One issue that has come up more than once in our lectures over the past two weeks is trying to understand if disease and disease outbreaks in marine environments are increasing or if we are just looking harder. Ward and Lafferty (2004) tried to quantitatively analyze this problem and found that reports did increase over time from 1970 to 2001 in most groups they examined.
Today during Lisa’s lecture on protists this question of increased disease or better surveys reared its head in her example of Bitter Crab Disease. When first documented, it infected 7 crab species but today has been documented in 30 species around the globe. I’m curious if museum collections could be used to answer the question of whether or not this disease is infecting more species or if we are simply looking at (fishing?) more species and therefore it seems to be increasing its taxonomic scope. Wet specimens in museum collections could be examined for some of the gross anatomical changes associated with some infections as well as soft tissues for histology and PCR. From my very brief afternoon literature search it seems like museum collections are an underutilized tool in setting infection baselines or tracking the spread of disease, with a few exceptions. It looks like collections have been used to understand the spread of chytrid among amphibians (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0052502). I’m going to dig into this more in the next few days.
We started the morning with Carolyn’s lecture on fungi, metazoan and bacterial diseases in marine organisms. I especially appreciated the examples that she gave of fungal disease (abalone shell mycosis) and metazoans (sabellid polychaetes) because both damage the hard shells of their hosts. I was much less familiar with fungal disease so I took to the internet during lunch and found this (slightly old) blogpost summarizing some of what it known about marine fungus
Looking forward to wandering further down this rabbit hole.
After the lecture we started on the experiment to see if Pacific oysters will filter laby out of the water. If they do, they may be a good candidate for a biological control. I have heard from people doing oyster restoration in San Francisco Bay that oysters benefit eelgrass beds by increasing water clarity and therefore light penetration in the water, which benefits adjacent eelgrass beds, but have never heard anyone talk about using oysters as way to prevent disease. It would be pretty exciting if it works!
The experiments have been ably described by others in my cohort already, so I’ll just briefly describe what Ruth and I observed when we went to collect our samples at 6:20, 4 hours after the start of the experiment. Our samples looked remarkably clear after both vortexing and centrifuging. Is it possible the the oysters exposed to Laby had already cleared it? Oysters move a tremendous volume of water through their bodies each day, so it seems plausible that 10 oysters could filter 225 ml of water pretty quickly. Looking forward to hearing what other groups observed in their sampling.
Carolyn gave two fascinating lectures today on ocean acidification (AM) and disease resistance/tolerance (PM).
Two take-aways from the morning lecture were; nearshore environments are different than the open ocean in terms of the CO2 in the water (which seems obvious but is not something I’ve ever thought about) and that decreasing pH can have transgenerational affects on populations as natural selection acts on populations.
I was especially intrigued in the afternoon lecture by the potential tradeoffs in selecting for resilience to ocean acidification. This is clearly an issue in aquaculture, where resilience to ocean acidification may be negatively correlated to desirable traits like flesh quality or disease resistance. While wild shellfish may not care about the palatability of their flesh, trade-offs in growth rate, age at maturity, fecundity and disease resistance could significantly affect fitness. This ties in nicely with some of the questions in my work regarding the ability of disease to act as an agent of selection in ecosystems and the effects of disease over evolutionary time.
Today’s lectures on immunology and epigenetics were really interesting for me. Since I work in deep time and spend most of my time working on preserved (or preservable) hard parts I haven’t spent much time post-undergrad working on DNA and soft-tissues. I’m looking forward to using my time in this class to think more deeply about the information that’s lost in the fossil record and developing a better understanding of the temporal and spatial scope of disease in modern ecosystems. Disease obviously can have profound consequences on the structure of ecosystems (e.g. loss of keystone predators) but how long term are those effects? What are the evolutionary consequences of disease and can the fossil record help us understand that? I’m still not sure, but I’m looking forward to learning more in the next month.
Today we spent a wonderful sunny morning collecting Z. marina in Indian Cove on Shaw Island.
While we were waiting for the tide to go out, Sandy showed us Z. japonica, a seagrass that was introduced from the western Pacific sometime in the early 1900’s with imported oysters. It lives in patches higher in the intertidal than the native Z. marina and has been classified as a class C noxious weed by the state of Washington (http://www.nwcb.wa.gov/detail.asp?weed=173). Oyster fisherman are concerned about Z. japonica because it uses space that could be occupied by oysters. It may also be an important resource for migrating birds.
Drew reminded us today that the concept of a keystone species was first introduced by Robert Paine due to his work with Pisaster. His seminal work on predator removal in the intertidal showed that the removal of some consumers had dramatic changes on the population densities of many other organisms in the ecosystem, but that the effect is not the same for all consumers. For example, he notes that Leptasterias, the small six-rayed star we found today, competes with Pisaster for food but its removal from an ecosystem does not have the same impact as the loss of Pisaster.
Looking back at Paine’s experimental manipulation of large tidal flats may provide us a window into the future of the rocky intertidal without these important predators. Both papers are short and make for some nice reading on a rainy afternoon!
R.T Paine (1966) Food Web Complexity and Species Diversity. The American Naturalist 101(910):65-75. http://www.jstor.org/stable/2459379
R.T. Paine (1969) A Note on Trophic Complexity and Community Stability. The American Naturalist 103(929): 91-93. http://www.jstor.org/stable/2459472