Boring crustaceans shape the land–sea interface in brackish Caribbean mangroves

Abstract

Abstract. Consumer effects on the structure and extent of habitat-forming foundation species such as trees and coral reefs are well known, but the role of non-consumer interactions is less studied. Red mangroves are major foundation species at the land-sea interface, creating critical habitat in the tropics and subtropics. The complex aerial roots of mangroves (Rhizophora mangle) provide structural support to the tree and support diverse marine biota including boring isopods (Sphaeroma terebrans). These isopods frequently bore into root tips of mangroves causing atrophy, which can alter the structure and extent of mangrove habitat. We conducted a large-scale isopod exclusion experiment across 18° of latitude at eight locations from Panama to Florida to test how isopods affect mangrove root structure and anchorage across a broad geographic range. We hypothesized that excluding isopods would increase root growth rates, morphological complexity, and anchorage compared to roots exposed to isopods. After one year, mangrove roots protected from boring isopods with cages increased growth by 2.5-19 times and exhibited a more complex morphology compared to uncaged controls. Further, 15% of caged roots became anchored in the sediment compared to none of the uncaged isopod-inhabited roots. This suggests that these isopods, which are native to the Indo-Pacific, are a major, widespread structuring agent of mangrove root habitat in the Caribbean and Florida, potentially limiting mangrove encroachment into estuarine waters.

Introduced mangroves escape damage from marine and terrestrial enemies

“…These values were within the lower range of other studies in Florida, Belize, and Panama (Farnsworth & Ellison, 1991; Feller, 1995; Feller et al, 2013), but even modest herbivory damage can influence tree and seedling performance (Ellison & Farnsworth, 1993; Whittaker & Warrington, 1985). Likewise, boring isopods, found in 95% of roots, reduce root growth rates, cause root mortality (Davidson et al, 2016), and are negatively correlated with performance and fecundity (Davidson et al, 2014). Galls and cankers were observed in half of our native sites and can cause seedling, root, and stem death, and occasionally kill entire trees (Rossi et al, 2020; Tattar et al, 1994; Wier et al, 2000).…”

“…Ultimately, field experiments were limited to eight introduced and eight native sites in 2015. Relatively similar sites were selected in the native and introduced range based on preliminary surveys and previous studies (Davidson et al, 2016), accessibility by kayak, boat, or walking, and logistical constraints. We defined sites as approximately 500 m sections of estuarine red mangrove shoreline that (1) were within an estuarine lagoon, river, or sheltered/semi‐enclosed embayment, (2) harbored established and healthy populations of red mangroves, and (3) exhibited relatively similar environmental characteristics (Appendix S1: Table S1).…”

“…can destroy apical buds (Feller, 1995). Terrestrial insect borers kill entire branches causing a 38%–46% loss of mangrove canopy (Feller, 2002; Feller & Mathis, 1997), while boring by marine isopods can reduce growth or destroy submerged R. mangle roots (Davidson et al, 2016). The viviparous propagules of mangroves are a particularly vulnerable life stage and susceptible to attack by numerous insects, crustaceans, and mammals that attack them while they are developing on the tree (Farnsworth & Ellison, 1997), while dispersing (Smith et al, 1989), and after they have established (Sousa et al, 2003).…”

Factors that affect migratory Western Atlantic red knots (Calidris canutus rufa) and their prey during spring staging on Virginia’s barrier islands

“…Some prey, like blue mussels, require a substrate (e.g., peat) on which to attach [113]. Other prey that do not attach to the substrate may prefer to live in peat to more easily hide from predators in dense vegetation and/or because they consume various decaying plant and animal material found in the peat banks [114][115][116][117]. In contrast, coquina clam density was higher in sand than in peat.…”

Historical baselines in marine bioinvasions: Implications for policy and management

“…The isopod S . terebrans was transported by ships prior to the 1860s from the Indian Ocean to the Western Atlantic, where it altered the mangrove forest communities over a vast area, and yet their remarkable ecological consequences have been rarely noted [ 352 ]. The bryozoan Amathia verticillata (“zoobotryon”) occurs worldwide in tropical and warm-temperate waters, mostly in ports and marinas, or anthropogenically altered areas such as shellfish farming bays and lagoons [ 353 ].…”