Physiology & physiological ecology
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Research study 1
 

photograph of scyphistoma of a jellyfishhistogram showing effects of temperature and salinity on bud and ephyra production in scyphostmae of jellyfishes Aurelia labiataJellyfish blooms that are becoming increasingly common throughout the world may proximally be regulated by number and asexual-budding activity of benthic scyphistoma stages.  Yet, little is known about environmental effects on this activity, a deficiency that could be important in this time of global warming.  Laboratory experiments on polyps of Aurelia labiata at Shannon Point Marine Center, Washington address this.  The researcher counts ephyrae released from polyps under 9 conditions of temperature and salinity (in the dark), and under 9 conditions of photoperiod and light intensity at ambient temperature and salinity.  Polyps under all combinations survive well 83-100%).  Results show that ephyrae production is highly responsive to temperature conditions, for example, from 0 per polyp at 7oC to 42 per polyp at 15oC over a 20wk period (see histogram) but, overall, it is amount of light (longest photoperiod and highest light intensity) that has greatest effect on strobilation. In the field, light increases seasonally much faster than seawater temperature, suggesting to the author that light may be the more important environmental cue for seasonal initiation of strobilation.  Purcell 2007 Mar Ecol Progr Ser 348: 183.

NOTE  as a reminder, a polyp known as a scyphistoma results from settlement of the planula larva.  The polyp feeds and grows for several years, and seasonally buds off juvenile jellyfish in a process known as strobilation

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Research study 2
 

graph showing strobilation intensity of moon jellies Aurelia labiata in Cornet Bay Marina, Washington over 3 years of studyIn a follow-up study, researchers at Shannon Point Marine Center, Washington undertake a comprehensive field study of effects of temperature, salinity, precipitation, and light intensity on strobilation rates in Aurelia labiata at Cornet Bay Marina, Washington.  The study is done on 15 populations of scyphistomae growing on the undersides of covered floating docks of the marina, that average 58% cover (9 polyps . cm-2) over the 3yr duration of study.  Although the population varies little photographs of strobilating and non-strobilating polyps of moon jellyfish Aurelia labiata, courtesy Purcell et al. 2009 Mar Ecol Progr Ser 375: 139in density, the times and amounts of strobilation and magnitude of all physical factors vary significantly among years.  Highest frequency of strobilation (63%) occurs in Year 2 (see graph) and correlates significantly and positively with pre-strobilation water temperatures and light levels, and negatively with low salinity.  Of these, water temperature is most important.  Unlike what is known from other studies on Aurelia spp., polyp density is not a significant factor in determining strobilation frequency. As these same factors of temperature and light are correlated with enhanced plankton growth that represents food for both polyps and ephyrae, the authors consider them as likely synchronizing cues.  The considerable value of the study is its use of data collected in situ. Purcell et al. 2009 Mar Ecol Progr Ser 375: 139.

NOTE  in laboratory experiments a reduction in salinity from 27 to 20ppt retards the seasonal onset of strobilation by 20d and reduces the number of strobilating polyps by 60%

 

Non-strobilating scyphistoma polyps (top)
and strobilating ones (below) 1X

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Research study 3
 

In the past decade ocean acidification has become an increasingly popular topic relating to climate change.  Most research in this regard, however, has focused on calcifying organisms such as echinoderms, and on the developmental stages of same.  The few studies that have been done on jellyfishes world-wide have mainly concerned broad effects on distribution and abundance, and results have been inconsistent.  A recent study at Shannon Point Marine Center, Washington on the effects of temperature1 and pH2 on strobilation rate and statolith3formation in jellyfishes Aurelia labiata finds no effect of pH on rate of strobilation but does on size of statolith.  Statoliths are significantly smaller in low-pH treatment than in the high-pH treatment (volumes of 304 vs 866um3, respectively).  The authors remark that the effect of smaller statoliths on the well-being of an ephyra is not known.  Winans & Purcell 2010 Hydrobiologia 645: 39.photograph of statoliths of a jellyfish ephyra Aurelia labiata

NOTE1  treatment temperatures selected are 9 and 15oC .  However, since no polyp strobilated at the lower temperature, the authors discard this part of the data set

NOTE2  3 pH levels are created by adding drops of 1M HCl or 1M NaOH to seawater, a method apparently used in other such studies: pH 7.9 (=within the range of seawater at the Shannon Point Marine Center), pH 7.5 (=expected in year 2000), and pH 7.2 (=year 2300)

NOTE3  an ephyra generally has a single statocyst associated with each rhopalium (8-12 rhopalia in total), each consisting of several statoliths.  Each statolith is a crystal of hydrated calcium suphate that is soluble in acidified water (see photograph)

The authors remark that even though smaller than ones from the
pH 7.9 treatment, the statoliths featured here from the pH
7.2 treatment show no pitting or other signs of dissolution

 
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