A lifetime at depth: vertical distribution of southern elephant seals in the water column

Although numerous studies have addressed the migration and dive behaviour of southern elephant seals (Mirounga leonina), questions remain about their habitat use in the marine environment. We report on the vertical use of the water column in the species and the potential lifetime implications for southern elephant seals from Marion Island. Long-term mark-resight data were used to complement vertical habitat use for 35 known individuals tagged with satellite-relay data loggers, resulting in cumulative depth use extrapolated for each individual over its estimated lifespan. Seals spent on average 77.59% of their lives diving at sea, 7.06% at the sea surface, and 15.35% hauled out on land. Some segregation was observed in maximum dive depths and depth use between male and female animals—males evidently being physiologically more capable of exploiting increased depths. Females and males spent 86.98 and 80.89% of their lives at sea, respectively. While at sea, all animals spent more time between 300 and 400 m depth, than any other depth category. Males and females spent comparable percentages of their lifetimes below 100 m depth (males: 65.54%; females: 68.92%), though males spent 8.98% of their lives at depths in excess of 700 m, compared to females’ 1.84% at such depths. Adult males often performed benthic dives in excess of 2,000 m, including the deepest known recorded dive of any air-breathing vertebrate (>2,133 m). Our results provide a close approximation of vertical habitat use by southern elephant seals, extrapolated over their lifespans, and we discuss some physiological and developmental implications of their variable depth use.     

Inshore migration,seasonal distribution and sizes of larval bonefish,Albula, in the Gulf of California

Synopsis The leptocephalous larval stages of the bonefish (Albulidae: Albula) are abundant in the coastal regions and hypersaline lagoons (esteros) throughout the Gulf of California during winter and spring. Inshore movements of leptocephali were studied by sampling the entrance to Estero Miramar, at Guaymas, Sonora, Mexico, from February to May, 1981. Thirty-three samples were taken at various times during flood tide. All but four of the samples were taken after sunset. Leptocephali were collected in all months except May. The results suggest that leptocephali enter the estero only during the first few hours of flood tide. Large numbers of larvae were observed during the day at ebb tide maintaining their near-shore position in the entrance channel. These larvae did not appear to be migrating into the estero. This, together with the absence of larvae in daytime samples, suggests that the migration is nocturnal. Most of the 667 leptocephali collected during the sampling period had completed larval growth or were just beginning the metamorphic interval. The median standard length (SL) was 61 mm and the mode was 62 mm. The largest leptocephali measured 71 mm SL. Since metamorphosis is accompanied by a decrease in length, it was concluded that the maximum size attained during larval growth is about 71 mm SL.     

Genetic diversity of Allium munzii (Amaryllidaceae), a rare southern California species and implication for its conservation

An understanding of genetic diversity within and among populations of rare plant species is a prerequisite to develop effective conservation management strategies and reintroduction programs. Allium munzii is a narrow endemic species distributed in western Riverside County, California, USA and known from 18 extant element occurrences. We sampled 119 individuals from 11 element occurrences and investigated within and among population genetic diversity using two variable chloroplast markers (rpL32–trnL intergenic spacer and rpoC1 intron). Of the total genetic variation detected in A. munzii, 87.65% was due to differences among occurrences. Furthermore, our results revealed that most of the element occurrences are strongly genetically differentiated. There are low levels of gene flow between occurrences, not due to isolation by distance but possibly resulting from habitat fragmentation. Non-significant values of Tajima's D and Fu's Fs were found in all occurrences suggesting no demographic expansion in A. munzii. Ex situ seed and bulb conservation is recommended to enable introduction of individuals to occurrences with low abundance and genetic diversity.     

