 15 and 23 dph). Otolith FA was also higher in larvae exposed to the EMF compared to control conditions, but the differences were not statistically significant. Thus, we can conclude that underwater constructions and cables which emit a MF of 10 mT or higher can affect living organisms that are within a distance of a few meters, especially those (as in the case of trout) in settled life stages.
This study was designed to accurately identify Cynoglossus eggs and larvae (Cynoglossus sp.), and to accumulate base data for further study on the taxonomy and early identification of Cynoglossus fishes. Cynoglossus sp. samples were collected in Qingshan Bay, Qingdao, between May and October 2015. Three eggs, 3 larvae and a total of 5 individuals from 2 species (C. joyneri and C. lighti) in the Jiaozhou Bay area were barcoded using COI, sequenced, and compared with 6 Cynoglossus species found in the Shandong Peninsula and recorded in GenBank. Under a light microscope, the egg had a circular shape and floated within a wider perivitelline space; eggs ranged in diameter from 0.68 to 0.87 mm with a mean diameter of 0.73±0.03 mm; eggs had a single layer membrane and were smooth and transparent; the oil globules were located opposite the yolk sac, ranged from 6 to 15 in number, and diameter ranged from 0.04 to 0.10 mm (mean diameter: 0.07±0.01 mm); there were obvious characteristics including the 2 dorsal fin rays and pigmentation and body length changes in the period of metamorphosis for larvae identification. Results of genetic analysis showed that the average K2P distances pairwise-species in Cynoglossus sp., C. joyneri and C.lighti ranged from 0.006 to 0.009, and was 0.002 for C. abbreviatus and C. purpureomaculatus. The two groups were placed in two different clades with the support of a high bootstrap value and had a close genetic relationship, separately. The neighbor-joining (NJ) phylogenetic trees were constructed for COI gene sequences of 8 species using MEGA 6.0, and Zebrias zebra was included as an outgroup. The above analysis and results showed that the Cynoglossus sp. is C. joyneri.
The early life history of a tongue fish Cynoglossus joyneri GÜNTHER was studied in the western Wakasa Bay, the Japan Sea.
General morphology of the larvae and juveniles ranging from 5.75mm to 16.25mm BL, was described. The characteristic features of the fish in early larval stages were elongations of the first 2 dorsal fin rays and distributional patterns of melanophores on the body surface.
Judging from gonad index and occurrence of larvae, actual spawning may occur during relatively long period from July to September in the western Wakasa Bay.
Early poslarvae were caught mainly off Wakasa Bay, and late postlarvae were caught in the inner part of the Bay. Early juveniles were captured in the shallow water of the Bay, and this area may be their nursery ground.
Food items in the gut contents were as follows: small copeods Microsetella norvegica and copepod nauplii in early larvae, copepods Paracalanus sp and M. norvegica in metamorphosis, and copepods Paracalanus sp. in early juveniles.
The problem of testing smooth components of an extended generalized additive model for equality to zero is considered. Confidence intervals for such components exhibit good across-the-function coverage probabilities if based on the approximate result, where f is the vector of evaluated values for the smooth component of interest and V f is the covariance matrix for f according to the Bayesian view of the smoothing process. Based on this result, a Wald-type test of f=0 is proposed. It is shown that care must be taken in selecting the rank used in the test statistic. The method complements previous work by extending applicability beyond the Gaussian case, while considering tests of zero effect rather than testing the parametric hypothesis given by the null space of the component's smoothing penalty. The proposed p-values are routine and efficient to compute from a fitted model, without requiring extra model fits or null distribution simulation.
The concept of nonlinear, sudden responses of ecosystems or species to environmental change has engendered significant interest in the past two decades. Many reviews and theoretical papers have addressed alternative states or stable states, regime shifts, tipping points and phase shifts, but the empirical evidence for these phenomena, which we refer to as stark changes, has not been evaluated in estuaries and nearshore marine ecosystems. We developed standard definitions for these phenomena and examined the functional forms of ecological responses to environmental pressures (i.e. proximate influences on ecosystem state). We searched for publications related to estuaries and nearshore marine ecosystems that included common descriptors of stark change in their keywords. Our search yielded 376 papers, of which we retained 98 that met four criteria: (1) claimed a stepped biological change; (2) inferred change from empirical data; (3) addressed changes that occurred in one or more semi-enclosed, tidally influenced ecosystems; and (4) described a connection to long-term patterns of ecological change. Although there were many instances of changes in ecological states, most were not stark changes. Evidence generally was not derived from time-series data, and many studies inferred temporal change from spatial differences. We describe the eight studies that provided some evidence of stark changes in ecosystem state. We suggest that compelling evidence of stark changes that can be related to pressures requires concurrent time-series data on the ecological response and pressures that were claimed to induce the stark changes.
