Hairy green seaweeds (Bryopsis sp.) carpeted the Sentosa shores when we visited yesterday for TeamSeagrass monitoring.
What are Hairy green seaweeds and is a bloom a bad thing?
Bryopsis seaweeds comprise a clump of fine filaments (6-8cm long) attached to a hard surface, such as small stones and coral rubble.
In some, the filaments form long feather-like structures that taper at the tips.
In others, the filaments are long, single strands with only a little bit of branching. They come in various shades of green, from bluish green to olive green.According to AlgaeBase there are more than 60 current Bryopsis species. So it's probably beyond mere mortals to figure out what kind of Bryopsis are carpeting Sentosa.
During a bloom is when we look out for tiny creatures that live among the seaweeds.Sometimes, there are countless tiny amphipods among this fine seaweed. These animals are not shrimps. They belong to a different group, the Order Amphipoda. They are sometimes also called beachfleas, sand hoppers or sandfleas. They are often the most numerous and most diverse of bottom-dwelling crustaceans.Another creature that occurs in large numbers among Bryopsis are these unidentified slugs. They are probably sap-sucking slugs (Order Sacoglossa) that suck the nutrients out of the seaweeds. They are really hard to spot as they look very much like the seaweeds!Here's a closer look at the slug.
There are probably lots of other animals that feed on the seaweeds especially at high tide. And the tiny animals found the seaweeds are part of the food chain for bigger creatures. So a seaweed bloom is not necessarily a bad thing.
Bryopsis blooms are quite encountered regularly on our shores. At times, the seaweeds are plentiful, like yesterday. And at other times, they are very sparse. Blooms don't last very long, seldom more than a month.
This might be part of a natural cycle. Seaweed blooms can be triggered by fresh nutrient inflows. Could the rainy weather recently have washed more nutrients from the forested natural cliffs that border the shore?
Or could the blooms be the result of increased sedimentation from coastal works nearby? These works include