Geology topics

Brian R. Silliman

Publications and source records attributed to Brian R. Silliman.

7 recordsLinked to original sources

USGS2024

Top-predator recovery abates geomorphic decline of a coastal ecosystem

The recovery of top predators is thought to have cascading effects on vegetated ecosystems and their geomorphology 1,2 , but the evidence for this remains correlational and intensely debated 3,4 . Here we combine observational and experimental data to reveal that recolonization of sea otters in a US estuary generates a trophic cascade that facilitates coastal wetland plant biomass and suppresses the erosion of marsh edges—a process that otherwise leads to the severe loss of habitats and ecosystem services 5,6 . Monitoring of the Elkhorn Slough estuary over several decades suggested top-down control in the system, because the erosion of salt marsh edges has generally slowed with increasing sea otter abundance, despite the consistently increasing physical stress in the system (that is, nutrient loading, sea-level rise and tidal scour 7,8,9 ). Predator-exclusion experiments in five marsh creeks revealed that sea otters suppress the abundance of burrowing crabs, a top-down effect that cascades to both increase marsh edge strength and reduce marsh erosion. Multi-creek surveys comparing marsh creeks pre- and post-sea otter colonization confirmed the presence of an interaction between the keystone sea otter, burrowing crabs and marsh creeks, demonstrating the spatial generality of predator control of ecosystem edge processes: densities of burrowing crabs and edge erosion have declined markedly in creeks that have high levels of sea otter recolonization. These results show that trophic downgrading could be a strong but underappreciated contributor to the loss of coastal wetlands, and suggest that restoring top predators can help to re-establish geomorphic stability.

California↗

USGS2021

Genetic analysis of red lionfish Pterois volitans from Florida, USA, leads to alternative North Atlantic introduction scenarios

The red lionfish Pterois volitans is a successful invasive predator across the western North Atlantic, Caribbean, and Gulf of Mexico. The southeast coast of Florida (USA) has been identified as the original introduction location, but genetic analyses including Florida lionfish have yet to investigate introduction scenarios. Here, we assessed the potential lionfish invasion pathways using 1795 sequences from previously published mitochondrial D-loop sequences (n = 1558) and new samples (n = 237) from 6 locations: The Bahamas, Florida Keys, northwest Florida, North Carolina, Panamá, and southeast Florida. None of the assessed Florida lionfish (n = 394) contained the H05-H09 D-loop haplotypes found in The Bahamas, North Carolina, and Bermuda (the Northern Region), indicating that Florida was not the source for these haplotypes. Assessing the mitochondrial population structure, the Florida east coast lionfish grouped with the Caribbean/Gulf of Mexico, as opposed to the Northern Region. To further explore connectivity and invasion pathways, 14 nuclear microsatellite loci were multiplexed on lionfish collected from 15 locations (n = 394). As found in other nuclear lionfish studies, the analyses identified a lack of population structure likely due to founding effects and/or inbreeding in aquaculture brood stocks. Together, the significant haplotype differences and H01-H04 haplotypes refute Florida as the sole source of red lionfish introduction. The results of this study support alternative invasion scenarios, in which Florida was colonized as a secondary introduction site or by individuals from the Northern Region. Understanding invasive species’ population boundaries and dispersal patterns informs local control efforts and management planning for future invasive species introductions.

Florida↗

USGS2015

Wide-ranging phylogeographic structure of invasive red lionfish in the Western Atlantic and Greater Caribbean

The red lionfish ( Pterois volitans ) is an invasive predatory marine fish that has rapidly expanded its presence in the Western Hemisphere. We collected 214 invasive red lionfish samples from nine countries and territories, including seven unpublished locations. To more comprehensively evaluate connectivity, we compiled our d-loop sequence data with 846 published sequences, resulting in 1,060 samples from 14 locations. We found low nucleotide diversity ( π = 0.003) and moderate haplotype diversity ( h = 0.59). Using haplotype population pairwise Φ ST tests, we analyzed possible phylogeographic breaks that were previously proposed based on other reef organisms. We found support for the Bahamas/Turks/Caicos versus Caribbean break ( Φ ST = 0.12) but not for the Northwestern Caribbean, Eastern Caribbean, or US East Coast versus Bahamas breaks. The Northern Region had higher variation and more haplotypes, supporting introductions of at least five haplotypes to the region. Our wide-ranging samples showed that a lower-frequency haplotype in the Northern Region dominated the Southern Region and suggested multiple introductions, possibly to the south. We tested multiple scenarios of phylogeographic structure with analyses of molecular variance and found support for a Northern and Southern Region split at the Bahamas/Turks/Caicos versus Caribbean break (percentage of variation among regions = 8.49 %). We found that Puerto Rico clustered with the Southern Region more strongly than with the Northern Region, as opposed to previous reports. We also found the rare haplotype H03 for the first time in the southern Caribbean (Panama), indicating that either secondary releases occurred or that the low-frequency haplotypes have had time to disperse to extreme southern Caribbean locations.

