Resampling 25 years later reveals fewer species but higher abundance of juvenile fishes in a Caribbean mangrove bay

Abstract

<jats:p> The prop roots of mangroves play an important role as habitat for juvenile fishes. Revisit studies (&gt;10 yrs apart) provide rare and valuable insights into the structure and stability of these systems in the face of escalating pressure from coastal development, climate change, and fisheries. We compared assemblages of juvenile fishes in the mangroves of a Caribbean estuary from 1991 to 1993 and 2018 to 2019 using trap collections to quantify changes and identify their potential drivers. Although the environmental and physical properties of the mangrove landscape were similar between the two periods, there were significant changes in many aspects of the fish assemblage. Compared to 25 yrs earlier, overall fish abundance (catch-per-unit-effort) was 3 to 7 times higher but overall biodiversity was 30% lower at the species level and 50% lower at the genus level. Taxa with dramatic changes in CPUE were mojarras (Gerreidae, 84% lower CPUE in 2018–2019), snappers (17 times higher CPUE), puffers (Tetraodontidae, 14 times higher CPUE), and moray eels (&gt;200 times higher CPUE). Traps in 2019 also captured the first documented invasive Indo-Pacific swimming crab (<jats:italic>Charybdis helerii</jats:italic>) in the US Virgin Islands. The observed changes in the fish assemblage may be due to natural variations in recruitment, environmental influences, and/or hurricane disturbance, but for some species likely relate to declines in adult reef fish populations in the region. </jats:p>

Green morays (Gymnothorax funebris) have sedentary ways in mangrove bays, but also ontogenetic forays to reef enclaves

“…Although mangroves and coral reefs are preferred habitats, green morays are not necessarily obligate users as they are occasionally reported off states northward along the US east coast lacking those habitats. Also of note, even younger and smaller eels were never caught in the mangroves in 2 years of trapping (Kendall et al 2021a) despite the mesh size being fine enough to catch them. Perhaps, like many other reef fish species, smaller green morays initially recruit to and reside in seagrass habitats which would provide ideal camouflage for an animal the same general color and appearance as turtlegrass (Thalassia testudinum).…”

“…These eels may have come back as older and larger individuals after the array was decommissioned, however, additional trapping observations suggest that this was unlikely. Eels larger than 99 cm were never caught in the small traps used to capture fish for this study (Kendall et al 2021a) nor were they caught in much larger Antillean fish traps (~ by by 200 cm traps with mesh size 3.8 cm) that were used extensively during biannual sampling throughout these bays as part of a research project in the 2 years prior to this study (Kendall et al 2021b). Only one large moray > 100 cm was ever captured inside the bays using these larger traps and it was next to a ship wreck in the central bay rather than associated with the mangroves (pers.…”

“…On multiple field missions from July to November 2018, green morays were live captured using fish traps deployed along the mangrove fringe in Sugar, Triton, and Bio Bay (Table 1). Trap deployment areas along the mangroves, bait (frozen local herring), and specifications (1.3 cm vinyl-coated wire mesh, 92 × 57 × 19 cm, funnel opening ~ 9 cm diameter) were generally dictated by a long term study of juvenile fishes in the area (Kendall et al 2021a). Most eels were trapped in the bay; the one exception was taken by a larger mesh trap outside the reef crest near receiver 8 (Fig.…”

“…Most individuals were more frequently detected at night than during the day suggesting greater nocturnal activity. Several of the larger eels (mean 2005; Chan 2017; Kendall et al 2021a). Moray eels play a unique role in structuring fish communities in complex habitats due to their characteristic ability to navigate rock crevices, reef holes, mangrove roots, and other three-dimensional structures (Parrish et al 1986;Hixon and Beets 1993;.…”