Times of the Islands Summer 2020

green pages newsletter of the department of environment & coastal resources
This close-up of Sargassum clearly shows the small gas bladders that help it float along the ocean’s surface.
Since their introduction to the Western hemisphere,
populations of invasive red lionfish (P. volitans) and the
common lionfish (P. miles) have sailed the Gulf Stream
north from Florida, reaching as far as New York and
Bermuda before exploding through the Caribbean and as
far south as Brazil. These two species in particular are
difficult to tell apart and may even breed to form hybrids.
Lionfish are ruthless pirates without a shed of mercy
for their captives. They exhibit a wide range of prey from
small fish to invertebrates, eating and competing with
native fish. Lionfish have been shown to consume as many
as 42 different species, including commercially important
species of grouper as well as species of herbivores, like
parrotfish, responsible for keeping reefs healthy and free
of excess algae. Their stomachs can expand up to 30
times normal volume, and with no natural predators in
their invasive range, lionfish can reproduce without limitations.
Joining the ranks of the lionfish is the lesser-known
Sargassum, a plant-like macroalgae commonly referred
to as a seaweed. Instead of growing in the ground, it
grows small gas bladders to help it float along at the
ocean’s surface where it can monopolize sunlight for
photosynthesis. Individuals stick together like Velcro to
form large aggregations, or mats. While these mats can
grow wide spatially and cover a significant surface area,
they can also be very dense, capturing other floating
trash, organisms and debris in their path.
Under normal circumstances, these aggregations
are considered extremely important habitats, rich in biodiversity
and necessary to support fisheries. However,
Sargassum influxes started increasing in 2011, with
2018 being the most extreme year on record. Surface
coverage was triple the average of the previous seven
years. Blooms negatively impacted coastal regions from
the Caribbean to the west coast of Africa, wreaking havoc
by smothering both seagrass beds and coastal tourism.
If seagrasses are robbed of essential sunlight, they
can’t photosynthesize, and their ability to support the
islands through sediment stabilization, carbon sequestration
and protection for juvenile fish is compromised. Eight
of the ten most abundantly caught fish species on South
Times of the Islands Summer 2020 55