APRIL 2020 Edition
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Earth Day: A Virtual Celebration!
Nature's Wisdom - Why Mangroves Matter
Basket Weaving Online Class
Visual Inspiration - Mangrove Exhibit
By Dr. Robbie Smith, Curator Natural History Museum
Mangroves are a distinct coastal habitat in Bermuda.
The red mangrove (Rhizophora mangle) and the black mangrove (Avicennia germinans)
are trees that can tolerate living in the intertidal zone, their roots capable of growing in salt water and the very low oxygen levels in the muddy sediments.
The red mangroves occupy the outer seaward edge of a mangrove forest because their extensive prop roots hold the trees up during hurricanes while the black mangroves live behind them on the shoreward side.

Mangroves provide several critical ecosystem services:

  1. They are an important nursery habitat for many juvenile reef fishes, such as snappers, who hide from predators within the tangle of prop roots.
  2. They are an important feeding ground for many juvenile and adult fishes who visit at high tide.
  3. The red prop roots are a substrate (hard surface) for numerous species of sponges, oysters and algae to live on. The sponges trap nutrients from the water, which are then delivered into the roots.
  4. Mangrove crabs bury old mangrove leaves in the mud to form a peat that helps trap sediments and allows the mangrove “floor” to rise with sea level. More importantly, today we understand that mangroves are a very significant global carbon sink (trees store carbon dioxide by transforming it into the cells that make wood and therefore forests can reduce the effects of carbon dioxide emissions) because of how densely mangrove forests grow.
All these benefits have been diminished because of the persistent degradation and removal of mangroves in 400 years of coastal development in our bays and harbours. Over 35% of Bermuda’s mangroves were lost due to landfill in the development of our airport in World War II. Today we recognize the steady threat of rising sea level — 2 mm per year according to tide gauge records. Existing mangroves cannot recover from storm damage because the water is now too deep on the seaward edge for the red mangrove seedlings to become established — thus, the mangrove “retreats”. This is clearly seen in Hungry Bay, where we have mapped the changes in the mangrove edge from 1898 to 2012; nearly 100m lost!

Without our extensive coastal developments (docks, marinas), the mangroves seedlings would simply establish further “uphill” but we have so “hardened” our coastline that there is little space for this to occur. Thus, it is imperative that we look for opportunities to re-establish mangroves where they can survive storms, move “uphill” with rising sea level and provide the benefits to our marine ecosystem.
By Patrick Talbot, Curator Aquarium & Zoo
After the roof renovation in 2015, themes were chosen to represent each gallery within the display hall to better tell the story of the marine world around Bermuda. When you enter the Aquarium just look above the tanks to see what those themes are.
The large tank, furthest to the east, in the display hall, was adapted into a mangrove exhibit. Mangrove forests are a very important coastal habitat and the trees are a protected species in Bermuda. They prevent coastal erosion and provide shelter for many marine organisms which find safety hiding amongst the tree roots.

Prior to the tank redevelopment, Aquarist Steve Davis had set up plant pots with seedling mangroves. The tank was then designed to be tidal using a standard loop drainage system to try to simulate the natural environment as much as possible. In addition to having salt water as the main feed to the tank, fresh water injectors and sprayers were added to the exhibit in order to make the tank slightly brackish and add ‘rainfall’. Light tubes were installed over the exhibit along with sky lights to expose the plants to natural sunlight. Metal halide and LED lighting was also added for cloudy days. Finally, soil and Walsingham rock was used as a stable substrate on which the plants could grow.

In the 4 years since the tank was redeveloped, the plants have thrived and the juvenile fish added have grown considerably. If we have done our job well, then you should be leaving the aquarium with a greater appreciation of this amazing habitat.