Size-frequency Distribution Data Research Articles

Intra-decadal increase in globally-spread Magallana gigas in southern California estuaries.

Introduction and establishment of non-indigenous species (NIS) has been accelerated on a global scale by climate change. NIS Magallana gigas' (formerly Crassostrea gigas') global spread over the past several decades has been linked to warming waters, specifically during summer months, raising the specter of more spread due to predicted warming. We tracked changes in density and size distribution of M. gigas in two southern California, USA bays over the decade spanning 2010-2020 using randomly placed quadrats across multiple intertidal habitats (e.g., cobble, seawalls, riprap) and documented density increases by 2.2 to 32.8 times at 7 of the 8 sites surveyed across the two bays. These increases in density were coincident with 2-4° C increases in median monthly seawater temperature during summer months, consistent with global spread of M. gigas elsewhere. Size frequency distribution data, with all size classes represented across sites, suggest now-regular recruitment of M. gigas. Our data provide a baseline against which to compare future changes in density and abundance of a globally-spread NIS of significant concern.

Quagga mussels continue offshore expansion in Lake Michigan, but slow in Lake Huron

The impacts of invasive dreissenid mussels on the Great Lakes ecosystem strongly depend on their biomass, distribution, and population trajectories. In order to assess recent population trends of dreissenids in the upper Great Lakes we conducted extensive ponar and benthic imaging system (BIS) surveys throughout Lake Michigan (including Green Bay), and the US portion of Lake Huron in 2018 and 2019. We used the two survey methods to quantify the biomass, density, size-frequency distributions, and small-scale spatial arrangement patterns of Dreissena spp. We show that dreissenid populations are continuing their expansion into deeper, offshore regions of Lakes Michigan since the most recent surveys conducted in 2015. In Lake Michigan, average areal biomass of Dreissena spp. was 25.4 g shell free dry mass (SFDM)/m2 with maximum biomass occurring between 81 and 100 m (76.1 g SFDM m2 ± 49.2). Average areal biomass was lower in US Lake Huron (20.7 g SFDM/m2) with peak biomass between 51 and 75 m (21.5 g SFDM m2 ± 58.9 SD). Size-frequency distribution data shows that recruitment is occurring in the deepest portions of both lakes, and suggests that the expansion of dreissenids to deep waters of the upper Great Lakes is likely to continue. We show good agreement between ponar and BIS data and join others in recommending regularly supplementing ponar sampling with BIS methods in dreissenids surveys to increase survey speed and collect novel types of data about mussel populations.

Measuring coral size-frequency distribution using stereo video technology, a comparison with in situ measurements.

Coral colony size-frequency distribution data offer valuable information about the ecological status of coral reefs. Such data are usually collected by divers in situ, but stereo video is being increasingly used for monitoring benthic marine communities and may be used to collect size information for coral colonies. This study compared the size-frequency distributions of coral colonies obtained by divers measuring colonies 'in situ' with digital video imagery collected using stereo video and later processed using computer software. The size-frequency distributions of the two methods were similar for corymbose colonies, although distributions were different for massive, branching and all colonies combined. The differences are mainly driven by greater abundance of colonies >50 cm and fewer colonies <10 cm recorded when using the in situ method. The stereo video method detected 93% of marked colonies >5 cm and was able to record measurements on 87% of the colonies detected. However, stereo video only detected 57% of marked colonies <5 cm, suggesting that this method may be unsuitable for assessing abundance of coral recruits. Estimates of colony size made with the stereo video were smaller than the in situ technique for all growth forms, particularly for massive morphologies. Despite differences in size distributions, community assessments, which incorporated genera, growth forms and size, were similar between the two techniques. Stereo video is suitable for monitoring coral community demographics and provided data similar to in situ measure for corymbose corals, but the ability to accurately measure massive and branching coral morphologies appeared to decline with increasing colony size.

Effect of pest–management operations on the abundance and size–frequency distribution of the New Zealand endemic frog Leiopelma hochstetteri

In New Zealand, introduced mammals, especially rats, have been considered a primary factor in the extinction of amphibians. (Leiopelma hochstetteri) is a riparian frog, and is the most widespread of the surviving species of native frogs in New Zealand. At present, all populations of this frog species coexist with introduced mammals, which in some cases have been subject to pest–management operations without monitoring the potential benefits or damage to the frogs. We investigated the influence of a 7–year rat management operation on frog abundance in the Waitakere Ranges, New Zealand. We identified which habitat characteristics had significant influence on frog abundance; confirmed that the study areas represented similar habitats both inside and outside the pest–managed area, and finally evaluated the effects of the pest–management activities. Frog abundance was positively correlated with percentage area covered by boulders and percentage area covered by water. Since the study sites were similar in terms of those variables, we could make a reliable comparison of frog abundance in relation to pest management. Presence/absence of pest–management operations did not have any significant effect on frog abundance. Size–frequency distribution data suggest that there has been recruitment of young frogs both inside and outside pest–management areas in the past 7 years.