Fluctuating asymmetry was described for the otolith width and length of adult teleost Beryx splendens. The results showed that the level of asymmetry of the otolith width was the highest among the two asymmetry values obtained for the otolith of B. splendens. For the otolith width character, the results showed that the level of asymmetry at its highest value in fish ranging in length be-tween 191–200 mm and in its lowest value in fish ranging in length between 121–180 mm. For the otolith length, the highest value of asymmetry is noticed in fish ranging in length between 231–244 mm and the lowest value in fish within the length of 121–190 mm. The possible cause of the asymmetry in this species has been discussed in relation to different pollutants and their pres-ence in the area. No trend of increase in the asymmetry values with the fish length was noticed for the otolith width, but there is a weak trend of increase with the fish length in case of otolith length character.
One of the more difficult tasks in evaluating the possible deleterious effects of multiple toxicants on natural communities is in defining subtle sublethal effects before the onset of chronic morbidity. We reason that before detectable changes in either species diversity or species abundance occur subtle changes must take place in a number of important processes, ranging from molecular to behavioral changes. Unfortunately, changes in these parameters have proven most difficult to detect with current methodology. We, therefore, have been examining the possible use of fluctuating asymmetry as a possible measure of environmental stress. Fluctuating asymmetry is simply the random deviation from perfect symmetry of any bilateral anatomical character. It is, therefore, a nonspecific measure of developmental perturbation. Using asymmetry analysis on three species of marine teleost-barred sand bass, Paralabrax Ilebulifer; grunion, Leureslhes lenuis; and barred surfperch, AlIlphistichus argellteus-from southern California and B
The correlations between the fluctuating asymmetries of different characters were investigated in three species (chaetae and wings of Drosophila melanogaster, cheek teeth of Peromyscus leucopus, and cheek teeth of the fossil horse Griphippus gratus). A mean correlation of 0 was found for the two former species, but a mean positive correlation of +0.046 was found for the horse. Reasons are given why this exception may be only apparent. The intensities of some morphological differences in Drosophila have a general component even though they may be bilaterally independent. The lack of variation for a general buffering capacity against minor developmental accidents was not expected. This and related matters are discussed.
A dimensionless measure of otolith mass asymmetry, χ, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in eight flatfish species (110 otolith pairs) and compared with data from a previously published study on roundfishes. As in the case of symmetrical fishes, the absolute value of χin flatfishes does not depend on fish length and otolith growth rate, although otolith mass and the absolute value of otolith mass difference are correlated with fish length. The values of χwere between −0·2 and +0·2 in 96·4% of flatfishes studied. The mean ±s.e. value of χin flatfishes was significantly larger than in standard bilaterally symmetrical marine fishes (‘roundfishes’), respectively 0·070 ± 0·006 and 0·040 ± 0·006. The most prominent distinction is the existence of downside prevalence of saccular otolith mass in flatfishes, which contrasts with no right–left prevalence in roundfishes found in a previous study. In the right-eyed flatfishes (Soleidae), the left saccular otoliths are heavier than the right otoliths. In the left-eyed flatfishes (Bothidae and Citharidae), the right saccular otoliths are heavier than the left otoliths. Not all flatfishes, however, fit in this design: 11·8% of flatfishes studied had the heavier saccular otoliths in the upside labyrinth and 5·4% of flatfishes had no otolith mass asymmetry (within the accuracy of the analysis). At the same time, the more mobile flatfishes (bothids and citharids) have more symmetrical and, hence, more precisely organized saccular otolith organs than the bottom-associated flatfishes (soleids). It is possible to assume that the value of the otolith asymmetry is not only correlated with flatfish placement in a particular family, or position of eyes, but also may correlate with general aspects of their ecology. Mathematical modelling indicated that for most flatfishes one-side saccular prevalence had no substantial significance for sound processing. On the other hand, calculations showed that 49% of flatfishes (but only 14·5% of roundfishes) have |χ| which exceed the critical level and, in principle, could sense the difference between the static displacement of the large and small paired otoliths. At that, the number of the soleids that could sense this difference is greater than the number of the bothids and citharids, 84 and 27%, respectively.
