Macrophytobenthos biomass in the Northwestern Cuban shelf, almost 50 years ago

Highlights

• Macrophytobenthos in the Northwestern Cuban shelf amounted to 1.88 million wet tons.

• Halimeda and turtle grass combined biomasses were 88 % the total wet biomass.

• Seasonal biomass variations were statistically different for Halimeda spp. only.

• There were significant correlations between macrophytobenthos biomass and depth.

Abstract

This study presents for the first time a comprehensive review of the macrophytobenthos on the Northwestern Cuban shelf using data collected almost 50 years ago, and can be considered as a baseline for present and future studies. During 1972−1973 the total estimated fresh biomass was 1.88 million tons (686 tons km⁻²). Compared with seagrasses, seaweeds were 1.40 times more frequent but had a total biomass 2.86 times smaller. Frequency wise, 90 % of all seaweeds were Chlorophyta, while Phaeophyta, and Rhodophyta were 5 % each. Six Bryopsidales genera (Avrainvillea, Caulerpa, Halimeda, Penicillus, Rhipocephalus, and Udotea) comprised 73 % of 16 Chlorophyta species collected, and 80 % of their total fresh biomass. Turtle grass (Thalassia testudinum) leaves fresh weight was 96 % of all seagrasses biomass, and 71 % of the total macrophytobenthos biomass. The combined biomass of five Halimeda species and that of turtle grass leaves were 88 % of the total regional macrophytobenthos fresh biomass. Species presence was greatest on sand substrate, and least on reef rubble, with a total biomass greater at 1 m depth on organic mud mixed with sand. Of all species, only Halimeda spp. showed seasonal changes in biomass. The total biomass of macrophytobenthos was higher in the western larger and deeper Gulf of Guanahacabibes than in the eastern smaller and shallower Buenavista cays to La Mulata Port section of the shelf. The total macrophytobenthos biomass and that of some species showed significant correlations with depth. The eight most frequent macrophytes in the Northwestern Cuba shelf had similar Caribbean presence.

Introduction

Cuba, the largest of the Greater Antilles, is an archipelago composed of a main island and approximately 1600 additional islets and cays (Knight and Levinson, 2019) with four unequal shelves, two wider and larger in the South, and two narrower and smaller in the North separated by depths in excess of 1000 m.

In 1964 artisanal fisheries in Cuban national waters took place in these four platforms. Total landings were 23,400 tons, 96 % corresponding to demersal species caught between the coast and the 200 m isobath, of which almost 26 % were caught in the Northwestern shelf (Buesa, 1964).

From San Antonio cape to La Mulata port the NW shelf can be divided into two areas: the larger, wider, and deeper Gulf of Guanahacabibes (GG) to the West, and the smaller, narrower and shallower Buenavista Cays to La Mulata port (BLM) 258 km to the East. From La Mulata port to Matanzas bay, 200 km further east, there is no a real submersion shelf, the 200 m isobath is seldom 100 m off the coast, and is the site of a minor marlin and swordfish pelagic fishery.

The phytoplankton primary production from surface to 25 m depth in the GG area was 0.36 gC.m⁻².d^-1 in 1964 (Kondratieva and Sosa, 1967) and it was 0.30 gC. m^-3.d^-1 in 1965 (Kabanova and López-Valuja, 1973). In 1964, the zooplankton fresh biomass was 0.4 to 1.5 g.m⁻² from surface to 10 m depth (Marikova and Campos, 1967), sustaining a minor clupeid fishery (Silva, 1974).

In 1963, the total combined commercial catch of both areas of this platform was 2.24 g.m⁻², of which 28 % were spiny lobsters, and 58 % benthophagous fish species (Buesa, 1964). In 1964 the zoobenthos biomass was 45.3 g.m⁻² with greater abundance and fresh biomass (69.1 g.m⁻²) in turtle grass meadows, than on silty sand bottoms (Murina et al., 1969). By 1986–1990 the total annual average commercial catch had been reduced 59 % to 0.92 g.m^-2 of which 8% were spiny lobsters, and 74 % corresponded to 32 finfishes (Claro et al., 2001; González-Sansón and Aguilar-Betancourt, 2007).

The high productivity of the platform is also noticeable in the primary production of its phytobenthos, with turtle grass (Thalassia testudinum) producing 4.7 gC. m⁻².d^-1 in a coastal meadow off Playa Habana in 1971 (Buesa, 1972). Assuming that P/B was constant throughout the shelf, and with knowledge on biomass distribution of the species across the shelf, Buesa (1974) estimated a production of 5.2 gC. m⁻².d^-1, almost 16 times that shelf’s average phytoplankton primary production. Impressive as such primary production difference was, it is a minimal estimate of phytobenthos production, as many more macrophytobenthos species are found on the shelf.

The objective of this manuscript is recording the biomass of all macrophytobenthos species on the NW Cuban shelf during a 1972−1973 sampling campaign. These data, can also serve as a comparison baseline with present and future data, especially for turtle grass meadows because, seagrasses are declining globally (Waycott et al. (2009), and historical data on larger meadows extensions providing baseline data measuring possible changes on biomass and cover of seagrass meadows are scarce, but essential to assess the present state of these vulnerable ecosystems.