Regeneration

Caribbean dry forests are among the most endangered tropical ecosystems on earth. Several studies exist on their floristic composition and their recovery after natural or man-made disturbances, but little is known on the small Dutch Caribbean islands. In this study, we present quantitative data on plant species richness and abundance on St. Eustatius, one of the smallest islands of the Lesser Antilles. We collected and identified trees, shrubs, lianas and herbs in 11 plots of 25 x 25 m in different vegetation types. We compared their floristic composition and structure to vegetation surveys from roughly the same locations in the 1990s and 1950s. We found substantial differences among our 11 plots: vegetation types varied from evergreen forests to deciduous shrubland and open woodland. The number of tree species ≥10≥10 cm DBH ranged between one and 17, and their density between three and 82 per plot. In spite that all plots were subject to grazing by free roaming cattle, canopy height and floristic diversity have increased in the last decades. Invasive species are present in the open vegetation types, but not under (partly) closed canopy. Comparison with the earlier surveys showed that the decline of agriculture and conservation efforts resulted in the regeneration of dry forests between the 1950s and 2015. This process has also been reported from nearby islands and offers good opportunities for the future conservation of Caribbean dry forests.

Sponges have a remarkable capacity to rapidly regenerate in response to wound infliction. In addition, sponges rapidly renew their filter systems (choanocytes)

to maintain a healthy population of cells. This study describes the cell kinetics
of choanocytes in the encrusting reef sponge Halisarca caerulea during early regeneration (0–8 h) following experimental wound infliction. Subsequently, we investigated the spatial relationship between regeneration and cell proliferation over a six-day period directly adjacent to the wound, 1 cm, and 3 cm from the wound. Cell proliferation was determined by the incorporation of 5-bromo-20-deoxyuridine (BrdU). We demonstrate that during early regeneration, the growth fraction of the choanocytes (i.e., the percentage of proliferative cells) adjacent to the wound is reduced (7.0 ± 2.5%) compared to steady-state, undamaged tissue (46.6 ± 2.6%), while the length of the cell cycle remained short (5.6 ± 3.4 h). The percentage

of proliferative choanocytes increased over time in all areas and after six days of regeneration choanocyte proliferation rates were comparable to steady-state tissue. Tissue areas farther from the wound had higher rates of choanocyte proliferation than areas closer to the wound, indicating that more resources are demanded from tissue in the immediate vicinity of the wound. There was no diVerence in the number of proliferative mesohyl cells in regenerative sponges compared to steady-state sponges. Our data suggest that the production of collagen-rich wound tissue is a key process in tissue regeneration for H. caerulea, and helps to rapidly occupy the bare substratum exposed by the wound. Regeneration and choanocyte renewal are competing and negatively correlated life-history traits, both essential to the survival of sponges. The eYcient allocation of limited resources to these life-history traits has enabled the ecological success and diversification of sponges.