Under pressure...how to succeed as a deepwater seagrass

As a functional group seagrasses are ubiquitous throughout the Great Barrier Reef World Heritage Area (GBRWHA), from offshore coral reefs to inshore estuaries and embayments. Mounting concern for acute and chronic anthropogenic pressures on seagrasses have steered efforts to develop indicators of light attenuation stress. Developing a “one-size-fits-all” model for the 15 species found in the GBRWHA is ineffective without accounting for functional differences in their life history traits. We investigated the growth attributes and adaptation of deepwater (>10m) seagrass communities with a goal to improve coastal management strategies impacting this functional group. We explored what role density and stratification of a seed bank plays in meadow resilience, and how the optical challenges of growing at depth may affect seed germination in these ephemeral meadows. Sediment cores were collected over three years from three Halophila spp. meadows within the GBRWHA. Seed densities varied over time and with depth (≤ 10cm) but followed similar trends among meadows. Collections of mature fruits afforded fresh seeds to establish the first successful seed viability test known for this genus. Fresh seeds were also used to examine the role spectrally-refined light at depth has on germination success. While strategically Halophila spp. are known to rely on seeds, having a more intimate understanding of the functionality of their seed banks and how they respond to environmental cues, bridges a science gap for effectively mitigating light-driven loss of tropical deepwater seagrasses