Influence of internal bores on larval fish abundance and community composition

A persistent semidiurnal internal tidal bore feature occurs at the head of the Monterey Bay Submarine Canyon and drives regular intrusions of cold, subthermocline waters onto the adjacent shelf. In this study, we examine the influence of this internal tidal bore feature on the larval fish community using over a year of periodic larval fish samples collected coincidently with physical measurements. Larval samples were categorized into one of two water mass periods: a “warm period” representative of shallow coastal shelf waters and a “cold period” characteristics of colder waters present during internal bore forcing. Using multivariate statistical methods, we show warm and cold periods, along with seasonality, are the primary drivers of larval fish community composition. A significantly different community composition was observed between warm and cold water mass periods. This difference was primarily due to decreased abundance in most taxa during the cold periods, and did not indicate an obvious shift in the assemblage of the taxa. However, our data do indicate that some taxa may show higher abundance during cold periods compared to warm periods, but further studies are warranted. Along with seasonality, the presence/absence of subthermocline waters driven by internal bores appears to be a key control on nearshore larval fish community composition at this location

Land Use and Salinity Drive Changes in SAV Abundance and Community Composition

Conserving and restoring submerged aquatic vegetation (SAV) are key management goals for estuaries worldwide because SAV integrates many aspects of water quality and provides a wide range of ecosystem services. Management strategies are typically focused on aggregated abundance of several SAV species, because species cannot be easily distinguished in remotely sensed data. Human land use and shoreline alteration have been shown to negatively impact SAV abundance, but the effects have varied with study, spatial scale, and location. The differences in reported effects may be partly due to the focus on abundance, which overlooks within-community and among-community dynamics that generate total SAV abundance. We analyzed long-term SAV aerial survey data (1984-2009) and ground observations of community composition (1984-2012) in subestuaries of Chesapeake Bay to integrate variations in abundance with differences in community composition. We identified five communities (mixed freshwater, milfoil-Zannichellia, mixed mesohaline, Zannichellia, and Ruppia-Zostera). Temporal variations in SAV abundance were more strongly related to community identity than to terrestrial stressors, and responses to stressors differed among communities and among species. In one fifth of the subestuaries, the community identity changed during the study, and the probability of such a change was positively related to the prevalence of riprapped shoreline in the subestuary. Mixed freshwater communities had the highest rates of recovery, and this may have been driven by Hydrilla verticillata, which was the single best predictor of SAV recovery rate. Additional species-specific and community-specific research will likely yield better understanding of the factors affecting community identity and SAV abundance, more accurate predictive models, and more effective management strategies

Multifaceted impacts of the stony coral Porites astreoides on picoplankton abundance and community composition

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Limnology and Oceanography 62 (2017): 217–234, doi:10.1002/lno.10389.Picoplankton foster essential recycling of nutrients in the oligotrophic waters sustaining coral reef ecosystems. Despite this fact, there is a paucity of data on how the specific interactions between corals and planktonic bacteria and archaea (picoplankton) contribute to nutrient dynamics and reef productivity. Here, we utilized mesocosm experiments to investigate how corals and coral mucus influence picoplankton and nutrients in reef waters. Over 12 days, we tracked nutrient concentrations, picoplankton abundances and taxonomic composition of picoplankton using direct cell-counts, sequencing of SSU rRNA genes and fluorescent in situ hybridization-based abundances of dominant lineages in the presence or absence of Porites astreoides corals and with mucus additions. Our results demonstrate that when corals are present, Synechococcus, SAR11 and Rhodobacteraceae cells are preferentially removed. When corals were removed, their exudates enhanced the growth of diverse picoplankton, including SAR11 and Rhodobacteraceae. A seven-fold increase in nitrate concentration, possibly caused by nitrogen remineralization (ammonification coupled to nitrification) within the coral holobiont, may have further facilitated the growth of these taxa. In contrast, the addition of mucus resulted in rapid initial growth of total picoplankton and Rhodobacteraceae, but no measurable change in overall community structure. This study presents evidence of the multifaceted influences of corals on picoplankton, in which the coral holobiont selectively removes and promotes the growth of diverse picoplankton and remineralizes nitrogen.NSF Grant Number: OCE-1233612; NSF Oceanic Microbial Observatory Grant Number: OCE-080199

