BNHC: Octopus of Sweetings Pond

A talk given at The Bahamas Natural History Conference 2020.

Transcript

1. Octopus Abundance in an Anchialine Lake from The Bahamas Duncan O’Brien*, Michelle Taylor, Heather Masonjones, Philipp Boersch-Supan and Owen O’Shea
2. Anchialine Ecosystems Perez-Moreno et al. (2016)
3. Sweetings Pond, Eleuthera
4. 0.2 miles N
5. Sweetings Pond Ecosystem Lined seahorse Caribbean reef octopus West Indian spider crab Cross-barred venus
6. Caribbean Reef Octopus (Octopus briareus) • Common throughout the Caribbean • Contributes common octopus catch • Mesopredator • Possible dominant predator in Sweetings
7. Previous Research • 1980s – octopus densities estimated for ‘Octopus Den’ • 2010s - seahorse research by University of Tampa • 2016 - established population of IUCN Redlist ‘vulnerable’ seahorses
8. Objectives 1. Estimate the current O. briareus population density and spatial distribution within Sweetings Pond 2. Compare current estimates to historic 1980s estimates 3. Identify possible drivers of octopus distribution in Sweetings Pond
9. Methods • Lake-wide 30 x 30 m quadrats (n = 27) • Five replicates per site during May-June 2019 • Systematic SCUBA surveys
10. • Point benthic surveys • Estimate of percentage cover • Explanatory variable for ecological models
11. Results • Seventeen octopus recorded from 27 surveys • ‘Control’ yielded most octopus (1.60 ± 1.52) Control Caves Octopus Den Quarry Grouper Cave
12. • No significant difference between years • Count predicted by increasing calcareous rubble (p < 0.05) • Negative influence of den abundance (p < 0.05)
13. • Significant difference in benthic composition between sites (ANOSIM: R2 =0.665, p < 0.001) • ‘Control’ and ‘Grouper Cave’ benthically similar • ‘Quarry’ displays a high percentage cover of flocculant [Dunn’s test: ‘Quarry’ > ‘Octopus Den’ (p < 0.001) & ‘Control’ (p < 0.05)] Stress = 0.1852
14. Discussion • Comparable to coastal Bermudan densities of common octopus (918.3 ind. per km2) • Apparent stable population over time Mesopredator release? Lake environmental characteristics?
15. • Calcareous rubble as habitat positively predicts octopus counts • Den abundance is negatively associated with octopus counts Den aggregation in non- optimal habitat?
16. Conclusions • Maintaining bivalve population will ensure stability • A ‘reference’ approach is required • ‘Natural laboratory’
17. O’Brien et al. 2020 Two more manuscripts currently being prepared for submission
18. Acknowledgments
19. References • Aronson, R. B. 1986. Life-history and den ecology of Octopus briareus Robson in a marine lake. Journal of Experimental Marine Biology and Ecology, 95: 37-56. • O'Brien D. A., Taylor M. L., Masonjones H. D., Boersch-Supan P. H. and O'Shea O. R. 2020. Drivers of octopus abundance and density in an anchialine lake: A 30 year comparison. Journal of Experimental Marine Biology and Ecology, 528:151377 • Pérez-Moreno, J. L., Iliffe, T. M., and Bracken-Grissom. H. D. 2016. Life in the Underworld: Anchialine cave biology in the era of speleogenomics. International Journal of Speleology, 45: 149-170.