Search

Habitat modification in California coastal areas has led to increased erosion and shoreline loss. Oyster restoration may reduce shoreline loss by reintroducing complex structure that slows wave action. The Port of San Diego installed spherical concrete Living Shoreline structures (“reef balls”) on the mudflats of the Chula Vista Wildlife Reserve in San Diego Bay to increase native Olympia oyster (Ostrea lurida) populations while aiming to discourage recruitment by non-native Pacific oysters (Magallana gigas). I surveyed the reef balls to determine the abundance and relative cover of native and non-native oysters to understand the distribution of both species relative to wind exposure and tidal elevation. I predict that there will be a higher abundance and relative cover of both species on leeward sides (protected from wind and waves) of reef balls, and higher abundance and relative cover of native oysters at lower tidal elevations. This project will support efforts by the Port of San Diego to further adapt the building and construction of Living Shorelines to restore the population of native oysters and reduce erosion in San Diego Bay.

To mitigate negative impacts from anthropogenic activities, resource managers are implementing multi-function projects such as artificial reefs to protect infrastructure while restoring native biodiversity. Artificial reefs can provide habitat for a wide array of fish and invertebrates, but the risk of favoring non-indigenous species motivates investigating whether season of deployment, depth, and habitat orientation could be manipulated to favor native communities. To test whether these factors yield distinct community compositions by impacting the priority settlement and successional sequence of recruiting invertebrates and macroalgae, replicate (n=6) recruitment tile sets were deployed via SCUBA on a new artificial reef (designated as FeISH - Fish, eelgrass, Subtidal, Intertidal Habitat) in San Diego Bay, CA, USA across 4 seasons and three depths (-5, -10, and -20ft. MLLW). Replicates were removed at 3-, 6-, and 12-months post deployment, and percent cover and density of identified species, species richness, and community composition were recorded. Significantly different communities across all deployment periods were driven by an interaction of season and depth, indicating these factors can drive early community structure on artificial reefs. Despite differences in community composition persisting after one year, nMDS trajectory plots revealed community convergence over time. Percent cover and abundance of key species such as nativeOstrea luridaand invasiveSargassumspp. varied across season, depth, and tile orientation. These factors can be manipulated to achieve particular outcomes if resource managers are targeting species of concern. However, community convergence over longer time periods may dilute the importance of this recommendation as other yet-unidentified factors exert their influence.

Eelgrass (Zostera marina) is a foundation species in coastal waters that provides vital ecosystem services, from habitat provision to trophic support. However, populations have declined globally at alarming rates within the last century. A recent restoration project within Upper Newport Bay (UNB), California, USA implemented a multi-habitat restoration approach usingZ. marinaandOstrea lurida,which may render additional ecosystem services and simultaneously promote more successful eelgrass restoration. Oysters may increase nutrient availability for eelgrass in sediment porewater by mediating nitrogen transfer via filter-feeding and subsequent deposition of nitrogenous waste. In summer 2021, I collected eelgrass shoots, porewater samples, and shoot and oyster densities from three sites within UNB, each restored with eelgrass alone and eelgrass adjacent to oysters. I measured leaf and rhizome growth rates, organic tissue nitrogen, above and below-ground dry weight, and porewater NH4+and NO3-concentrations. Since sedentary species may have limited spatial range of impact, spatially explicit co-variogram models, novel to this field of study, related response metrics to distance from and density of associated oysters in restored beds. I found positive associations among oyster density and eelgrass below-ground dry weight and rhizome growth rates that increased in strength inversely to distance between samples. Porewater ammonium and tissue nitrogen also increased with presence, density, and proximity to oyster beds.For above-ground metrics, including dry weight, growth rates, and shoot density, the relationship between oysters and eelgrass was site-dependent, varying from negative to non-significant to positive. The enhanced eelgrass below-ground growth attributable to interaction with oysters suggests that these species can be restored together in a spatial design similar to that used for this study. To capture the full complexity of oyster-eelgrass interactions, future studies should incorporate spatially explicit models and consider a large suite of both above-ground and below-ground eelgrass metrics.

