Functional properties of the isomorphic biphasic algal life cycle

Many species of marine algae have life cycles that involve multiple separate, free-living phases that frequently differ in ploidy levels. These complex life cycles have received increasing scientific attention over the past few decades, due to their usefulness for both ecological and evolutionary studies. I present a synthesis of our current knowledge of the ecological functioning and evolutionary implications of the isomorphic, biphasic life cycles commonly found in many species of marine algae. There are both costs and benefits to life cycles with 2 morphologically similar but separate, free-living phases that differ in ploidy levels (haploids and diploids). Evolutionary theory predicts that the existence of subtle yet important differences between the phases may be what allows these life cycles to be maintained. Different phases of the same species can vary in abundance, in demographic parameters such as mortality and fecundity, in their physiology, and in their resistance to herbivory. Some taxonomic groups within the red algae have received significant attention toward these issues, while our knowledge of these properties for brown and green algae remains limited

Examination of \u3cem\u3eUlva\u3c/em\u3e bloom species richness and relative abundance reveals two cryptically co- occurring bloom species in Narragansett Bay, Rhode Island

Blooms caused by the green macroalga Ulva pose a serious threat to coastal ecosystem 20 around the world. Despite numerous studies of the causes and consequences of these blooms, we still have a limited understanding of Ulva bloom species richness and abundance due to difficulties in identifying Ulva species using morphological features. Along the northeastern U.S. coastline, all blooms of distromatic Ulva blades were previously identified as U. lactuca. Recent molecular sequencing, however, discovered the presence of additional distromatic Ulva species. Therefore, in order to determine the relative abundance of Ulva species within blooms, we conducted monthly surveys at four Narragansett Bay, RI, sites representing a gradient of bloom severity. We found that the biomass of Ulva within blooms was a mix of U. compressa and U. rigida, not U. lactuca as previously reported. In contrast, sites not impacted by blooms that were located near the mouth of Narragansett Bay were dominated by U. lactuca. We also observed spatial and temporal differences in Ulva and total macroalgal diversity between bloom-impacted sites, indicating that Ulva bloom composition can be radically different between similar sites within close proximity. We discuss our results in the context of Ulva blooms worldwide, highlighting the need to definitively determine bloom species composition in order to fully understand bloom dynamics

Snail Grazing Facilitates Growth of a Bloom-Forming Alga

Herbivory often has a negative effect on plants. However, there is a growing number of examples, primarily in terrestrial ecosystems, where herbivory causes an increase in plant size, growth rate, and/or reproductive output. In marine ecosystems, the positive effects of herbivores on macroalgae are not as well studied, although limited evidence exists for herbivore-induced increases in macroalgal growth rates via 2 mechanisms: nutrient addition via grazer defecation, and epiphyte removal. In this study, we examined the effects of grazing by the mud snail Ilyanassa obsoleta on Ulva lactuca, the dominant bloom-forming macroalga in many New England estuaries. We found that the presence of I. obsoleta had a significant positive, rather than negative, effect on U. lactuca. Through caging experiments, we established that this positive effect was not due to fecal nutrient inputs from the snail. Similarly, snail contact in the absence of grazing did not affect U. lactuca growth rates. In contrast, grazing by I. obsoleta significantly reduced the microalgal cover on heavily fouled U. lactuca blades, indicating that snail herbivory of microalgal films likely facilitates U. lactuca growth. Our study demonstrates the surprising, positive effect that an abundant herbivore can have on the growth of a macroalgal bloom species

Utilization of the Invasive Alga Gracilaria Vermiculophylla (Ohmi) Papenfuss by the Native Mud Snail Ilyanassa Obsoleta (Say)

