Environment and life cycles influence distribution patterns of hydromedusae in austral South America

Abstract

We analysed hydromedusa assemblages of South America (from 22°S to 56°S and from 040°W to 080°W), their association with water masses and the influence of the life cycle on medusa distributions. The geographic distribution of 130 species of hydromedusae was compiled from literature reports (62 publications between 1913 and 2012). Seven areas were defined: Atlantic Magellanic, Argentinean, Pacific intermediate zone, Pacific Magellanic, Peruvian-Chilean, South Brazilian and Oceanic. The variance of the species-environment relationship was explained by depth and temperature. Distribution patterns of Atlantic hydromedusae are associated with neritic water masses, supporting previously proposed biogeographical provinces. Assemblages on the Pacific side of South America are under the influence of the Humboldt Current system, with a break in species distribution around Chiloé Island. Only the oceanic assemblage contained the same species in both the Pacific and Atlantic zones. We found that meroplanktonic medusae contributed more to define the neritic assemblages, while the oceanic assemblage was better defined by holoplanktonic medusae. Therefore, our data suggest that meroplanktonic hydromedusae appeared to be more restricted in distribution than holoplanktonic ones.

Macroscale abundance patterns of hydromedusae in the temperate Southwestern Atlantic (27°–56° S)

“…The location of the G 8 group, which broadly followed the slope and was entirely composed by R . velatum , matched with previous biogeographic studies [14, 75] and with the oceanic feature that this holoplanktonic hydromedusa is associated with [77,78]. The austral assemblages, G 9 and G 10 groups, located mainly in the Magellanic Province and on the slope, correspond to hydromedusan species associated to sub-Antarctic waters [78,79].…”

“…The regional patterns observed in our study were in accordance to the biogeographic distribution of hydromedusan species in the region (see [14,75]). As stated by Rodriguez et al [75], the distributional patterns of hydromedusae in the temperature SWA were related to neritic water masses coinciding with previously suggested biogeographical provinces (i.e., the South Brazilian, the Argentine, and the Magellanic Provinces) ([27], see Fig 1).…”

“…tetraphylla was the main contributor to both groups, highlights its plasticity and points out its distributional range, which reaches up the ~40° S in the SWA. Aglaura hemistoma , mainly associated to warm waters in the SWA, particularly to the tropical water mass of the Brazil Current [43,45], was absent in the G 4 group and those found southward in colder waters, in accordance with Rodriguez et al [75]. Continuing south, the finding of the assemblages composed by the contributions of many meroplanktonic hydromedusae (G 5, G 6, and G 7 groups) was in accordance with the environmental and faunistic features of the transitional neritic zone such as the Argentine Province [27].…”

Traits and depth: What do hydroids tell us about morphology and life‐history strategies in the deep sea?

“…On the other hand, greater dispersal could help individuals get away from conspecifics to avoid competition in an environment with scarce resources (Comita, 2017) and/or decrease chances of predation and parasitism. In fact, species that release medusae usually have wider geographical ranges than benthic species (Gibbons, Buecher, Thibault-Botha, & Helm, 2010;Gibbons, Janson, Ismail, & Samaai, 2010;Rodriguez et al, 2017), although the opposite was found in the family Hydractiniidae (Miglietta & Cunningham, 2012 (Carré & Carré, 2000). It is important to note, however, that patterns inferred in this study are for depths below 50 m deep.…”

“…On the other hand, greater dispersal could help individuals get away from conspecifics to avoid competition in an environment with scarce resources (Comita, ) and/or decrease chances of predation and parasitism. In fact, species that release medusae usually have wider geographical ranges than benthic species (Gibbons, Buecher, Thibault‐Botha, & Helm, ; Gibbons, Janson, Ismail, & Samaai, ; Rodriguez et al, ), although the opposite was found in the family Hydractiniidae (Miglietta & Cunningham, ). A reasonable explanation for the increased proportion of meroplanktonic records would be that the medusae released in deep‐sea environments are monoecious, an advantageous condition in an environment with scarce food, allowing for greater dispersal and colonization of new environments along with ease of sexual reproduction in an environment with low population densities.…”