Assessing Viral Abundance and Community Composition in Four Contrasting Regions of the Southern Ocean

We explored how changes of viral abundance and community composition among four contrasting regions in the Southern Ocean relied on physicochemical and microbiological traits. During January–February 2015, we visited areas north and south of the South Orkney Islands (NSO and SSO) characterized by low temperature and salinity and high inorganic nutrient concentration, north of South Georgia Island (NSG) and west of Anvers Island (WA), which have relatively higher temperatures and lower inorganic nutrient concentrations. Surface viral abundance (VA) was highest in NSG (21.50 ± 10.70 × 106 viruses mL−1) and lowest in SSO (2.96 ± 1.48 × 106 viruses mL−1). VA was positively correlated with temperature, prokaryote abundance and prokaryotic heterotrophic production, chlorophyll a, diatoms, haptophytes, fluorescent organic matter, and isoprene concentration, and was negatively correlated with inorganic nutrients (NO3−, SiO42−, PO43−), and dimethyl sulfide (DMS) concentrations. Viral communities determined by randomly amplified polymorphic DNA–polymerase chain reaction (RAPD-PCR) were grouped according to the sampling location, being more similar within them than among regions. The first two axes of a canonical correspondence analysis, including physicochemical (temperature, salinity, inorganic nutrients—NO3−, SiO42−, and dimethyl sulfoniopropionate -DMSP- and isoprene concentrations) and microbiological (chlorophyll a, haptophytes and diatom, and prokaryote abundance and prokaryotic heterotrophic production) factors accounted for 62.9% of the variance. The first axis, temperature-related, accounted for 33.8%; the second one, salinity-related, accounted for 29.1%. Thus, different environmental situations likely select different hosts for viruses, leading to distinct viral communities.En prens

Spatial variations in bacterial and archaeal abundance and community composition in boreal forest pine mycorrhizospheres

Mycorrhizal fungi have a strong impact on soil biota. In this study, bacterial and archaeal populations in different parts of Suillus bovinus - Pinus sylvestris mycorrhizospheres in boreal forest were quantified and identified by DNA analysis. The numbers of bacterial and archaeal 16S rRNA gene copies were highest in uncolonized humus and lowest in fruiting bodies. The numbers of bacterial 16S rRNA gene copies varied from 1.3 x 10(7) to 3.1 x 10(9) copies g(-1) fw and archaeal copies from 4.1 x 10(7) to 9.6 x 10(8) copies g(-1) fw. The relatively high number of archaeal 16S rRNA gene copies was likely due to the cold and highly organic habitat. The presence of hyphae appeared to further promote archaeal numbers and the archaea:bacteria ratio was over one in samples containing only fungal material. Most detected archaea belonged to terrestrial Thaumarchaeota. Proteobacteria, Actinobacteria and Acidobacteria were predictably the dominating bacterial taxa in the samples with clear trend of Betaproteobacteria preferring the pine root habitats.Peer reviewe

A stationary visual census technique for quantitatively assessing community structure of coral reef fishes

A new method is described and evaluated for visually sampling reef fish community structure in environments with highly diverse and abundant reef fish populations. The method is based on censuses of reef fishes taken within a cylinder of 7.5 m radius by a diver at randomly selected, stationary points. The method provides quantitative data on frequency of occnrrence, fish length, abundance, and community composition, and is simple, fast, objective, and repeatable. Species are accumulated rapidly for listing purposes, and large numbers of samples are easily obtained for statistical treatment. The method provides an alternative to traditional visual sampling methods. Observations showed that there were no significant differences in total numbers of species or individuals censused when visibility ranged between 8 and 30 m. The reefs and habitats sampled were significant sources of variation in number of species and individuals censused, but the diver was not a significant influence. Community similarity indices were influenced significantly by the specific sampling site and the reef sampled, but were not significantly affected by the habitat or diver (PDF file contains 21 pages.

