Pigments of meso- and bathypelagic chaetognaths

Pigments of the meso- and bathypelagic chaetognaths Sagitta macrocephala and Eukrohnia fowleri were studied by chromatographic analysis. Supplementary histological studies were also performed. Fat-soluble properties and absorption spectra of the chaetognath pigments indicated that all pigments were carotenoid, independent of chaetognath species or habitat. The major carotenoid in chaetognaths was very soluble in nonpolar solvents such as carotenes, although its absorption spectrum formed a single broad peak at around 460 nm. The characteristics of the carotenoids in the chaetognaths were different from those of the pigments in the plankton which formed their diet. It is therefore inferred that carotenoids in chaetognaths are not formed by the deposition of food pigments in the intestinal tissue, but are synthesized by the chaetognaths themselves.     

Reproduction of meso- and bathypelagic chaetognaths in the genus Eukrohnia

Reproduction of meso- and bathypelagic chaetognaths, a major group of zooplankton and hermaphroditic animals, became clear after the microscopic examination of samples collected from the Pacific Subarctic Water. Species of the genus Eukrohnia carry their developing eggs in two marsupial sacs, one on each side, and the young are retained in these marsupia for at least some period after hatching. This is in line with a general trend for low fecundity, as care of the young increases. Almost all individuals are protandric, the testes maturing sooner than ovaries. These facts suggest that the reproduction of these species depends upon cross-fertilization.     

Growth and breeding of meso- and bathypelagic organisms of the Rockall Trough,northeastern Atlantic Ocean and evidence of seasonality

Seasonality of growth and reproduction of a variety of epimeso-and bathypelagic organisms living in the Rockall Trough is examined in samples collected between 1973 and 1978. Rates of growth change seasonally. Epipelagic and shallow-living mesopelagic migrators tend to grow most rapidly in the spring and summer while deeper-living mesopelagic migrators tend to accelerate their growth in the summer and autumn when seasonal water temperatures at these depths are at their seasonal maxima. Mesopelagic migrators all breed seasonally. Rates of growth of bathypelagic non-migrating species could not be determined through analyses of body length/frequency histograms because of the continuous (aseasonal) breeding and recruitment of juveniles to the adult populations. An exception was the mysid crustacean Boreomysis microps that had a seasonal period of spring recruitment of juveniles to the population. Several of the mesopelagic crustaceans and fish have extended periods of approximately linear growth in body length. There is no evidence that organisms living in the mesopelagic or bathypelagic environments have rates of growth that are markedly slower than those of congeners in shallower environments.     

The decline and recovery of four predatory fishes from the Southern California Bight

What to do about fisheries collapse and the decline of large fishes in marine ecosystems is a critical debate on a global scale. To address one aspect of this debate, a major fisheries management action, the removal of gill nets in 1994 from the nearshore arena in the Southern California Bight (34°26′30″N, 120°27′09″W to 33°32′03″N, 117°07′28″W) was analyzed. First, the impetus for the gill net ban was the crash of the commercial fishery for white seabass (Atractoscion nobilis; Sciaenidae) in the early 1980s. From 1982 to 1997 catch remained at a historically low level (47.8 ± 3.0 mt) when compared to landings from 1936–1981, but increased significantly from 1995–2004 (r = 0.89, P < 0.01) to within the 95% confidence limit of the historic California landings. After the white seabass fishery crashed in the early 1980s, landings of soupfin (Galeorhinus galeus; Triakidae) and leopard shark (Triakis semifasciata; Triakidae) also significantly declined (r = 0.95, P < 0.01 and r = 0.91, P < 0.01, respectively) until the gill net closure. After the closure both soupfin and leopard shark significantly increased in CPUE (r = 0.72, P = 0.02 and r = 0.87, P < 0.01, respectively). Finally, giant sea bass (Stereolepis gigas; Polyprionidae) the apex predatory fish in this ecosystem, which was protected from commercial and recreational fishing in 1981, were not observed in a quarterly scientific SCUBA monitoring program from 1974 to 2001 but reappeared in 2002–2004. In addition, CPUE of giant seabass increased significantly from 1995 to 2004 (r = 0.82, P < 0.01) in the gill net monitoring program. The trends in abundance of these fishes return were not correlated with sea surface temperature (SST), the Pacific Decadal Oscillation (PDO) or the El Niño/Southern Oscillation (ENSO). All four species increased significantly in either commercial catch, CPUE, or in the SCUBA monitoring program after the 1994 gill net closure, whereas they had declined significantly, crashed, or were absent prior to this action. This suggests that removing gill nets from coastal ecosystems has a positive impact on large marine fishes.     

