Tropical Mangroves

Just like seagrasses, mangroves serve several important ecological roles in the coastal environment.  Mangroves provide habitat for juvenile fish (including gamefish) and invertebrates (like spiny lobster) that use the mangrove habitats seasonally, as well as a whole community of fish and invertebrates that spend almost their entire life cycle within the mangrove ecosystem.  Mangroves also filter sediments from land that would otherwise smother seagrasses and corals, they stabilize shorelines against erosion, and they are important players in the nutrient cycle in the coastal environment (for example, mangroves remove nitrogen from land-based runoff that might otherwise contribute to algal blooms).  In short, mangroves are an essential part of a healthy coastal ecosystem.

Overall, the roles of mangroves are the same in the tropics as they are in warm-temperate environments, but since the communities of fish and invertebrates that depend on mangrove habitats in these two regions differ in many ways, I will discuss the ecology of mangroves and their importance to gamefish separately for each climate.  This article will focus on mangroves in the tropics.  Although mangroves occur and serve similar functions in the tropics throughout the world, the variety of organisms is too great to include in a single article, so I will provide specific examples for the area with which I am directly familiar – the Caribbean.  The species of gamefish a fly angler is most likely to encounter in mangrove areas of the Caribbean are gray snapper, barracuda, tarpon, snook (usually fat snook (Centropomus parallelus) on islands and common snook (Centropomus undecimalis) in continental areas), bonefish, permit, and numerous species of jacks.

Worldwide there are dozens of mangrove species, but there are only two species in the Caribbean that are considered essential fish habitat.  The species of mangrove that you will most likely encounter while fishing in the Caribbean, and that is most important as habitat for gamefish and their prey, is the red mangrove, Rhizophora mangle.  Black mangroves, Avicennia germinans, are also ecologically important in coastal environments, but are usually farther inland than red mangroves so are not as frequently encountered by anglers in the Caribbean.  Mangroves are unique in their ability to tolerate sea water due to a variety of special physiological and physical adaptations.  One of the most important adaptations of red mangroves is the support structures that suspend the plants above the water, which are called prop-roots.  These prop-roots provide a complex labyrinth of habitat for fishes, crabs, shrimp, and a host of other organisms. 

In addition, the mangroves are an important part of the food web in coastal environments.  The combination of sediments trapped by the mangrove prop-roots, the continual dropping of leaves from the mangrove trees, and activities of organisms within the mangroves form the center of the food web in mangrove habitats (known as detritus), which is fed upon by fungi and bacteria.  There is also an extensive community of algae, sponges, barnacles, oysters, clams, mussels, and other organisms that grow directly on the prop-roots.  In turn, small organisms, such as shrimp, crabs, worms, and fish feed on the detritus, and are then preyed upon by larger organisms.  The turbid water, the structure of the mangrove prop-roots, and the abundant food combine to make these great habitats for small fish and invertebrates, which in turn attracts larger  predators, including gamefish.

The communities of fish and invertebrates that inhabit mangroves are generally made up of two components: resident species and seasonal species.  Resident species are present throughout the year and are usually the most common species, while seasonal species are present for only a portion of the year and are fewer in number.

There is a core group of resident species that make up the majority of the community.  Organisms that are members of this group are going to be important prey items for gamefish throughout the year, so you should be familiar with these prey species.  Important families of fish in this group include herring (family Clupeidae), silversides (family Atherinidae), anchovies (family Engraulidae), mojarras (family Gerreidae), mullet (family Mugilidae), killifish (family Cyprinodontidae), and gobies (family Gobiidae).

There is a high diversity of invertebrates that are also resident in mangrove habitats, but most important to fly anglers are the mobile species that can be imitated with a fly (as opposed to species that are attached to the prop-roots, such as oysters, or burrow into the sediments, such as many species of worms).  The prey species of invertebrates that a fly angler should focus on when selecting flies include: shrimp – common shrimp (family Penaeidae) and snapping shrimp (family Alpheidae) the most important; crabs – swimming crabs (family Portunidae), especially blue crabs (genus Callinectes), that feed among the prop-roots and surrounding bottom habitats, and flat crabs (family Grapsidae) that live and forage on the prop-roots and in the mangrove trees; and insects – which are an important component of the community that lives above water in mangroves.  This last group, tree-dwelling insects can be an important part of the diet of juvenile tarpon in mangrove estuaries.  This could explain why small poppers, which may imitate insects falling from the mangrove trees, often work so well for these small tarpon.

