Sponge white patch disease affecting the Caribbean sponge Amphimedon compressa.

We report on a novel sponge disease, hereafter termed 'sponge white patch' (SWP), affecting the Caribbean sponge species Amphimedon compressa. SWP is characterized by distinctive white patches of variable size that are found irregularly on the branches of diseased sponges. Nearly 20% of the population of A. compressa at Dry Rocks Reef, Florida, USA, showed symptoms of SWP at the time of investigation (November 2007-July 2010). Approximately 21% of the biomass of SWP individuals was bleached, as determined by volume displacement. Scanning electron microscopy analysis showed severe degradation of bleached tissues. Transmission electron microscopy of the same tissues revealed the presence of a spongin-boring bacterial morphotype that had previously been implicated in sponge disease (Webster et al. 2002; Mar Ecol Prog Ser 232:305-309). This particular morphotype was identified in 8 of 9 diseased A. compressa individuals investigated in this study. A close relative of the aforementioned disease-causing alphaproteobacterium was also isolated from bleached tissues of A. compressa. However, whether the spongin-boring bacteria are true pathogens or merely opportunistic colonizers remains to be investigated. Molecular fingerprinting by denaturing gradient gel electrophoresis (DGGE) demonstrated a distinct shift from the microbiota of healthy A. compressa to a heterogeneous mixture of environmental bacteria, including several phylotypes previously implicated in sponge stress or coral disease. Nevertheless, tissue transplantation experiments conducted in the field failed to demonstrate infectivity from diseased to healthy sponges, leaving the cause of SWP in A. compressa to be identified.

Foundations of gregariousness: a dispersal polymorphism among the planktonic larvae of a marine invertebrate.

Theory predicts that selection should favor genotypes that can vary their tendency to disperse in habitats that are spatially or temporally variable or those that remain near their carrying capacity. Although many marine habitats appear to fit these criteria, confirmed examples of dispersal polymorphism among marine invertebrates are exceedingly rare. Competent larvae of the gregarious tubeworm, Hydroides dianthus, settle specifically in response to living conspecific worms, but a small proportion of each spawn settle nonspecifically on uninhabited substrata concurrently with their gregarious siblings. Here, using a parental half-sib analysis, we show that the proportion of a spawn settling in response to uninhabited biofilm is highly heritable. When estimated as a continuous trait based on a one-way ANOVA, heritability is estimated to be 0.83 +/- 0.31. When founder production was analyzed as a threshold trait, heritability was estimated to be 0.68 +/- 0.10 based on the breeding design experiment and 0.65 +/- 0.09 based on the artificial selection experiments. Realized heritability based on the selection experiments was considerably lower, however (0.17 per generation and 0.02 cumulative). Artificial selection was ineffectual at sequentially increasing the proportion of founder larvae among inbred family lines, but after three generations of selection, the proportion of larvae settling in response to biofilm was significantly higher among inbred lines than among the field-collected parents. The obligate planktonic larval stage common among so many marine invertebrates is thought to preclude the evolution of dispersal polymorphisms in these animals. Theoretical expectations of variable dispersal may instead be realized through individual behavioral differences resulting in differential transport or settlement preference, but this possibility remains largely unexplored among marine invertebrates.

New antifeedant triterpene glycosides from the Caribbean sponge Erylus formosus.

Two groups of antifeedant triterpene glycosides were identified from the Caribbean sponge Erylus formosus. The structure of formoside B, a novel N-acetyl amino derivative of the known penasterol tetrasaccharide formoside, was elucidated using NMR and mass spectral data. Four triterpene hexasaccharides and two triterpene trisaccharides, characterized by a 31-carbon aglycone, proved difficult to isolate and therefore only the structure of their aglycone was determined. Gas chromatographic analysis of derivatized saccharides from these mixtures established the carbohydrate content of these compounds. All of the triterpene glycosides isolated contributed to the chemical defenses of this sponge, although with differing activities.

Amphitoxin, a new high molecular weight antifeedant pyridinium salt from the Caribbean sponge Amphimedon compressa.

A new polymeric pyridinium alkaloid named amphitoxin [2] has been isolated from Amphimedon compressa, and its structure determined by spectroscopic analysis. In laboratory feeding experiments, crude extracts and purified amphitoxin [2] from A. compressa at lower than natural concentration levels effectively deterred feeding of a generalist predatory Caribbean reef fish, Thalassoma bifasciatum.

Hydrodynamic facilitation of gregarious settlement of a reef-building tube worm.

Experiments testing the effects of hydrodynamic processes and chemical cues on substrate selection were conducted with larvae of the marine tube worm Phragmatopoma lapidosa californica. In flume experiments, larvae were presented an array of sand treatments, including two substrates previously shown to induce metamorphosis in this species, under fast and slow flow regimes. Larvae preferentially metamorphosed on the inductive substrates in both flows. Delivery to the array was higher in fast flow because larvae tumbled along the bottom, whereas in slow flow, larvae were observed swimming in the water column. Thus, in addition to chemical cues, behavioral responses to flow conditions may play an important role in larval recruitment to the benthos.