This study examines the bryozoan fauna encrusting on the common Pacific half-slippersnail,Crepipatella lingulata. This suspension-feeding calyptraeid gastropod is common at shallow depths off the coast of California and is also common in the fossil record. The shell lengths ofC. lingulataspecimens dating back to the late Pliocene-early Pleistocene were examined, as well as the area of shells encrusted with bryozoans. Holocene shells were significantly larger than other shells, and modern (specimens collected in the present day) encrusted shells were significantly shorter than encrusted shells from the ancient past, but the latter could reflect collection bias. I also determined that modern shells are more fully covered with bryozoans than fossil shells. However, there was significant statistical interaction in the Holocene and modern data; thus, if more specimens were to be added that were relatively less prone to sampling biases from these time periods, the observed patterns could change. Finally, I identified bryozoan species encrusting on modernC. lingulatashells: 34 of the 41 specimens examined were found to be the speciesRhynchozoon rostratumand, because one bryozoan species seems to dominate the encrustation, this implies a symbiotic association betweenC. lingulataandR. rostratum.

Free-spawning marine animals such as the red abalone,Haliotis rufescens,need densely aggregated populations for successful external fertilization in the water column. Red abalones are known to contract their muscular bodies while spawning, which may increase gamete dispersal by pushing plumes of gametes higher up into the water column, ushering gametes within reach of other spawning adults. We hypothesized that the heights of egg plumes would increase with increasing contractile forces. We measured the contractile forces of 15 female adult red abalones and captured the changes in the heights of the resultant egg plumes during free-spawning using high-speed videos at the Cabrillo Marine Aquarium, San Pedro, California between September 2019 and February 2020. We found that the egg plume heights were positively and non-linearly impacted by the contraction forces, and abalones possessing a third open respiratory pore had plumes that were 2.69 cm taller on average. We also found that larger gonad widths positively impacted the plume heights. This new information about the impact of abalone contraction forces on egg plumes will enhance our knowledge of abalone reproductive behaviors, launch future studies, and guide restoration strategies and policies for protected abalone species.

Estuaries have been armored with artificial habitat to protect coastal infrastructure from erosion, but armoring may have negative ecological impacts. Other shoreline protection strategies, such as eco-engineered seawalls and living shorelines, offer more natural, rugose substrata to native species while limiting coastal erosion. The Port of San Diego plans to build a living shoreline using concrete reef balls that recruit the native oyster,Ostrea lurida, but the Port wants to avoid recruitment of non-indigenous species (NIS), especially the non-indigenous oyster,Crassostrea gigas. I modified concrete tiles that acted as proxies for reef balls with added shell cover and rugosity to determine if there is a treatment that can achieve these goals. I deployed six treatment types embedded into 15 x 15 cm concrete tiles: two with surface shell (100% cover of crushed or large shell fragments), two without shell (smooth or rough concrete), and two reference treatments (50% shell cover and terracotta). Seven replicates per treatment were deployed at two sites in San Diego Bay and one site in Newport Bay, California, USA, at 0 and 0.6 m Mean Lower Low Water (MLLW) from May to September 2018. I used three-way ANOVAs, ANCOVAs, and PERMANOVAs to test for the effects of tile orientation, tidal elevation, shell cover, and rugosity on the recruitment of oysters and other fauna.O. luridarecruited in higher abundance and generally higher percent cover thanC. gigasonto all treatments across all sites at 0 m MLLW and treatments that combined 100% shell cover with high rugosity at two of three sites at 0.6 m MLLW, a tidal elevation to whichO. luridararely recruits. Some NIS recruited in lower abundance to 100% shell treatments and/or rugose treatments, although the effects were not consistent across species. Recruitment strength of both native and NIS varied across sites and treatments and should be tested on a site-specific basis prior to reef ball deployment, but I suggest projects that utilize reef balls in living shoreline designs in southern California should generally add shell cover and rugosity to the concrete to favor native species and discourage NIS.

