Diet comparison among demersal marine fish from the Canadian Arctic

Summary The diets of 12 species of demersal marine fish from various locations in the Canadian Arctic comprised a grand total of 267 prey species, mainly invertebrates. The total number of prey species taken by a single fish species ranged from 9 to 91, and the mean number per stomach from 2.0 to 9.4. The most important prey were Crustacea, most frequently epibenthic or planktonic species; Polychaeta, mainly the larger species; and Mollusca, notably the cropped siphons of Macoma calcarea. Generally, only a few species comprised the bulk of the food. Most of the fish had a predominantly benthic or epibenthic diet, a notable exception being Triglops pingeli which ate zoo plankton almost exclusively at the three sites from which it was collected. To a lesser extent, Triglops murrayi, Icelus spatula and Liparis gibbus also fed planktonically. No significant correlations in diet were found among sympatric fish populations, implying a division of resources and reduced interspecific competition.     

Importance of Shallow Water Habitats for Demersal Fishes and Decapod Crustaceans in Penobscot Bay, Maine

We characterized demersal fish and decapod crustacean habitats in 14 shallow (< 12m) areas in Penobscot Bay, Maine, by mapping the distribution of subtidal substrata with an acoustic sea bottom profiler. We identified the aquatic vegetation and the fishes and decapods associated with these habitats. Samples of fishes and decapods in each habitat were collected with a small beam trawl. The seabed at most of the stations sampled was composed of a mosaic of substrata. More species of fishes tow^-1 and higher abundances of fishes and decapods were found in stations with vegetation present, particularly eelgrass, Zostera marina. Decapod species richness tow^-1 was similar between vegetated and unvegetated habitats. Shallow habitats in Penobscot Bay were dominated by juvenile fishes and function as nursery areas. The greater species diversity and higher abundances of epibenthic fishes and decapod crustaceans observed in vegetated habitats, particularly beds of Zostera marina, compared with unvegetated areas in Penobscot Bay conform to the hypothesis that increased habitat complexity results in increased species richness and abundance.The first author is also senior author     

The first demersal trawl survey of benthic fish and invertebrates in the Beaufort Sea since the late 1970s

This study represents the first demersal trawl survey of marine fishes and invertebrates in offshore waters of the Beaufort Sea since 1977. Species composition, distribution, and abundance of demersal fish and benthic invertebrates were assessed with standard methods and demersal trawl gear by the Alaska Fisheries Science Center. Fishes made up 6% of the total catch weight, and invertebrates made up the remaining 94% of the catch weight. A total of 32 species of fish were identified, two taxa were identified to genus and one to family, and 174 taxa of invertebrates were identified. The most abundant demersal fishes were polar cod (Boreogadus saida), eelpouts (Lycodes spp.), Bering flounder (Hippoglossoides robustus), and walleye pollock (Theragra chalcogramma). The most abundant invertebrates were notched brittle stars (Ophiura sarsi), snow crab (Chionoecetes opilio), mussels (Musculus spp.), and the mudstar (Ctenodiscus crispatus). We documented or confirmed extension to the known ranges of four species of fishes: walleye pollock, Pacific cod (Gadus macrocephalus), festive snailfish (Liparis marmoratus), and eyeshade sculpin (Nautichthys pribilovius). We also documented the presence of commercial-sized snow crab (Chionoecetes opilio), which has not previously been recorded in the North American Arctic.     

Demersal fish assemblages associated with hard bottom habitat in the South Atlantic Bight of the U.S.A.

