Habitat Loss: Faunal Community

Few studies have directly investigated the effects of mangrove deforestation on fish assemblages, but when they have, they reported that species richness and relative abundances were higher at mangrove sites than at deforested sites, and that community structure was different between natural and modified habitats.  Even a partial clearing of mangroves along the shore can affect community structure.  Since 2005, construction of a large resort has encroached into the North Sound, where approximately 39% of the mangrove wetlands was cleared and filled.  The objective of this study was to investigate the effects of anthropogenic habitat loss on mangrove-associated taxa within a lemon shark nursery. 

1. Do taxonomic composition, abundance and biomass differ between disturbed and intact nurseries over time?

2. Do taxonomic abundance and biomass differ between deforested and intact sides of the disturbed nursery over time?

3. Are there differences between disturbed and intact habitats in mangrove-associated taxa that are the preferred juvenile lemon shark prey? 

Despite their well-documented importance, mangroves worldwide are being lost due to development.  In the past few decades, an estimated 30-50% of global mangrove forests have been destroyed.  Almost 40% of the North Sound’s mangrove shoreline was deforested, and after this disturbance, there were significant changes in the marine faunal community within the nursery.  We have learned that despite the development, juvenile lemon sharks remain in the nursery.  Therefore, they are bound to a system in which there have been significant declines in their most important prey, the mojarra.  These changes could potentially have negative effects on their growth and survival.  As one of the top predators within the system, lemon sharks are an important indicator of overall ecosystem health.  The importance of Bimini’s lagoons as essential fish habitat in a nursery capacity should be weighed against future development plans.

Many studies investigating the effects of environmental disturbances lack data prior to the disturbance and must compare affected areas to similar intact areas.  In Bimini, a pre-disturbance community assemblage dataset exists for both a disturbed area (North Sound) and a nearby control (South Bimini) with which to compare data collected after the disturbance. Therefore, this study was a unique opportunity to quantify actual changes in an anthropogenically altered habitat.  A total of 131 seines was pulled between 2009 and 2001, and these data were compared to 550 pre-disturbance seines (2000-2003). 

1. Do taxonomic composition, abundance and biomass differ between disturbed and intact nurseries over time?

Yes.  The two nurseries (disturbed North Sound and intact South Bimini) are quite different from each other both before and after the disturbance.  However, the changes that occurred over time within each nursery were very different in both direction and magnitude.  In South Bimini, a few taxa declined in abundance, but most actually increased.  In the disturbed North Sound, however, many fish families decreased by large orders of magnitude in terms of both abundance and biomass.  In addition, overall community composition changed after the disturbance in the North Sound in terms of richness, diversity and taxonomic dominance.  No changes were found in the intact South Bimini nursery. 

2. Do taxonomic abundance and biomass differ between deforested and intact sides of the disturbed nursery over time?

No. The declines in fish and invertebrate families in the disturbed North Sound were not limited to just the side of the nursery that was deforested.  The changes were detected along the shoreline throughout the entire lagoon. 

3. Are there differences between disturbed and intact habitats in mangrove-associated taxa that are the preferred juvenile lemon shark prey?

Yes.  In the disturbed North Sound, there were significant declines in the mean abundances of mojarra and barracuda, which had previously been shown to important prey items for juvenile lemon sharks.  Mojarra, which account for almost 70% of the sharks’ diet, declined in mean abundance by 52% after the disturbance. 

Principal Investigator:

Dr. Kristine Stump – University of Miami

Collaborators

Leigh Kroeger, B.S. – Cardiff University, UK

Ornella Weideli, M.S. – University of Basel, Switzerland

Dr. Samuel Gruber – Bimini Biological Field Station

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