Prospekt Depths, Intresting facts

Photo 1. Accumulation of Neptune grass on the pebble beach of a cove not far from Kunfin Cove (Punta Križa, Cres Island). Photo taken on 2 July 2015 (Photo by Marko Randić)


While taking part in the Mediterranean Shag ringing scheme on Oruda Island, we came across copious accumulations of dead leaves of Neptune grass, a marine phanerogam, washed ashore by sea waves. The dead Neptune grass leaves in these accumulations are densely compacted, forming raised heaps running parallel to the shoreline. Although the waves are not able to completely tear apart these heaps, they keep them constantly wet.

Because of the wetting action of the sea and, on occasion, of rain, a gradual yet complex process of decay and decomposition takes place, involving entire networks and chains of microorganisms and other tiny organisms. Widespread throughout the Cres-Lošinj archipelago, this phenomenon is also impressive as a landscape feature of the marine environment (the seashore), although beach-goers and tourism workers are probably not too happy with it (because it reduces so-called beach capacity) and sometimes they resort to drastic measures to remove the accumulations. On the other hand, people who know the Croatian coast and who can appreciate its (still)  preserved nature and, especially, the role of this type of habitat in marine cycles and the circulation of matter in the sea (and on the shore), care about and are thrilled by this phenomenon. We hope that in the future there will be more and more of this type of people, in particular among the ranks of tourism workers.

We are saddened, however, by the fact that so many exceptionally natural beaches, including beaches with accumulations of dead Neptune grass, are currently (and short-sightedly) being converted into beaches with amenities, deprived of all their natural values.

On Oruda Island large accumulations of dead Neptune grass cover beaches made of small-sized sandy material, making them even more charming and special (in the eye of the connoisseur, of course). Sometimes the accumulations are more than a metre high! According to the National Habitat Classification, these habitats are classified as type F.2.2 Supralittoral sands – Supralittoral habitats on sandy beaches (F.2.2.1 Biocenosis of supralittoral sands) and sub-type F. Facies of marine phanerogam remains washed ashore – Facies of supralittoral sands with marine phanerogam remains washed ashore (Photo 3).

By coincidence, not far from Punta Križa we discovered yet another interesting type of habitat with accumulations of Neptune grass on the seashore. In a picturesque little cove in the Kraji area, not far from Kunfin Cove, there is a pebble strand marking the end of a torrent-carved ravine that stretches from the wooded hinterland of the Matalda area. Unlike the Neptune grass accumulations on Oruda Island, the ones here are not as thick (only some 10 – 30 cm) and lie on large to medium-large gravel or sea pebbles (Photo 2) shaped by waves from the material carried by torrential waters. The accumulations are compacted and constantly wet from the sea, except on the surface, which is exposed to the drying effect of the sun and takes on a glaring, reflective light colour (Photo 1).

When we lifted the wet layer, we saw that the leaves were teeming with amphipods, jumping vigorously to try and hide from the sun in the moist and dark safety of the leaves. We also found some species of millipedes and ground beetles, probably highly specialized for these particular conditions of living.

If we succeed in studying this community in more detail in the future, we will be sure to write about some of its representatives on our Web pages.

According to the National Habitat Classification, the community in the cove at Punta Križa belongs to another habitat type, namely, habitat type F.3.2. Supralittoral pebbles and stones – Supralittoral habitat on a pebble and stone bed, sub-type F.3.2.1 Biocenosis of slow-drying accumulations of marine vegetation remains on pebbles – biocenosis developing in accumulations of remains of marine phanerogams and algae on supralittoral pebbles (Photos 1 and 2).

Thematic units: sea, coastal landscapes

Key words: Neptune grass (Posidonia oceanica), biocenosis of slow-drying accumulations of marine vegetation remains on pebbles, facies of supralittoral sands with marine phanerogam remains washed ashore, Cres Island, Oruda Island

Marko Randić

Photo 2. Biocenosis of slow-drying accumulation of marine vegetation remains on pebbles in a cove at Punta Križa (Cres Island) (Photo by Marko Randić)

Photo 3. Facies of supralittoral sands with marine phanerogam remains washed ashore on Oruda Island (Cres-Lošinj archipelago) (Photo by Marko Randić)