Synopsis Demersal fish communities associated with hard bottom habitats in the South Atlantic Bight were investigated in three depth zones (inner, middle and outer shelf) between 30° and 33°N latitudes. Fishes were sampled with trawls and baited fishing gear, and were observed by remotely operated underwater television. Most demersal hard bottom fishes demonstrated seasonal differences in abundance in each depth zone, especially at the inner and outer shelf stations. Diversity values from trawl catches were higher in winter than summer at inner and outer shelf stations, but lower in winter at middle shelf stations. Species richness was higher in summer than in winter at most stations, but H' diversity patterns were more influenced by community evenness. Diversity values were higher than those reported for similar depths in the Middle Atlantic Bight. Mean biomass of demersal teleosts for all stations combined was slightly greater in winter than in summer. There was no significant difference in biomass between stations in summer, however, middle shelf stations had significantly greater biomass than inner or outer shelf stations in winter. Biomass estimates from the hard bottom areas studied were considerably higher than those reported in the literature for sand bottom areas in the South Atlantic Bight, but less than those reported for tropical reefs. Cluster analysis revealed differences in community composition between day and night trawl tows at all stations, and greater seasonal differences in species composition at inner and outer shelf stations than at middle shelf depths. Underwater television provided useful complementary data to trawl catches, documented the presence of large fishes which avoided the trawl, and provided information on the community composition at high relief stations which could not be trawled.     

Diet of two large sympatric teleosts, the ling (Genypterus blacodes) and hake (Merluccius australis)

Ling and hake are tertiary consumers, and as a result both may have an important structuring role in marine communities. The diets of 2064 ling and 913 hake from Chatham Rise, New Zealand, were determined from examination of stomach contents. Ling was a benthic generalist, and hake a demersal piscivore. The diet of ling was characterised by benthic crustaceans, mainly Munida gracilis and Metanephrops challengeri, and demersal fishes, mainly Macrourids and scavenged offal from fishing vessels. The diet of hake was characterised by teleost fishes, mainly macrourids and merlucciids. Multivariate analyses using distance-based linear models found the most important predictors of diet variability were depth, fish length, and vessel type (whether the sample was collected from a commercial or research vessel) for ling, and fish length and vessel type for hake. There was no interspecific predation between ling and hake, and resource competition was largely restricted to macrourid prey, although the dominant macrourid species predated by ling and hake were different. Cluster analysis of average diet of intraspecific groups of ling and hake confirmed the persistent diet separation. Although size is a central factor in determining ecological processes, similar sized ling and hake had distinctly different foraging ecology, and therefore could influence the ecosystem in different ways, and be unequally affected by ecosystem fluctuations.     

Ecological relevance of temporal stability in regional fish catches

The concept of habitat selection based on 'Ideal Free Distribution' theory suggests that areas of high suitability may attract larger quantities of fishes than less suitable or unsuitable areas. Catch data were used from groundfish surveys to identify areas of consistently high densities of whiting Merlangius merlangus , cod Gadus morhua and haddock Melanogrammus aeglefinus in the Irish Sea and plaice Pleuronectes platessa , sole Solea solea , lemon sole Microstomus kitt in the English Channel over a period of 10 and 9 years respectively. A method was introduced to delineate areas of the seabed that held consistently high numbers of fishes objectively from large datasets. These areas may constitute important habitat characteristics which may merit further scientific investigations in respect to 'Essential Fish Habitats'(EFH). In addition, the number of stations with consistently high abundances of fishes and the number of stations where no fishes were caught gave an indication of the site specificity of the fish species analysed. For the gadoids, whiting was found to be less site specific than cod and haddock, while for the flatfishes, plaice and sole were less site specific than lemon sole. The findings are discussed in the context of previously published studies on dietary specializm. The site specificity of demersal fishes has implications for the siting process for marine protected areas as fish species with a strong habitat affinity can be expected to benefit more from such management schemes.     