Seasonal and Interannual Variability of Phytoplankton Abundance and Community Composition on the Central Coast of California

Variations in the abundance and composition of phytoplankton greatly impact ecosystem structure and function. Within the California Current System (CCS), phytoplankton community structure is tightly coupled to seasonal variability in wind-driven coastal upwelling, a process that drives changes in coastal water temperatures and nutrient concentrations. Based on approximately a decade (2008-2018) of weekly phytoplankton measurements, this study provides the first characterization of the seasonal and interannual variability of phytoplankton abundance and composition in San Luis Obispo (SLO) Bay, an understudied region within the CCS. Overall, the seasonality of phytoplankton in SLO Bay mirrored that of the larger CCS; diatoms dominated the community during the spring upwelling season, whereas dinoflagellates dominated the community during the fall relaxation period. While we observed considerable interannual variability among phytoplankton taxa, of particular note was the absence of a fall dinoflagellate-dominated period from 2010 through 2013, followed by the return of the fall dinoflagellate-dominated period in 2014. This compositional shift coincided with a major phase shift of both the Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO). In addition to exerting a strong influence on the seasonality of phytoplankton community succession and transition between diatom- and dinoflagellate-dominated periods, the state of both the PDO and NPGO also influenced the extent to which environmental conditions (temperature and upwelling winds) could predict community type. These results highlight the importance of long-term datasets and the consideration of large-scale climate patterns when assessing local ecosystem dynamics

Abundance and community composition of invasive Intertidal Watersipora on the San Francisco Bay Area Outer Coast

Invasive species can lead to serious ecological changes. The San Francisco Bay area is one of the most invaded areas in the world due to the commercial shipping industry and recreational water vessels. While the intertidal is not widely invaded, the harbors and docks are. One exception to this is the invasive, colonial filter-feeding bryozoan Watersipora, which has been found at various rocky outer coast sites. Further investigation into how the sites are invaded by this organism and their impact on native species must be carried out. In this project, at four intertidal sites around the SF Bay outflow, we compared Watersipora abundance at two tidal heights and assessed interactions with organisms. Using two parallel transects, separated by approximately 8 meters, we documented size and growth form of all colonies located one meter to each side of the transect. To assess community interactions, we centered a 15x15 centimeter quadrat over every other colony and photographed it. Using the photographs, organisms within each quadrat were quantified and interactions between Watersipora and organisms were assessed. At all sites, Watersipora abundance was higher in the lower intertidal than the shoreward transect. Comparing the four sites, the two sites more distant from the outflow had more total counts of colonies, in comparison to the two bay proximal sites. This may suggest that the bay outflow isn’t the source of Watersipora spread along the coast, even though it is abundant inside the Bay itself. Investigating community composition around Watersipora colonies showed most interactions with coralline algae, sponges, polychaete tubes, and anemones. Specifically, it was observed overgrowing Phragmatopoma californica tubes, and both overgrowing and being overgrown by sponges. Looking forward, investigation into how Watersipora impacts species in the same ecological niche will be critical to understanding how this invasive organism is impacting the rocky intertidal community

Landscape position and depth affect microbial abundance and community composition at three positions in an agricultural landscape

Non-Peer ReviewedStabilization/destabilization mechanisms of deep soil carbon are not well understood. A number of different controlling mechanisms are suggested; here we explore differences in microbial abundance and community structure as a controlling mechanism. Microbial abundance and community composition with depth was assessed at three different positions within an agricultural landscape. Microbial abundance was significantly affected by sampling depth, while differences in community structure could be attributed to depth, landscape position, and conditions found within the depositional position. Interestingly, substantial biomass existed at a depth of 81cm in a buried A horizon found in the depositional position