The recent invasions of the red alga, Gracilaria vermiculophylla, to the Atlantic and Eastern Pacific Oceans have the potential to significantly alter intertidal and subtidal soft sediment communities. In particular, G. vermiculophylla increases habitat complexity and provides a novel hard substrate in an otherwise two dimensional habitat. Following our observations that the native omnivorous mud snail Ilyanassa obsoleta utilizes G. vermiculophylla for egg capsule deposition, our field surveys demonstrated that the in situ abundance of egg capsules on G. vermiculophylla matched abundances on a native alga Ceramium virgatumandwere at least 11–50 times greater than on all other co-occurring macrophytes. Additionally, through mesocosm experiments, we showed that I. obsoleta preferentially deposits eggs on the invasive G. vermiculophylla over native substrates. However, despite the thick layer of egg capsules found on G. vermiculophylla, no detrimental effects were seen on thalli growth. In contrast, growth of the native red alga Ceramium virgatum was significantly reduced when egg capsules were present, suggesting G. vermiculophylla can out-compete native macrophytes in areas of I. obsoleta abundance, while facilitating reproduction of the native mud snail. This novel interaction has the potential to significantly alter biological interactions in soft sediment communities through a variety of different mechanisms, including the alteration of trophic cascades via the increase in mud snail abundance. Furthermore, facilitation of the reproductive success of I. obsoleta may lead to increases in the occurrence of cercarial dermatitis, as I. obsoleta is a known intermediate host organism

Herbivore Impacts on Two Morphologically Similar Bloom-Forming Ulva Species in a Eutrophic Bay

Herbivore impacts on macrophyte growth vary with the identity of the herbivores and macrophytes, as well as under different abiotic conditions. This interaction is further complicated by anthropogenic alterations to the environment, such as eutrophication. In this study, we utilized in situ herbivore exclusion experiments and mesocosm feeding preference assays to examine the impacts of different herbivores on the growth of two morphologically similar, co-occurring macroalgal bloom Ulva species in a nutrient-rich environment. We found that herbivory had a measurable impact on Ulva biomass, though the rate of consumption rarely surpassed growth for either Ulva species. We determined that the primary herbivores within the blooms were amphipods and mud crabs, and that their effects varied among study sites and months. Our results also confirmed that, even with a diverse suite of consumers, Ulva blooms are capable of escaping herbivore control, particularly early in the growing season when growth rates peak and herbivore activity is limited. Furthermore, our experiments revealed species-specific feeding preferences among herbivores, as well as differences in growth rates and chemistry between the two Ulva species, which likely influence bloom dynamics

Chemical Warfare in Narragansett Bay: Determining the Allelopathic Effects of Ulva

Several species of Ulva are commonly found in the waters of Narragansett Bay, especially in eutrophic waters, where they can form fast growing blooms that can have ecological and economic consequences. The formation and release of allelopathic chemicals has been previously documented in some species of Ulva, including Ulva lactuca. Three species of blade-forming Ulva are commonly found in Narragansett Bay and coastal Rhode Island, namely, U. compressa, U. lactuca, and U. rigida. We aimed to determine if these three species of Ulva had allelopathic effects by testing their impacts on the growth of other macroalgae. Cystoclonium purpureum, Chondrus crispus, and Ceramium virgatum tips were grown alone (control) or with either U. compressa, U. rigida, or U. lactuca in mesocosms separated by mesh for eight days, in two separate trials. The blotted-dry fresh weight of Cystoclonium, Chondrus, and Ceramium was recorded every other day and tips were photographed for surface area analysis. Nutrients were checked daily using NO3 as a proxy and adjusted to prevent nutrient limitation. All three species of Ulva had a significant negative effect on the growth of Cystoclonium, Chondrus, and Ceramium, although the effect was dependent on time. In the Cystoclonium trial, U. compressa and U. rigida treatments had the largest negative effect on Cystoclonium growth with overall mass loss observed after 6 days of co-culture. U. lactuca had a smaller negative effect on growth, with the average Cystoclonium growth rate after 8 days of co-culture (2.9 ± 0.9 % day-1) significantly below controls (5.0 ± 0.8 % day-1). In the Chondrus trial, there was a striking effect of all three Ulva species on the growth of Chondrus after only two days of co-culture. Growth rates of tips with all species of Ulva were \u3c1% day-1 for the duration of the experiment, while the control tips increased in growth over time from 1.83 (± 0.7) % day-1 on Day 2 to 5.56 (± 0.9) % day-1 on Day 8. Overall mass loss was observed after 8 days of co-culture with U. compressa. The Ceramium growth was more variable over the course of the trial, but clear separation was seen on day 8 between the controls and the decreased growth of the tips co-cultured with Ulva. All three species of Ulva had a similar effect on the growth of Ceramium at the end of the trial. Our results indicate that U. compressa, U. lactuca, and U. rigida can significantly inhibit the growth of other macroalgae. This has implications for secondary effects of Ulva blooms reducing the algal diversity in addition to primary effects of eutrophication