Risks of ocean acidification in the California Current food web and fisheries: ecosystem model projections

The benefits and ecosystem services that humans derive from the oceans are threatened by numerous global change stressors, one of which is ocean acidification. Here, we describe the effects of ocean acidification on an upwelling system that already experiences inherently low pH conditions, the California Current. We used an end‐to‐end ecosystem model (Atlantis), forced by downscaled global climate models and informed by a meta‐analysis of the pH sensitivities of local taxa, to investigate the direct and indirect effects of future pH on biomass and fisheries revenues. Our model projects a 0.2‐unit drop in pH during the summer upwelling season from 2013 to 2063, which results in wide‐ranging magnitudes of effects across guilds and functional groups. The most dramatic direct effects of future pH may be expected on epibenthic invertebrates (crabs, shrimps, benthic grazers, benthic detritivores, bivalves), and strong indirect effects expected on some demersal fish, sharks, and epibenthic invertebrates (Dungeness crab) because they consume species known to be sensitive to changing pH. The model's pelagic community, including marine mammals and seabirds, was much less influenced by future pH. Some functional groups were less affected to changing pH in the model than might be expected from experimental studies in the empirical literature due to high population productivity (e.g., copepods, pteropods). Model results suggest strong effects of reduced pH on nearshore state‐managed invertebrate fisheries, but modest effects on the groundfish fishery because individual groundfish species exhibited diverse responses to changing pH. Our results provide a set of projections that generally support and build upon previous findings and set the stage for hypotheses to guide future modeling and experimental analysis on the effects of OA on marine ecosystems and fisheries.     

Subtroprical wetland fish assemblages and changing salinity regimes: Implications for everglades restoration

During the 1960s, water management practices resulted in the conversion of the wetlands that fringe northeastern Florida Bay (USA) from freshwater/oligohaline herbaceous marshes to dwarf red mangrove forests. Coincident with this conversion were several ecological changes to Florida Bay’s fauna, including reductions in the abundances of top trophic-level consumers: piscivorous fishes, alligators, crocodiles, and wading birds. Because these taxa rely on a common forage base of small demersal fishes, food stress has been implicated as playing a role in their respective declines. In the present study, we monitored the demersal fishes seasonally at six sites over an 8-year time period. During monitoring, extremely high rainfall conditions occurred over a 3.5-year period leading to salinity regimes that can be viewed as “windows” to the area’s natural past and future restored states. In this paper, we: (1) examine the changes in fish communities over the 8-year study period and relate them to measured changes in salinity; (2) make comparisons among marine, brackish and freshwater demersal fish communities in terms of species composition, density, and biomass; and (3) discuss several implications of our findings in light of the intended and unintended water management changes that are planned or underway as part of Everglades restoration. Results suggest the reduction in freshwater flow to Florida Bay over the last several decades has reduced demersal fish populations, and thus prey availability for apex consumers in the coastal wetlands compared to the pre-drainage inferred standard. Furthermore, greater discharge of freshwater toward Florida Bay may result in the re-establishment of pre-1960s fauna, including a more robust demersal-fish community that should prompt increases in populations of several important predatory species.     

Some Effects of a Power Plant Effluent on Estuarine Epibenthic Organisms

A study using the submerged test panel method was conducted at the Oyster Creek Nuclear Generating Station near Barnegat Bay, New Jersey to investigate effects of the heated effluent on epibenthic communities. Test panels were placed in the intake and discharge canals and collected using SCUBA at 28, 84, 168 and 335-day intervals between October 1970 and October 1971. Exposed panels were replaced by clean panels upon collection. Faunal resemblance, both between stations during a sampling date and within stations from one sampling date to the next, was low. Numbers of species were higher at the discharge station than at the intake station from late fall to early summer and lower from midsummer to early fall. Overall differences in diversity at the two stations could not be detected. The optimum temperature for growth of Balanus sp. was approached more closely during winter in the discharge canal than in the intake canal where growth was retarded by cold water. Balanus eburneus appeared to have an extended breeding season. Because of dilution of the discharged water with cooler intake water through a plant bypass system during the summer, the effluent was not seriously harmful to amphipod reproduction. Season abundances of numerous invertebrates at both stations are reported and possible power plant effects are discussed.     