Vicariance and dispersal form a ring distribution in nightsnakes around the Gulf of California

Plate tectonics can have profound effects on organismal distribution and is often the driving force in speciation. Through geologic processes, the Baja California Peninsula depicts two faunal patterns: one through southern vicariance with Cape separation, and the other through dispersal onto the northern peninsula, referred to as a ‘dual-peninsular effect.’ Here we apply a hierarchical sampling strategy that combines population-level sequence data (800 bp, nad4 region) with complete mt-genome data (aligned 15,549 bp) and 5 nuclear protein encoding loci (3315 bp), to test whether both patterns have occurred in one group of nightsnakes (Hypsiglena). The geologic formation of the peninsula is thought to have occurred in three stages: (1) Cape separation from mainland Mexico; (2) the northern peninsula separated, forming the northern Gulf of California; and (3) the peninsula was united through volcanic activity, while moving northward causing collision with southern California. However, the timing of events is debated. We explore phylogenetic relationships and estimate dates of divergence for nightsnakes using our hierarchical sampling strategy. Our data support both ‘southern-vicariance’ and ‘northern-dispersal’ have occurred in nightsnakes, forming a ring distribution around the Gulf of California. Two divergent forms are sympatric on the southern half of the peninsula with no indication of hybridization. Nightsnakes represent the first group to depict the ‘dual-peninsular effect’ with extensive overlap on the Baja California Peninsula.     

Population genetic structure of the round stingray Urobatis halleri (Elasmobranchii: Rajiformes) in southern California and the Gulf of California

The round stingray, Urobatis halleri, is a viviparous elasmobranch that inhabits inshore, benthic habitats ranging from the western U.S.A. to Panama. The population genetic structure of this species was inferred with seven polymorphic microsatellite loci in samples collected at three sites in coastal southern California, one near Santa Catalina Island, California and one in the eastern Gulf of California. Urobatis halleri is relatively common, but little is known of its movement patterns or population structure. Small F_ST values (?0·0017 to 0·0005) suggested little structure among coastal populations of southern and Baja California. The population sampled at Santa Catalina Island, which is separated by a deep‐water channel from the coastal sites, however, was significantly divergent (large F_ST, 0·0251) from the other populations, suggesting low connectivity with coastal populations. The Santa Catalina Island population also had the lowest allele richness and lowest average heterozygosity, suggesting recent population bottlenecks in size.     

Seasonal phenology and reciprocal transplantation of Sargassum sinicola Setchell et Gardner in the southern Gulf of California

Length, presence and weight of receptacles were compared in two populations of Sargassum sinicola Setchell et Gardner from El Cajete and Las Pacas in the southern Gulf of California, México. The length of El Cajete plants started to increase and reached their maximum during the colder months of the year during three consecutive years. Attrition occurred in September after the growing and reproducing peaks. Large and short laterals were clearly distinct when El Cajete plants reached their maximum size. Large and short laterals from the same plant, reproduced in spring and summer, respectively. The maximum size of Las Pacas plants did not reach those of El Cajete plants. The distinction between large and short laterals was not seen in the Las Pacas plants. Only one reproduction peak was observed in these plants. The adaptive significance of the difference between the two populations is discussed. Some differences persisted after reciprocal transplantation. On this basis, genotypic differentiation of the two populations of S. Sinicola is suggested.     

Size–weight relationships of batoids captured by artisanal fishery in the southern Gulf of California,Mexico

This study reports the size–weight relationships (SWR) for nine batoid species that are frequently fished by the artisanal fisheries in the southern Gulf of California. Analysis included a total of 2,012 specimens, caught from October 2013 to July 2016. The slope values (b) oscillated from 2.80 to 3.56. Growth was isometric for five species and positively allometric for four. There were differences in SWR between sexes for three species being in all cases the female greater and heavier than males. This is the first analysis of SWR for the batoid species studied in the Gulf of California.     

