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Puerto Rico Cruise Day 9
Habitats
To date, we have conducted fish surveys on a variety of habitats. In addition to fish distributions on the reef and in the mangroves themselves, we are examining fish utilization of vegetated substrates (seagrass and algae) adjacent to mangrove and reef areas.
Seagrasses
Syringodium seagrass meadow
Photo: Giuseppe Di Carlo
The coastal waters of Puerto Rico are home to a number of seagrass species, including
- Thalassia testudinum (turtle grass),
- Syringodium filiforme (manatee grass),
- Halodule wrightii (shoal grass), and
- Halophila decipiens (paddle grass).
Yes, turtles do eat turtle grass and manatees do eat manatee grass! Manatees will
feed on any vegetation present in an area, including other seagrasses and
algae. Manatees are very destructive during foraging (see Day 7 photo of
manatee grazed area), bull-dozing through an area and removing not only green
blades and stalks, but also below-ground root material. You can see how this
behavior has the capacity to alter the marine landscape. Turtles are a bit
more refined in their eating habits. Turtles crop seagrass blades at the
base of the shoot leaving behind a meadow that looks as if someone ran over
it with a lawn mower! It is easier for a seagrass meadow to recover from
turtle grazing than from manatee grazing. The undisturbed root and rhizome
system stores nourishment to aid new blade production. We have observed a
number of turtle-grazed meadows during our surveys.
Mangroves
Photo: John Burke
Mangroves are salt tolerant flowering trees that grow along sheltered coasts on muddy bottoms. Mangroves may also form islands in the tidal regions of shallow lagoons and estuaries. Mangrove trees are supported by dense prop roots that curve outward and downward from the base of the tree and extend several meters down into the substrate. The submerged prop roots often support a dense community of algae in addition to sponges and other small colonial invertebrates.
Algae
The algae fields that we have encountered have been primarily dominated by three species of green algae,
- Udotea flabellum (mermaid’s fan),
- Penicilus capitatus (mermaid’s shaving brush), and
- Halimeda incrassata (three-finger leaf alga).
These three species of green algae are stalked and calcified, producing a rigid and erect plant. It is common to find these species mixed in with seagrass.
Photo by John Burke
We have found several species of green alga of the genus Caulerpa mixed in with seagrass, These algae are composed of upright fronds connected by a runner.
The two most common species of Caulerpa we have encountered were:
- C. sertularoides
- C. cupressoides
although we have also spotted C. prolifera and C. mexicana on occasion.
Photo: John Burke
At one of our sites, a brown algae, Lobophora variegata was found in high densities amongst a predominantly Syringodium seagrass meadow.
Reefs
Photo: Amy V. Uhrin
Padina boergesenii is a brown algae that attaches to rocky substrates in most reef environments. Perhaps the most notable feature on this species is the concentrically banded blades. P. boergesenii is quite common at our reef sites. The majority of our reef sites have been low relief, mixed reefs where the seafloor is colonized by small stony corals, gorgonians, sponges, and algae.
Photo: Kevin Kirsch
Stony corals secrete a hard calcium carbonate skeleton, forming the basic building blocks of tropical coral reefs. The lobed star coral, Montastraea annularis, grows in long, thick, clustered columns with dome-like tops. This species is a common reef-building species.
Photo: Mike Judge