Bonaire's Lac Bay: Mangroves & Reef Fish Nurseries

On a guided snorkel at Lac Bay, look into the gaps between submerged mangrove roots before swimming past the edge. Small fish tucked among those roots and others moving through the seagrass offer a view of reef life at a size you may have missed on Bonaire’s dive sites.

Follow the change in cover: roots, grass, then open reef. Research on Bonaire found different juvenile fishes concentrated in different parts of that sequence. A schoolmaster snapper and a yellowtail snapper did not simply use the same nursery. Learning where to look for each turns a shallow snorkel into a way of reading the reef’s earlier life stages. 1

What the roots provide beneath the surface

From the water, submerged red-mangrove roots form a maze of uprights, arches, and shaded gaps. Small fish can slip between them; growth attached to the roots adds more surfaces and food. At the edge of the seagrass, the arrangement changes to blades with spaces between them and sediment below. Compare where a fish pauses in each habitat: close to solid cover, between leaves, or out in open water. 2

Stay outside the root tangle and let the fish move. A school that vanishes when you approach can reappear as separate individuals once you stop. Notice their sizes and the distance they keep from cover. Those details make a more revealing nursery observation than a photograph that records only a large number of fish.

The nursery connection runs beyond the small fish in your frame. What matters is whether this habitat helps juveniles survive and later contribute to adult populations. Researchers use evidence about size, habitat use, survival, and movement to investigate that connection. A resting school gives a visitor the first clue; it does not reveal where each fish hatched or where it will eventually live.

Red mangrove roots extending into coastal water in Florida — Red mangrove roots in Florida illustrate the root architecture discussed here. This comparison photograph was not taken at Lac Bay.
Photo: Steve Hillebrand / U.S. Fish and Wildlife Service. Image source · Public domain (photographer rights release / USFWS source). Resized and converted to WebP. Index thumbnails use a display crop. Image remains under the stated license.

Schoolmasters at the roots, yellowtails over the grass

Use the habitat edge to organize your search. In a 2000 Bonaire study, Ivan Nagelkerken and colleagues compared sixteen selected fish species across mangrove prop roots, turtle-grass beds, and four reef-depth zones extending to twenty meters. Recording fish sizes as well as numbers let them distinguish the small fish using the shallows from larger animals on the reef. 1

Juvenile schoolmaster snappers favored mangroves in those comparisons; yellowtail snappers and stoplight parrotfish favored seagrass. Several other juveniles favored shallow reef habitat, and young Atlantic blue tangs occurred in all six habitat categories. So watch the roots for one kind of juvenile, then deliberately shift your attention to the grass instead of expecting the same group to occupy both. 1

Ask your guide to help separate species and sizes, then compare them with the larger fish on your next reef dive. The historical survey gives you a search question, rather than a current roll call for every channel. If the expected juveniles are not visible on your visit, record the habitat and what you do see; a single snorkel samples only a small part of the bay.

A juvenile schoolmaster snapper photographed off western Bonaire — A juvenile schoolmaster snapper, Lutjanus apodus, photographed off western Bonaire. The photograph illustrates the species and life stage; it was not taken in Lac Bay.
Photo: Paul Asman and Jill Lenoble. Image source · CC BY 2.0. Resized and converted to WebP. Index thumbnails use a display crop. Image remains under the stated license.

The reef connection extends beyond the bay

A separate Caribbean study led by Peter Mumby found that mangrove connections were associated with substantial differences in fish communities on neighboring reefs. Several commercially important species had more than twice the biomass where adult habitat connected to mangroves. The work also highlighted a close dependence of rainbow parrotfish on mangrove habitat. Those findings came from that study’s Caribbean sites, not a measurement of today’s fish biomass at Lac Bay. 3

Picture an adult fish cruising along the reef edge, then the smaller fish sheltered back among roots. Protecting only the adult’s visible feeding ground can miss habitat used earlier in life. That is the practical force of the nursery research: the route between habitats can matter as much as either endpoint.

This also changes the meaning of a species map. A marker on a reef shows a documented occurrence. It cannot reconstruct the fish’s route from juvenile habitat to that point. Reading habitat alongside location helps you ask a better question: which nearby environments could support different parts of this species’ life?