Distribution and abundance of the epipelagic mollusk Carinaria japonica in waters off Southern California

The distribution and abundance of the heteropod mollusk Carinaria japonica Okutani is described from midwater trawl records off Southern California (USA) and northern Baja California (Mexico). Maximal numbers of individuals were recorded during August in oceanic waters off Southern California. In oceanic waters near Guadalupe Island, Baja California, low population levels were recorded irrespective of season. In neritic waters over the continental shelf off Southern California, C. japonica were present in low numbers, mainly between July and December when conditions seemed most favorable for their entry into the Southern California Eddy.     

Subsurface patch of a dinoflagellate (Ceratium tripos) off Southern California: Patch length,growth rate,associated vertically migrating species

Ceratium tripos dominated a multi-species dinoflagellate patch in the sub-surface chlorophyll maximum in August 1978 on the Southern California shelf. The specific growth rate () ofC. tripos averaged 0.25 d^-1. Patch length was about 45 km along the shelf. Several members of the subsurface dinoflagellate assemblage were also present in surface samples, but only during the daytime. These apparent vertical migrators includedProrocentrum micans, C. furca, Gonyaulax polyedra and other less common forms. The growth ofC. tripos in the California patch is compared with that in aC. tripos patch off New York in 1976.     

Net primary production, growth, and standing crop of Macrocystis pyrifera in Southern California

Marine macroalgae are believed to be among the most productive autotrophs in the world. However, relatively little information exists about spatial and temporal variation in net primary production (NPP) by these organisms. The data presented here are being collected to investigate patterns and causes of variation in NPP by the giant kelp, Macrocystis pyrifera, which is believed to be one of the fastest growing autotrophs on earth. The standing crop and loss rates of M. pyrifera have been measured monthly in permanent plots at three sites in the Santa Barbara Channel, USA. Collection of these data began in June 2002 and is ongoing. Seasonal estimates of NPP and growth rate are made by combining the field data with a model of kelp dynamics. The purpose of this Data Paper is to make available a time series of M. pyrifera NPP, growth, and standing crop that is appropriate for examining seasonal and interannual patterns across multiple sites. Data on plant density in each plot and censuses of fronds on tagged plants at each site are also made available here. NPP, mass-specific growth rate, and standing crop are presented in four different metrics (wet mass, dry mass, carbon mass, and nitrogen mass) to facilitate comparisons with previous studies of M. pyrifera and with NPP measured in other ecosystems. Analyses of these data reveal seasonal cycles in growth and standing crop as well as substantial differences in M. pyrifera NPP among sites and years.     

Triacylglycerols and wax esters in the lipids of deep midwater teleost fishes of the Southern California Bight

