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PHYCOLOGICAL SOCIETY OF AMERICA

Gelidium is found in every geographic region in the world except for the Arctic and Antarctic. Particular species of Gelidium may be much more localized to specific regions. Species of Gelidium are generally found on rocky substrate in the low intertidal to high subtidal areas. The picture below shows the habitat where Gelidium is found at the Hopkins Marine Station during low tide. During most of the tidal cycle, this area is completely covered with water.

In looking for Gelidium at Hopkins, I noticed that it is abundant in some areas but completely absent in other areas. The areas where Gelidium grows are only accessible during low tides. Gelidium growing at Hopkins ranged in size from about 6 to 18 cm. It was identified as G. Robustum rather than G. purpurescens despite the small size due to the coarseness of the axes. The reduced length for G. Robustum could be due to seasonal growth or reduced photosynthesis and growth in exposed intertidal specimens in comparison to subtidal specimens. Also, studies show that during winter storms, longer axes are more likely to be ripped from the substrate by wave action.

To get a better idea of the small-scale distribution patterns, I spent an afternoon in February during low tide walking through the intertidal at Hopkins and observing the areas where I encountered Gelidium. I found that the only place where Gelidium grows at Hopkins is along the point which juts out into the bay more than the surrounding coast. This area is highly exposed to wave action. A map of Hopkins Marine Station is shown below with the area where Gelidium is located marked in red.




I researched this topic and found that higher abundance in wave exposed areas has been recorded for a number of different species of Gelidium. Though there is no conclusive reason for this distribution pattern, Gelidium does exhibit some adaptations that may give it a selective advantage in a high energy habitat. The internal rhizoidal filaments offer support to protect the thallus from being ripped by waves. Also, a hydrodynamics study of G. nudifrons showed that the external morphology of the algae affected water motion. As water entered the area of the branched thallus, turbulent flow was suppressed into laminar flow. However, at the same time, when water was flowing above a critical velocity that ranged between 6 and 12 cm/s depending on the particular plant's morphology, the branches generated microturbulence. The microturbulence was of the scale that may be beneficial to nutrient uptake and gas exchange, therefore suggesting that a high energy environment might benefit Gelidium.

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