Month: May 2021

Thesis Abstract:

In fission-fusion societies, individuals do not need to conform to a social structure in which their demographic or relatedness dictates their behavioral state or associations. Therefore, studies of fission-fusion societies provide a framework in which to compare the feeding dynamics across demographics unrestrained by stable associations. This study used bio-logger data and surface observations combined with long-term population data from the Gulf of Maine humpback whale, Megaptera novaeangliae, population to better understand the influence of demographics on feeding methods, time spent feeding and determine if a coordinated feeding method, kick-feeding, was a cooperative behavior. The results suggest that demographics did influence the feeding method used and highlighted the need to determine how energetic needs change across the feeding season. The results suggest that kick-feeding was not a form of cooperation. In contrast, demographics and the broader population structure did influence the roles that individuals filled in kick-feeding dyads.  Additionally, females’ extensive use of bottom-feeding, compared to males, suggests that different energetic requirements influence the feeding methods used. Preferential use of the lower water column by mother-calf pairs and pregnant females should be considered in future studies about anthropogenic threats.

Images taken under NOAA permit #981-1707, 775-1875, 605-1607, 605-1904, and 18059

Thesis Abstract:

Changes in the Earth’s climate are closely associated with the changes in the concentration of CO₂ in the atmosphere. One process that may play a major role in modulating CO₂ availability is the chemical weathering of silicate rocks into clays. Chemical weathering and the associated CO₂ drawdown are especially efficient in the islands of the Indonesian Archipelago, including New Guinea, due to the combination of warm, wet conditions and tectonic uplift.  Despite New Guinea’s potential global significance as a major contributor to Earth’s carbon cycle, few studies have addressed its rapid geological evolution and the weathering conditions associated with it during the Pleistocene.

As direct products of weathered silicate rocks, clay minerals are a useful and widespread tool for reconstructing past weathering environments and source rocks. Clay mineral data from New Guinea are limited, with no clay records from the Sepik-Ramu Rivers, the island’s largest river system and one of the largest contributors of sediments to the world’s ocean. Deep-sea sediment cores collected by the International Ocean Discovery Program (IODP) Expedition 363 just offshore of the Sepik River mouth provide an unprecedented opportunity to evaluate the history of chemical weathering in a critical, rapidly-evolving region during the middle to late Pleistocene (the past ~550 kyr). This thesis identified and quantified the relative abundance over time of the clay mineral species in the core record in order to establish the regional weathering conditions, test a recent model of the Sepik’s development from an epicontinental sea to an enclosed river valley, and examine the relationship of tropical weathering rates with sea level change during glacial-interglacial cycles. Additionally, this thesis evaluated weathering microtextures on silt-sized feldspar particles to provide a secondary supporting dataset.

This project processed and analyzed the clay compositions of 124 samples from two IODP Expedition 363 sites: Sites U1484 and U1485, along with 16 samples from Site U1486, a site located further offshore from the Sepik River mouth. Isolated clay fractions from each sample were measured with x-ray diffractometry and quantified as clay percentages using simulation software (NewMod). For the corollary study, fine sand-sized feldspar particles were evaluated for weathering microtextures using a scanning electron microscope.

Overall, the clay assemblage is dominated by illite (~25-62%) and chlorite (~20-62%) with secondary amounts of smectite (~2-26%) and kaolinite (~3-32%), suggesting that mechanical rather than chemical weathering is the dominant mechanism responsible for clay generation in this region, possibly due to the active tectonic setting. The record also shows an increase in chlorite over time, attributed to ongoing tectonic uplift and the associated expansion of high-altitude glaciers and mechanical weathering. In addition, a sharp decrease in illite after the oldest samples is interpreted as the cessation of the diagenetic transformation of smectite to illite.

The clay mineral record also shows short-term compositional shifts—the most notable of which include two shifts in clay abundance from 400-430 ka and 125-140 ka characterized by an increase in smectite and kaolinite and a decrease in illite and chlorite. These shifts coincide with glacial terminations, suggesting that rapid sea level rise during deglaciations may have resulted in the reworking of older and more chemically weathered soils. The 400-430 ka shift also coincides with a unit of coccolith ooze indicative of a pelagic environment. This suggests that in the oldest part of the record, marine deposition and sea level transgression may have both contributed to the short-term enrichment of smectite, whereas later clay mineral shifts were driven mainly by sea level rise. The apparent increase in influence from marine transgressions may reflect increasing areas of lowland created by the filling of the Sepik Basin.  These results highlight the numerous processes controlling tropical weathering and document their changing relative significance throughout the evolution of the region.