Total lipid contents and the proportions of triacylglycerols and wax esters were examined in 23 species of deep-sea fishes collected between 1977 and 1980 in the Santa Catalina, San Clemente and San Pedro Basins off Southern California, USA. Mean total lipid content ranged from 1 to 22% of wet weight. Triacylglycerols accounted for 1 to 91% of total lipids present and were more abundant than wax esters in the lipids of all but a single species. Wax ester contents ranged from 0 to 24% of total lipids but in 20 species were 10% of the lipids. These results do not substantiate the previously suggested idea that wax esters are important constituents of the lipids of deep-sea fishes. Moreover, the hypothesis that wax ester content increases with increasing depth of occurrence is not supported. To assess the importance of the lipids present in bouyancy regulation, the water content and swimbladder inflation of these species were also examined. Neither total lipids nor wax esters appear to play an important role in buoyancy regulation in the majority of these fishes. Eight species have gas-filled swimbladders. Of the species lacking inflated swimbladders, 7 have watery bodies (87 to 95% H₂O) and 6 with low lipid (8.3%) and water (85%) contents may need to swim continuously to maintain their position in the water column. Lipids, largely in the form of triacylglycerols, may be important in the buoyancy of three species with lipid contents>10% of wet weight. Two of these species also possess inflated swimbladders. The reasons for the production of large quantitites of was esters by certain deep-sea teleosts, especially gonostomatids and myctophids, remain unknown.     

Variability in the gut contents of individual A cartia tonsa from waters off Southern California

The gut contents of 169 individual Acartia tonsa from Los Angeles Harbor, California, USA, were measured during a 24 h period (16–17 June 1986) by gut pigment (fluorescence) and microscopic analyses. Individual gut-pigment levels varied 10-fold or more within sampling intervals. Some copepods with moderate (0.2 to 0.5 ng) to high (>0.5 ng) gut-pigment levels were present in samples from both day and night collections. While the percentage of copepods containing>0.5 ng pigment was about the same during the day (8%) as at night (10%), the percentage of copepods with 0.2 to 0.5 ng pigment rose from 17% during the day to 55% at night. Significant differences between pigment levels in copepods collected before and after evening twilight were suggestive of a nocturnal feeding habit regardless of intense individual variability in gut-pigment content. Food in the gut was distributed in parcels, indicative of intermittent feeding that potentially contributes to individual variability. Feeding was not synchronized during most of the day and night, but synchrony increased at evening and morning twilights. Although synchrony declined after evening twilight, individual gut-pigment contents were relatively elevated in most of the nighttime samples. Thus, active feeding seems neither to require nor to imply synchrony.     

Chemical composition and buoyancy of midwater crustaceans as function of depth of occurrence off Southern California

Water, ash, C, H, N, lipid, carbohydrate, chitin and protein contents were determined for 28 species of midwater crustaceans. Variation of these components as a function of depth of occurrence, relative buouancy and respiratory rate of these species was examined. Vertical distribution data for 10 of the species based on discrete depth crawls is provided. The relative bouyancies of 16 of these species were measured. The caloric contents of 21 species were calculated. Lipid content (percent wet weight) and caloric density increased at intermediate depths, but apparently decreased at the greatest depths; it is suggested that this decrease is related to the relatively large size of these organisms and the energy limiting conditions in the deep-sea. Protein content (percent wet weight) decreases with increasing depth of occurrence, and is apparently related to a substantial fraction of the decrease in respiratory rate with increasing depth of occurrence in these species. Within the range of values examined, relative buoyancy appeas to be independent of metabolic rate. It is, therefore, suggested that the energy involved in maintaining an animal in the water column is generally insignificant compared to its overall activity. Furthermory, advantages of neutral buoyancy other than energy conservation may be more important selective factors for this characteristic.     

Light and temperature demands for growth and reproduction of laminarian gametophytes in southern and central California

The gametophytes of 9 laminarian species (4 from southern California, and 5 from central California, USA) became fertile in the unicellular stage (female gametophytes) or in a few-celled stage (male gametophytes), when appropriate temperatures and a sufficiently high quantum irradiance in the blue part of the spectrum were supplied. Vegetative growth, leading to the formation of filamentous gametophytes was light-saturated at relatively low irradiances (4 W m^-2; equivalent to about 2 nE cm^-2 sec^-1 or an illuminance of 1000 lux), whereas 2 to 3 times this irradiance in continuous fluorescent cool white light was needed to induce the majority of the gametophytes to become fertile. An illuminance of 8300 lux did not inhibit the development of the gametophytes from southern Californian species. Egregia menziesii exhibited an exceptionally low quantum demand for induction of fertility. Gametophytes of species from central and southern California differed in regard to their temperature optimum for growth (12°C in the former, 17°C in the latter) and their upper temperature limit for reproduction (17°C in the former, 20°C in the latter).     