Relationship between pelagic larval duration and abundance of tropical fishes on temperate coasts of Japan

The influence of pelagic larval duration (PLD) and egg type dispersal capabilities of 35 demersal and pelagic-spawning tropical fish species is examined in relation to their abundance on the temperate coasts of Japan. The PLDs of pelagic spawners were significantly longer than those of demersal spawners, and a high occurrence of pelagic spawners on the temperate coasts suggests that these fishes are more easily transported to temperate coasts than demersal spawners. For demersal spawners, the common species on the temperate coasts had significantly longer PLDs than the rare species; this suggests that PLD is a major factor influencing the distribution patterns of tropical demersal spawners on temperate coasts. Moreover, a negative correlation between PLD and the abundance of some species of pelagic and demersal spawners suggests the presence of reproductively active fishes in northern subtropical and even in temperate waters.     

Comparison of fish communities between above‐ and below‐dam sections of small streams; barrier effect to diadromous fishes

To analyse the effects of small‐scale dams on fish communities, species diversity, population density, biomass, migration over dams and trophic relationships were investigated in the above‐ and below‐dam sections of three Japanese streams. The dams were 1·5–3·9 m high, constructed within 400 m of the sea, and had no impoundment or fishway. Fish communities were mainly composed of diadromous fishes. Of the 17 species sampled, only a few species of gobies, Rhinogobius spp. and Gymnogobius spp. were able to climb and migrate upstream over the dams. Consequently the number of species, and total density and biomass of fishes below the dams was high, but low above the dams. One of the most dominant fish below dams, Plecoglossus altivelis altivelis , predominantly fed on benthic algae, whereas other fishes preyed on benthic invertebrates. Trophic relationships above dams were very simple, the few species of gobies preying on chironomid larvae and other aquatic invertebrates.     

Changes in the fish fauna of the Ria de Aveiro estuarine lagoon (Portugal) during the twentieth century

The fish biodiversity of the Ria de Aveiro has been analysed during the 20th century, as an indicator of the biological integrity of the ecosystem. Ninety-two distinct species and 38 families of Agnatha, Chondrichthyes and Osteichthyes occurred during the period. The family and species richness showed two levels of magnitude, from the 1910s, with high values (26–28 families and 51–52 species), and during the last two decades with more variable values (20–27 families and 38–55 species). A total of 13 species (four non-sporadic species) have disappeared recently. The lagoon system has been affected by large-scale anthropogenic influences mainly the substantial development of industries and the increasing population in the watershed, in addition to overfishing, climatic changes and dredging. In general, as shown by an analysis of the ecotrophic guilds present, the area maintained a similar structure during the whole period. No significant differences in time were recorded for any of the designated guilds. The twenty-two frequent species, which occurred in six or seven surveys, were mainly estuarine resident species or marine adventitious species, living in the substratum (benthic fish), on soft substratum and vegetated bottoms. They were feeding either on invertebrates alone or on invertebrates and fish, and producing pelagic or benthic eggs. The 19 sporadically-recorded species, recorded only once, were mostly marine adventitious, demersal fishes, living above rough bottom and vegetation, feeding strictly on invertebrates, and producing eggs benthically or deposited into vegetation. It is concluded that the Ria de Aveiro estuarine coastal lagoon has supported similar fish communities during the past century and that these comprise representatives of various ecological types.     

Spatio-temporal variability in fish recruitment to a coral reef (Moorea,French Polynesia)

Spatial and temporal patterns of recruitment of juvenile coral reef fishes were studied on the reefs of the high island of Moorea (Society Archipelago, French Polynesia) during the wet season (October 1988 to April 1989). Two size-classes of fishes (new-recruits and juveniles) were censused by visual counts within 24 quadrats along a transect across the lagoon. Correspondence analysis was used to calculate the hypothetical movements of the two size classes. Spatial variability was far more important than temporal variability; six main spatial communities were revealed, which could result from differences among habitats. Temporal variability in recuitment occurred only at nearshore stations; stations on the outer fringing reef and inner barrier reef displayed stable recruitment patterns.     