A green meadow can change without disappearing

Seagrass is not one interchangeable green covering. Research in Lac Bay documented the expansion of the non-native Halophila stipulacea after its establishment there in 2010. The plant spread through clonal growth, and detached fragments could remain viable and root again. In the study, tethered fragments began producing roots and leaves within ten days. 4

From the surface, two meadows may both look green. Put your face in the water and compare the leaves, the height of the growth, and how much open sediment lies between plants. The expansion study raised questions about how a changed meadow affects sediment and habitat functions. Those effects require measurement, but the changed structure is something an attentive snorkeler can begin to notice. 4

For an observer, the useful habit is to notice what makes up the meadow. Broad or narrow leaves, plant height, exposed sediment, and the animals using it provide more information than the label seagrass alone. Avoid pulling plants to inspect them; a photograph can preserve the detail without disturbing the bottom.

Turtle grass at Grahams Harbour, San Salvador Island, Bahamas — Turtle grass, Thalassia testudinum, at Grahams Harbour in the Bahamas. This comparison image shows a Caribbean seagrass habitat, not the Halophila invasion studied in Lac Bay.
Photo: Jstuby. Image source · Public domain (released by the photographer). Resized and converted to WebP. Index thumbnails use a display crop. Image remains under the stated license.

Why restoring water movement matters

Look along a mangrove channel and the opening through the trees becomes part of the habitat. Water must move around and between the roots. A 2025 Bonaire report describes poor circulation and high salinity in backwater areas where mangroves had been lost. A stand of trees can therefore be affected by what happens to water passage beyond the small patch you are viewing. 5

Local restoration work by Internos and the Mangrove Maniacs includes reopening channels and planting in selected areas. A newly cleared passage is visible work; whether nearby trees survive and habitat recovers must be followed over time. If your guide points out a restoration channel, look at the water route it reconnects as well as the seedlings beside it. 6

For the reef story, this is the connection worth carrying away: land-derived sediment, channel condition, tree health, juvenile fish habitat, and adult reef communities can form parts of the same coastal system. The reef does not end at the waterline in the way a postcard frame suggests.

Watch the nursery without stirring it up

Use a guided route into the mangroves and confirm the permitted snorkeling area and equipment with your operator. Mangrove Center’s kayak-and-snorkel tours use designated stops with guides. Follow their instructions about fins and footwear rather than assuming ordinary reef-snorkeling equipment suits every shallow channel. 7 8

Where snorkeling is permitted, float clear of the bottom and keep hands, feet, and equipment away from roots and vegetation. Do not stand in the meadow or pull yourself through the roots. If your movements raise sediment, stop and give it space to settle instead of chasing the fish through the cloud. A clear, undisturbed view is better for both the nursery and the observation.

Open the Bonaire map, then read about yellowtail snapper, stoplight parrotfish, or the Atlantic blue tang. Each offers a different way to follow the same question from the bay to the reef: where does this animal find what it needs as it grows?

Sources & further reading

Nagelkerken and colleagues (2000), Importance of mangroves, seagrass beds and the shallow coral reef as a nursery for important coral reef fishes — Estuarine, Coastal and Shelf Science 51, 31–44; Bonaire visual censuses.
Nagelkerken and colleagues (2008), The habitat function of mangroves for terrestrial and marine fauna: a review — Aquatic Botany 89, 155–185; habitat structure and connections.
Mumby and colleagues (2004), Mangroves enhance the biomass of coral reef fish communities in the Caribbean — Nature 427, 533–536; wider Caribbean evidence, distinct from the Bonaire census.
Expansion and fragment settlement of the non-native seagrass Halophila stipulacea in a Caribbean bay (2017) — Marine Biology Research; observations and experiments in Lac Bay.
Conservation state of the mangrove forests of Bonaire, Caribbean Netherlands (2025) — Research report addressing mangrove condition and water circulation.
Bonaire Naturalesa — Mangrove restoration at Lac Bay — Account of the local restoration project.
STINAPA — Lac Bay and marine park visitor guidance — The protected bay, its habitats, and links to current park guidance.
Mangrove Center Bonaire — Guided kayak and snorkel tours — Operator information about guided routes and snorkeling stops; confirm current equipment instructions before visiting.

Bonaire’s reef begins in the mangroves: the hidden nurseries of Lac Bay