Nitrogen supply,tissue composition and frond growth rates for Macrocystis pyrifera off the coast of southern California

Seasonal changes in ambient NO ₃ ^– and NH ₄ ⁺ , tissue composition (N, C, and C/N ratio), and frond growth rates for Macrocystis pyrifera (L.) Agardh were examined. Ambient NO ₃ ^– showed distinct seasonal variations. Frond growth rates were variable, but showed no clear correlation to ambient NO ₃ ^– . The average N content of plant tissue did, however, show the same seasonal variations as ambient NO ₃ ^– . The longitudinal distribution of total tissue N and various components of tissue N along fronds were also analyzed. Several distinct patterns were found: high levels of protein N at growing tips and elevated levels of soluble N in lower parts of the frond. Free amino acids accounted for a major portion of the soluble N, but neither NO ₃ ^– nor NH ₄ ⁺ accumulated in the plant tissue. The longitudinal distribution of N along the fronds is compared to reported variations in C metabolism, and it is concluded that C and N sourcesink relations do not always coincide and bidirectional translocation may occur.     

Moult in relation to some aspects of reproduction and growth in swarms of Antarctic krill,Euphausia superba

In a 14-d period 38 swarms of Antarctic krill,Euphausia superba Dana, were sampled in an area 55.5 x 55.5 km to the southwest of Elephant Island, at the north of the South Shetland Islands. Moult stage, maturity stage, and size of ca. 100 krill from each swarm were measured. Each of the characteristics varied greatly between swarms. Moulting krill were found in most swarms, but in one swarm all of the krill were just about to moult. Ways in which moulting may act as a possible sorting mechanism are discussed. Data for all the analysed krill (ca. 3000 specimens) were used to investigate the interdependence of moult rate, sexual maturation and growth. While all immature krill moulted at approximately the saine rate in the study, there were significant differences in the moulting rates of mature male and female krill. Gravid female krill continued to moult, although less frequently than mature males. As a consequence males had to attach spermatophores to females after each moult. It is likely that variation in moult rate of females and males was related to the energy expenditure required for ovary development in females and spermatophore production and searching behaviour in males. Spawning and moulting were only partly coupled in gravid females. Spawning appeared to take place predominantly during Moult Stage D₂. There was no evidence of intermoult growth by intersegmental dilation.     

Abnormal reproduction of the sand crab Emerita analoga in the vicinity of a nuclear generating station in Southern California

Female sand crabs (Emerita analoga) were sampled from 12 beaches along a 350 km stretch of Southern California coastline during the reproductive season in July, 1982. The percentage of mature females with egg masses and the condition of those egg masses were examined at each site. The proportion of mature females with egg masses varied only slightly between beaches. However, at sites within about 20 km of the San Onofre Nuclear Generating Station, a high percentage of females carried egg masses consisting of empty egg shells. A transplant experiment was conducted. Females with empty egg masses were taken from the 6.5 km N study site, where only 5% of the mature females carried normal egg masses, and transferred to running unfiltered seawater in Santa Barbara. After 2 wk, about a third of the transplanted females carried normal egg masses, while at the same time the proportion of mature females with normal egg masses remained at 5% on the beach of origin. Heated water discharged from the nuclear generating station is probably not the cause of the abnormal reproduction of sand crabs along the nearby coast. More likely causes are: (1) runoff of agricultural pesticides from a creek 3 km north of the nuclear generating plant; (2) release of metals from corroding cooling pipes, and/or (3) increased turbidity of the nearshore waters.     