Seasonal distribution of juvenile Atlantic cod in the southern Gulf of St Lawrence

Seasonal changes in the geographic distribution of juvenile (ages 1–4) Atlantic cod Gadus morhua were determined from research surveys conducted in the southern Gulf of St Lawrence during 1986–87, 1990–91, and 1994. From late June to early October, juvenile cod were most abundant in shallow water (<50 m deep). By early November, all age groups (adults and juveniles) had migrated to deep (>100 m) offshore waters for the winter. For most juveniles, this represented a minimum migration of >225 km (each way). Age 3 and 4 cod migrated greater distances than age 1 and 2 fish. Some age 3 and 4 cod migrated as far as 650 km from their summer and early autumn areas. Although there was partial geographic segregation of juvenile and adult fish during summer and winter, all age groups were found together during the migration. No cod were present in the shallow waters (<80 m deep) of the south-western Gulf during April due, in part, to later than average ice-melt. Large numbers of all age-classes were present in most of the south-eastern Gulf by mid-May.     

Spatial distribution of small pelagic fish larvae in the Gulf of California and its relation to the El Nino 1997-1998

Sardinops caeruleus larvae were almost absent during the ElNiño 1997–1998, when the sea surface temperature(SST) increased by 4°C. After the event, these larvae appearedin high abundance between 18 and 22°C SST. Engraulis mordaxlarvae were recorded in high abundance during the El Niño(17 and 25°C SST) and afterwards (14 and 22°C). Duringthe event, they tended to concentrate close to Isla Angel deLa Guarda and Isla Tiburón, the coldest zone. The ElNiño conditions affected the spawning of S.caeruleusmore than E.mordax, with the latter more adapted to strong environmentalchanges.     

Annual distribution and abundance of Ceratium dens (Peridinales: Ceratiaceae) in the Gulf of California, Mexico

Ceratium dens distribution in the Gulf of California was studied based on three oceanographic campaigns, monthly abundance (1995-96) and during three red tide events in Mazatlán Bay. 52 phytoplankton samples with a Bongo net and 64 microns mesh light, during the year 120 water samples with a van Dorn bottle were collected in two sampling stations and from three red tide events. All samples were counted by the inverted-microscope method. The results showed that C. dens was present in the upper Gulf of California and surroundings of Cabo San Lucas. Two peaks were observed during spring and autumn in Mazatlán Bay during 1995-1996. The highest densities (20-360 cells.-l-1) were observed in coastal areas, whereas the lowest densities (1-14 cells.-l-1) were recorded in the open sea. During red tide events in 1985, 1989 and 1997, 144,000-256,000 cells.-l-1, 100,000-400,000 cells.-l-1, and 189,000-592,000 cells.ul-l was observed, respectively. During the red tide events C. dens varied, although sometimes was replaced by Skeletonema costatum or Pseudonitzchia spp and Ceratium furca. C. dens, seems to prefer areas with high productivity.     

Predicting the distribution of shrub species in southern California from climate and terrain-derived variables

Abstract. Generalized additive, generalized linear, and classification tree models were developed to predict the distribution of 20 species of chaparral and coastal sage shrubs within the southwest ecoregion of California. Mapped explanatory variables included bioclimatic attributes related to primary environmental regimes: averages of annual precipitation, minimum temperature of the coldest month, maximum temperature of the warmest month, and topographically-distributed potential solar insolation of the wettest quarter (winter) and of the growing season (spring). Also tested for significance were slope angle (related to soil depth) and the geographic coordinates of each observation. Models were parameterized and evaluated based on species presence/absence data from 906 plots surveyed on National Forest lands. Although all variables were significant in at least one of the species’ models, those models based only on the bioclimatic variables predicted species presence with 3–26% error. While error would undoubtedly be greater if the models were evaluated using independent data, results indicate that these models are useful for predictive mapping – for interpolating species distribution data within the ecoregion. All three methods produced models with similar accuracy for a given species; GAMs were useful for exploring the shape of the response functions, GLMs allowed those response functions to be parameterized and their significance tested, and classification trees, while some-times difficult to interpret, yielded the lowest prediction errors (lower by 3–5%).     