Piscivory and diet overlap between two non‐native fishes in southern Chilean streams

Trophic relations among introduced species may induce highly variable and complex effects in communities and ecosystems. However, studies that identify the potential impacts for invaded systems and illuminate mechanisms of coexistence with native species are scarce. Here, we examined trophic relations between two introduced fishes in streams of NW Patagonia, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta). These species originate from different regions of the Northern Hemisphere but they now coexist as invading species over the world. We used gastric contents and stable isotopes analysis to compare the diets of two size‐classes of these two invaders in three localities of southern Chile. Both species displayed similar ontogenic diet shifts with smaller trout consuming mostly invertebrates and larger trout being more piscivorous and epibenthic feeders. However, piscivory was more prevalent in brown trout than in rainbow trout and highest at the site with the greatest density of native fishes suggesting that the availability of native fishes as trout prey may limit the occurrence of trout piscivory. We found an elevated dietary overlap between the two trout species at larger sizes while at smaller size a higher intraspecific dietary overlap occurred suggesting a potential interference competition among the two fish invaders especially at larger sizes. Our results highlight that the impacts of invading species on non‐native fishes are context specific (i.e. species and ontogenic stages) and thus, difficult to generalize.     

Elevated feeding rates of fishes within octocoral canopies on Caribbean reefs

Increasing abundance of arborescent octocorals (often referred to as gorgonians) on Caribbean reefs raises the question of whether habitat structure provided by octocorals can mediate a transition between coral- and algal- dominated states by increasing fish abundance and herbivory. This study tested the hypotheses that feeding rates and densities of demersal reef fishes are affected by the habitat structure provided by dense octocoral communities. Surveys of fishes on coral reefs in St John, US Virgin Islands, found 1.7-fold higher densities, and 2.4-fold higher feeding rates within versus outside of dense octocoral canopies. This difference, however, was only seen at sites with octocoral densities > 8 colonies m⁻². Furthemore, the proximity of octocoral colonies to fish had an effect on the grazing rate of key herbivores (surgeonfishes and parrotfishes), with a 53% higher feeding rate (1.90 ± 0.11 bites min⁻¹ m⁻²) near octocorals (< 20 or 30 cm, depending on the site) versus farther from them (1.24 ± 0.09 bites min⁻¹ m⁻²). Finally, within the canopy of dense octocoral communities (17 colonies m⁻²), reef fishes fed at a rate that was 2.2-fold higher within the community than at the edge of the community that faced an adjacent sand patch. Fish abundance, however, was not uniformly higher within versus at the edge of the octocoral community, as ecotone specialists such as gobiids, blennioids, ostraciids, holocentrids, labrids, and pomacentrids were 1.3—2.3 times more abundant at the edge. In contrast, other taxa of demersal fishes, notably herbivores, were twice as abundant within octocoral communities than at the edges. Together, these results reveal an association between habitat structure created by octocorals on shallow reefs and increased feeding rates of demersal fishes (including those of herbivores). The potential of octocorals to increase herbivory that could mediate stony coral recovery is therefore worthy of further study.

     

The trawlfauna of the Mauritanian shelf (Northwest Africa): density,species composition,and biomass

In May 1988, epifaunal trawlsamples were collected at 17 stations on the Mauritanian shelf off the Banc d'Arguin. The species composition and biomass of the invertebrates and demersal fish were analysed. On the basis of species abundances, three station groups could be distinguished each corresponding to a subregion of the shelf: an inner shelf, a midshelf and an outer shelf station group. The average depth increased from 20 m for the inner to more than 100 m for the outer shelf stations. The biomass of mobile epifauna and fish was lowest on the inner shelf stations where the trawlfauna was dominated by large sessile filterfeeders. The trawlfaunas of the mid- and outer shelf were more similar in species composition. Demersal fish and crustaceans appeared to be more abundant on the outer shelf. The increase in density and biomass from inner to outer shelf is discussed in relation to the distribution of the infauna and the hydrographical conditions on the Mauritanian shelf. Being a demersal fishing area, density and biomass of the epifauna on the shelf are compared with that of the demersal fishing grounds in the southern North Sea. The result of this comparison shows that, except for echinoderms, all taxa attain higher densities and biomasses at the Mauritanian shelf.     

