Bail Out
Dislodgement of invertebrates from the hard substratum to which they cling is a chronic risk in the wave-washed rocky intertidal zone. For example, a large mussel (a bivalve mollusk), with all of its attached invertebrates, can be dislodged by a large wave; many such dislodged mussels are consumed, along with their ‘hangers-on’ by nearby sea anemones. We discovered that most limpets do not go along on that ride down an anemone gullet, but instead respond to dislodgment of its mussel substratum by “bail out” (9, 20): limpets on a horizontally rotating mussel simply let go and reattach much more rapidly than their bivalve host (9).
Rocks Weaponize Waves
Limpets may also end their decades-long life bashed by wave-born rocks (8). Many more sustain damage, which they survive (arrows).
Territorial Chase Risks Dislodgement
Even in the absence of dislodged substratum, or damage by rocks, risk of wash-off by large waves is a chronic problem for limpets, especially if they are territorial like the owl limpet, Lottia gigantea (6). Our early studies found that patrolling limpets cease moving at high-tide during large swells (33), thereby reducing risk of wash-off. More recently (39), we directly tested tenacity of limpets engaged in a territorial chase (in the dark of the night when the tide and waves are washing them). This “limpet wrassling” technique revealed that limpets are particularly vulnerable to being dislodged by waves while engaged in “territorial chase”.
Baiting owl limpets into territorial chases during a medium tide and a moderate swell:
Territorial chase refers to both the territorial resident’s pursuit of intruders, as well as the rapid retreat of an intruder upon detection by the resident. Limpets engaged in chase move 10-60 times faster than when they are grazing on the rock’s micro-algae (33); this rapid movement makes them four times more vulnerable to being washed off by even moderate-sized (1.5 m height) waves (39).
Territorials Dislodge Intruders
Territorial limpets employ a surprisingly explosive thrusting behavior in their efforts to defend their territory from other intruding limpets. The force of that thrust is sufficient to overcome the resistance of smaller intruders, thereby dislodging them (40).
*click on image to open limpet thrust video
Learning in the Neighborhood
Limpets that encounter a territorial whose intensive thrusting loosens their grip on the substrate, learn from that encounter, and employ a short latency rapid retreat upon future encounters (17). This behavioral plasticity likely reduces intruders’ risk of dislodgement by territorial residents.
Consequence of Dislodgement
Most intertidal researchers assume that a dislodged limpet is a dead limpet. We (40) measured survival of limpets dislodged during territorial chase, and found it to be surprising high (>44%). This high survival rate, combined with the accelerated growth rate of small limpets with access to defended territories (6), helps to explain the dynamic tension of this territorial system: Dislodgement of intruders effectively rids a territorial resident of a significant exploitative competitor; conversely, repeated intrusion by small limpets gives such intruders otherwise unavailable resources, where the main risk is relatively low: dislodgement followed by continued survival in a new location (see discussion in 40).