Desiccation,predation, and mussel-barnacle interactions in the northern Gulf of California

Summary Field experiments were conducted in order to determine the potential for desiccation and predation to mediate the effect of mussels (Brachidontes semilaevis) on barnacles (Chthamalus anisopoma) in the highly seasonal northern Gulf of California. We did this by removing both mussels and a common mussel predator (Morula ferruginosa: Gastropoda) and by spraying selected sites with sea water during summertime spring low tides. We also determined the effect of crowding on resistance to desiccation in barnacles, and the effect of barnacles on colonization by mussels. The mussel-barnacle community was not affected by keeping experimental quadrats damp during daytime low tides throughout the summer. Exposure to summertime low tides, however, did affect the survivorship of isolated, but not crowded, barnacles; and barnacle clumps enhanced the recruitment of mussels. Hence crowding in barnacles had a positive effect on both barnacle survivorship and mussel recruitment. Morula had a negative effect on mussel density, and mussels had a negative effect on barnacle density. The effect of Morula on barnacle density was positive, presumably due to its selective removal of mussels. These results suggest an indirect mutualism between barnacles and the gastropod predator, because barnacles attract settlement or enhance the survival of mussels, and the predator reduces the competitive effect of mussels on barnacles.     

Distribution of living coccolithophores in the California Current system,southern California borderland

The distribution of living coccolithophores in the California Current system of southern California at 10 m water depth was investigated on two dates in March and June, 1982. Six closely spaced stations were sampled in March, of which three were resampled in June. Thirty-six euphotic species were identified of which four,Emiliania huxleyi, Umbilicosphaera sibogae, Gephyrocapsa oceanica, andRhabdosphaera longistylis, respectively, were the most abundant. Both the “cold” and “warm” morphotypes ofE. huxleyi were present, in varying proportions. Large ranges in community structure, diversity (0.35–2.64 natural bels), and standing crop (1.0 × 10⁴–6.2 × 10⁵cells/l) were recorded. This range of end-member values is approximately that found in the open ocean from 0° to about 65° latitude.The distributions of four coccolithophore assemblages recognized in March samples from the Borderland area appear to reflect the following distinct water masses: (1) California Current; (2) Southern California Counter Current; (3) Transitional Zone; (4) Near Shore. The coccolithophore assemblages from the June stations were more uniform, indicating that the Borderland was experiencing more stable conditions than in March.     

Mass balance on water column trace metals in a free-surface-flow-constructed wetlands in Sacramento, California

A mass balance has been performed on trace metals concentrations and hydrology observed between 1994 and 1996 at the Sacramento Demonstration Constructed Wetlands using a first-order areal plug flow model. Water losses to infiltration and evapotranspiration from a typical cell are estimated to average 35 and 7% of influent flow, respectively. The wetlands effluent metals concentrations consistently meet proposed discharge criteria. Annual total mass loadings for all trace metals average 14.0 kg ha⁻¹ yr⁻¹, 88% of which consists of zinc, copper, and nickel. Effluent metals leaving the wetland average 3.1 kg ha⁻¹ yr⁻¹, 79% of which consists of the same three metals. Annual vegetation harvest events do not appear to account for more than 5% of annual trace metals mass removal, although harvest does appear to represent a significant loss pathway for some metals like mercury, lead, nickel, and chromium. Metals mass removals resulting from first-order removal interactions within the wetland range from 27 to 81%, with the exception of arsenic and nickel which display poor mass removals in part due to their high dissolved concentrations. An average of 7.6 kg ha⁻¹ yr⁻¹, or 54% of influent metals loadings, is sequestered within the internal wetland compartments.     