The second part of the community of fishes and invertebrates found in mangroves is made up of the species that use these habitats on a seasonal basis.  These species are most often represented by juveniles, who use the mangrove habitat as a nursery area.  In the Caribbean, these species are in highest abundance during the summer and fall months, and usually are either absent or in low abundance in other parts of the year.  The more common species include: grunts (family Pomadasyidae) – french grunts (Haemulon flavolineatum) are often the most abundant; snappers (family Lutjanidae) – schoolmaster snapper (Lutjanus apodus) and yellowtail snapper (Ocyurus chrysurus) are most common; parrotfish (family Scaridae) – juveniles often have longitudinal stripes;  squirrelfish (family Holocentridae) – most species are red in color; and jacks (family Carangidae) – most species are similar in shape and coloration to adults. 

The high number of small juveniles of many species is a good seasonal source of food for gamefish, so in addition to selecting flies based on the resident prey species that are most likely present, you may want to have an assortment of sizes of flies to account for these seasonal changes.  (Remember from Part 1 of the series that most juveniles are lost to predation early on, so including flies that imitate small fishes in this vulnerable life stage in your fly selection is a good strategy.)  Many of the species that use seagrass habitats as nursery areas are also found in mangrove habitats in the same seasons (see Part 2 of the series). 

Common invertebrates that can be abundant on a seasonal basis include: lobster – juvenile spiny lobster (Panulirus argus) use the shelter provided by mangrove prop-roots as a nursery; and shrimp – some species of common shrimp use the mangrove prop-roots as a nursery and move into deeper water as they mature.

Numerous studies of mangrove habitats in the Caribbean have revealed that the composition of fish and invertebrate communities varies based on where the mangroves are located (semi-enclosed lagoons, mangroves on shorelines exposed to open sea, mangrove flats, or mangroves along a back-water estuary), what habitats are adjacent to the mangroves (seagrass, sand, or mud), and the depth of the water near the mangroves.  Although there is natural variation even among similar habitats, some generalities can be made about species most likely to be found in these different areas. 

Mangroves adjacent to creeks often have more total species and a greater number of individuals of resident and seasonal species than shallow areas and even seagrass beds.  In part this is because many species will follow the flooding tide into the mangroves to feed on the rich and diverse communities in these intertidal areas and then retreat as the ebbing tide drains from the mangroves.  The creek provides a deep water refuge close to the food source for these species. 

In turn, the greater number of organisms and the behavior of the species that utilize this strategy attract gamefish, which can often be found at the edges of these creeks opportunistically feeding on prey that is washed out of the mangroves with the dropping tide.  The higher tides that are associated with the new and full moons are especially good for fishing the edges of mangrove creeks because the increased amount of water being moved by these strong tides creates stronger currents that forces more prey from the mangrove shallows to the creek.

Areas with seagrass adjacent to the mangroves generally support more species than areas with mud or sand.  Small juvenile fishes prefer locations with seagrass adjacent to mangroves, but as they grow the juveniles often move to areas where open bottom is adjacent to the mangroves because the larger juveniles are able to avoid more predators, the feeding opportunities are better for their changing diets (burrowing worms, crabs, and shrimp often inhabit these habitats), and the shelter of the mangrove prop-roots is nearby as protection from the larger predators.

Mangroves that are exposed to the open ocean are likely to harbor high numbers of  juveniles of seasonal fish species during the summer and fall months, similar to many of the seagrass beds that surround coral reefs (see Part 2 of the series).  In contrast, mangroves that are more removed from the ocean (such as lagoons that are connected to the ocean by only a narrow channel) or are deep within estuaries will be more dominated by the core group of species that are primarily associated with mangrove habitats.

Mangrove lagoons with moderate depths, large areas of open water, and good water clarity often support schools of herrings, silversides, and anchovies that spend a significant portion of their lives in the vicinity of mangroves.  Many times I have watched small barracuda suspended in the shadows among the mangrove prop-roots suddenly dart out and engulf a mouthful of silversides from a school as it passed along the outer edge of the mangroves.  Groups of barjacks (Caranx ruber) and blue runner (Caranx crysos) will often strafe schools of small baitfish in the open water sections of these mangrove lagoons.  And I have seen tarpon herd herring along a mangrove shoreline and take turns rolling open-mouthed through the panicked baitfish.

