A regular Source column, Undercurrents explores issues, ideas and events developing beneath the surface in the Virgin Islands community.
As if the lionfish weren’t enough to worry about, now we have to be concerned with another invasive marine species – Halophila stipulacea.
This one isn’t a fish, or a crustacean, not even a coral. It’s sea grass. And it’s spreading rapidly in the waters around St. John and St. Thomas.
Consequences are decidedly unknown. Researchers are just beginning to study it. They don’t know yet whether it will choke out native sea grasses or peacefully coexist. They don’t know whether it will result in an increase of some fish populations or a decrease or if it will maintain the status quo.
They don’t know whether it will have sudden dramatic effects or settle in with little notice and cause subtle changes perceptible only in the long-term.
But they do think it’s worth looking at because sea grass is basic to any marine ecosystem. It provides shelter, foraging sites, spawning habitat and nurseries for thousands of marine species.
The Virgin Islands Experimental Program to Stimulate Competitive Research (VI-EPSCoR) is sponsoring research on H. stipulacea through the University of the Virgin Islands. Recognized international sea grass expert Sandy Wyllie-Echeverria is one of the researchers involved and said it is far too early to discuss anything about the V.I. study since it is barely in the preliminary stages.
Wyllie-Echeverria is coauthor of a paper outlining the importance of sea grass, discussing threats to it, and noting “the global trend of local extinction, fragmentation and general degradation of the seagrass biome.”
Other authors of “Seagrass Conservation Biology: An Interdisciplinary Science for Protection of the Seagrass Biome” are W. Judson Kenworthy, Robert C. Coles, Gérard Pergent and Christine Pergent-Martini.
The introduction of alien species is listed in the paper as one of the threats to sea grass. Others are overexploitation of natural resources, the physical alteration of habitat and substrate, nutrient and sediment pollution, and global climate change.
As referenced in the paper, H. stipulacea migrated from the Red Sea to the Mediterranean some time after the opening of the Suez Canal (in 1869.) Another sea grass species, Zostera japonica, showed up in the Pacific Northwest in 1952 and quickly spread to British Columbia, Canada, California and Washington state.
Researchers believe it came in either as seeds or fragments of vegetation in oyster crates or in ballast water. H. stipulacea may also have hitched a ride on vessels traveling between the Red Sea and the Mediterranean, although there is no scientific proof.
And how it made its way to the Caribbean is equally uncertain. But V.I. resource management experts have been seeing it for several years.
Caroline Rogers, a marine scientist with the U.S. Geological Survey in its Southeast Ecological Science Center Caribbean field Station on St. John, sounded the alarm two years ago, though it was heard mostly only by her peers. Having spent most of her life and career on St. John and in the seas surrounding it, Rogers couldn’t miss the intruder.
She was the principal author of a very short paper published in the “Write back” section of the scientific journal “Frontiers in Ecology and the Environment in 2014 titled “Rapidly Spreading Seagrass Invades the Caribbean with Unknown Consequences.”
On Monday, Rogers said H. stipulacea has continued to spread and is now in most of St. John’s bays. It’s also in some St. Thomas waters but she said she is not aware of it being near St. Croix.
The nonnative species may or may not replace native sea grasses. In the 2014 paper, Rogers said H. stipulacea’s impact on native sea grasses in the Mediterranean has been “minimal to absent” because it grows at a different depth and in a different type of medium than the native sea grass. In contrast, in the Pacific Northwest, the only other known invasive sea grass, Zostera japonica, has displaced native sea grass in some areas.
“Biodiversity, connectivity of marine ecosystems and recovery of degraded coral reefs could all be affected (by H. stipulacea),” Rogers wrote. But she also said, “without additional research, the ecological ramifications of this invasion are difficult to predict.”