Spatial structure and dynamics of breeding bird populations at a distribution margin,southern California

Aim Local‐scale processes at species distribution margins can affect larger‐scale distribution dynamics, but are rarely studied. The objective of this research was to elucidate the nature of distribution limits by studying the comparative structure, dynamics and environmental associations of breeding bird populations at their distribution margin. We hypothesized that climate is principally responsible for setting distribution limits, whereas biotic habitat features are more strongly associated with distribution patterns within the range. Location Southern California, USA. Methods During 2005–2007 we studied the distribution patterns of breeding birds in three study areas, each spanning a low‐elevation (200–1800 m) desert scrub‐to‐chaparral gradient. We used logistic regression with hierarchical partitioning to assess the independent effects of environmental variables (e.g. climate versus habitat) on distributions. We tested for shifts in the relative importance of these environmental variables in determining distribution limits versus within‐range patterns, and we also compared higher‐ and lower‐elevation groups of species. Results Distribution patterns were highly variable among species, but were remarkably static over the three study areas and 3‐year study period. Across species, habitat floristic variables performed relatively well at explaining distribution patterns. For higher‐elevation species (chaparral birds), climate was relatively important in setting their lower distribution limits, and there was a shift to a greater importance of biotic habitat (mainly habitat structural variables) for determining within‐range patterns. Relationships were more mixed for lower‐elevation species (desert scrub birds), but with respect to distribution limits, biotic habitat variables tended to be more important relative to climate than we observed for chaparral birds. Main conclusions Along this warm, arid elevational gradient, higher‐elevation chaparral birds are more limited by climate at their lower margin than are lower‐elevation desert birds at their upper margin, suggesting that climate plays a strong role (relative to other values) in excluding non‐desert birds from desert. However, given the strong differences among species, predictive distribution models will need to be individually tailored, and for most species biotic habitat variables were of greater importance than climate in determining limits. This research highlights the usefulness of studying environmental relationships at distribution margins and the importance of considering biotic relationships in forecasting distribution shifts under changing climates.     

Latitudinal and bathymetric distribution of the most abundant and frequent species in the shrimp bycatch from the Gulf of California, Mexico

The Gulf of California is one of the most mega-diverse regions in the world, for which few fishery information is available. We present here latitudinal and bathymetric distribution of the most abundant and frequent bycatch species from the Gulf of California. The samples were obtained from a total of 111 hauls taken during seven research cruises of the closed shrimp season (2002-2005-2007), and also, from research cruises made at depths up to 90 m. Due to the high variety species in this experimental shrimp bycatch, only those with highest biological value index (BVI) were selected. A total of fifteen species had the highest BVI and represented about 60% of the total abundance. A total of 16 508 organisms were analyzed, representing 243 fish, crustacean, mollusk and echinoderm species. Fish were the most abundant, being the most frequent species: Urobatis halleri, Synodus scituliceps, Diplectrum pacificum, Haemulopsis nitidus and Eucinostomus argenteus. A wide latitudinal distribution of these species along the study area, as well as a bathymetric distribution from 9 to 67 m depth, was observed. Two of these species were found at 325 m depth. Due to the wide bathymetric distribution obtained, total abundances and sizes for each species by depth strata should be determined, and one can assume that deeper than 25 m, the capture of these species decreases, and these areas can be used as natural repopulation areas, for depths where they are mainly captured by the commercial shrimp fishery.     

Climate-driven changes in abundance and distribution of larvae of oceanic fishes in the southern California region

We examined climatic effects on the geographic distribution and abundance of 34 dominant oceanic fishes in the southern California region using larval fish data collected from the 50‐year long California Cooperative Oceanic Fisheries Investigations (CalCOFI) surveys. The oceanic species responses to environmental changes in their geographic distributions were not very pronounced, perhaps because they lived in the deep layer where temperature change was relatively small or because the environmental variation of the CalCOFI region is not strong enough (with an average temperature gradient of the upper 100 m around 91 km °C^?1). Among the 34 taxa, 16 showed a significant distributional shift (median latitude or boundaries) in relation to environmental variables, and eight species significantly shifted their geographic distribution from the 1951–1976 cold period to the 1977–1998 warm period. Interestingly, the vertically migrating taxa more often showed a significant response to environmental variables than the nonmigrating mesopelagic taxa, reflecting the more significant increase in heat content of the upper ocean (<200 m), compared with the deeper zone (300–500 m) where the mesopelagic fishes typically remain. Climate change has significant effects on the abundances of oceanic fishes. Twenty‐four taxa exhibited a significant change in abundance in relation to environmental variables, and 25 taxa, including both warm and cold‐water taxa, showed a significant increase in abundance from the cold to warm period. Analysis of physical data indicated that the surface‐layer (20–200 m) warmed significantly and the isotherms approached shoreward from the cold to the warm period. We further show that the spatial distribution of coastal–neritic fish retreated shoreward and oceanic fish extended shoreward from the cold to warm period. Our results suggest intensified stratification of the southern California region during the warm period may create a suitable habitat for the oceanic species. Moreover, such an unfavorable condition (e.g. changes in food habitat) for coastal–neritic species might result in competitive release for the oceanic fishes to flourish.     

