On the dry part of the shoreline, take a sand sample. Place it into your plastic collecting container. Be sure to label it with the location and the date. You can look at the particles in the field with your hand lens. When you get back to the classroom, you can examine the sample more closely.
If you see vegetation along the shoreline, but emerged from the water, you may encounter mangroves or marsh plants. Sarasota Bay is near the northern end of the range for mangroves. We have three that are common in our area: black mangrove (Avicennia germinans), white mangrove (Laguncularia racemosa) and red mangrove (Rhizophora mangle). Another tree often associated with mangrove community is the buttonwood (Conocarpus erectus). Though the classical model of the mangrove forest places the red mangrove the most seaward and the buttonwood the most terrestrial, it is evident that all of the different mangrove species can co-occur at the same water/land level. The black mangrove can be easily identified by the pneumatophores (aerial roots) that occur around its base. These roots allow the tree to increase gas exchange. The white mangrove has leaves that are typically thickened and may feel rubbery. The leaves are generally rounded. There are salt glands on the surface of the leaves, so you will find salt crystals common near the base of the leaves. The red mangrove has what are known as prop or drop roots. If the roots come from the trunk they are called prop roots and if they come from branches, they are called drop roots. Gastropods can be found commonly on the roots of mangroves. The coffee bean snail (Melampus coffeus) occurs in great numbers on the roots. In addition, we are at the northern range of the mangrove tree crab (Aratus pisonii). These crabs have long legs and sometimes are mistaken for spiders. We are at the northern end of the range for these tree crabs. If you find some on the baywalk, take a few minutes to observe their behaviors. If the tide is low, they may be down on the roots or even on the sand feeding. If the tide is high, they generally move along the tree trunk and canopy relative to their sizes. [teacher note: these crabs can be kept easily in the lab, but they are very hard to catch in the field.]
Often, it is difficult to find the actual trunk of the mangrove tree because the prop roots are so numerous. Determining tree size of a single individual can be challenging as the roots of several individuals come together in dense forest areas. Their propagules (seedlings) develop directly on the tree and drop off when mature (they do not have seeds like other flowering plants; can you think of why this might be of advantage for the tree?). These seedlings float around until they come to an area where the end can begin to set down roots. The propagule is “weighted” so that the end that will grow roots is always pointed downward. [teacher note: Mangroves are now being used in refugia (living filters) of large aquarium systems to uptake nitrogen and other waste products from animals. If you are talking to students about recreating captured environments, this is a good place to ask them about the function of the mangrove in this shoreline system.] The buttonwood tree generally is found in drier areas; it is sometimes used as an ornamental tree in landscaping. Like the white mangrove, it has distinctive salt glands. However, its glands are found on the underside of the leaves, near the middle.
Along the shoreline, you may also see Spartina alterniflora. This is a type of grass that is usually found in saline or brackish waters of the Atlantic and Gulf coasts and is native to the area. It is of great value to stabilize sediment in areas and provides habitat for shore dwelling organisms. Because of the tremendous growth rate of the plant, it also contributes to the detritus (decaying material) that is important to the health of the nearshore ecosystem. Take a sample of the sediment from the grass area. Is it different from the sand on the shoreline? Look at it with the hand lens. In Florida, its growth along creeks also promotes its use as food for grazing cattle. [teacher note: This type of grass is also considered a non-native invader for the US west coast. This could be a nice place to talk to students about how organisms in the wrong system can be harmful. There are many invaders in Florida. This is also a nice webquest project. You can find a general guide to a scavenger hunt prepared for a beach field trip here; this is a good exercise for younger students especially and can be easily adapted for a short field trip. Because the soils in this area typically have high clay content and they have high activities of micro-organisms, they are excellent to use in creating mud cloth. See the activities at the end of the baywalk to learn how to do this.]
Next: Shoreline animals