Life in False Bay presents a special challenge to local organisms because, as water drains out, sediment and the animals it contains are exposed. Protection must be thought of in two different ways.  Organisms must protect themselves from both changes in the physical environment and other organisms. Although these are distinct problems, the common solution to predation and physical pressures is living within the sediment (infaunally). The problems of protection faced by the organisms at False Bay provide an interesting contrast to those at Cattle Point, which is a high-energy, rocky intertidal habitat.
    During the summer, False Bay usually empties once during the day at low tide. Exposure to bright sun for several hours can increase the surface temperatures of standing water and sand significantly. Many organisms survive these fluctuations by finding a way to avoid them. Infaunal organisms take advantage of the insulation provided by the  sand. By living well below the sediment surface, they are able to maintain a more constant  temperature regime, protected from the heat of the sun. One can test this easily without a thermometer. Simply reaching a finger into the burrow of a bivalve, mud shrimp, ghost shrimp, or polychaete on a sunny day will reveal water that is significantly cooler than the water standing in the tide pools.

    A corollary of temperature stress is the problem of desiccation due to heat and exposure during low tide. Desiccation is also avoided by burrowing. One easy way to demonstrate this is to walk over and around many of the burrows in False Bay. Near the north end of the bay, bivalve burrows will spout water when you compress them. Chaetopterid tubes also spout water, presumably as they move due to the disturbance of footsteps. Since the bottom of False Bay is flat, the water table is extremely high. Even during low tide, the sand is saturated with water within a few centimeters of the surface, allowing burrowing animals to remain immersed.

    Non-burrowing (epifaunal) organisms, such as crabs and fishes, avoid desiccation in a different way. They solve this problem by staying in tide pools and channels during the low tide. Although this provides protection from desiccation, it does not provide protection from the warm temperatures achieved by tide pools exposed to continuous sunlight.
Chaetopterid tube on sandbar 
in the sandbar area of False Bay.
Castings of the Arenicolid worm Aberinicola next to bivalve burrows (holes) in the lugworm area of False Bay.

    Protection from predators is also necessary for many of the organisms in False Bay. One particularly striking example of the need for protection emerged from our fieldwork in the bay. Digging in the shrimp habitat, we disturbed several mud shrimp (Upogebia) and ghost shrimp (Neotrypaea) from their burrows. Although in pools of water, the animals had not all begun burrowing when we left the habitat. When we returned less than two hours later, several had been eaten, leaving only pieces of carapace behind. It is likely that they were eaten by local birds, such as crows or gulls. Although these shrimp live for as many as ten years in their burrows (Kozloff, 1996), once exposed at the surface they are extremely vulnerable to predators. This experience provides two messages. First, burrowing is an essential protective strategy for Upogebia and Neotrypaea. Second, care should be taken to disturb as few individuals as possible, because a trip to the surface may spell death for members of these species.

    A few organisms even take advantage of the burrows and tubes of other organisms in order to find protection. Orobitella rugifera is a small bivalve that lives attached to the underside of the abdomen of mud shrimp (Upogebia). In this way it is able to take advantage of the burrowing power of the shrimp. It can live well below the surface of the sediment (and any surface predators) without exposing its siphon, but while obtaining sufficient water flow with which to feed. This bivalve is remarkable for the number of modes of protection it has. It lives in a burrow well below the sediment surface, it is protected by the shrimp by virtue of living on its abdomen, and it has the protection of its two calcified valves, even if the shrimp falls victim to a predator.

    Pinnixa tubicola is a small brachyuran crab found in the tubes of Terebellid worms (spaghetti worms) in the Ulva area. Like Orobitella, Pinnixa takes advantage of the camouflage provided by living within the Terebellid tube, as well as its own exoskeleton.


    It may seem that protection from predators and protection from the physical environment go hand in hand at False Bay. There may, however, exist tradeoffs within this life strategy. Some species, such as Chaetopterus, live in tubes formed of mucous, while others, such as Upogebia, live in burrows whose sides are formed primarily of sediment. It is easy to imagine that tube dwelling
organisms may have more control over their immediate environment than mere burrowers, due to slightly greater isolation from the surrounding conditions. Why donāt all infaunal animals live in tubes, then? A partial answer may come from the observations of Woodin (1972). She determined that the crab Cancer magister selectively targets as prey tube-dwelling species with tubes exposed at the surface in preference to burrowing species with only burrow holes exposed at the surface. One might imagine that it is easier to pull up a tube than to dig into a burrow. Thus, although tubes may provide an organism with more active control over the conditions within which it lives, mere burrowing may be a better deterrent to epifaunal predators. When considering the protection provided by living within the sediment, one must also consider the relative needs for protection from predators and protection from fluctuations in the physical environment.


    A walk around False Bay during low tide will provide ample evidence of the number of burrowing organisms. This infaunal lifestyle provides protection against both predators and fluctuations in the physical environment. Careful observation demonstrates that the burrows are not all the same, and that different types occur in different areas. The type of burrows present may reflect the relative pressures of predation and physical stresses.  These burrows are not merely a convenient way to avoid the footsteps of human visitors; they are an essential part of survival in a bay subject to rapid and extreme changes in temperature, water level, and numerous predatory organisms.

    The problems of protection at False Bay provide an interesting contrast to those at Cattle Point, Argyle Lagoon, on the FHL dock floats, and in the local plankton.