Herbarium records of terrestrial plants are nonrandomly collected and suffer from a number of significant data gaps and biases in multiple dimensions, potentially leading to spurious conclusions. Just as the occurrence records of terrestrial biodiversity is limited and prevalent with gaps and uncertainties, our knowledge of marine biodiversity might be characterized by key data gaps and sampling biases. Seagrasses and mangroves constitute the only vascular flowering plants in the marine environment, anchoring several marine food chains and are under threat from anthropogenic activities. Yet, the only data available for studying marine plants at large scales are expert-opinion range maps derived from opportunistic records, sightings and specimen collections, and might be characterized by nonrandom sampling. In this study, I mapped the spatial, phylogenetic and temporal distributions of marine plants (seagrasses and mangroves) at a global scale using global datasets to examine key data gaps. I discuss significant gaps in marine plants diversity data across the world's coastal regions, and provide solutions for the biases inherent in these biological collections.

The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that are located approximately 30 km offshore, support the only marine seagrass beds in Louisiana, and are the sole location of the climax seagrass species turtlegrass (Thalassia testudinum) across nearly 1,000 km of the Gulf Coast from west Florida to central Texas. Seagrass beds at the Chandeleur Islands are considered relatively pristine, because of the inaccessibility of the Islands and lack of direct human impacts; however, this area is a hotspot for dynamic changes in seagrass cover, as seagrass presence relies on the protection provided by land area, which has decreased by over half during the last 150 years. Long-term monitoring of seagrass beds provides valuable information on bed status and trends, can inform predictions under future scenarios, and is an essential component of ecosystem-based and adaptive management. Seagrass monitoring at the Islands has been sporadic, often coinciding with a major disturbance such as a hurricane or oil spill, and monitoring methodologies have not been standardized, making quantification of changes in cover and community composition difficult. In 2018, we established a long-term monitoring program of seagrasses at the Chandeleur Islands following the widely-used and recommended tiered monitoring approach. Here, we present the results of our first year of monitoring, combined with a finer-scale assessment of turtlegrass distribution and plant biomass, and frame these results in the context of previous monitoring efforts along the Islands. mple drag and drop elements like text, images and links, or connect to data from your collection.

​

Severe meteorological events can impart extensive damage on coastal ecosystems depending on the intensity and proximity to the storm. Hurricane Harvey battered the Texas coast on August 25, 2017 with maximum winds of 130 knots and produced prolific rainfall as the storm stalled over the state. To assess the immediate impacts of this major hurricane on coastal marine ecosystems, we examined the response of two seagrass species and sediment dynamics to storm intensity. Following the landfall of Hurricane Harvey, we obtained measurements of percent cover and blade length for the dominant seagrass species, Halodule wrightii and Thalassia testudinum, at 525 permanent stations along the Texas coast. We collected sediment cores for the analyses of total organic carbon (TOC), grain size, and ammonium from a bay exposed to the storm’s eyewall. We compared post-storm measurements to pre-hurricane observations from the most previous sampling year for all analyses. For both species, greater wind intensity corresponded with a significant decrease in mean blade lengths relative to pre-storm measurements (R2 T. testudinum=0.42, R2 H. wrightii=0.05). Only T. testudinum displayed significant reductions in percent cover (R2 T. testudinum=0.13, R2 H. wrightii=0.01) with some stations exhibiting complete loss of aboveground and belowground biomass. We did not observe a difference in sediment ammonium concentrations or TOC. We found significant differences among groups for rubble, sand, silt, and clay percentages (ANOVA, α=0.05) with a shift to sand-dominated sediments. The variance in the grain sizes of the post-hurricane measurements relative to pre-storm compositions suggest the redistribution of sediments in remnant seagrass beds. Our observations document the acute effects of wind intensity on habitat structure in response to a category 4 hurricane. The poor colonization abilities of T. testudinum coupled with the changes in sediment composition may prolong the recovery of seagrass meadows directly impacted by Hurricane Harvey.