The Ascraeus Mons fan-shaped deposit: Volcano–ice interactions and the climatic implications of cold-based tropical mountain glaciation

Amazonian-aged fan-shaped deposits extending to the northwest of each of the Tharsis Montes in the Tharsis region on Mars have been interpreted to have originated from mass-wasting, volcanic, tectonic and/or glacial processes. We use new data from MRO, MGS, and Odyssey to characterize these deposits. Building on recent evidence for cold-based glacial activity at Pavonis Mons and Arsia Mons, we interpret the smaller Ascraeus fan-shaped deposit to be of glacial origin. Our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat, including: (1) a ridged facies, interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat, (2) a knobby facies, interpreted to represent vertical downwasting of the ice sheet, and (3) complex ridges showing a cusp-like structure. We also see evidence of volcano–ice interactions in the form of: (1) an arcuate inward-facing scarp, interpreted to have formed by the chilling of lava flows against the glacial margin, (2) a plateau feature, interpreted to represent a subglacial eruption, and (3) knobby facies superimposed on flat-topped flows with leveed channels, interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till. We discuss the formation mechanisms of these morphologies during cold-based glacial activity and concurrent volcanism. On the basis of a Mid- to Late-Amazonian age (250–380 Ma) established from crater size-frequency distribution data, we explore the climatic implications of recent glaciation at low latitudes on Mars. GCM results show that increased insolation to the poles at high obliquities (>45°) forces sublimation of polar ice, which is transported to lower latitudes and deposited on the flanks of the Tharsis Montes. We assess how local orographic effects, the mass balance of the glacier, and the position of equilibrium line altitudes, all played a role in producing the observed geomorphologies. In doing so, we outline a glacial history for the evolution of the Ascraeus Mons fan-shaped deposit and compare its initiation, growth and demise with those of Arsia Mons and Pavonis Mons.

Population Structure, Growth, Mortality, and Size at Sexual Maturity of Palaemon Gravieri (Decapoda: Caridea: Palaemonidae)

Abstract Population characteristics such as population structure, growth, mortality, and size at sexual maturity of P. gravieri inhabiting warm temperate waters were investigated using size-frequency distribution data (January 1999 to December 2000). Sexual differences for carapace length/total weight and carapace length and total length were statistically significant in the intercept of the regressions in the former relationship and the slope in the latter, respectively. Population size based on size-frequency distribution between female and male and between two years were described. Population density was high in March and April during two years of sampling. Sex ratio was biased toward females for most of the months sampled. Growth was continuous and seasonally oscillated throughout the year. Adult females were larger and grew faster than males. The von Bertalanffy growth parameters for two-year pooled samples between females and males were estimated as L∞ = 23.20, K = 0.8, C = 0.4, WP = 0.1, Rn = 0.269...

A computer-simulated restriction fragment length polymorphism analysis of bacterial small-subunit rRNA genes: efficacy of selected tetrameric restriction enzymes for studies of microbial diversity in nature.

An assessment of 10 tetrameric restriction enzymes (TREs) was conducted by using a computer-simulated restriction fragment length polymorphism (RFLP) analysis for over 100 proximally and distally related bacterial small-subunit (SSU) rRNA gene sequences. Screening SSU rDNA clone libraries with TREs has become an effective strategy because of logistic simplicity, commercial availability, and economy. However, the rationale for selecting the type and number of TREs has not been systematically evaluated. Our objective was to identify the optimal combination of TREs for RFLP screening of cloned SSU rRNA genes from undefined bacterial clone libraries. After computer-simulated TRE digestion, the resultant fragments were categorized on the basis of the frequency of different restriction fragment size classes. Three groups of distribution patterns for the TREs were determined and further examined via graphical exploratory data analysis. The RFLP size-frequency distribution data for each group of enzymes were then used to infer phylogenetic relationships via the neighbor-joining method. The resulting bootstrap values and the correct placement of node bifurcations were used as additional criteria to evaluate the efficacy of the selected TREs. These RFLP data were compared with known phylogenetic relationships based on SSU rRNA sequence analysis as defined by the Ribosomal Database Project. A heuristic approach testing random combinations of TREs showed that three or more TRE combinations detected > 99% of the operational taxonomic units (OTUs) within the model data set. OTUs that remained undetected after three TRE treatments had a median sequence similarity of 96.1%. Of the 10 restriction enzymes examined, HhaI, RsaI, and BstUI (group 3) were the most efficacious at detecting and differentiating bacterial SSU rRNA genes on the basis of their ability to correctly classify OTUs. Group 3 TREs are therefore recommended for screening in studies using bacterial SSU rRNA genes as descriptors of in situ microbial diversity.

Oxygen consumption and ammonium excretion of mega-sized benthic invertebrates in a tropical seagrass bed

In a Papua New Guinean seagrass bed community, oxygen consumption rates and ammonium excretion rates of various size classes of six dominant species of megafauna, Tripneustes gratilla (Linnaeus), Axius acanthus A. Milne-Edwards, Conomurex luchuanus (Linnaeus), Malleus malleus (Linnaeus), Holothuria atra Jaeger and H. scabra Jaeger, were measured using a differential gas-volumeter method and an oxygen bottle method. The metabolism/weight exponent “b” (R = aWb) for the six species ranged from 0.11 to 0.64 and was thus lower than the general value of “b” in poikilotherms. O/N ratios for the six species ranged from 19.3 to 44.2. The O/N values were discussed in relation to the various species' feeding habits. The abundance and size-frequency distributions of six species were estimated. Oxygen consumption and ammonium excretion rates could thus be calculated for the populations of the six species from metabolism/ weight relationships and the abundance and size-frequency distribution data. The total energy demand for respiration of the six megafaunal species in the seagrass bed of 6.56 ha was 12285 kcal·day−1. The importance of the megafauna to overall energy budgets for tropical seagrass bed communities was emphasized.

Gypsum-Oolite Dunes, Great Salt Lake Desert, Utah

A series of large lateral or transverse dunes occurs on the eastern margin of the Great Salt Lake desert near the village of Knolls, Tooele County, Utah. The dunes are composed primarily of gypsum crystals and cleavage fragments, oolites, with minor amounts of shell fragments and fine quartz, derived from lake waters during the waning stages of Lake Bonneville in the area of the present Great Salt Lake Desert. Size-frequency distribution data and photomicrographs demonstrate the lithologic distribution of the component minerals through the various size fractions of the dune material. In addition, the dunes were found to contain identifiable ostracods which are described and illustrated.