Fitting a parabola to growth data of fishes and some applications to fisheries

Denoting a fish length or weight at age t by X _t , a reference age by t _m , and the corresponding fish length or weight by X _m , the relation between age and length or weight may be described by a parabola as follows: $$\left| {X_t } \right. - X_m \left| = \right.a + b(\left| {t - t_m } \right.\left| ) \right. + c(\left| t \right. - t_m \left| ) \right.^2$$ or $$X_t = A + b(\left| {t - t_m } \right.\left| ) \right. + c(\left| t \right. - t_m \left| ) \right.^2$$ where a, b and c are constants. Each of the above Eqs. describes one curve at ages older than t _m and another one at younger ages, which is made possible by means of the transformation of t to (|t-t _m |). In 2 cases out of 10, the parabola takes the form of a cubic equation. Evidence is given that, as the growth data become fewer, the better fit of the parabola or cubic equation will probably be less in comparison to the von Bertalanffy equation (1938, 1949) as developed by Beverton and Holt (1957) and the power-growth equation (Rafail, 1971), and vice versa. This growth equation is used to derive models for estimating the optimum age and yield for fish populations.     

Feeding strategies of some demersal fishes of the continental slope and rise off the Mid-Atlantic Coast of the USA

Stomach contents of 729 fishes comprising 16 species were examined from the continental slope and rise off the Middle Atlantic States of the USA. Two main feeding modes among demersal deep-sea fishes were evident: those feeding primarily on pelagic food items, and those feeding on benthic invertebrates. Both pelagic and benthic predators were euryphagous. Most pelagic predators also fed on the epibenthos. These findings support Dayton and Hessler's (1972) suggestion that benthic predators should have a generalized diet which may be responsible for the high diversity found in the deep-sea infauna. The mesopelagic fauna is an important food source for some demersal fishes on the continental slope. Pelagic prey, which are also important to ecologically dominant demersal fishes on the lower slope and continental rise, may be nutritionally supported by suspended particulate organic matter in a nepheloid layer close to the bottom, and they may exist in much higher concentrations than in the bathypelagic zone above.Virginia Institute of Marine Science Contribution No. 835.     

A growth profile for the rock scallop Hinnites multirugosus held at several depths off La Jolla,California

Juvenile Hinnites multirugosus were held in cages secured at 6 depths (maximum 120 m) to a buoyed line in the ocean 5 km off Scripps Institution of Oceanography for 95 days (August–November, 1977). The line was retrieved on December 2, and the scallops were measured, weighed and sacrificed for internal study. A second similar line, lowered at the same time as the first, was allowed to remain at the station for observation until later in 1978. Scallops at the shallowest depths (8, 15, and 30 m) displayed the most rapid growth, groups (n=10) averaging 19.3, 25.5 and 21.7 mm increases in shell diameter, respectively. These growth rates were comparable to the best results for scallops held in food-rich waters of Mission Bay, San Diego, California. Groups at the deeper levels (60, 90 and 120 m) grew by averages of 15.3, 8.5 and 7.8 mm, respectively. Growth was less than expected at 8 m, presumably due largely to competition for food and growing space by fouling organisms (barnacles, bryozoans, hydroids and colonial tunicates). Fouling was minimal at depths exceeding 30 m. The known vertical distribution of temperature and particulate organic matter in the ocean off La Jolla indicates that both influenced scallop growth in this study. A temperature range of 5 to 10 C° from the surface to a depth of 100 m is common to the area. Phytoplankton are generally concentrated in the upper 50 m.     

Patterns and selectivity in the feeding of certain mesopelagic fishes

Stomach contents were analysed from the 7 most numerous species of mesopelagic fish caught in a series of 11 hauls over a 24 h period at 230 to 266 m depth in the eastern North Atlantic Ocean. The numerical abundance of organisms per filled stomach and the frequency of occurrence of empty stomachs were used to indicate feeding periodicity. The ecological significance of the feeding periodicity was considered by examining it in connection with an investigation of the day-night vertical distribution of zooplankton and micronekton to 2000 m at the same station. Additional dietary evidence on the 7 species considered was also obtained from the vertical series. Feeding selectivity was examined by comparing the composition of the zooplankton population, sampled separately but simultaneously with the micronekton, with that from the overall stomach contents of the species examined. Feeding periodicity was demonstrated for 6 species, of which 3 were found to be feeding selectively: Valenciennellus tripunctulatus on calanoid copepods, Argyropelecus aculeatus on ostracods, and Lampanyctus cuprarius on amphipods and possibly euphausiids. The limited data available on the other 3 species suggested that they were either random feeders (A. hemigymnus and Lobianchia dofleini) or perhaps selecting against a particular group (Notolychnus valdiviae). No indication of feeding periodicity or selectivity was found for Chauliodus danae. The overall pattern of results confirmed the supposed close correlation between vertical migration and feeding in mesopelagic fish.     

