Ceramium: Ecology

Seasonality
Ceramium can be either an annual plant or a perennial plant. In 2004, Back and Likolammi found that some Ceramium species that lived lower down in the intertidal zone were perennial, flourishing in the spring after wintering as a tiny filament. Other species seemed to be annual, getting completely removed from the substratum by ice and storms during the winter. Around the Monterey Peninsula, species appear to be annual. Most specimens from the Hopkins Marine Station herbarium are from the months of April through August. When searching for Ceramium in the field, it was easy to find C. codicola but difficult to find any other species, which I attribute to annual seasonality. Additionally, the fast growth rate (see next section) of Ceramium seems to suggest a typically annual life history.

Growth Rate
Various studies have looked at the effects of nitrogen on the growth rates of Ceramium, particularly in estuarine settings. Since Ceramium is a relatively thin filamentous alga, its surface area to volume ratio is high, allowing it to take up large quantities of nutrients from its environment. Pederson and Borum (1997) found that Ceramium rubrum was exceptionally good at uptake of nutrients and that Ceramium had higher surge uptake of nutrients (initial nutrient uptake when in excess nutrients) than either Cladophora or Ulva, two notoriously fast-growing algae. Schramm (1999) also found that Ceramium spp. are capable of high amounts of nutrient uptake and storage during times of nutrient availability. They suggest that seasonal, fast-growing epiphytes such as Ceramium will outcompete perennial, benthic algae in the initial stages of a eutrophication event. In contrary, Karez et al. (2004) found that when nutrient availability was high (but not quite to eutrophication) Ceramium was outcompeted by other perennial algae for space. In environments with low nutrient levels, Ceramium persisted.

Epiphytism
Ceramium species are often found living on other algae, called epiphytism. Generally, epiphytism is a response to competition for space on the substratum. Epiphytes can affect the anchor species both negatively and positively. Epiphytes can impede gas and nutrient exchange of, negatively shade, or increase drag on the anchor species. On the other hand, epiphytes, especially filamentous ones such as Ceramium, can keep the anchor species moist, preventing dessication, and can provide shade for shade-loving species.

Most species of Ceramium, and algae in general, are not obligate epiphytes. Some species, such as C. codicola, are only found on other algae. Obligate epiphytism makes the epiphyte dependent on a particular anchor species, which has both positives and negatives as well. In the case of C. codicola, it is only found on one other genus of algae, Codium. While this does appear to severely limit the C. codicola’s range, it may serve to ensure that C. codicola only lives in good environments (the logic being that Codium will only live in environments that C. codicola prefers). In addition, because it is an obligate epiphyte, C. codicola is probably particularly well evolved to live on Codium and can likely outcompete other Codium epiphytes for space.

Biotic interactions
Because Ceramium is an opportunist when it comes to finding spaces to live, occasionally, it will grow on animals, as well as on plants or rocky substratum. Laudien and Wahl (1999) observed C. strictum, among other epibionts, growing on the blue mussel Mytilus edulis in Kiel Fjord in Germany. They found that epibionts, especially algae such as C. strictum, significantly reduced predation on the mussels by sea stars. Although they did not state a mechanism for this, one would imagine that with a covering of filaments of algae, it would be difficult for a sea star to get a clear opening in which to attack the mussel.

Another study in Northern Europe looked at the feeding preferences of the isopod Idotea baltica for various species of algae. Jormalainen et al. (2001) identified six species of algae (reds, greens, and browns) and compared them for concentration of nitrogen as well as amount of herbivory. Unexpectedly, they found that Ceramium tenuicorne had the highest concentration of nitrogen in its tissues but the lowest rates of herbivory. They also found that isopods feeding on C. tenuicorne had low rates of growth, as compared to isopods feeding on the other algae. Because the paper focused on the isopod’s preferences, they do not state a reason C. tenuicorne’s effects. However, it could be hypothesized that something about the structure of the filaments or chemicals inside the filaments that could be inhibiting herbivory. One hypothesis is free sulfur in the cells; see the Biochemistry section.