Settlement cue selectivity by larvae of the destructive crown-of-thorns starfish

This study assessed the relative capacity of a diversity of coralline algae to induce COTS settlement in order to test the hypothesis that the alga Lithothamnion cf. proliferum promotes higher settlement rates than the other species.

Western Pacific COTS (Acanthaster cf. solaris) larvae were reared at the Australian Institute of Marine Science (AIMS) National Sea Simulator. Larval development was microscopically examined until metamorphic competency 14 days post-fertilization was determined. Experimental treatments included 14 living coralline algae species and one living Peyssonneliaceae alga plus structural control (sterile aragonite) and filtered seawater (FSW) control treatments. 12 replicate settlement assays were conducted for each of the 17 experimental treatments with six well cell culture plates, and fully randomised distrubution of all replicate assays among the 204 wells.

After adding 10 ml FSW and a single chip of one of 15 different algal species or sterile aragonite to the wells, approximately 10 competent COTS larvae per well were introduced using glass pipettes. All well plates were kept in a temperature-controlled room (28°C) matching the light conditions during larval rearing (12 L : 12 D, light–dark).

Larval settlement was scored 24 and 48 h after larvae were introduced using stereo microscopes. Scoring included:

the number of competent late-brachiolaria larvae remaining in the water column (= swimming)

he number of individuals that had successfully attached to the treatment chip or well bottom and commenced or completed metamorphic transformation into a juvenile with radial symmetry (= settled)

Statistical analyses were performed using R software (v. 4.1.3).

The molecular sequences for each algal species can be accessed in the GenBank database under accession numbers OP830444 to OP830473

species | psbA GenBank accession No. | rbcL GenBank accession No.
Melyvonnea cf. madagascariensis | OP830452 | OP830467
Neogoniolithon fosliei | OP830450 | OP830465
Adeylithon bosencei | OP830454 | OP830469
Hydrolithon cf. reinboldii | OP830457 | OP830472
Lithophyllum cf. insipidum | OP830456 | OP830471
Lithothamnion cf. proliferum | OP830448 | OP830463
Titanoderma cf. tessellatum | OP830447 | OP830462
Amphiroa foliacea | OP830453 | OP830468
Sporolithon sp. | OP830455 | OP830470
Ramicrusta sp. | OP830458 | OP830473
Lithophyllum cf. pygmaeum | OP830449 | OP830464
Porolithon sp. A | OP830446 | OP830461
Porolithon sp. B | OP830444 | OP830459
Lithophyllum cf. kotschyanum | OP830451 | OP830466
Porolithon sp. | C OP830445 | OP830460

Experimental assay data and description are available from the Dryad Digital Repository linked below.