I walked to the water’s edge along the shore of Poponessett Bay. Winter was finally beginning to recede and the frozen waters were once again in motion under the warmer April sun. Still there were signs that the water temperature was still cold and I observed a couple of marine algae species that are usually present near the end of winter. Scytosiphon and Petalonia are two brown cold water species that often grow together.
Scytosiphon lomentaria, also called the sausage alga, is the more interesting of the two. Examine this alga with a hand lens to observe the periodic indentations which gives it the appearance of a group of sausages. Growing up to two feet long, the sausage alga attaches to rocks in the lower intertidal zone. The alga grows through repeated cell divisions and its presence is temperature dependent. It disappears on the Cape during the warm summer months.
Its relative, Petalonia fascia, grows in the same habitat and at the same time so the two species are often found together. Petalonia consists of flat narrow blades a few inches long. Though this brown alga looks like a small piece of kelp, it lacks the large root-like holdfast or the distinct midrib. This alga also frequently grows in clumps.
I’ve had the most success in collecting these two species in mid to late winter and at low tide where access to small groins and rocks is easier. Both are members of the brown algae division, the Phaeophyta, and they are quite distinct when located.
In fact most marine algae species are distributed in specific zones depending on the wavelength of light that is absorbed by the pigments in the cells. For example, red algae are usually found in deeper water because they absorb blue light. The brown algae including Scytosiphon and Petalonia are in a lower zone just below mean low water. In addition many brown algae species need a strong substrate for attachment. The most common group are the rockweeds and they form large clumps and populations along the base of jetties and the lower edges of salt marsh banks below the cordgrass.
In general the distribution of marine algae starts with the green algae in the upper intertidal zone followed by brown algae just below the low tide mark, and then the red algae in the lower zones. Like marine animal populations, algae are affected by these physical parameters such as light, temperature, and season.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.