Larval vertical migration and hierarchical selectivity of settlement in a brooding marine sponge

Abstract

Knowledge of larval behaviours of sessile marine invertebrates from release to recruitment and of the role these behaviours play in determining adult distributions is limited. In manipulative experiments using larvae from the Great Barrier Reef sponge Rhopaloeides odorabile, we quantified larval behaviours associated with vertical migration, phototaxis and swimming ability. We also measured settlement responses to cues associated with light, settlement surface micro-topography, coral rubble and biofilms. Following an afternoon release, the majority of larvae (72%) migrated vertically to the surface (light) for 6 to 18 h. After 24 h, 55% of active larvae had moved from the surface to the bottom and maintained this position for up to 54 h before settling. Larvae did not display gregarious settlement patterns, or a preference for settlement surface topographies, but did preferentially settle to light-exposed surfaces. Initial settlement to biofilms or coral rubble was higher than in controls with no cue. However, the transition from initial settlement and attachment to metamorphosis was much higher when treatments comprised a combination of biofilm and coral rubble compared to biofilm-only treatments (49 vs. 9%). Overall, this demonstrates that hierarchical cues contribute to selective settlement. Vertical migration to surface waters facilitates passive dispersal via wind-driven surface currents and contributes to wide-scale dispersal, while a subsequent demersal phase, where larvae actively explore the benthos for settlement sites, enables dispersal over fine, micro-geographic spatial scales.KEY WORDS: Dispersal · Settlement cues · Vertical migration · Metamorphosis · Larvae · Marine invertebrate · Sponge Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 368: [145][146][147][148][149][150][151][152][153][154] 2008 temperature, pressure and gravity all contribute to the settlement process (Young 1995, Underwood & Keough 2000, Maldonado 2006). In addition, cues associated with physical and chemical surfaces affect larval settlement. Surface micro-topography can provide settlement adhesion points (Verran & Boyd 2001) and micro-refuges . Chemical cues have also been widely investigated for marine invertebrate larvae and include cues associated with biofilms of micro-organisms (Pawlik 1992, Hadfield & Paul 2001, Heyward & Negri 1999, Huang & Hadfield 2003, conspecifics (Raimondi 1991, Head et al. 2004, and host organisms (Swanson et al. 2004).Larval dispersal and settlement is well documented for charismatic taxa such as corals, although holistic approaches quantifying the entire pre-settlement phase from larval release to recruitment are rare (Harrison & Wallace 1990, Raimondi & Morse 2000. There are even fewer studies demonstrating these processes in other important benthic taxa including sponges (see review by Maldonado 2006). This is surprising given the remarkable biodiversity of sponges and their global distributions in benthic ecosystems (Hooper & Van So...

Incongruence between the distribution of a common coral reef sponge and photosynthesis

“…One explanation for this pattern may be that the depth distributions across shelf locations are regulated by light availability and larval settlement behaviours. Larvae of R. odorabile display positive phototactic behaviours prior to settlement, coinciding with a preference to settle on light-exposed surfaces (Whalan et al 2008). Alternatively, changes in food availability associated with light may be driving the observed differential depth distributions of R. odorabile, since food availability can be linked to the distribution patterns of coral reef sponges (e.g.…”

Ontogenetic change in the lipid and fatty acid composition of scleractinian coral larvae

“…Larvae dispersal distance depends on many factors, both physical, such as currents and winds (Siegel et al 2009), and biological, such as larval energy reserves (Burgess et al 2009), survival and settlement competence dynamics (Connolly and Baird 2010), buoyancy and swimming ability (Whalan et al 2008), and a full understanding of dispersal potential requires all these factors to be considered (Jones et al 2009). …”

Mangrove-sponge associations: a possible role for tannins

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