The Friends of the Charlotte Harbor Aquatic Preserves (FCHAP) is a Citizen Support Organization for the Charlotte Harbor Aquatic Preserves and the Charlotte Harbor Preserve State Park.
Critical Habitat for Small-tooth Sawfish
Juvenile small-tooth sawfish, born in April and May, use shallow habitats with a lot of vegetation, such as mangrove forests, as important nursery areas. Loss of mangrove fringe reduces habitat for the juvenile sawfish and harms this critically endangered species. Humans are the main cause of mangrove loss and thus the pressure on the small-tooth sawfish.
The pups were born live, with the eggs held inside the female's body until hatched. The young emerge from the female ready to swim. The pups have a sheath that covers their fully formed-sawtooth denticles so that they don't damage the female. Their mouth is lined with small, dome-shaped teeth for eating small fish and crustaceans; sometimes the fish swallows them whole. Sawfishes are nocturnal, usually sleeping during the day and hunting at night. As cousins to rays (not sharks), small-tooth sawfish breathe with two spiracles just behind the eyes that draw water to the gills and expel water from their lower surface.
Juvenile Shrimp Now in the Estuary
The pink shrimp, Farfantepenaeus duorarum, belongs to the order Decapoda, with crayfishes, lobsters, and crabs. They have ten legs and a well-developed carapace. Pink shrimp (with white and brown varieties found elsewhere in the Gulf) are an important commercial catch while others such as grass shrimp are important to estuary food chain.
Pink shrimp spawn on the outer continental shelf near the Dry Tortugas and migrate as postlarvae to nursery grounds in Florida Bay and southwest Florida estuaries. They spend the summer and early fall in the estuary nursery to growing from juveniles to adults. In the Fall, the shrimp migrate back to their spawning grounds to produce a new generation of shrimp and support a multimillion dollar fishing industry. Shrimp can be considered an annual crop, since adults do not usually live more than 24 months.
The larval shrimp in the Gulf pass through various stage, one called a nauplius, at left, only 1/10 of one millimeter in size. The ten legs are already visible. After the larvae develop into a form that begins to appear like a shrimp, the juvenile animals begin to move into our estuary.
The stream of incoming postlarvae into Southwest Florida estuaries is strongly seasonal. The postlarvae arrive on the flood tides of spring and early summer. They grow through their juvenile stage in summer, consuming phytoplankton, benthic algae, and organic debris. Mangrove forests and seagrass meadows are ideal habitat for food supply and refuge from predation. Juveniles prefer mildly brackish waters but may be found along the entire estuary salinity gradient.
Post-larval shrimps ride the night flood tide into the estuaries. During a new moon, the majority of postlarvae coincide with the highest current speeds. However, during a full moon, postlarvae appear to prefer the second half of the flood period near the slack tide. Peak postlarval concentrations suggest peak postlarval transport in the July-September; the annual cycle of night length might be responsible for the strong summer signal. Juveniles emigrate back into the Gulf in the fall in a behavior and migratory pattern opposite to that of postlarvae. Juvenile pink shrimp were found almost exclusively near the surface on the ebb tide, preferring to move when there is no moonlight.
Researchers investigated if the density of juvenile pink shrimp in the estuary was due to habitat conditions (e.g., salinity and patchy seagrass) or to restrictions to the supply of postlarvae coming from offshore spawning grounds. They suggested that the production of juvenile pink shrimp could be increased if salinity conditions were improved. That implies a sufficient flow of fresh water into the estuary early in the rainy season.
Pink Gold – the Florida Pink Shrimp – depends on the health of our estuaries – our mangroves and our seagrass beds.
The Autumnal Equinox
This astronomical event – the equal day and night in the Fall – usually gets overshadowed by football games and the new school schedule. The equinox occurs the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth's equator – from north to south. The Earth's axis is always tilted at an angle of about 23.5°, causing our seasons as we revolve around the Sun. On the equinox, the Earth's axis tilts neither away from nor towards the Sun but is perpendicular to the Sun's rays. In 2014, the equinox is Monday, September 22, 2014 at 10:29 PM EDT, to be precise.
So who cares? Plants and animals do! The day length, called photoperiod, is more noticeable in the northern states, where shorter days are thought to trigger migration in some bird species. For example, ducks migrating to Florida seem to experience hormonal changes related to day length. Monarch butterflies begin their migration towards Mexico shortly after the equinox. Pink shrimp juveniles leave the brackish estuaries for the open Gulf shortly after the equinox. Commercially important plants like Poinsettia and chrysanthemum determine when to flower as the photoperiod shortens.