Browsing by Subject "Polychaetes"
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Item Factors Shaping Macrofaunal Polychaete Communities in the Gulf of Mexico(2013-04-23) Carvalho, Russell GThis dissertation addresses large-scale trends in composition, density, taxonomic and functional diversity in deep-sea benthic polychaete communities in the Gulf of Mexico (GoM). The study includes samples from two major sampling programs: the Deep Gulf of Mexico Benthos (DGoMB) program (2000?2002) (51 stations, 200-3700 m) and the SIGSBEE program (Universidad Nacional Aut?noma de M?xico), 2008-2010 (27 stations on the Sigsbee Abyssal Plain). Polychaete density decreased exponentially with depth. Alpha diversity did not show a mid-depth maximum and reached its peak near the Mississippi trough. Feeding guild diversity was also highest in the Mississippi trough. The environmental parameters that determine diversity and density of polychaete assemblages and species distribution ranges were examined. Depth, export flux of particulate organic carbon (POC), percent sand and silt were the best predictors of heterogeneity of polychaetes in the GoM. We performed an ecological niche modeling analysis (ENM) based on ?presence-only? data of four cosmopolitan species belonging to the Cirratulidae and Spionidae in the GoM. The GoM, being a semi-enclosed ocean basin, offers complex topographic features and hydrographic processes. Comparisons of the overall polychaete diversity and richness patterns from this study for this region indicate a strong geographic variation with increasing depth and distance from the shore. Additionally, the environmental gradients observed play a major role in shaping the spatial distribution of polychaete communities in this region.Item Patterns in biodiversity and distribution of benthic Polychaeta in the Mississippi Canyon, Northern Gulf of Mexico(Texas A&M University, 2006-04-12) Wang, YuningThe distribution of benthic polychaetes in the Mississippi Canyon was examined to evaluate impacts of environmental variables on species assemblages. Environmental variables considered included depth, bathymetric slope, hydrographic features, sediment grain size, food availability and sediment contamination. Samples were collected using GOMEX boxcorer. Density decreased with increasing depth exponentially. Diversity exhibited a unimodal pattern with depth with a maximum value in the intermediate depth range (about 1269 m). Deposit feeders were the most abundant feeding guild. Both the feeding guilds and faunal composition could be divided into three groups along the depth gradient: shallow (300 ?? 800 m), intermediate (800 ?? 1500 m) and deep (> 1500 m). Results of statistical analyses revealed that depth was the most important determinant in organizing polychaete assemblages in the study area. The Mississippi Canyon and the Central Transect (a non-canyon area) were found not contaminated by trace metals or Polynuclear Aromatic Hydrocarbons (PAHs) in sediments, although the highest PAHs concentration occurred at the head of the Canyon, MT1. The mean density was higher in the Mississippi Canyon (1668 N/m2) than in the Central Transect (979 N/m2), while the mean diversity in the Canyon (ES(100) = 26.9 ) was lower than the Central Transect (ES(100) = 33.1). Large amounts of terrigenous input from the Mississippi River to the Canyon could enhance polychaete density and accelerate competitive exclusion, and thus lead to lower diversity. The faunal composition was significantly different between the two transects, with higher species richness in the Mississippi Canyon (301 species). This could be attributed to structure complexity in the Mississippi Canyon. The distribution of feeding guilds was similar between two transects. The differences observed in polychaete assemblages between two transects may be largely due to high terrigenous sediment and organic matter input to the Mississippi Canyon by the Mississippi River.Item Polychaete Annelid Dynamics in the Northern Gulf of Mexico, From Shallow Water to the Deep-Sea(2014-12-16) Qu, FangyuanPolychaete annelids dominated the macrobenthos in sediments located 5 to 9 km from the Deep Water Horizon (DWH) Oil Spill site five months after the event. Numbers of species, abundance, and biodiversity indices in the polychaete taxa were significantly lower than pre-spill values from similar depths in the eastern Gulf of Mexico (GoM). Both non-selective and selective deposit feeders were the most frequent feeding guilds, but their abundances were significantly lower. An increase in the number of carnivorous Sigalionidae may be a response to an accumulation of petroleum hydrocarbons on the sediment. The concentration of oil in the sediments was low and the source of the oil remains equivocal. Multivariate analyses illustrated the differences between communities near the DWH and those from prior studies in similar deep GoM habitats. In summary, Deep Water Horizon oil spill appears to have had a measurable impact on the polychaetes. A time series of benthic samples from 2004 to 2012 has been utilized to assess the influence of hypoxia on the mean sizes (wet weight) of polychaeteannelid worms.While the mean body size over the entire study was 3.99?4.66 mg wet weight per individual, the mean ranged from 2.97?2.87 mg during consistently hypoxic conditions (< 2 mg/L)to a high of 7.13?7.60 mg (p < 0.01)under oxic conditions (> 2 mg/L). The decline in size was due to the elimination of large species under hypoxic conditions, not a reduction in size within species. At 'severe' levels of hypoxia (< 1 mg/L), the smallest species also declined in abundance, whereas the ubiquitous ?medium sized? Paraprionospio pinnata flourished. The infaunal benthos of the upper continental slope, a transition zone between the dynamic continental shelf and the deep sea, has been sampled in 1983-85 and then again in 2000-02 at nine locations. The polychaete annelid worms, the dominant taxon within the samples, exhibited remarkable stability in abundance, diversity, depth-related zonation, and species composition (> 35% similarity in species) over that period. At 7 of the 9 locations, single appearances of several dominant species resulted in the 1983-85 samples being more abundant but less diverse than the 2000-02 survey.