En esta tesis se estudiaron los efectos sobre el sedimento de la fauna que habita los fondos blandos de planicies de marea y marismas del estuario de Bahía Blanca. En particular se evaluaron los efectos de la presencia de poliquetos, como Laeonereis culveri, sobre la estabilidad del sedimento y su interacción con otros organismos como los cangrejos cavadores (Neohelice granulata) y peces bentófagos (Micropogonias furnieri) en la determinación de las propiedades de los sedimentos que habitan. El trabajo se realizará bajo la siguiente hipótesis: la infauna bentónica del estuario de Bahía Blanca cumple un rol preponderante en la desestabilización de los sedimentos colonizados y ejerce influencia en la exportación de materiales del sistema. En el Capítulo I se evaluó cuáles son los efectos de la presencia de Laeonereis culveri, una de las especies bentónicas más importantes de estuarios del Atlántico sudoccidental, en los sedimentos de fondos blandos de marismas del estuario de Bahía Blanca. Se llevaron a cabo una serie de muestreos y experimentos de campo (Exclusiones, etc.) y experimentos de laboratorio (mesocosmos). En el Capítulo II se centró en el estudio de la actividad de alimentación de la corvina rubia, que produce al buscar su presa unas depresiones elípticas en el sustrato. En este trabajo surgió la pregunta de qué efecto tendría la turbulencia generada dentro de las depresiones en la resuspensión del sedimento depositado en su interior. Se llevaron a cabo una serie de muestreos y experimentos de campo. En el Capítulo III, los objetivos determinar cuál es el grado de interacción entre estas dos importantes especies de invertebrados de las marismas del estuario de Bahía Blanca, el poliqueto Laeonereis culveri y el cangrejo cavador Neohelice granulata, y su efecto en las propiedades físicas del sedimento y los cambios producidos por la presencia de N. granulata sobre la comunidad macrobentónica especialmente en la diversidad y abundancia. En el capítulo IV se determinó cual es el rol de la densidad de la biota en los procesos de erosión y depositación. Para cumplir con el objetivo de este capítulo se realizó un experimento de mesocosmos. Como conclusiones generales resaltan la determinación del efecto desestabilizador de L. culveri, afectando la estructura del sedimento y a las comunidades de microalgas bentónicas. Además se determinó un efecto sinérgico entre el poliqueto en cuestión y el cangrejo cavador Neohelice granulata afectando ambos la estabilidad del sedimento al disminuir la densidad de microalgas. A su vez se registró un efecto negativo del cangrejo cavador en la estructura de las comunidades betónicas. Se evaluó también el rol de los peces en la determinación de la composición sedimentaria de planicies de marea del estuario de bahía blanca a través de su actividad de alimentación. Por último se determino como varia el efecto de la densidad de L. culveri en las propiedades del sedimento que caracterizan la erodabilidad del mismo. Los resultados alcanzados en esta tesis permitieron corroborar las hipótesis planteadas al inicio de esta investigación. / The focus of this thesis was the study of the faunal effects on the sediment at tidal flats and salt marshes from the Bahía Blanca estuary. The effects of the presence of Laeonereis culveri on the sediment stability and the effects of its interaction with other organisms like crabs (Neohelice granulata) and fish (Micropogonias furnieri) in the same processes were evaluated. The main hypothesis was: The benthic infauna of the Bahía Blanca estuary plays a preponderant role in the destabilization of the sediments that inhabits and exerts influence in the export of materials of the system. In Chapter I the effects of the presence of Laeonereis culveri on salt marshes sediments at the Bahía Blanca estuary were evaluated. A series of samplings and field experiments was carried out (Exclusions, etc.) and laboratory experiments (mesocosmos). In Chapter II the study was centered on the white croaker (Micropogonias furnieri) feeding activity, which produces elliptical depressions in the substrate when it is looking for its prey. In this work the focus was on the effect of turbulence generated within the depressions on sediment suspension. A series of field samplings and experiments was carried out. In Chapter III, the objectives were to determine the degree of interaction between Laeonereis culveri and the crab Neohelice granulata, and the effect of this interaction on the sediment physical properties. The changes produced by the presence of N. granulata on the macrobenthic community were also studied. In Chapter IV the role of biota density in the erosion and depositation processes were tested. In order to fulfill the aim of this chapter mesocosmos experiment was carried out. As a general conclusion, a destabilizing effect of L. culveri was found. A synergic effect between L. culveri and the crab Neohelice granulata were affecting the stability of the sediment when they feed of microalgae. Also, a negative effect of N. granulata on the benthic community’s structure was found. The role of fish in the determination of sediment composition was also evaluated, and a negative impact of fish was found. Finally, a density dependent effect was found, found a negative relationship between abundance of L. culveri and sediment bed shear stress. The results generated in this thesis make possible to probe the hypotheses raised at the beginning of this investigation.

