Foods eaten, feeding behaviour, & growth

The topic of growth is considered here, while those of FOODS EATEN and FEEDING BEHAVIOUR are found in their own sections. Growth is a topic not well investigated for any species of west-coast sea anemone. Any such study might prove to be a long-term enterprise for most or all species are relatively long-lived and it would be difficult to measure mass changes in the field. Recent methods for marking and identifying anemones through injection of vital dyes is described here that has made growth studies in the field more feasible.

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Research study 1

photograph of sea anemone Anthopleura xanthogrammica marked with number "8" using a vital stain neutral red applied as a pasteField studies on sea anemones usually require that individuals be marked in some way. Regular plastic or wire tags tend to work themselves out in a short time, and likely irritate the animal as the tags wiggle about in waves. A non-invasive method of marking is described whereby a vital stain, neutral red, is applied as a paste to outer epithelium of the anemones in situ. Numbers and other marks created in this way last for 12mo in the lab, and 9-12mo in the field (at Tatoosh Island, Washington; see accompanying photograph). Sebens 1976 J Fish Res Bd Can 33: 1407.




Sea anemone Anthopleura xanthogrammica marked with the numeral "8"

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Research study 2

photographs comparing colours of sea anemones Metridium farcimen after injection with vital dyesA later study at Friday Harbor Laboratories, Washington also uses vital dyes, not applied to the outside, but injected through the column into the sea anemone’s gastrovascular cavity. The dye turns the whole animal pink or blue, depending on the particular vital dye used, and best results would be expected with anemones that are white in colour such as the giant plumose Metridium farcimenn. The dyeing is quite dramatic as can be seen in the photos. Coloration lasts for 7mo with neutral red and 1.5mo for methylene blue. Growth, measured as change in basal diameter can be monitored in neutral-red individuals for more than 150d. The marking technique is especially useful for in situ growth studies on sea anemones, for it eliminates risk of tissue damage during removalfor size measurements. Growth experiments using M. farcimen on dock pontoons are done both in situ and in the laboratory over time-periods of 156d and 40d, respectively (see histograms showing both lab and field results, sample sizes of 10 and 21 for each treatment). While the data overall show no significant effect on growth of stained animals over seawater-injected controls it is clear that neutral red is having some sort of variable and/or harmful effect on growth, especially in the laboratory setting, but also possibly contributing to high variation in the field. Growth is 1-1.5 orders of magnitude greater in the lab than the field, owing to supplementary feeding of lab animals histograms comparing growth rates of sea anemones Metridium farcimen in laboratory and field following injections of different vital dyeswith brine-shrimp nauplii. Although pedal-disc measure- ments might work well on uniform surfaces such as dock pontoons, they may be less reliable on natural substrata such as rocks. The study is the first of its kind on growth in field specimens of a west-coast sea anemone. Wells & Sebens 2017 PLoS ONE 12 (11): e0188263.

NOTE stains used include neutral red, methylene blue, and fluorescein. The first two are thought by the authors to be harmless (however, the data suggest that neutral red may be less harmless than puported), but fluorescein is toxic in high concentration and even at low concentration loses its staining effectiveness within a few days. The stains mainly act on the gastrodermis, especially the acontia

NOTE lack of significance can owe to several factors, in this case likely to high variance in the data (see histograms). The authors do not discuss possible causes for this, but one wonders if it could relate to temporal variability in basal-disc diameter, such as might occur during deflation-inflation behaviour or normal crawling movements. If this were the case then measure of basal-disc size may not be as reliable as hoped. This should be checked

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