Polychaete Annelid Biomass Size Spectra: The Effects of Hypoxia Stress

Abstract

Quantitative benthic samples were taken during spring and summer at three locations on the Louisiana continental shelf from 2004 to 2012 to assess the influence of hypoxia on the mean sizes (wet weight) of polychaete annelid worms. While the mean body size over the entire study of 64 samples 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 variations in size within assemblages were estimated from conventional biomass size spectra (BSS) and normalized biomass size spectra (NBSS) across a broad range of oxygen concentrations. The decline in size was due to the elimination of large species under hypoxic conditions (<2 mg/L), 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 pinnataflourished. These results suggest that there will be enhanced selection for small sizes and species with enlarged branchial palps such as those inP. pinnataif, as predicted, hypoxia becomes more commonplace in time and space worldwide.

Response of the benthic biomass-size structure to a high-energy submarine canyon

“…It also means that the "canyon" conditions removed larger individuals with the effect increased toward the larger size classes. Similar patterns (i.e., steeper NBSS slope) have been observed in benthic communities from the coastal hypoxic zone in the Gulf of Mexico (Qu et al, 2015), oxygen minimum zones off Chile (Quiroga et al, 2005), and the Antarctic continental slope (Saiz-Salinas and Ramos, 1999). These studies suggest that the low oxygen conditions and food limitations may impact large organisms more than small ones.…”

“…Small organisms can better satisfy their metabolic demands (i.e., oxygen demand or nutritional need) due to the relatively large surface area to body volume ratio. Under extreme hypoxia (DO < 1 mg/L), even the small species may decline in abundance, leading to the dominance of medium-sized species (Qu et al, 2015). However, this might not be the case in this study because the medium-size individuals dominated (i.e., dome patterns in Figure 2B) both the disturbed (i.e., canyon) and nondisturbed habitat (i.e., adjacent slope).…”

“…Thus, deviations in the size spectrum may be used to identify environmental impacts. Efforts have been devoted to detect responses of the benthic size spectrum to environmental conditions, such as the oxygen minimum zone (Quiroga et al, 2005), coastal hypoxia (Qu et al, 2015), seasonal input of organic matters (Soltwedel et al, 1996), and declining food supply with depth (Goŕska et al, 2020). However, some studies have found that the shapes of the size spectrum are not strongly affected by latitudinal temperature (Mazurkiewicz et al, 2020) and water depth variations (Schewe and Soltwedel, 1999).…”

Modeling the Population Effects of Hypoxia on Atlantic Croaker (Micropogonias undulatus) in the Northwestern Gulf of Mexico: Part 2—Realistic Hypoxia and Eutrophication

“…We focus on two possible linkages: (1) low DO causing direct mortality of benthos and (2) food being linked to hypoxia conditions via river flow-driven productivity whereby high nutrient fluxes via riverine loadings lead to more food and more severe hypoxia. Hypoxia effects on benthos (e.g., mortality, body size) has been documented for the NWGOM Qu et al 2015) and other coastal systems (e.g., Levin et al 2009;Kodama and Horiguchi 2011).…”

Temperature-Modulated Expression of Allometric Respiration Strategies Supports a Metabolic Scaling Rule

“…An allometric metabolic scaling rule proposed by Rakocinski (2009), hypothesized that the slope of the log-log body mass vs. K1/K2 relationship for oxyconforming was −0.285 (i.e., intermediate between 3/4 and 2/3 scaling rules). Furthermore, the proposed relationship was symmetrically centered on 1 (i.e., the transitional capacity for regulating OCR; Chen et al, 2001) across eight common geometric scaled (octaves base 2) size-classes spanning the estuarine infaunal size spectrum for the northern Gulf of Mexico (Qu et al, 2015). However, this metabolic scaling rule has not been tested using any robust data sets.…”