In addition to the feeding in open water of mangrove lagoons, gamefish can be found among the prop-roots – especially on flooding tides, but these fish are often unreachable with a fly.  The fish that I have found to be most actively feeding and most receptive to a fly are either cruising along the outer edges of the mangroves in search of prey that has strayed too far from the shelter of the mangrove prop-roots or are feeding in the seagrass or mud bottoms adjacent to the mangroves.

There are many species of fish that use the mangrove prop-roots as shelter during the day and then venture out at night to feed in the adjacent open areas of seagrass, sand, or mud.  This is especially common for juvenile grunts of two to five inches.  Grunts will form large schools along the edges of the mangrove prop-roots just prior to dusk, and will venture out into the lagoon feeding areas as darkness falls.  This period, which is from sunset to approximately 30 minutes after sunset, has been termed the ‘quiet period’ because there is little activity relative to the daytime as fishes either retreat to night-time shelter or get ready to venture out under the cover of darkness.  The ‘quiet period’ is somewhat of a misnomer, however, because it is a time of peak predatory activity.  Large mutton snappers (Lutjanus analis) and barracuda (Sphyraena barracuda) will focus on the juvenile grunts that aggregate along the edges of the mangroves, especially as the grunts begin to move out into the adjacent habitats.  If you find a section of mangroves that harbors a large number of grunts during the day, you may want to mark the place on your map and return just prior to dusk.  There are no guarantees, of course, but you may find yourself witness to a flurry of feeding by large predators.  Yellow over white deceivers are suitable imitations of these small grunts.

I’ve ended each article in this series with a statement of the importance of these coastal habitats to our favorite gamefish and the major activities that threaten each habitat.  Unfortunately, the threats to mangroves are extreme and warrant immediate attention.  Like wetlands worldwide, these critically important habitats have declined significantly, and continue to be under stress.  Diversion of fresh water from mangrove areas, filling in of mangrove wetlands for development, cutting of mangroves for wood products, pollution, and global warming are all immediate threats to these habitats and to the communities that depend on them.  Without these fragile habitats many species will not be able to survive, plus we will lose a fantastic habitat for fly fishing.

Sidebar 1 – I have provided the common name and scientific name of many of the species of fish and prey in this article.  I have done this so an angler interested in finding out more about these species can easily do so.  Common names change from place to place: in some locations a single species has a different common name for different life stages because of color changes, while in other locations a few species may all have the same common name.  If you are interested in imitating a particular species with a fly, very often using the scientific name during your search will lead you to the best pictures and descriptions (including size range, colorations, seasonality, and geographic range).  In addition, in many instances I’ve provided the family names for a group of species.  I do this when a particular family of fishes is found in a certain habitat, but where the actual species may vary according to location.  For the most part, species that are members of a family will have similar coloration and body shapes, so can be approximated with a single fly pattern.  For example, the mojarras (family Gerreidae) have a silver coloration, a high vertical body profile, and often have a touch of yellow on their ventral side.  Books that will provide basic information for most of these species and pictures for many are: Peterson Field Guides: Atlantic Coast Fishes, by Robins, Ray, and Douglas.  Published by Houghton Mifflin; and The Audubon Society Field Guide to North American Seashore Creatures, by Meinkoth. Published by Alfred A. Knopf.

Sidebar 2 – Fishing around mangroves requires caution for two reasons.  First, because the roots of mangroves trap sediments and dampen currents, the bottom in and around mangroves can be rather soft.  Of course, this is not always the case (there are some great hard-bottomed wading opportunities along mangrove shorelines), but this is something an angler should take into consideration when fishing an area for the first time.  Wade with caution!  Second, because mangroves provide protection from wind and are home to many insects, be sure to take along your bug repellant.  The mosquitos and gnats (no-see-ums) can be brutal, and can end an otherwise productive day of fishing.

Sidebar 3 – Although there are often large fish along mangrove shorelines and in mangrove lagoons, I have found that most of the fish associated with mangroves in the Caribbean are in the medium to small size classes.  Since the wind is usually not a problem in the protected lagoons, the flies are often small, and the fish are generally not very large, I will often use a 6-weight fly rod.  Of course, if I am in a boat I always have a heavier rod rigged in case larger fish make an appearance, but a 6-weight rod makes for good sport.