The Trophic Role of the Endangered Caribbean Manatee Trichechus manatus in an Estuary with low Abundance of Seagrass

Abstract

Chetumal Bay is a refuge for the manatee, Trichechus manatus, a large and strictly herbivorous aquatic mammal. The ecosystem is notoriously poor in subaquatic vegetation, the main components of manatees' diet. Due to the constant presence of manatees in the bay and their ability to consume large volumes of plant material, it is assumed that the species has a relevant trophic impact on the system. A mass-balance trophic model was designed to describe the flows of energy and matter in the bay, with the goal of assessing the role of manatees in the system. The system was aggregated in eight effective trophic levels. The biomass was intensely concentrated in the detritus, suggesting that the matter on the bottom sediment is the main regulator of the energy flow in the system. Primary producers comprised of detritus, mangrove, benthic autotrophs, and phytoplankton. The apex predators were dolphins and large piscivorous fishes. Manatees occupied the trophic level 2.0. Manatees were directly or indirectly impacted by autotrophs, mangrove, and detritus; but the competition between manatees and other groups was insignificant. In comparison to other ecosystems where manatees occur, Chetumal Bay (BCh) has the lowest relative biomass of seagrasses. Several ecological and behavioral mechanisms to compensate the lack of macrophytes biomass (or a combination of several) are suggested.Ecopath with Ecosim models are useful to describe the flow of energy and matter in the ecosystems. However, there are still critical gaps in the knowledge of BCh and its manatee population. It is difficult to assess the uncertainty associated with the estimates obtained; therefore, results should be interpreted with caution. Improving this preliminary model with robust local information on the Chetumal Bay ecology and its manatee population is recommended.

Using Pooled Local Expert Opinions (PLEO) to Discern Patterns in Sightings of Live and Dead Manatees (Trichechus senegalensis, Link 1785) in Lower Sanaga Basin, Cameroon

“…However, for females with dependent calves, three factors are of critical importance: low ambient noise, to enable auditory contact between mothers and calves; absence of currents, to ease the movement of mother-calf pairs; and increased foraging requirements, due to the increase of metabolism associated with nursing a calf [ 65 ]. Manatees are large, opportunistic herbivores that require a high biomass of aquatic macrophytes to sustain their nutritional needs [ 1 , 6 , 9 , 66 ], notwithstanding the occasional carnivory [ 67 – 68 ]. Therefore, it can be reasonably conjectured that manatees would shift to the consumption of mangrove (and perhaps detritus) materials when the ecosystem is poor, i.e.…”

“…Therefore, it can be reasonably conjectured that manatees would shift to the consumption of mangrove (and perhaps detritus) materials when the ecosystem is poor, i.e. has a low biomass of primary producers: detritus, mangroves, aquatic autotrophs, and phytoplankton [ 66 ] or, alternatively, when forage amount and quality decline in the late dry season. In either case, efforts are needed to curb the high rate at which the mangroves of West-Central Africa are currently vanishing, i.e.…”

The Seagrass Holobiont and Its Microbiome

“…Manatees, dugongs, green sea turtles and geese use living seagrass leaves directly as a food source, despite unfavorably high C:N ratios and high cellulose levels [ 18 , 36 , 40 ]. Manatees can consume 30–55 kg of seagrass daily [ 41 , 42 ], dugongs can eat between 28 and 40 kg, and sea turtles can eat up to 2 kg of seagrass per day [ 36 ]. Crustaceans and snails also occasionally consume seagrass leaves [ 36 ].…”

Osteological Associations With Unique Tooth Development in Manatees (Trichechidae, Sirenia): A Detailed Look at Modern Trichechus and a Review of the Fossil Record

“…This is especially evident in the portions of the early western Amazon Basin's paleo‐Orinoco River in the area now within the borders of Peru, Venezuela, and Colombia (Hoorn, 2006). This may have not only enabled populations of marine seacows to get into the shallows of the Amazon Basin and eventually evolve into trichechines, but growing evidence shows that plants came and went with these transgressions, including mangroves (Hoorn, 2006), which form a common habitat for manatees today (Castelblanco‐Martínez et al, 2011). The uncertainty about whether the spread of phytolith sources in South America tracked the spread of C4 grasses, coupled with the increased sources of siliclastic sediment exposure at the time of the evolution of trichechines in South America, make it difficult to know which factor had the greatest influence on the evolution of this unusual tooth replacement system.…”