Evaluation of particulate organic carbon from MODIS-Aqua in a marine-coastal water body.

La Paz Bay (LPB) in Mexico is one of the largest marine-coastal bodies of water in the Gulf of California (GC) and is ecologically important for the feeding, reproduction, and refuge of marine species. Although particulate organic carbon (POC) is an important reservoir of oceanic carbon and an indicator of productivity in the euphotic zone, studies in this region are scarce. This study evaluates the performance of satellite-derived POC in LPB from January 2003 to December 2020. The metrics obtained for COP ( RMSE = 33.8 mg m - 3 ; P bias = 29.6 % y r P = 0.4 con p < 0.05 ), Chla-a ( RMSE = 0.23 mg m - 3 ; P bias = - 4.3 % y r P = 0.94 con p < 0.05 ), and SST ( RMSE = 2 . 3 ∘ C ; P bias = - 2.2 % y r P = 0.92 con p < 0.05 ) establish that although in some cases there was a slight over/underestimation, the satellite estimates consistently represent the variability and average values measured in situ. On the other hand, the spatio-temporal analysis of the POC allowed us to identify two seasons with their respective transition periods and five subregions in which the POC is characterized by having its maximum variability; two of these coincide with the locations of the eddies reported for the winter and summer seasons in the LPB, while the following three are located: one in the coastal zone and in the two areas in which the LPB interacts with the GC. The associations, variability nodes, and multiple linear regression analysis suggest that POC fluctuations in the LPB respond mainly to biological processes and, to some extent, to the seasonality of SST and wind. Finally, our results justify the use of the MODIS-Aqua satellite POC for studies in marine-coastal water bodies with similar characteristics to the LPB and suggest that this water body can be considered a reservoir for the marine region of northwestern Mexico.

Temporal distribution patterns of metals in water, sediment, and components of the trophic structure in a tropical coastal lagoon of the Gulf of Mexico.

Trophic transfer and bioaccumulation of trace metals have a profound impact on the structure and function of coastal areas; however, the metal accumulation patterns in detritus-based food webs and the influence of climatic variability have not been thoroughly investigated. The Tampamachoco Lagoon (Gulf of Mexico) is a coastal system impacted by emissions from a thermoelectric plant. We evaluated the spatial-temporal distribution patterns of Al, Cd, Hg, Cr, Cu, and Pb in water, sediments, and in organisms categorized by trophic levels (TLs), trophic guilds, and habitat preferences. The sediments had the highest concentrations of metals with no significant differences between seasons. The indices of geo-accumulation and potential ecological risk classified sediments as "moderately contaminated", evidencing a threat to human health through consumption of detritivores and filter-feeders. The lowest TLs (filter-feeders and detritivorous) reached the maximum Metal Pollution Index in the rainy season. According to discriminant analyses of metals and species, omnivorous and zoobentivorous organisms were associated with Hg during the rainy and dry seasons; while Al, Cd, and Cu were related to low TLs, and seston was associated with Pb. Food web magnification factor analysis showed that: (a) Pb, Cu, and Cr were biodiluted as trophic levels increased; (b) Cd and Hg showed temporal biomagnification trends; (c) Al, Pb, Cu, and Cd showed significant biodilution from the lowest TL to intermediate TLs; and (d) Hg was transferred from the lowest to intermediate TLs with clear biomagnification effects.

Isotope-based inferences of the seasonal foraging and migratory strategies of blue whales in the eastern Pacific Ocean.

Migratory marine megafauna generally move vast distances between productive foraging grounds and environmentally stable breeding grounds, but characterizing how they use these habitats to maintain homeostasis and reproduce is difficult. We used isotope analysis of blue whale skin strata (n = 621) and potential prey (n = 300) to examine their migratory and foraging strategies in the eastern Pacific Ocean. Our results suggest that most whales in the northeast Pacific use a mixed income and capital breeding strategy, and use the California Current Ecosystem as their primary summer-fall foraging ground. A subset of individuals exhibited migratory plasticity and spend most of the year in the Gulf of California or Costa Rica Dome, two regions believed to be their primary winter-spring breeding grounds. Isotope data also revealed that whales in the southern Eastern Tropical Pacific generally do not forage in the northeast Pacific, which suggests a north-south population structure with a boundary near the equator.

Impact of freezing and ethanol preservation techniques on the stable isotope analysis of humpback whale (Megaptera novaeangliae) skin.