Thesis Abstract:

Demon catsharks (Carcharhiniformes: Pentanchidae: Apristurus Garman) are one of the most diverse genera of sharks, with 39 described species. The genus is further divided formally into three subgroups based on morphological characters and molecular phylogenies, and referred to as the brunneus-, longicephalus-, and spongiceps subgroups. Six Apristurus species are considered valid in the Southwestern Indian Ocean (SWIO) where the spongiceps subgroup makes up a third of the species in the area. This study identifies and formally describes two additional Apristurus species in the spongiceps subgroup from the SWIO Ridge based on morphometric and meristic data, and includes re-examination of type specimens of Apristurus species from the North Atlantic and Southwestern Pacific oceans due to their close morphological relationship to one of the species found in the area. In this study, morphological characteristics and meristics, along with multivariate statistical tests, were used to determine that significant differences existed between the putative species, confirming species designations. Overall, two species were identified with the first record of A. ampliceps in the area and one new species, referred here to as A. cf. albisoma. An improved Apristurus identification key for the Western Indian Ocean (WIO) will assist fisheries managers in developing conservation policies for fisheries operating in this area.

Matthew Jew grew up in Southern California and attributes his passion for Marine Science to Mr. Tom Clarke, his science teacher during his senior year of high school.  He attended California State University, Monterey Bay, and graduated Magna Cum Laude with degrees in Marine Science and Mathematics.  As an undergraduate, he worked with Dr. James Lindholm and Paul Clerkin as a research assistant.  He credits Dr. Lindholm for fostering his love for research and SCUBA which led him on his career path to MLML.

Thesis Abstract:

In marine communities, there are often multiple species that occupy the same or similar niches. When resources are in short supply, competitive interactions can negatively affect the survival of one or both of the species involved. Understanding the trophic habits and interactions of species helps explain their role in a given ecosystem. Additionally, knowing the trophic habits of targeted or bycaught species captured in fisheries can help to influence management decisions on an ecosystem level. Apristurus brunneus and Parmaturus xaniurus (Family: Scyliorhinidae) are abundant deep-sea predators native to the Northeastern Pacific Ocean. Central California offers a unique opportunity to study these sympatric species in a location where they have large populations and the potential to compete for dietary resources. This study identifies: (1) the dietary composition each predator; (2) what biological and environmental factors are associated with variation in their trophic habits; (3) the trophic level of each species; and (4) the level of trophic overlap and potential for interspecific competition between the two species. To investigate the trophic habits of these two predators, this study used two complimentary techniques: stomach content analysis (SCA) and stable isotope analysis (SIA). Specimen from both species were collected during fishery-independent trawl surveys along the central California coast. Stomachs (for SCA) and dorsal white muscle tissue (for SIA) were removed from sharks after biological and catch data were recorded for each individual, including potential explanatory variables (e.g., depth, latitude, longitude, maturity, season, sex, trawl composition, and total length). Trophic habits and trophic position were calculated for each species independently and the level of trophic overlap between each species were calculated for SCA and SIA. Both shark species consumed the same three major prey groups (shrimp, squid, and fishes), however A. brunneus exhibited a similar preference for all three prey categories, while P. xaniurus placed a disproportional preference for shrimp. Apristurus brunneus diet composition varied with sampling season, latitude, sex, and total length. In contrast, the diet of P. xaniurus only varied with sampling season and total length. The results of the SIA indicated similar results. In A. brunneus, δ 15 N varied with latitude, sex, and total length while δ 13 C varied with latitude and total length. Parmaturus xaniurus’ SIA variation was as a function of total length, latitude, and season for δ 15 N and δ 13 C varied with latitude and season. SCA and SIA metrics indicated that the size of dietary niche was consistently smaller for P. xaniurus. Species with a smaller niche size are considered to implement specialist feeding strategy, whereas a much larger niche (like A. brunneus) would indicate generalist diet. Despite the differences in the size of the dietary niche, both SCA and SIA found significant trophic overlap between the two species, such that P. xaniurus samples are nearly completely contained within the isotopic space of A. brunneus. While there is significant dietary overlap, in order for there to be competition between species resources must be limiting. In central California, resources are likely not limiting and these two species have implemented feeding strategies that maximize their net energy gain even when a strong co-competitor is present. Ultimately, the knowledge gained on the dietary and competitive habits of these two species improves our understanding of their role in the deep-sea ecosystem of central California and this new knowledge will aid managers in the implementation of ecosystem-based fisheries management.