Inter-annual variability in somatic growth rates and mortality of coastal fishes off central Chile: an ENSO driven process?

The effects of El Niño (EN) and La Niña (LN) events upon marine organisms inhabiting the Eastern Pacific coast have been widely studied in recent years, concentrating primarily on changes in species composition and on population size. In this study, using somatic growth rates as metabolic response variables, we evaluated the mortality rates of coastal fishes inhabiting a central Chilean upwelling marine ecosystem in the South Pacific between 1990 and 2003. Four coastal fish species belonging to different trophic levels (one herbivore, one omnivore, and two carnivores) were analyzed. In all species, the estimated cohort somatic growth rates were low for those recruited during EN and high for those recruited during LN events. Annual cohort mortality rates were highest during EN events and lower during LN and transitional years. We propose that productivity (as a bottom-up driver) acts as a primary exogenous factor upon annual cohort mortality rates. We also propose that a plausible mechanism underlying this process is the negative effect the low somatic growth rates may have on fish ecological attributes such as their competitive abilities, condition factors, and predation risks, which ultimately may affect their fitness.     

Diets of the demersal fishes on the shelf off Iwate,northern Japan

Diets of demersal fishes were determined on the shelf (ca. 130 m deep) off Iwate, Japan. Samples were taken in three different types of habitat, an artificial reef (AR) site, a natural reef (NR) site, and sandymud bottom (SB) site, from May 1987 to September 1991, mostly every two months. A total of 67 prey items were recognized in the stomachs of 45 predator fish species. The most important preys were the pelagic fishes Sardinops melanostictus and Engraulis japonicus, which comprised 37% wet wt of the overall stomach contents. The percentage of pelagic fishes was highest at AR site, where fish density was highest. The dominant ten species could be divided into five feeding types. The pelagic fish feeders Physiculus maximowiczi and Gadus macrocephalus fed mainly on S. melanostictus. The dietary breadth of P. maximowiczi was wide, while that of Gadus macrocephalus was narrow. The pelagic crustacean feeder Theragra chalcogramma mostly consumed Themisto japonica and euphausiids and showed the least dietary overlap with other fishes. Benthic fish feeders were Hemitripterus villosus and Liparis tanakai. The benthic crustacean feeders Alcichthys alcicornis and Hexagrammos otakii consumed benthic crustaceans as well as pelagic and benthic fishes and showed the largest dietary breadth. The benthic invertebrate feeders Gymnocanthus intermedius, Dexistes rikuzenius and Tanakius kitaharai fed mainly on polychaetes and benthic crustaceans. But Gymnocanthus intermedius consumed a significant proportion of pelagic fishes. Ontogenetic dietary shift was recognized for these fishes. Pelagic fishes were consumed more intensively by larger individuals, especially true of A. alcicornis, Theragra chalcogramma and Gadus macrocephalus. Predominancy of the two most adundant species, P. maximowiczi and A. alcicornis, may be supported by their wide dietary breadth and the significant proportion of pelagic fish in their diets. Interspecific dietary overlap was low in most cases suggesting that food resources were well partitioned, although some high overlap was observed among the pelagic fish feeders, A. alcicornis, and Gymnocanthus intermedius, and among the benthic invertebrate feeders. Interspecific competition seemed more likely in the benthic invertebrate feeders than in the pelagic fish feeders partly because of superabundance of the pelagic prey S. melanostictus.