Monterey Bay Aquarium Research Institute
Marine Botany

Pugetia fragilissima & Pugetia firma

Ecological Interactions

In the natural world, no species is completely isolated, but instead, is part of dynamic ecological interactions. In communities such as the rocky intertidal and subtidal rocky reefs, the battle for space can create intensive competition between algae, which can be further complicated by the stress of herbivory. Pugetia firma and Pugetia fragilissima have many interesting and unique ecological relationships with other algae and animals in the ecosystem.

Many algae (and sessile animals) overcome the problem of limited space by becoming epiphytic (growing on other plants) or epizoic (growing on animals). Pugetia does both. Pugetia firma normally grows on rock, but has been documented growing on both on tunicates and Calliarthron, a coralline alga. During this study Pugetia firma was additionally observed growing on the stalk of a brown alga in the Laminariales. Pugetia fragilissima also utilizes other organisms as substrates, growing epiphytically on other red algae, such as Calliarthron and Chondracanthus. Most notable however, is Pugetia fragilissima’s growth on the tubes of specific polychaete worms. This relationship is explored in more detail below.

Pugetia clearly benefits from its ability to grow on a variety of substrates, however the advantages don’t always extend to the host alga as well. Epiphytes generally shade the anchor species, impede gas and nutrient exchange, and thereby decrease its growth rate (Lobban and Harrison, 1997). Additionally, epiphytes can be responsible for increasing the drag force felt by the anchor species. Within the scope of this study, Pugetia has not been observed with any other algae growing on it. Some red algae defend themselves from epiphytes by periodically shedding layers of cortex or producing chemical properties in their cells that discourage other organisms from attaching (Lobban and Harrison, 1997). No such strategies have been researched in Pugetia, but the lack of epiphytes suggests that perhaps Pugetia has developed some level of defense.

However, Pugetia is not completely immune to invading species, but often serves as a host for endophytic alga. Many pressings of both Pugetia firma and Pugetia Fragilissima in the G.M. Smith Herbarium reveal endophytic algae within their tissue. One Pugetia firma specimen dissected in this study was shown to have a small endophytic brown alga living within its medulla. Using Keys to the Seaweeds and Seagrasses of Oregon and California (Gabrielson et al., 2004) it was identified as the gametophyte of either Desmarestia or a Laminariales. The identification has not been verified, but both these groups of algae have been known to have an endophytic gametophyte stage in red algae.

Pugetia fragilissima was also found to have a highly calcified bryozoan colony growing on it. Although the blades of Pugetia fragilissima are probably too delicate to support the colony independently, the bryozoans extended their growth from the tube of a worm they were both living on. More than likely, Pugetia fragilissima would not be able to survive long with the weight and shadow of the colony.

Perhaps the most interesting ecological interaction observed was between Pugetia fragilissima and one of two species of Chaetopteridae polychaete worms, Phyllochatopterus prolifica and Spiochaetopterus costarum. Pugetia fragilissima is most reliably found growing on the translucent chitinous tube built by these two species of Chaetopteridae polychaete worms. Considering a living worm could never be collected and the tube itself is virtually identical between these two species, it remains unclear whether Pugetia fragilissima grows on both species or is limited to just one. Exploring this question could be an interesting extension of this study.

Phyllochatopterus prolifica and Spiochaetopterus costarum themselves are specialized segmented worms in the family Chaetopteridae. These polychaetes are filter feeders. They produce mucus bags or ropes, which they extend and use to collect particles as small as 0.5 micrometers (Rouse and Pleijel, 2001). They secrete a chitin-like tube from their J-shaped burrows, which can extend down 2m into the substrate or attach to a hard surface (Rouse and Pleijel, 2001). One end of the tube tends to protrude out of the sandy or muddy substrate to allow the worm to feed. On this end many algae have made a home, but none are as dominant as Pugetia fragilissima, which grows off the sides of the tube and then often concentrates around the opening forming a rose-like shape. When they are abundant, diving over the sandy flats can almost look like a wild flower meadow, with scattered stalks topped by pinkish red petals. These dense patches are the product of highly successful asexual reproduction in these worms. At times as many as six young worms can occupy one tube (Morris et al,1990).

In addition to providing substrate in a space -limited ecosystem, living on tubeworms may also help Pugetia fragilissima avoid some herbivory. With their relatively delicate and erect thalli, Pugetia fragilissima and Pugetia firma would seem to be very vulnerable to herbivores. Although specific herbivory events have not been observed, Pugetia may make an excellent meal for some other type of organism. Interestingly, Pugetia fragilissima specimens growing on tubes far out in sand flat appear to be much larger than those closer to rocky substrates or artificial reefs like pipelines. Perhaps by growing on tubeworms slightly away from the concentrated community on the rocks, it avoids some potential herbivores that choose not to venture out onto the sand.

© 2005 Laure Sierra Katz.
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Last updated: Oct. 21, 2005