Fluctuating asymmetry (FA), which has been examined in a variety of plants and animals, is widely promoted as a useful bioindicator
of exogenous stressors in habitats, whether of natural or anthropogenic origin. Wildlife managers and researchers often use
a specific group of organisms as an indicator of the health of a given habitat. The purpose of this review is to demonstrate
that FA can be an effective fish biomonitoring tool by presenting a vote counting meta-analysis of 81 fish FA studies published
between 1966 and the first half of 2009. The vote counts were analyzed with the G test for independence to determine whether
the probability of observing significant morphological asymmetry is determined by character type, exogenous stressor type,
or fish order. The information obtained from these papers and their analysis is then used to outline areas in which FA studies
can be improved: (1) carefully considering character choice; (2) distinguishing between asymmetry types; (3) determining the
level of measurement error in between-sides character variation; (4) determining baseline FA levels in populations; (5) increasing
the number of laboratory studies which corroborate field observations of FA; (6) conducting true replications of studies to
validate previous findings. Only with more critical experimental design and data analysis can FA be used as a powerful tool
for assessing environmental degradation.
KeywordsFluctuating asymmetry–Fishes–Environmental stress–Sub-lethal stress–Exogenous stress
Habitatrestoration encompasses a broad range of activities, emphasizing very different issues, goals, and approaches depending on the operational definition of ‘restoration’. This is particularly true for many shellfish (molluscan) dominated systems (e.g. oyster reefs, mussel beds, vermetid gastropod reefs). In contrast to other well-studied biogenic habitats, such as seagrasses, mangroves, or salt marshes, bivalves are directly consumed as a resource. Hence resource extraction has direct consequences for habitat health. Restoration objectives have typically included reduction of public health risks through improved water quality to increase harvest. Restoration or enhancement of populations of commercially exploited shellfish depressed by overharvesting and/or reduced environmental quality remains the principal motivation behind most shellfish ‘restoration’ efforts. Direct and indirect ecosystem services (e.g. filtering capacity, benthic–pelagic coupling, nutrient dynamics, sediment stabilization, provision of habitat, etc.) derived from oyster habitat have been largely ignored or underestimated. Only recently, the restoration of lost ecological function associated with shellfish communities has been included in our discussions and related research examining habitat development and function through a scientific approach. The former area has been reviewed extensively and will not be our focus here. In this review, we examine some of the restoration efforts made in the name of fisheries enhancement, address their effectiveness, and discuss some of the issues associated with realizing the broader goal of ecological restoration. We note the importance of linking success criteria to specific goals and make the case for a greater need in clarifying the ecological functions of shellfish and shellfish habitats. We recognize the limitations of existing datasets and summarize ongoing attempts to address oyster habitat restoration throughout the broad geographic distribution of the American oyster, Crassostrea virginica (Gmelin). In many ways this topic parallels the ongoing debate over ‘attraction versus production’ associated with artificial reef management. We consider how local conditions (e.g. tidal range, bottom topography, turbidity, salinity) and resulting habitat traits affect restoration strategies. We also discuss the underappreciated value of shellfish populations from those areas designated as closed to harvesting due to their intrinsic worth as habitat/larval reserves. The necessity of ecosystem (adaptive) management strategies emerges from this discussion. Finally, this overview supports our contention that shellfish habitat should be included in discussions of ‘essential fish habitats’ (or EFH).
Application analysis of “three fields and one channel” theory in marine ranching habitat construction
- Suo
Generalized additive models: an introduction with R
- Anderson Cook
Evaluation of the prediction effect of two GAMs on the distribution of Cynoglossus joyneri in the Haizhou Bay
- Sun
Bilateral asymmetry in size of otolith of Otolithes ruber (Bloch and Schneider, 1801) collected from the marine waters of Iraq
- Jawad