How do nutrient conditions and species identity influence the impact of mesograzers in eelgrass-epiphyte systems?

Coastal eutrophication is thought to cause excessive growth of epiphytes in eelgrass beds, threatening the health and survival of these ecologically and economically valuable ecosystems worldwide. Mesograzers, small crustacean and gastropod grazers, have the potential to prevent seagrass loss by grazing preferentially and efficiently on epiphytes. We tested the impact of three mesograzers on epiphyte biomass and eelgrass productivity under threefold enriched nutrient concentrations in experimental indoor mesocosm systems under summer conditions. We compared the results with earlier identical experiments that were performed under ambient nutrient supply. The isopod Idotea baltica, the periwinkle Littorina littorea, and the small gastropod Rissoa membranacea significantly reduced epiphyte load under high nutrient supply with Rissoa being the most efficient grazer, but only high densities of Littorina and Rissoa had a significant positive effect on eelgrass productivity. Although all mesograzers increased epiphyte ingestion with higher nutrient load, most likely as a functional response to the quantitatively and qualitatively better food supply, the promotion of eelgrass growth by Idotea and Rissoa was diminished compared to the study performed under ambient nutrient supply. Littorina maintained the level of its positive impact on eelgrass productivity regardless of nutrient concentrations

Vegetative Ecological Characteristics of Restored Reed (Phragmites australis) Wetlands in the Yellow River Delta, China

In this study, we compared ecological characteristics of wetland vegetation in a series of restoration projects that were carried out in the wetlands of Yellow River Delta. The investigated characteristics include plant composition structure, species diversity and community similarity in three kinds of Phragmites australis wetlands, i.e. restored P. australis wetlands (R1, R2, R3 and R4: restored in 2002, 2005, 2007 and 2009, respectively), natural P. australis wetland (N) and degraded P. australis wetland (D) to assess the process of wetlands restoration. The coverage of the R1 was 99%, which was similar to natural wetland. Among all studied wetlands, the highest and lowest stem density was observed in R1 and R2, respectively, Plant height and stem diameter show the same trend as N > R2 > R1 > R3 > D > R4. Species diversity of restored P. australis wetlands became closed to natural wetland. Both species richness and Shannon–Wiener index had similar tendency: increased first and then decreased with restored time. The highest species richness and species diversity were observed in R2, while the lowest values of those parameters were found in natural P. australis wetland. Similarity indexes between restored wetlands and natural wetland increased with the restoration time, but they were still less than 50%. The results indicate that the vegetation of P. australis wetlands has experienced a great improvement after several years’ restoration, and it is feasible to restored degraded P. australis wetlands by pouring fresh water into those wetlands in the Yellow River Delta. However, it is notable that costal degraded P. australis wetland in this region may take years to decades to reach the status of natural wetland

Casual observations, random musings and wild extrapolations based on some actual data on the impact of invasive tunicates to eelgrass

Tunicates, more commonly known as sea squirts, can grow as a solitary organism or as part of extensive colonies. Tunicates are more frequently associated with hard substrate, but a number of invasive tunicate species have now been found to colonize eelgrass. We attempted to quantify what impact these tunicates may have on eelgrass. Using HOBO light sensors, we measured the ability of 5 different tunicate species to block light. In several ponds on Martha\u27s Vineyard, we measured a number of eelgrass parameters (canopy height, leaves per shoot, growth rate, tissue sugar concentration) in both plants without tunicates and plants heavily colonized by tunicates. We found that all species of tunicates tested blocked between 70-85% of ambient light. We found that plants colonized by tunicates had fewer leaves per shoot, smaller canopy height, lower growth rates, but high tissue sugar concentrations than plants not colonized by tunicates. In 2013, we attempted to assess the extent of the problem, by coordinating a study of 19 different sampling locations from New Jersey to Canada. Particiapnts sampled eelgrass meadows and documented the presence/absence of tunicates, identified tunicate species, estimated the extent of the colonization, measured eelgrass shoot density and canopy height and in some locations collected water temperature. Invasive tunicates were observed on eelgrass in all meadows sampled from Newfoundland to New Jersey, though the number of species present and the extent of the colonization varied greatly

Biogeographical patterns of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39 degrees and 47 degrees north latitude (New Jersey to Newfoundland)

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Carmen, M. R., Colarusso, P. D., Neckles, H. A., Bologna, P., Caines, S., Davidson, J. D. P., Evans, N. T., Fox, S. E., Grunden, D. W., Hoffman, S., Ma, K. C. K., Matheson, K., McKenzie, C. H., Nelson, E. P., Plaisted, H., Reddington, E., Schott, S., & Wong, M. C. Biogeographical patterns of tunicates utilizing eelgrass as substrate in the western North Atlantic between 39 degrees and 47 degrees north latitude (New Jersey to Newfoundland). Management of Biological Invasions, 10(4), (2019): 602-616, doi: 10.3391/mbi.2019.10.4.02.Colonization of eelgrass (Zostera marina L.) by tunicates can lead to reduced plant growth and survival. Several of the tunicate species that are found on eelgrass in the northwest Atlantic are highly aggressive colonizers, and range expansions are predicted in association with climate-change induced increases in seawater temperature. In 2017, we surveyed tunicates within eelgrass meadows at 33 sites from New Jersey to Newfoundland. Eight tunicate species were identified colonizing eelgrass, of which four were non-native and one was cryptogenic. The most common species (Botrylloides violaceus and Botryllus schlosseri) occurred from New York to Atlantic Canada. Tunicate faunas attached to eelgrass were less diverse north of Cape Cod, Massachusetts. Artificial substrates in the vicinity of the eelgrass meadows generally supported more tunicate species than did the eelgrass, but fewer species co-occurred in northern sites than southern sites. The latitudinal gradient in tunicate diversity corresponded to gradients of summertime sea surface temperature and traditional biogeographical zones in the northwest Atlantic, where Cape Cod represents a transition between cold-water and warm-water invertebrate faunas. Tunicate density in the eelgrass meadows was low, ranging generally from 1–25% cover of eelgrass shoots, suggesting that space availability does not currently limit tunicate colonization of eelgrass. This survey, along with our 2013 survey, provide a baseline for identifying future changes in tunicate distribution and abundance in northwest Atlantic eelgrass meadows.We thank Benedikte Vercaemer, Dann Blackwood, Jonathon Seaward, Dani Cleary, Sam Hartman, Kim Manzo, and Jason Havelin for field assistance. Thank you too to Alicia Grimaldi for map construction and Page Valentine for constructively reviewing the manuscript. Thank you to the Community Preservation Committee of Oak Bluffs, Massachusetts, and the USGS-WHOI Cooperative Agreement for funding (Carman). All data used in this paper are publicly available through USGS ScienceBase at https://doi.org/10.5066/P9GDBDFQ. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government