RATIONALE: Distinct techniques employed to preserve different types of tissues may affect stable isotope analyses conducted on samples, and this is critical when field work takes place in remote areas. To investigate this, the stable isotope ratios (δ13 C and δ15 N values) obtained using two methods commonly used to preserve humpback whale (and other cetaceans) skin samples were compared. METHODS: A total of 54 pairs of skin samples of humpback whales from the southern Baja California Peninsula, Mexico, were preserved in ethanol (90%) and by freezing, between 2007 and 2009. The δ13 C and δ15 N values were determined using a PDZ Europa ANCA-GSL elemental analyzer interfaced to a PDZ Europe 20-20 isotope ratio mass spectrometer. Parametric and nonparametric tests were used to compare the isotopic results. RESULTS: A significant (t = 4.93; p = 0.000003) variation of −0.92‰ was found between the mean δ13 C values in ethanol (from −19.38‰ to −16.07‰; mean = −17.86‰) and freezing (from −20.67‰ to −16.44‰; mean = −18.78‰) techniques. No significant (U = 1314, p = 0.38) differences were observed in the δ15 N values. The δ13 C values were compared between preservation methods for each of the three years under analysis. Significant differences were observed in 2007 (t = 3.45; p = 0.0012) and 2008 (t = 3.13; p = 0.0030), but not for 2009 (t = 1.66; p = 0.12). CONCLUSIONS: Based on the results of this study, the use of ethanol to preserve humpback whale skin samples collected for stable isotope analysis is not recommended, particularly regarding the analysis of δ13 C values. This study serves as a point of reference for future research on humpback whales or other whales involving skin samples preserved by freezing or in ethanol.

Habitat degradation alters trophic pathways but not food chain length on shallow Caribbean coral reefs.

Habitat degradation can affect trophic ecology by differentially affecting specialist and generalist species, and the number and type of interspecific relationships. However, the effects of habitat degradation on the trophic ecology of coral reefs have received limited attention. We compared the trophic structure and food chain length between two shallow Caribbean coral reefs similar in size and close to each other: one dominated by live coral and the other by macroalgae (i.e., degraded). We subjected samples of basal carbon sources (particulate organic matter and algae) and the same 48 species of consumers (invertebrates and fishes) from both reefs to stable isotope analyses, and determined the trophic position of consumers and relative importance of various carbon sources for herbivores, omnivores, and carnivores. We found that both reefs had similar food chain length and trophic structure, but different trophic pathways. On the coral-dominated reef, turf algae and epiphytes were the most important carbon source for all consumer categories, whereas on the degraded reef, particulate organic matter was a major carbon source for carnivores. Our results suggest that the trophic structure of the communities associated with these reefs is robust enough to adjust to conditions of degradation.

Estimating blue whale skin isotopic incorporation rates and baleen growth rates: Implications for assessing diet and movement patterns in mysticetes.

Stable isotope analysis in mysticete skin and baleen plates has been repeatedly used to assess diet and movement patterns. Accurate interpretation of isotope data depends on understanding isotopic incorporation rates for metabolically active tissues and growth rates for metabolically inert tissues. The aim of this research was to estimate isotopic incorporation rates in blue whale skin and baleen growth rates by using natural gradients in baseline isotope values between oceanic regions. Nitrogen (δ15N) and carbon (δ13C) isotope values of blue whale skin and potential prey were analyzed from three foraging zones (Gulf of California, California Current System, and Costa Rica Dome) in the northeast Pacific from 1996-2015. We also measured δ15N and δ13C values along the lengths of baleen plates collected from six blue whales stranded in the 1980s and 2000s. Skin was separated into three strata: basale, externum, and sloughed skin. A mean (±SD) skin isotopic incorporation rate of 163±91 days was estimated by fitting a generalized additive model of the seasonal trend in δ15N values of skin strata collected in the Gulf of California and the California Current System. A mean (±SD) baleen growth rate of 15.5±2.2 cm y-1 was estimated by using seasonal oscillations in δ15N values from three whales. These oscillations also showed that individual whales have a high fidelity to distinct foraging zones in the northeast Pacific across years. The absence of oscillations in δ15N values of baleen sub-samples from three male whales suggests these individuals remained within a specific zone for several years prior to death. δ13C values of both whale tissues (skin and baleen) and potential prey were not distinct among foraging zones. Our results highlight the importance of considering tissue isotopic incorporation and growth rates when studying migratory mysticetes and provide new insights into the individual movement strategies of blue whales.