The brown macroalga Colpomenia peregrina (Sauvageau, 1927) reaches Rhode Island, USA

Introduced, or nonnative, marine species are a threat to local biodiversity, disrupt marine industries, and can have negative effects on coastal communities. Colpomenia peregrina (Sauvageau, 1927) is one of the most successful brown algal invaders in the world. Originating from the Northwest Pacific, Colpomenia peregrina was first collected in the Northwest Atlantic in Nova Scotia, Canada in the 1960s. Since then populations of C. peregrina have been discovered at 57 sites ranging from Grand Barachois Lagoon, Saint Pierre and Miquelon to South Wellfleet, MA, USA. The spread of Colpomenia peregrina can be attributed to its broad tolerance to environmental conditions, buoyant morphology that aids dispersal, and generalist epiphytic biology. Here we report the occurrence of Colpomenia peregrina at five sites in Rhode Island, USA for the first time, representing the crossing of a major biogeographic boundary by this species. The spread of C. peregrina will likely continue, warranting research on its impact on native communities and host algae

Implementing adaptive management into a climate change adaptation strategy for a drowning New England salt marsh

Due to climate change and other anthropogenic stressors, future conditions and impacts facing coastal habitats are unclear to coastal resource managers. Adaptive management strategies have become an important tactic to compensate for the unknown environmental conditions that coastal managers and restoration ecologists face. Adaptive management requires extensive planning and resources, which can act as barriers to achieve a successful project. These barriers also create challenges in incorporating adaptive management into climate change adaptation strategies. This case study describes and analyzes the Rhode Island Coastal Resources Management Council\u27s approach to overcome these challenges to implement a successful adaptive management project to restore a drowning salt marsh using the climate change adaptation strategy, sediment enhancement, at Quonochontaug Pond in Charlestown, RI. Through effective communication and active stakeholder involvement, this project successfully incorporated interdisciplinary partner and stakeholder collaborations and developed an iterative learning strategy that highlights the adaptive management method

Using Non-Dietary Gastropods in Coastal Shell Middens to Infer Kelp and Seagrass Harvesting and Paleoenvironmental Conditions

Archaeologists analyzing shell middens typically focus on larger (\u3e2 cm) mollusks to examine subsistence practices, impacts on littoral habitats, and paleoenvironmental conditions as well as a host of other natural and cultural phenomena. Small (\u3c2 cm), non-dietary gastropods in archaeological shell middens also provide important clues regarding human resource procurement in littoral areas and coastal paleoenvironments. We present data from two sites on the California Channel Islands to demonstrate the range of information that can be gained by analyzing small gastropod shells. Identifications revealed the remains of over 4500 non-dietary small gastropods from 75 taxa. Human harvesting of marine macrophytes is suggested by the presence of 18 species that are predominantly associated with seaweeds and seagrasses. Quantification measures revealed high diversity and equitability indices, oscillating taxonomic richness, and decreasing densities through time at both sites. Likelihood ratio tests revealed differences in assemblage composition between Early Holocene and later components at one site, and demonstrated similarities in the relative composition of non-dietary shell assemblages between both sites during the Middle Holocene. Incorporating detailed studies of less conspicuous “incidental” shellfish remains in archaeological midden studies has the potential to contribute to our understanding of past human land use practices and littoral paleoecology. Our findings are applicable to archaeologists working in coastal settings around the world, as well as marine ecologists interested in intertidal paleo-habitats and kelp forest ecosystems

Overwintering Strategies of Bloom-Forming Ulva Species in Narragansett Bay, Rhode Island, USA

Temperate coastal estuaries worldwide, such as Narragansett Bay, Rhode Island, are influenced by seasonal macroalgal blooms (e.g., Ulva) during warm months, whereas bloom-forming macroalgae are rarely encountered during winter. We assessed the ability of distromatic Ulva to overwinter through fragments, recruits, and/or microscopic propagules. We documented (a) small tissue fragments in sediment cores and the water column, (b) recruits and microscopic propagules on field-based settlement tiles, and (c) production of reproductive propagules, throughout the winter months. Laboratory culturing experiments indicated that both fragments and propagules are viable. Our data indicate that bloom-forming overwintering Ulva simultaneously use multiple reproductive strategies