With increasing anthropogenic (human induced) stresses affecting the marine environment, there has been much focus placed on coral reefs and how they are being affected as a result; for good reason too. Despite only contributing 1% of the ocean’s surface area, the complex structures of coral reefs are home to an estimated 25% of all the world’s marine species and harbour more biodiversity than terrestrial rainforests. Additionally, they protect coastlines from wave-mediated erosion, play a vital role in the cycling of nutrients and carbon, and support the human masses with food, tourism income and even medical advances. Taking all this into consideration, it’s no surprise that we here at diveLIVE have focussed almost exclusively on educating and inspiring people on the marvel and importance of coral ecosystems, however, there are still so many other aspects of the ocean environment that deserve the focus and respect of humans.
In an attempt to get you thinking about the oceans’ habitats in a broader sense and to demonstrate, I have chosen two underrated and often overlooked ecosystems to discuss in this article – intertidal rocky shores and mangrove forests. I have also selected these two habitats because I have worked closely with them back home in temperate South Australia and they are also prominent here in tropical Grand Cayman. I will also try to show you how these environments in Grand Cayman are linked to the coral reefs and hopefully through this, you can start to build a picture of environmental connectivity and how, in some way or another, everything is linked.
Intertidal Rocky Shores
Most people that grew up close to, or have visited any coastline as a child would have most likely been taken down to poke around the rockpools. These are a perfect example of an intertidal rocky shore. ‘Intertidal’ refers to the region between the high and low tidal zone on any tidal shoreline, and rocky shore, well, that’s pretty self-explanatory. The invertebrate communities associated with this habitat were the focus of my honours thesis and it wasn’t until this experience that I realized just how much happens in these dynamic environments.
Life in the intertidal range is at the mercy of the tidal cycle, and depending on location, these tidal fluctuations can cover extreme distances, or be virtually non-existent. High tides on rocky shores may make these habitats seem like any other shallow-water reef, bringing with it a wide variety of organisms, however, when the tide drains to low, only the well-adapted will survive. When the tide drains out only a little water is retained in rockpools. This water is often heated in the sun, and undergoes sharp changes in temperature and salinity and the rest of the rocky shore stands as bare, exposed rock. Despite this, a wide variety of marine molluscs, crustaceans, echinoderms and even the odd fish have adapted to survive in not one, but two environments. To me personally, one of the most fascinating of these adaptations is the ability to ‘trap’ salt water over the gills to continue respiration even when not in the water. So next time you see a crab walking around rocks covered in attached snails, both exposed to the air, you can be sure that’s some of evolution’s finest work at play.
Although there is not a huge tidal range here in Grand Cayman, the rocky shorelines are still home to a whole range of critters. On the iron shore of Don Fosters alone there are a plethora of organisms including crabs, chitons, snails, urchins, anemones, sea stars, algae, corals and juvenile fish; and that’s just the non-cryptic species. Unfortunately rocky shores are often overlooked as a productive ecosystem and are destroyed for anthropogenic coastal development. If people were to look a little closer, however, they may think twice before destroying such a valuable habitat.
Mangrove forests are as fascinating as they are valuable and what I have to say about them far exceeds the word limits on this blog post, so I will try to keep it concise.
Mangroves are a type of tree that has adapted to tolerate saline waters, which makes them very special in that they can grow in the swampy margins of coastlines. They are mainly restricted to tropical areas of the planet, such as the forests here in Grand Cayman, however, I was lucky enough to live among one of the only temperate mangrove forests in the Southern Hemisphere in Adelaide, South Australia. The early settlers of this state had an immediate dislike towards mangroves and were quick to start deforestation. The settlers described the mangroves as desolate, mosquito-ridden wastelands. How very, very wrong they were. The services that mangroves contribute to their respective marine and terrestrial environments are too many to fit into a logical sentence, so I’ll list them as dot points.
- Act as a nurseries for juvenile and small fish
- Exposed roots act as substrate for invertebrates to settle on, adding further complexity of habitat and abundance of species to the ecosystem
- Contain double the biomass (weight of living things) than tropical rainforests
- Act as sediment and nutrient traps, improving water quality and reducing turbidity of the connected ocean – including coral reefs
- Prevent inland flooding
- Act as huge ‘carbon sinks’, meaning that they store massive amounts of carbon that otherwise would be free in the atmosphere and add to global warming
The diveLIVE team here in Grand Cayman are all lucky enough to live in a house with a small dock right amongst the mangroves and one of my favorite pastimes is to look around the clear water to see what I can find. It really is no surprise how productive these ecosystems are after doing this, because in the small space of our dock I’ve seen huge mussel beds, lobsters, crabs, anemones, jellyfish, tarpon, juvenile reef fish, massive schools of minnows, barracuda, thick algal mats, a potential shark (or huge fish) breach and even the odd iguana swimming past.
It’s unfortunate that the services mangroves play are unknown to a lot of people and that the old mentality of mangroves being nothing more than a nuisance is still adopted by some today, leading to the destruction of these beautiful and delicate ecosystems. Destroying these forests does not only have primary effects on the ecosystem, but secondarily effects the nearshore coral reefs and other marine habitats, the inshore locations near them and even the earth’s atmosphere. Remember, in some way or another, all life is connected.
Written and images provided by: Patrick Fitzgerald