Marine Biology↗

USGS2015

Factors affecting individual foraging specialization and temporal diet stability across the range of a large “generalist” apex predator

Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators ( Alligator mississippiensis ), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and available prey types. Stable isotopes revealed that over longer time spans alligators exhibited remarkably consistent use of variable mixtures of carbon pools (e.g., marine and freshwater food webs). We conclude that INS in large-bodied reptilian predator populations is likely affected by variation in available prey types and habitat heterogeneity, and that INS should be incorporated into management strategies to efficiently meet intended goals. Also, ecological models, which typically do not consider behavioral variability, should include INS to increase model realism and applicability.

Oecologia↗

USGS2013

Habitat use patterns of the invasive red lionfish Pterois volitans : a comparison between mangrove and reef systems in San Salvador, Bahamas

The Indo-Pacific red lionfish Pterois volitans is widespread both in its native and its non-native habitats. The rapid invasion of this top predator has had a marked negative effect on fish populations in the Western Atlantic and the Caribbean. It is now well documented that lionfish are invading many tropical and sub-tropical habitats. However, there are fewer data available on the change in lionfish abundance over time and the variation of body size and diet across habitats. A recent study in San Salvador, Bahamas, found body size differences between individuals from mangrove and reef systems. That study further suggested that ontogenetic investigation of habitat use patterns could help clarify whether lionfish are using the mangrove areas of San Salvador as nurseries. The aim of the present study is to determine temporal trends in lionfish relative abundance in mangrove and reef systems in San Salvador, and to further assess whether there is evidence suggesting an ontogenetic shift from mangroves to reef areas. Accordingly, we collected lionfish from mangrove and reef habitats and calculated catch per unit effort (a proxy for relative abundance), compared body size distributions across these two systems, and employed a combination of stable isotope, stomach content, and genetic analyses of prey, to evaluate differences in lionfish trophic interactions and habitat use patterns. Our results show that populations may have increased in San Salvador during the last 4 years, and that there is a strong similarity in body size between habitats, stark differences in prey items, and no apparent overlap in the use of habitat and/or food resources. These results suggest that there is not evidence an for ontogenetic shift from mangroves to reefs, and support other studies that propose lionfish are opportunistic forages with little movement across habitats.

San Salvador↗

USGS2013

The roles of large top predators in coastal ecosystems: new insights from long term ecological research

During recent human history, human activities such as overhunting and habitat destruction have severely impacted many large top predator populations around the world. Studies from a variety of ecosystems show that loss or diminishment of top predator populations can have serious consequences for population and community dynamics and ecosystem stability. However, there are relatively few studies of the roles of large top predators in coastal ecosystems, so that we do not yet completely understand what could happen to coastal areas if large top predators are extirpated or significantly reduced in number. This lack of knowledge is surprising given that coastal areas around the globe are highly valued and densely populated by humans, and thus coastal large top predator populations frequently come into conflict with coastal human populations. This paper reviews what is known about the ecological roles of large top predators in coastal systems and presents a synthesis of recent work from three coastal eastern US Long Term Ecological Research (LTER) sites where long-term studies reveal what appear to be common themes relating to the roles of large top predators in coastal systems. We discuss three specific themes: (1) large top predators acting as mobile links between disparate habitats, (2) large top predators potentially affecting nutrient and biogeochemical dynamics through localized behaviors, and (3) individual specialization of large top predator behaviors. We also discuss how research within the LTER network has led to enhanced understanding of the ecological roles of coastal large top predators. Highlighting this work is intended to encourage further investigation of the roles of large top predators across diverse coastal aquatic habitats and to better inform researchers and ecosystem managers about the importance of large top predators for coastal ecosystem health and stability.

Florida;Georgia;Massachusetts↗

USGS2010

The present and future role of coastal wetland vegetation in protecting shorelines: Answering recent challenges to the paradigm

For more than a century, coastal wetlands have been recognized for their ability to stabilize shorelines and protect coastal communities. However, this paradigm has recently been called into question by small-scale experimental evidence. Here, we conduct a literature review and a small meta-analysis of wave attenuation data, and we find overwhelming evidence in support of established theory. Our review suggests that mangrove and salt marsh vegetation afford context-dependent protection from erosion, storm surge, and potentially small tsunami waves. In biophysical models, field tests, and natural experiments, the presence of wetlands reduces wave heights, property damage, and human deaths. Meta-analysis of wave attenuation by vegetated and unvegetated wetland sites highlights the critical role of vegetation in attenuating waves. Although we find coastal wetland vegetation to be an effective shoreline buffer, wetlands cannot protect shorelines in all locations or scenarios; indeed large-scale regional erosion, river meandering, and large tsunami waves and storm surges can overwhelm the attenuation effect of vegetation. However, due to a nonlinear relationship between wave attenuation and wetland size, even small wetlands afford substantial protection from waves. Combining man-made structures with wetlands in ways that mimic nature is likely to increase coastal protection. Oyster domes, for example, can be used in combination with natural wetlands to protect shorelines and restore critical fishery habitat. Finally, coastal wetland vegetation modifies shorelines in ways (e.g. peat accretion) that increase shoreline integrity over long timescales and thus provides a lasting coastal adaptation measure that can protect shorelines against accelerated sea level rise and more frequent storm inundation. We conclude that the shoreline protection paradigm still stands, but that gaps remain in our knowledge about the mechanistic and context-dependent aspects of shoreline protection.

Climatic Change↗