Examining the area effect for parasite communities of bluegill x green sunfish hybrids in five constructed ponds in Kansas

The parasite communities of bluegill x green sunfish hybrids were examined from 5 constructed ponds in Kansas in an attempt to evaluate the separate effects of habitat area and habitat heterogeneity on parasite community structure. Characterization of fish community structure and collection of hybrid fishes was conducted using an electrofishing boat. Benthic invertebrates were sampled, and substrate types examined at 30 evenly spaced points in each pond. Nonmetric multidimensional scaling of the parasite infracommunities, in concert with an analysis of similarities, indicated significant clustering of infracommunities by locality. The number and diversity of habitat types, and the richness and diversity of both fishes and benthic invertebrates, were positively correlated with the first axis of the infracommunity ordination. Pond surface area, parasite richness, and stocking pressure were negatively correlated with the first axis of the infracommunity ordination, suggesting that pond area, stocking pressure, or both was a stronger determinant of parasite community structure in these systems than habitat and host heterogeneity.     

Nearshore subtidal community structure compared between inner coast and outer coast sites in Southeast Alaska

Processes that structure subarctic marine communities, particularly in glaciated regions, are not well understood. This understanding is needed as a baseline and to manage these communities in the face of future climate-driven changes. This study investigates two coastal regions of Southeast Alaska with the goals to (a) identify and compare patterns of subtidal community structure for macroalgal, fish, macroinvertebrate (>5?cm), and small epibenthic invertebrate (<5?cm) communities between inner coast and outer coast sites and (b) link patterns of community structure to habitat and environmental parameters. Species assemblage and benthic habitat data were used to compare species diversity and community composition at 6?m and 12?m depths at nine inner coast and nine outer coast sites. Multivariate analysis was applied to reduce environmental variables to major gradients, to resolve community structure, and to relate community structure to habitat and environmental variables. Increased salinity and decreased temperature at outer coast sites compared with inner coast sites were associated with community structure, with greater species diversity at outer coast sites at 6?m depth. Invertebrate community composition was associated with benthic habitat, including crust and coralline algae for macroinvertebrates, and algal cover and substrate for small epibenthic invertebrates. This research suggests that marine communities in glaciated regions are strongly influenced by freshwater input and that future climate-driven changes in freshwater input will likely result in marine community composition changes.     

General characteristics of the diet of Trachinotus paitensis (Teleostei: Carangidae) from San Ignacio Lagoon, Baja California Sur, Mexico

The food habits of Trachinotus paitensis, in San Ignacio Lagoon B.C.S., Mexico, were investigated. We observed that T. paitensis is carnivorous, feeding mainly on benthic invertebrates (the gastropods Anachis spp., Bittium spp., and the crustacean larvae). We concluded that T. paitensis is an opportunist predator that impacts mainly on epibenthic invertebrates.     

Invertebrate Community Associated with the Macroalga Halimeda kanaloana Meadow in Maui,Hawaii

An expansive meadow of the native macroalga Halimeda kanaloana has been found in west Maui, Hawaii. This study examined the invertebrate community associated with the H. kanaloana meadow. Analyses of samples collected by SCUBA divers found that the meadow supports a diverse and unique benthic community. The meadow provides a suitable habitat for a variety of epibenthic and epifaunal invertebrates in the otherwise homogeneous sandy habitat. Infaunal polychaete abundances, species richness and Shannon‐Wiener diversity index were also higher inside the meadow. Abundances of epibenthic organisms, and dissimilarities of the polychaete assemblage, inside and outside the meadow were greater at deeper stations. This might be due to an effect of the Halimeda density rather than depth, suggesting that the macroalgal density might play an important role in shaping the benthic community. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)