Summer’s wound up for another year, which means the end of a field season. Sea star wasting is, however, only just ramping up. We’ve sadly learned of wasting in several constantly monitored populations of sea stars which had shown a strong recovery since the 2013-2014 mass die-off, including at Langley Harbor (Whidbey Island), in the northern Salish Sea, strangely, in the National Aquarium in Washington DC. It’s a depressingly familiar situation.
Wasting Pisaster ochraceus – Davenport, CA, July 2018
Our efforts to manipulate physical conditions to test their impact on sea star wasting started well; together with our superstar REU Citlalli Aquino (Junior at UC Santa Cruz), we collected 12 animals near Santa Cruz, CA and placed them in aquaria at the Long Marine Laboratory in late May. All seemed to be going well, until about 2 weeks later, when one, then two, then 7 then 12 ochre stars developed lesions, body wall erosions, then lost rays, and finally died. We carefully monitored in situ temperature during this period, and there was no prior temperature swing or elevated temperature at the time. Animals were constantly monitored for water quality and physical conditions, and nothing changed. Was it the collection that caused wasting? Did they dry out during collection? Did they cause physical injury to each other during collection?
All stars were lost, but we did manage to collect some samples to look at whether their microbial communities changed between healthy and diseased and dead states.
Wasting up close… a wasting lesion. Note that white color indicative of lesion simply reflects the absence of overlying purple epidermis.
Discouraged but with a new impetus to look more closely at waterborne chemistry, we went back to California again in mid- June to perform a second round of experiments. This time, we collected a further set of individuals and tested whether: 1) flow-rates into the aquaria related to wasting speed; 2) whether wasting could be sped up by challenge with proteins from a wasting star (we found one in the field) – compared to the same proteins treated with proteinase; 3) whether wasting could be accelerated by desiccation in air; and 4) whether being blasted on the epidermis with a jet of solid parts of a starfish (i.e. pedicellaria, spines, paxillae, etc) induced wasting faster than being blasted with just seawater. We also performed an experiments where we collected individuals separately and collected them together in the same holding bucket, just to see if it was being bumped against each other that led to wasting. The first four of these experiments were run in an aquarium system that was cleaned routinely to remove calcareous algae and in the dark; and fourth experiment was performed in a system which had some sediment and schmutz in it, and with some ambient light.
Desiccating stars in the Santa Cruz sunshine!
Well, the results were perplexing… Dessiccation significant sped up wasting regardless of whether animals were held in high or low-flow conditions. Wasting was also sped up by inoculation with proteins from a wasting star, and by being blasted with the hard surface stuff on a wasting star. However, all animals, including controls wasted when we sampled them (sampling on controls occurred when sampling of experimental animals began so as not to compare apples and oranges!) with a biopsy punch. We also noted some bizarre bubbling of the outer epidermis of wasting stars after they had been emersed. What does this mean? Not sure yet, but perhaps compromised animals lose their ability to heal themselves? And whatever starts wasting is proteinaceous in nature – which may be concentrated under low-flow conditions in aquaria.
A ‘high’ flow star…
The most interesting result was that those animals which were incubated in the ‘dirty’ aquarium system never wasted on their own, while at the same time animals which were collected simultaneously and placed in the ‘clean’ system all wasted. Still thinking about how this may have occurred.
Pedicellaria – small claws on the surface of Pisaster ochraceus that are razor-sharp and only open when the ligaments that hold them down in tissue are relaxed…
So, armed with this new knowledge, we went back to Santa Cruz for a third round of experiments starting in late July. This time, rather than manipulate individuals, we choose to simply use those animals which never wasted in the ‘dirty’ system, place them in the ‘clean’ system and then monitor their microbiology over time. Should have resulted in predictable wasting, right?
…5 weeks later, only 2 of the 6 stars had wasted. Whatever causes wasting can apparently be ‘cured’ or ‘abated’ by putting them in a dirty tank with some natural light for a period of time. How? Why? We really don’t know, but we are looking at microbiology of the stars now via genomics and community-based analyses.
So 3 rounds of experiments later, what do we know that we didn’t know before? Nothing definitive, unfortunately, but we’re getting there. It’s clear there is some kind of microbiology involved, and that the stars have some kind of inability to recover from injury. They also seem not to be able to deal with any kind of stress.
All of this work was made possible through collaboration with Pete Raimondi and Betsy Steele at UCSC. Without their provision of lab space, sea table space and logistical assistance this wouldn’t have been possible. And definitely this could not have happened without the extensive and awesome help of REU Citlalli!
Stay tuned for the results of microbial analyses.
Still lots of healthy and large Pisaster ochraceus on the Santa Cruz Pier!