Oyster Larvae Settle in Response to Habitat-Associated Underwater Sounds

Abstract

Following a planktonic dispersal period of days to months, the larvae of benthic marine organisms must locate suitable seafloor habitat in which to settle and metamorphose. For animals that are sessile or sedentary as adults, settlement onto substrates that are adequate for survival and reproduction is particularly critical, yet represents a challenge since patchily distributed settlement sites may be difficult to find along a coast or within an estuary. Recent studies have demonstrated that the underwater soundscape, the distinct sounds that emanate from habitats and contain information about their biological and physical characteristics, may serve as broad-scale environmental cue for marine larvae to find satisfactory settlement sites. Here, we contrast the acoustic characteristics of oyster reef and off-reef soft bottoms, and investigate the effect of habitat-associated estuarine sound on the settlement patterns of an economically and ecologically important reef-building bivalve, the Eastern oyster (Crassostrea virginica). Subtidal oyster reefs in coastal North Carolina, USA show distinct acoustic signatures compared to adjacent off-reef soft bottom habitats, characterized by consistently higher levels of sound in the 1.5–20 kHz range. Manipulative laboratory playback experiments found increased settlement in larval oyster cultures exposed to oyster reef sound compared to unstructured soft bottom sound or no sound treatments. In field experiments, ambient reef sound produced higher levels of oyster settlement in larval cultures than did off-reef sound treatments. The results suggest that oyster larvae have the ability to respond to sounds indicative of optimal settlement sites, and this is the first evidence that habitat-related differences in estuarine sounds influence the settlement of a mollusk. Habitat-specific sound characteristics may represent an important settlement and habitat selection cue for estuarine invertebrates and could play a role in driving settlement and recruitment patterns in marine communities.

Antarctic icebergs: A significant natural ocean sound source in the Southern Hemisphere

“…The potential impacts of increased ocean noise on marine animals' reproduction [Lillis et al, 2013], feeding [Simpson, 2005], communication [Edds-Walton, 1997], and physiology [Rolland et al, 2012] have raised concerns about ecosystem health. Studies have shown that the distance to major ports and shipping lanes, changes in shipping routes, as well as economies and regulatory policies, may affect low-frequency noise levels [Miksis-Olds et al, 2013;McKenna et al, 2012].…”

Behavioral responses of invertebrate larvae to water column cues

“…When larvae are preparing to settle, vertical position can be especially important in permitting them to identify and investigate suitable settlement sites (e.g., [23,24,4]). Some examples of physical cues for the regulation of vertical position include turbulence (Chapters 2, 3, 4, [25,26,27,28,29]), sound [30], and light (Chapter 5, [31,32,33,34,35]). Cues incorporating biological and chemical signals include exudates from predators [36,37], prey or host species [38,39], and conspecific settlement sites (Chapter 6, [40,41]).…”

“…Indeed, larval oysters appear to use acoustic signatures typical of oyster reefs [30] and chemical cues released by adult oysters [95] to initiate settlement.…”

“…Oyster larvae experience and respond to a variety of cues, including light [6] turbulence [27,28,29], and sound [30], in addition to the previously described chemical inducers. Larval responses to settlement cues may also change over the competency period, a phenomenon which has long interested larval ecologists.…”

Light stimulates swimming behavior of larval eastern oysters Crassostrea virginica in turbulent flow

“…We further examined the effect of light and turbulence on specific 37 characteristics of helical trajectories, and found that these environmental cues induce changes to due to a combination of overharvesting and long-term environmental changes (Rothschild et al 55 1994, Kemp et al 2005), and efforts at population restoration and conservation require us to study oysters at the vulnerable larval stages. Understanding larval behavior during planktonic 57 stages is important for both dispersal modelling (North et released by adult oysters to initiate settlement (Tamburri et al 1996), and more recent work 71 suggests a possible role of acoustic signatures typical of oyster reefs (Lillis et al 2013). …”