Soft-sediment ecosystems can be degraded through anthropogenic development, leading to reduced habitat suitability for biological communities. On the North Coast of British Columbia, Canada, intensive industrial activity and coastal development has occurred, specifically around the Skeena and Kitimat River Estuaries. In addition to current development, both regions have the potential for further development, while also undergoing passive restoration from historical disturbances. Therefore, I aimed to broaden our understanding of passive restoration and non-invasive monitoring of intertidal soft-sediment ecosystems, by carrying out experiments at mudflats in both estuaries during the summer of 2017. Specifically, I aimed to expand the use of a non-invasive population assessment technique to novel species in soft-sediment ecosystems. Relationships between burrowing decapod abundance and burrow openings have been successfully used to estimate population sizes, but this technique has yet to be applied to large burrowing polychaetes, bivalves, or in regions of high macrofaunal diversity. As such, I assessed mudflats in regions of low (n = 1 species) and high (n = 8 species) biodiversity to determine if macrofauna abundances could be estimated from burrow openings on the sediment surface. Where only one burrowing bivalve species was present, a relationship between burrow openings and population abundance was not feasible, but burrow openings were useful in estimating total macrofaunal community abundance at a high diversity mudflat. This suggests that monitoring through burrow opening counts has the ability to detect overall changes in population abundance. Next, I examined the infaunal community, sediment conditions, and nutrient availability at one intertidal mudflat in the Skeena River Estuary following the cessation of heavy industrial activities (i.e. a salmon cannery and pulp mill) to determine the capacity for passive restoration. Sediment conditions varied spatiotemporally, and nutrient availability showed temporal variation but trends were difficult to relate to historical or current potential disturbances. The legacy of past development is still apparent on the infaunal community in the form of patchy distributions of disturbance-indicating taxa, but the mudflat appears to be in an overall healthy state with a diverse and functioning food web, indicating community recovery from historical activities. Results from these studies indicate passive restoration can be appropriate for estuarine soft-sediment ecosystems, while monitoring population abundance through burrow openings could be a method of detecting disturbances or tracking recovery of macrofaunal populations. / Graduate / 2020-06-28

Contaminated sediments pose a direct risk to sediment fauna and have the potential to affect other benthic assemblages. Disturbances that resuspend and remobilise contaminants may impact on filter-feeding, hard-substrate organisms that live immediately above sediments. This thesis uses laboratory and field manipulations to examine the impact of metal-contaminated sediments on sediment fauna and hard-substrate fauna simultaneously. It also compares the response of assemblages to metal contamination in a temperate and polar ecosystem. Simulated resuspension exposures in the laboratory indicated that contaminated sediments have the potential to affect hard-substrate organisms. Spirorbid polychaetes responded to both aqueous metals and to resuspended, particulate-bound metals. Impacts on hard-substrate fauna were however, not observed in manipulative field experiments using metal-spiked sediments. The recruitment and cover of hard-substrate organisms were either not affected or enhanced above contaminated sediments. In contrast, metal contamination had direct negative effects on sediment fauna, with a reduction in the abundance of most taxa. Results suggest that sediment fauna may interact with hard-substrate fauna through physical and/or biological mechanisms. In a reciprocal transplant experiment, established Antarctic hard-substrate assemblages were also unaffected by contaminant concentrations at an impacted site. Overall, metal-contaminated sediments are unlikely to pose as serious a threat to hard-substrate fauna as they do to sediment fauna. Contaminated sediments are not restricted to industrialised regions, and human activities in Antarctica have resulted in localised contamination near research stations. Although Antarctic assemblages are thought to be more sensitive than temperate assemblages to contaminants, few studies have explicitly examined this. Little evidence was found to support the theory that Antarctic assemblages are more susceptible to contaminated sediments. The response of Antarctic and temperate assemblages in the field to metal-contaminated sediments over a 10-11 month period was comparable. Responses were of a similar magnitude, despite differences in the composition of assemblages. In 10-d toxicity tests, the mortality of a common Antarctic hard-substrate organism was relatively insensitive to aqueous Cu, Zn and Pb. These results suggest that using current sediment quality guidelines from Australia may be a useful screening tool to assess the risk associated with contaminated sediments in Antarctica.

Changes in the biosphere require ecological baselines in order to compare past, present, and future conditions and identify their effects. Establishing ecological baselines for infauna in southeastern Florida is a key component to understanding effects of current and future disturbances; however, nearshore sediment infaunal communities are neither as thoroughly investigated nor as well understood as, for example, coral reefs, seagrass beds, and mangroves. Baseline studies help assess and monitor changes due, for example, to human population growth, sea level change, and global warming. Therefore, six benthic cores were collected quarterly from six locations from May 2015 to February 2016 using a 7.7-cm PVC corer to examine macroinfaunal composition, richness and diversity in relation to environment, month, and sediment characteristics (e.g., composition and sphericity). Results suggest a latitudinal gradient of infaunal abundance and diversity, which was negatively correlated with median grain size. The middle sites located nearer the Florida Current and adjacent to the extensive carbonate deep ridge complex recorded higher percentages of carbonate and median grain size than the northernmost and southernmost sites. The dominant fauna included polychaetes (chiefly Armandia agilis, Paraonis fulgens, and Leitoscoloplos fragilis), isopods (Eurydice piperata and Ancinus depressus), and mysid shrimp (Chlamydopleon dissimile). Polychaetes dominated most samples and sites; however, peracarid crustaceans (chiefly isopods) dominated three sites in May and four sites in February samples. The recency of beach replenishments showed no long term effects on the infauna. This study provides an initial baseline that will permit comparison with future macroinfaunal and sediment studies along the southeastern Florida coast.

