New Zealand is full of contrasts, both among and within its incredibly diverse landscape. Volcanoes form natural forest boundaries in the North Island, while glacial deposits at the mouth of South Island's fjords create a dramatic freshwater habitat that sits precariously on top of the 'deep-ocean' habitat beneath it. It is in these transition zones, at these boundaries of often contrasting conditions, where only the most extreme life forms have learned or adapted to survive.
The underground constellations made by the carnivorous fungus gnat (aka glow worm) are a prime example of the extreme strategies often required for survival in such a place. Living where the daylight of earth's surface fades into the darkness of what is below ground, these graciously named invertebrates produce light to attract their food. But as this resource is not always reliable, the worms are also known to feed on the competition for this scarce food resource. In other words, they'll eat their neighbors, even if they're family. Nevertheless, from a human perspectives they're beautiful, and amazing for their ability to thrive in such an inhospitable place as a cave.
However, even more amazing than the glow worms are the life forms that live at an ecosystem boundary so efficiently, that they actually buffer the changes, helping to make that environment more livable for a wide variety of organisms. They form an ecosystem in of itself, supporting both organisms unique to this 'buffer zone', and those from the habitats on either side.
Mangroves form the foundation of one of these transitional ecosystems in coastal areas. These trees have adapted to grow in the extreme conditions present in the salty, water-logged, oxygen deprived, temperature varied, sedimentary environment that is constantly changing with tides and coastal currents. By trapping and holding sediments with their complex root systems, mangroves help to shape and stabilize the coastline, as well as to filter runoff from rivers before they can overwhelm shallow offshore reefs. They provide important habitat for small marine invertebrates and fish that are vulnerable as larvae and juveniles by keeping out predators and providing food. The sediments that accumulate are enriched by birds that also find refuge in the trees.
Such buffer zones further the diversity of habitats that serves to support the diversity of organisms that is so high in New Zealand. Just as the mangrove-founded system buffers the impacts of terrestrial runoff to the offshore coast, the biodiversity of a place is directly related to its resilience to impacts, both natural and introduced. Whether dominated by mangroves or other specialized wetland plants, these coastal ecosystems throughout the world are being out competed by introduced plant species, and their ability to function is being compromised. Wetland restoration efforts, such as that of the salt-marsh reserves scattered around the Tauranga coastline are in an effort to restore this habitat, an investment in the important ecosystem services that, when healthy, it provides for free. Letting your eyes follow the developed ridge lines to where houses and sidewalks meet one of these marshes, scanning through the reeds to where the wetland gives way to the sea, it's obvious how effective the system is. The water nearest the land and storm drains is cloudy with an oily slick on the surface, but as you look through the expanse of mangroves, the water gradually changes to clear. And while marveling at the ecological value of such a wetland habitat and the interesting wildlife within, it's impossible not to also appreciate its recreational potential that isn't just limited to juvenile fish!