Jellyfish Jelly cruising vs. ambush foraging
home   links   references   comments






Fig. 1. Eight co-occurring hydromedusae of the Puget Sound, Washington, USA depicted in their feeding modes. The jetters (A), Aglantha digitale, Sarsia sp., Leuckartiara sp. and Stomotoca atra, are sitting motionlessly with their tentacles extended. The rowers (B), Aequorea victoria, Mitrocoma cellularia, Phialidium gregarium and Eutonina indicans, are swimming with their tentacles extended. Notice the different scales for the jetters versus rowers.

Colin, S. P. and Costello, J. H., Klos, E. 2003. In situ swimming and feeding behavior of eight co-occurring hydromedusae. Mar. Ecol. Prog. Ser. 253: 305-309




(PDF File 327 KB)






Abstract:
The morphology, swimming kinematics and prey selection of hydromedusae have been shown to be closely related to hydromedusan foraging mode. In order to confirm this link, we examined the in situ foraging behavior of hydromedusae by video recording and quantifying the in situ swimming activity and tentacle-extension behavior of eight co-occurring hydromedusae from the waters surrounding Friday Harbor, Washington. The cruising-predatory medusae, Aequorea victoria, Mitrocoma cellularia, Phialidium gregarium, and Eutonina indicans, spent a greater proportion of their time swimming (on average from 74.1 to 92.1%), than the ambush-predatory medusae, Aglantha digitale, Sarsia sp., Leuckartiara sp., Stomotoca atra (on average from 19.5 to 47.0%). In addition, the cruising-predatory medusae were observed with their tentacles extended almost continuously, regardless of whether they were swimming or drifting. In contrast, the ambush-predatory medusae drifted with their tentacles extended but contracted their tentacles when swimming. These patterns indicate that cruising-predatory medusae can feed while both swimming and drifting; whereas, the ambush-predatory medusae feed while drifting but not while swimming. Thus, swimming plays a distinctly different role within the behavioral repertoire of each of these medusan foraging modes. Furthermore, the swimming activity and tentacle-extension behavior we observed were consistent with strategies that optimized feeding by each of the predator types.


Video (click thumbnail):



Video of jellyfish assemblage in the waters off of Friday Harbor Laboratories, Washington, USA. The ambush foraging medusa, Aglantha digitale, is seen several times typical foraging behavior – drifting with its tentacles splayed out . Several cruising foraging medusae, including Mitricoma cellularia and Aequorea victoria, are displaying their typical foraging behavior – pulsing their bells continuously to create a feeding current. Notice at the end of the video that when Aglantha needs to swim its jet propulsion is very effective. Also seen are several tentaculate ctenophores. (Quicktime File 21,869 KB)




Fig. 2. The means (bars) and medians (dots) of the percent time each species was observed swimming. As the video suggests, the large oblate rowing species swim almost continuously in order to feed as cruising foragers (Aequorea, Mitrocoma, Phialidium, Eutonina) and the smaller prolate jetting species rarely swim in order to feed as ambush foragers (Aglantha, Sarsia, Leuckartiara, Stomotoca).


Costello, J. H. and Colin, S. P. 2002. Prey resource utilization by a guild of hydromedusae from Friday Harbor Washington, USA. Limnol. Oceanogr. 47: 934-942.
(PDF File 705 KB)


Abstract:
Prey selection patterns were quantified for a sympatric group of hydromedusae from Friday Harbor, WA, USA. Selection patterns varied between species, but were largely replicable between sample dates and resembled dietary patterns found in similar studies from neighboring regions. Ambush foraging medusae (Aglantha digitale, Sarsia tubulosa, Proboscidactyla flavicirrata) fed primarily on crustacean and ciliated prey but the dietary niches of these hydromedusan species centered on different fractions of the available plankton. Consequently, little dietary overlap occurred between the ambush foraging hydromedusae. In contrast, the dietary niches of cruising predators (Aequorea victoria, Mitrocoma cellularia, Phialidium gregarium) overlapped substantially because those species all fed on similar soft-bodied prey such as eggs and appendicularians. These results have two important implications for trophic patterns involving medusae. First, different mechanisms of prey encounter and capture used by hydromedusae (ambush vs. cruising patterns) result in important interspecific dietary differences and, hence, trophic roles of the medusae. Second, whereas cruising medusae may consume similar prey and hence form a feeding guild, ambush-foraging medusae may experience substantially less prey overlap and, for the community examined here, do not experience potentially strong feeding competition from other medusan species.


Fig. 2. Conceptual comparison of prey availability and medusan dietary niches. Data represent averages of all sample dates. Bell shapes indicate species as in Figures 2-4. The figure is conceptual rather than actual because prey are class variables of discrete levels rather than continuous variables as implied in the figure. Prey concentrations were based on net tow data. Biomass estimates combined prey concentrations with literature values (Ikeda 1974, Larson 1987a) for carbon content of individual taxa.