Shallow seagrass ecosystems frequently experience physical disturbance from vessel groundings. Specific restoration methods that modify physical, chemical, and biological aspects of disturbances are used to accelerate recovery. This study evaluated loss and recovery of ecosystem structure in disturbed seagrass meadows through plant and soil properties used as proxies for primary and secondary production, habitat quality, benthic metabolism, remineralization, and nutrient storage and exchange. The efficacy of common seagrass restoration techniques in accelerating recovery was also assessed. Beyond removal of macrophyte biomass, disturbance to seagrass sediments resulted in loss of organic matter and stored nutrients, and altered microbial and infaunal communities. Evidence of the effectiveness of restoration actions was variable. Fill placement prevented additional erosion, but the resulting sediment matrix had different physical properties, low organic matter content and nutrient pools, reduced benthic metabolism, and less primary and secondary production relative to the undisturbed ecosystem. Fertilization was effective in increasing nitrogen and phosphorus availability in the sediments, but concurrent enhancement of seagrass production was not detected. Seagrass herbivores removed substantial seagrass biomass via direct grazing, suggesting that leaf loss to seagrass herbivores is a spatially variable but critically important determinant of seagrass transplanting success. Convergence of plant and sediment response variables with levels in undisturbed seagrass meadows was not detected via natural recovery of disturbed sites, or through filling and fertilizing restoration sites. However, several indicators of ecosystem development related to primary production and nutrient accumulation suggest that early stages of ecosystem development have begun at these sites. This research suggests that vessel grounding disturbances in seagrass ecosystems create more complex and persistent resource losses than previously understood by resource managers. While the mechanics of implementing common seagrass restoration actions have been successfully developed by the restoration community, expectations of consistent or rapid recovery trajectories following restoration remain elusive.

Oyster reefs are important estuarine ecosystems that provide habitat to many species including threatened and endangered wading birds and commercially important fishes and crabs. Infaunal organisms (i.e. small, aquatic animals that burrow in the sediment) are also supported by oyster reef habitats. Infaunal organisms are critical to marine food webs and are consumed by many important species that inhabit coastal estuaries. However, over the past century 85% of shellfish reef habitats have been lost, making restoration of these areas vital. Due to their important role in coastal food webs, infauna is hypothesized to be a strong indicator of habitat productivity to document the transition from a dead to a restored and living intertidal oyster reef. Research was conducted in Mosquito Lagoon of the northern Indian River Lagoon system. Three replicate samples were collected from 12 intertidal oyster reefs (four dead, four live, four restored). Samples were collected one-week pre-restoration and one month and six months post-restoration. Infauna was counted and sorted into six taxonomic categories: polychaetes, amphipods, isopods, gastropods, bivalves, and decapods. Reef infaunal abundance increased following restoration: restored reefs became more similar to live reefs one month following restoration. Six months after restoration restored reefs were also significantly different than dead reefs. Live reefs consistently had high infaunal abundance and dead reefs consistently had low abundance, while restored reefs were intermediate. These data suggest restored reefs are more productive than their dead counterparts, with restoration showing a positive trajectory to impact numerous infaunal species and their associated food webs.

Relatively little is known about either the biological (i.e., predation) or physical (i.e., current, sedimentation) effects that artificial reefs may have on surrounding benthic infaunal communities. Following deployment of artificial reefs (concrete boulders) between the first and second reefs off Fort Lauderdale, Florida, on 30 October 2009, sediment cores were taken at 4 distances along three replicate 10-m transects on 13 and 26 September 2013, and 24 and 25 May 2014 at each of four artificial reef sites and four of their adjacent natural reef sites using SCUBA. Infauna (>0.5mm) were extracted from the sediment and identified to the lowest possible taxonomic level. Statistical analysis (PRIMER, PERMANOVA, SIMPER) focused on four main variables: type of reef, year, site, and distance. Type of reef, year, and site was significantly different between samples, while distance did not affect density. There is a clear separation of communities between the artificial and natural reefs. From 2013 to 2014, a slight shift occurred between communities suggesting the artificial reef community composition became slightly more similar to the natural reef. All four artifical reef sites were more taxonomically distinct at the phylum and class level then the natural reef, which had higher diversity, higher species richness and more low-density taxa. This two year study provides insight on infauna communities four and five years out from deployment, but follow up monitoring in 3-5 years could shed light on whether these patterns of shift to more similar assemblages between reefs will continue as the artificial reef matures. Environmental data collection including longer time-series datasets, longer transects, and physical and geological data could provide more knowledge of how the artificial reef infaunal communities are changing over time.