Plocamium pacificum is an intertidal and subtidal alga. It can be found in the mid to low intertidal zone and subtidally to depths of 40 meters. In the Monterey Bay it is one of the deepest growing red algae found, having been collected at depths of 38 meters in the Submarine Canyon.
It is occasionally found growing on other algae (epiphytic), but is usually found on rocky substrate that has been lightly covered by sand. It is a perennial species (lives for many years) that is usually abundant in its habitat, but its fronds are annual (live only one year) and can often be found in the drift.
In the intertidal zones P. pacificum is often found in tide pools with Laminaria spp., Ptilota sp., and the sea grass Phyllospadix sp.
In the subtidal zones P. pacificum can often be found with other algae, especially: Polyneura latissima, Phycodrys setchellii, Desmarestia ligulata var. ligulata, and encrusting corallines. These species make up part of the bottom cover under canopies of either Macrocystis pyrifera or Pterygophora californica.
Areas with P. pacificum are usually grazed by small snails, crabs, and urchins. Haliotis species (abalone) are known grazers on Plocamium (Britz 1996).
Epiphytes on Plocamium:
In the British Isles there is a disc shaped epiphyte that is found on a Plocamium species. The epiphyte is Ulvella (Crouan 1859). There is a species of Ulvella in California, so it may also be an epiphyte on P. pacificum.
The similar looking Microcladia species are also epiphytic on P. pacificum in California. This branching red alga grows on the surface of its hosts.
Within the same family as Plocamium there is Plocamiocolax. Plocamiocolax pulvinata is the species found in California. It is an obligate epiphyte, because it is exclusively found growing on Plocamium cartilagineum (since this site is using all P. reports in California as P. pacificum reports it is assumed that the epiphyte is an obligate on P. pacificum). It looks like a small, 5 mm diameter, bush. It is white to tan in color with lots of small branches. Plocamiocolax pulvinata acts as a parasite on Plocamium by injecting its nuclei and mitochondria into the host cells. It has been proposed that P. pulvinata evolved from Plocamium violaceum (Goff and McLaughlin 1997).
Photograph by Goff, L. Used with permission, May 29, 1999.
Plocamium as an Epiphyte:
Plocamium pacificum has been found to be epiphytic on the stipes (thick, supporting main axis) of Laminaria species in the subtidal zones.
This specimen of P. pacificum was found living epiphytically on the branch of Ptilota filicina at Davenport Landing in Santa Cruz County, California. The epiphyte is hard to distinguish from the host alga without magnification due to the similar colors and branching styles.
Plocamium hamatum has been found to suppress the growth of some invertebrates by releasing a toxin. In some sponges, gorgonians and soft corals, tissue death occurred after contact with P. hamatum (Leone et al. 1994).
In areas that have high sewage flow to the ocean Plocamium species are not present, even if the habitat is right (Klenk 1985).
Plocamium cartilagineum growth is limited by light. Like all algae it needs enough light to photosynthesize, but when there is too much light photoinhibition occurs. Evidence can be seen for this in the vertical distribution. In shallow subtidal depths it lives under canopies of large kelp and in the intertidal zones it lives under beds of the seagrass Phyllospadix sp. By living in shaded areas it avoids photoinhibition. However, it can not get too shaded because unlike some algae, P. cartilagineum lacks stored materials and constantly relies on photosynthesis (Kain 1987).
In the southern part of the North Sea it was found that deep subtidal P. cartilagineum is more sensitive to UV radiation than other intertidal and subtidal species. It was also shown that, among individuals of the species, there was a difference in UV radiation sensitivity depending on the depth at which it had grown. The sensitivity varied little with seasons, probably due to the lack of seasonal affects at deeper depths (Gonzalez et al. 1993).
Plocamium cartilagineum is a cosmopolitan species. Surprisingly it can survive and grow in both warm and cold waters. In Antarctica it grows optimally at 0-5 ºC and can survive only up to 7 ºC. Other Antarctic algae have wider ranges. This strikingly low and tight temperature requirement leads some researchers to believe that P. cartilagineum is endemic to Antarctica (Bischoff-Basmann and Wiencke 1996). Other researchers believe that P. cartilagineum has evolved to live in a chronically cold environment (Vayda and Yuan 1993).