Biophysical and anthropogenic influences on the status of Tonga's coral reefs and reef fish fishery.

Despite increasing threats to Tonga's coral reefs from stressors that are both local (e.g. overfishing and pollution) and global (e.g. climate change), there is yet to be a systematic assessment of the status of the country's coral reef ecosystem and reef fish fishery stocks. Here, we provide a national ecological assessment of Tonga's coral reefs and reef fish fishery using ecological survey data from 375 sites throughout Tonga's three main island groups (Ha'apai, Tongatapu and Vava'u), represented by seven key metrics of reef health and fish resource status. Boosted regression tree analysis was used to assess and describe the relative importance of 11 socio-environmental variables associated with these key metrics of reef condition. Mean live coral cover across Tonga was 18%, and showed a strong increase from north to south correlated with declining sea surface temperature, as well as with increasing distance from each provincial capital. Tongatapu, the southernmost island group, had 2.5 times greater coral cover than the northernmost group, Vava'u (24.9% and 10.4% respectively). Reef fish species richness and density were comparable throughout Tongatapu and the middle island group, Ha'apai (~35 species/transect and ~2500 fish/km2), but were significantly lower in Vava'u (~24 species/transect and ~1700 fish/km2). Spatial patterns in the reef fish assemblage were primarily influenced by habitat-associated variables (slope, structural complexity, and hard coral cover). The biomass of target reef fish was greatest in Ha'apai (~820 kg/ha) and lowest in Vava'u (~340 kg/ha), and was negatively associated with higher human influence and fishing activity. Overall mean reef fish biomass values suggest that Tonga's reef fish fishery can be classified as moderately to heavily exploited, with 64% of sites having less than 500 kg/ha. This study provides critical baseline ecological information for Tonga's coral reefs that will: (1) facilitate ongoing management and research; and (2) enable accurate reporting on conservation targets locally and internationally.

Zampanolides B-E from the Marine Sponge Cacospongia mycofijiensis: Potent Cytotoxic Macrolides with Microtubule-Stabilizing Activity.

Four new compounds (2-5) structurally related to the microtubule-stabilizing agent (-)-zampanolide (1) have been isolated from the Tongan marine sponge Cacospongia mycofijiensis. Three of these new structures, zampanolides B-D (2-4), exhibit nanomolar cytotoxicity toward the HL-60 cell line, are antimitotic, and induce in vitro tubulin polymerization at levels comparable to 1. Zampanolide E (5), saturated at C-8/C-9, was significantly less potent and does not stabilize purified tubulin, even at 10-fold higher concentrations. The structural differences across these compounds reveal a plasticity of the zampanolide pharmacophore. While unsaturation is required at Δ8, the configuration of this alkene and those of Δ4 and Δ4' have little effect on tubulin polymerization. The first natural co-occurrence of 1 and (-)-dactylolide (6) from the same sponge extract is also noted.

Microtubule-stabilizing activity of zampanolide, a potent macrolide isolated from the Tongan marine sponge Cacospongia mycofijiensis.

Zampanolide (1), a 20-membered macrolide from a Tongan marine sponge, stabilizes microtubules and blocks cells in G(2)/M of the cell cycle. Zampanolide is cytotoxic in the low nanomolar range and induces microtubule bundles in cells. It leads to tubulin assembly in cells and in purified tubulin preparations and is not a substrate for the P-glycoprotein drug efflux pump. Zampanolide, with only four stereogenic centers, may be amenable to large-scale synthetic preparation.