Influence of river inflows on plankton distribution around the southern perimeter of the Salton Sea,California

The influence of river inflows (2.5–5 g l⁻¹) on phytoplankton and zooplankton was assessed with samples collected at 17 sites around the 50 km perimeter of the southern basin of the Salton Sea (41–45 g l⁻¹) along the 5 m isobath on 2 September and 11 December 2000. Phytoplankton generally increased in abundance downcurrent of the points of inflow, but patterns in downcurrent abundance varied widely among species. Several diatom species showed large increases; Chaetoceros muelleri var subsalsum, Cylindrotheca closterium and Thalassionema sp. increased up to 800-fold in abundance by ca. 20 km downcurrent from inflow points in September. In contrast, the dinoflagellates Gyrodinium uncatenum and Prorocentrum minimum increased 6- and 4-fold, respectively, in December, and Gonyaulax grindleyi actually decreased downcurrent of the rivers in September. In September, patterns in downcurrent abundance were correlated with the ratio of cell surface area to cell biovolume, with species with high ratios showing the largest increases. Zooplankton abundances did not show regular trends downcurrent of river inflows except for the larvae of Balanus amphitrite, which increased in density ca. 100-fold. This increase most likely reflected the abundance of adult-colonized rocky substrates near river inflow points. The strong upcurrent trends documented for some species seemed to have been due to the injection of nutrient-rich water from central to nearshore areas and near-site mortality due to the presence of hydrogen sulfide. This study gives a first glimpse of the complexity of the responses of nearshore plankton to river inflow and provides evidence for how changes in factors such as current speed, nutrient supply and salinity stratification may influence plankton dynamics. Guest Editor: John M. Melack Saline Waters and their Biota     

Species traits affect the performance of species distribution models for plants in southern California

Questions: To what extent do plant species traits, including life history, life form, and disturbance response characteristics, affect the degree to which species distributions are determined by physical environmental factors? Is the strength of the relationship between species distribution and environment stronger in some disturbance‐response types than in others? Location: California southwest ecoregion, USA. Methods: We developed species distribution models (SDMs) for 45 plant species using three primary modeling methods (GLMs, GAMs, and Random Forests). Using AUC as a performance measure of prediction accuracy, and measure of the strength of species–environment correlations, we used regression analyses to compare the effects of fire disturbance response type, longevity, dispersal mechanism, range size, cover, species prevalence, and model type. Results: Fire disturbance response type explained more variation in model performance than any other variable, but other species and range characteristics were also significant. Differences in prediction accuracy reflected variation in species life history, disturbance response, and rarity. AUC was significantly higher for longer‐lived species, found at intermediate levels of abundance, and smaller range sizes. Models performed better for shrubs than sub‐shrubs and perennial herbs. The disturbance response type with the highest SDM accuracy was obligate‐seeding shrubs with ballistic dispersal that regenerate via fire‐cued germination from a dormant seed bank. Conclusions: The effect of species characteristics on predictability of species distributions overrides any differences in modeling technique. Prediction accuracy may be related to how a suite of species characteristics co‐varies along environmental gradients. Including disturbance response was important because SDMs predict the realized niche. Classification of plant species into disturbance response types may provide a strong framework for evaluating performance of SDMs.