I’m Marina Fernandez, a PhD candidate from the University of São Paulo, in Brazil. Since February, I’ve been studying benthic hydroids from the NMNH-SI collection, under supervision of Dr. Allen Collins.
Hydroids are incredibly beautiful and diverse sea animals from the phylum Cnidaria. Their morphological and biological traits can vary greatly from one species to another. An evident variation is in size, with individuals ranging from a few millimeters to more than a meter. Also, most species grow in colonies, but some are solitary. Among colonial forms, the polyps composing one same colony can have different morphologies and functions – some are specialized in feeding, others in reproduction, and there can be a third group responsible for defending the colony. Even more striking is the fact that some hydroid species release a medusa, a life cycle stage in which these animals live in the plankton, where they release gametes for reproduction. Some species do not release a medusa, however, and thus it is the benthic stage that produces gametes.
Such kinds of diversity within a group make us wonder if different forms are evenly distributed among different environments of the sea. Studying how traits correlate with environments may help us understand how they evolved. And that’s what I’m trying to do here: associate information on traits from specimens in the collections with the place where they occur, in order to understand patterns of distribution. Some of the traits I’m looking are size, colony ramification patterns and presence of certain structures. This is then combined with information from the literature regarding the life cycle, that is, if a medusa is released or not.
This search for patterns is focused mainly on bathymetric gradients. As you go deeper in the ocean, the sunlight decreases rapidly until complete darkness. Without light, and hence photosynthesis, the phytoplankton, which is the primary food source in the ocean, can no longer survive. At those depths, food must somehow arrive from surface waters (except in chemosynthetic environments such as hydrothermal vents), making food scarcer as you go deeper. Temperature also decreases quickly, until it stabilizes below 1000 meters. Hard substrates are more difficult to find on deeper parts of the sea, the ocean floor being mostly formed by muddy bottoms in the abyssal plains. All these variations make the deep sea a very interesting environment for studying the diversity of traits in hydroids.
By Marina Fernandez, Visiting Grad Fellow