A busman’s holiday in Malta

You are never far from the sea in Valletta, Malta’s tiny capital city. You can gaze across the Grand Harbour and admire the yachts in the marina, or look out to sea and watch the sun setting. The temptation, as always, is to go for the grand, panoramic views. Perhaps, occasionally, it is worth adjusting your focus to take in some smaller scale delights?


Mats of Cystoseira sp. in the Grand Harbour at Valletta, Malta, April 2015.

My eye was caught by mats of brown seaweed at the water’s edge which, on close inspection, was not a type that I recognised from my limited experience of the UK. The fronds resembled pleurocarpous mosses – or leaves of cypress trees – except that they were swollen and brown in colour rather than green.   These belong to the brown alga genus Cystoseira and play an important role in the littoral ecology of areas of the Mediterranean where the substratum is rocky.   The mats that fill the foreground of the first picture are actually the upper canopy of a submerged “forest” and, just as in terrestrial forests, numerous other organisms, both plant and animal, are able to thrive in the different levels, from encrusting organisms living in deep shade on the rocks at the base of the forest to the seaweed equivalents of “herbs” and “shrubs” living amidst the Cystoseira.   All these, in turn, create many microhabitats for invertebrates which, in turn, support the fish that, probably, ended up on the tables of Valletta’s restaurants, supporting the local economy. The Malta Environment and Planning Authority have some useful web pages explaining more about marine habitats around the island.


Close-ups of Cystoseira sp from the Grand Harbour in Valletta, April 2015.

Cystoseira seems to prefer the part of the shoreline that is permanently submerged (there are virtually no tides in the Mediterranean so there is virtually no intertidal zone). However, on the pitted limestone just above the permanently submerged area, there were several patches of reddish algae which turned out to be composed of mats of intertwined filaments.   It is a member of a red algal genus called Polysiphonia, possibly P. urcolata (suggested by Mike Guiry).   This is a species of the mediolittoral zone, which will be periodically submerged.   My immediate impression of this was of a two-dimensional mat, but exposure from the water has meant that the filaments have collapsed in on themselves, so any sense of a three-dimensional structure is lost.


A patch of Polysiphonia cf urcolata on exposed limestone at the edge of Grand Harbour, Valletta, April 2015.

The microscopic views show that the branched filaments are composed of several rows of elongate cells. Also visible were some large, more opaque cells within the filaments. These are, I think, tetrasporophytes. The plants I was looking at in Valletta are, like most algae, “haploid”. That is, they each contain only a single set of chromosomes.   Most higher organisms spend most of their lifecycle with two sets of chromosomes (“diploid”). In the case of humans, it is just our sperm and eggs that are haploid, but these quickly fuse to form a diploid zygote, which develops into a baby and, thence, to the adult.   The tetrasporophyte is the diploid phase of the red alga, living piggy-back (as it were) on the haploid phase. The life-cycle of red algae is particularly complicated (see “The schizophrenic life of red algae …”) and details differ between orders.   There is also a lot of specialist terminology … all in all, not ideal material for a blogger to use to enthuse his audience.   Malta, on the other hand has plenty of botanical delights packed into a small space (and an excellent bus service, with day tickets costing just 1.50 Euros).   Somewhere, on a blog not very far away, someone might even be writing about some of these …


Microscopic views of Polysiphonia cf. urcolata, from Grand Harbour, Valletta, April 2015: a. vegetative filaments, showing multiple rows of elongate cells; b. two tetrasporangia (?) on a vegetative filament. Scale bar: 25 micrometres (= 1/40th of a millimetre).