Mytilus californianus, the California mussel, is a foundation species and dominant space-holderin the rocky intertidal zone, an environment that goes through extreme temperature shifts on a daily basis as organisms are submerged in seawater during high tide and exposed to terrestrial conditions during low tide. Mussels create protein ‘anchors’ called byssal threads that allow them to attach to rocks and each other.To my knowledge, no studies have addressed the role of temperature during low tide on attachment strength of mussels, despite the clear importance of this topic in the context of the rising temperatures predicted with a changing climate.Iused laboratory manipulations to investigate how temperature during low tide and the number of low-tide exposures affected three components of mussel attachment: byssal thread production, individual mussel attachment strength, and single byssal thread thickness (as a proxy for strength). We collected mussels from sites in Washington and California and set up a five-day lab experiment with two types of treatments: number of low tide exposures (exposure on the first day followed by four days of submersion or exposure each day for five days) and temperature during low tide exposure (ambient or elevated temperature).Overall, neither number of low tides nor low tide temperature affected the number of byssal threads produced by mussels, but the number of low tides had strong effects on the amount of force required to remove mussels from the substratum and on the thickness of individual byssal threads (a proxy for thread strength). Mussels exposed to multiple low tides required less force to remove from the substratum and had thinner (and thus weaker) threads than mussels exposed to a single low tide, and the combination of multiple low tides and warm low tide temperatures had negative impacts on mussel attachment. In the context of a changing climate, these data help us to understand important hurdles to persistence for this ecosystem engineer.

Organisms in the intertidal zone, which experience terrestrial conditions during low tide emersion and are submerged in seawater during high tide, are threatened by sea level rise (SLR) which could reduce annual emersion time by over 50% over the next 100 years. I tested the hypothesis that coastal squeeze and SLR conditions would negatively impact the performance of individuals of the canopy-forming seaweedPelvetiopsis californica.Over four seasons, I performed population surveys at four sites in southern California, to collect baseline data on differences in physiology, reproduction, and tissue chemistry between individuals at the high and low edges of the natural vertical distribution for this species. At two of these sites, I conducted a 16-month manipulative experiment with three treatments: marked in place individuals (transplant controls: MIP) were not moved; transplant individuals within the natural vertical distribution (In Place Transplants=IPT) were relocated at the same tidal elevation; and Sea Level Rise Transplants (SLRT) were moved to a lower tidal elevation, exposing them to shorter emersion times (= SLR conditions). I assessed algal performance through monthly measurements of size, cover of epiphytic seaweeds (which grow on the host, blocking light and nutrients), reproductive potential, and photosynthetic potential (as Maximum Quantum Yield). While SLRT individuals had high photosynthetic potential and did reproduce, they lost more tissue (on average, 25% of their original length) than individuals in other treatments. More than three times as many individuals in the SLRT treatment were infected with epiphytic seaweeds than in IPT or MIP treatments. These data indicate substantial risk of SLR to populations of this seaweed and may help managers develop mitigation efforts for this important intertidal producer.

Canopy-forming seaweeds can function as both ecosystem engineers and foundation species in intertidal systems. In this study, I focused on the canopy-forming seaweedEgregia menziesii(feather boa kelp) withtwo main objectives: 1) compare community structure between areas with and withoutEgregiaand 2) compare community structure before and afterEgregiawas manipulatedin situ.In the intertidal zone in two regions: southern California (Los Angeles County) and northern Washington (San Juan County) I conducted a two-year experiment with three treatments: NaturalEgregia(no manipulation),Egregia(Egregiaremoval), and No NaturalEgregia(no manipulation). I surveyed community structure at approximately 6-month intervals and analyzed metrics of community composition and diversity. Community structure differed among treatments and seasons in both regions, butEgregiacover was highly variable over time. During low tide on hot days, temperature and light intensity were lower underneathEgregiacanopy than out on unshaded surfaces. At the cover levels used in my study,Egregiadid not exert an obvious influence as a foundation species, although it did function as an ecosystem engineer through the amelioration of abiotic stressors. One additional component of this study was to test the ability of a commercially available aquarium-grade replica to mimic the effects of naturalEgregiaindividuals in the field. The mimics copied morphological characteristics of naturalEgregiabut did not ameliorate heat and light stress during low tide to the same degree as natural thalli. Community structure in plots withEgregiamimics was not the same as in plots with NaturalEgregia. Overall, the mimics did not provide insight on the mechanisms through whichEgregiainfluences community structure.&nbsp